Confidential
TECHNICAL REPORT
Health, Safety and Environmental Policy Guideline
Prepared by:
Mercury Technology Services
23014 Lutheran Church Rd.
Tomball, TX 77375
S. Mark Wilhelm, Ph.D.
Prepared for:
Petroleum Development Oman
PO Box 81
Muscat 113
Sultanate of Oman
Mr. Nasser Naamani
W. J. Towell & Co. (LLC)
P.O. Box 1040 Ruwi
Postal Code 112
Sultanate of Oman
Mr. Philip Goddard
March 20, 2003
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Table of Contents
1.0 INTRODUCTION
2.0 HEALTH, SAFETY and ENVIRONMENTAL POLICY
2.1 Risk Assessment
2.2 Worker Health and Safety
2.3 Environmental Protection
2.4 Training
2.5 Analytical Basis
3.0 HEALTH AND SAFETY
3.1 Routes of Worker Exposure
3.2 Exposure Limits
3.3 Personal Protective Equipment
3.4 Diagnosis and Treatment of Exposed Workers
4.0 ENVIRONMENTAL ISSUES
4.1 Mercury Emissions to Water
4.2 Mercury Emissions to Air
4.3 Mercury Emissions Via Solid Waste Streams
5.0 TRAINING
6.0 CONCLUSIONS and RECOMMENDATIONS
Appendix A - Mercury in Hydrocarbons; Chemical Background
Appendix B - PDO Background
Appendix C – Canadian Guideline for Mercury, Questions and Answers
Appendix D – U.S. NIOSH Guideline for Mercury Vapor
Appendix E – U.S. OSHA Guideline for Elemental Mercury
Appendix F – Occupational Health Guideline for Organo (Alkyl) Mercury
Appendix G – Emergency Treatment
Appendix H – Employee Hygiene Facility
Appendix I – Personal Protection Equipment
Appendix J – Mercury Training Viewgraphs
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1.0 INTRODUCTION
Mercury Technology Services (MTS) was requested by Petroleum Development Oman (PDO) to compile information concerning mercury-related health, safety and environmental (HSE) concerns associated with natural gas production and processing in Oman. Of interest were the methods to minimize risks associated with mercury in produced fluids. MTS provided technical services to PDO under contract to W. J. Towell and Company (WJT, principal contact Philip
Goddard).
Mercury is a trace component of fossil fuels including coal, crude oil and natural gas. In hydrocarbon processing and petrochemical manufacture, mercury in process feeds can contaminate equipment and can segregate to sludge and other waste streams. Opportunities therefore exist for workers to be exposed to mercury and its compounds in routine repair, maintenance and inspection activities and when handling process fluids and waste materials.
Because of mercury’s toxic nature and its harmful effects on the environment, such activities must be structured to prevent acquisition of mercury by workers, to avoid contamination of processing facilities and to avoid escape of mercury into the environment.
This document is designed to provide technical information and advice to assist managers and responsible health, safety and environment (HSE) personnel in the oil and gas production and processing industries to formulate policies and procedures that minimize the detrimental impacts of mercury on company operations. Such policies are necessary to reduce health risks and to avoid liabilities associated with inadvertent discharges of mercury to the environment.
Mercury is the primary focus of the following discussion although it is acknowledged that petroleum also contains other toxic components that are also problematic. The primary reasons for this focus are that mercury is a well-known constituent of oil and gas, its properties are unusual compared to the other metals and facile avenues of exposure accentuate the toxicity of mercury. In addition, mercury is one of a special class of pollutants that includes those simultaneously toxic, persistent and accumulative in the environment. For these reasons, mercury deserves special attention.
Companies operating oil and natural gas production and processing facilities (gas and oil production systems, primary field fluid conditioning, gas separation/liquefaction, refining, transportation and storage facilities) should be aware of the concentration of mercury in processed/transported fluids. From this knowledge decisions can be made concerning the likelihood and magnitude of contamination in the workplace and steps can be taken to mitigate the impact of mercury on workers, equipment and the environment.
The consequences of inadvertent exposure of workers to mercury, dispersal of mercury in processing facilities or inadvertent discharges of mercury to the environment are universally detrimental. Clear incentives exist to adopt plans and policies that minimize the risks and problems that accompany mercury’s presence in hydrocarbons. This guideline document compiles and discusses the technical aspects of mercury found in petroleum and natural gas so as to assist the development of engineering practices and operating policies that are based on a comprehensive understanding of the existing science and the current successfully-applied practice within the oil and gas industry.
Mercury exists as more than one chemical species in oil and gas. Background information regarding the chemistry of mercury in hydrocarbons and the distribution of mercury species in production and processing systems is provided in Appendix A. The technical approach to HSE policy should take into account the chemical and physical properties of the major mercury species and their individual and collective toxicologies. It is not possible to lump mercury in hydrocarbons into one general chemical category and thus formulate policies based solely on
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Details concerning PDO’s gas production and processing operations in Oman are contained in
Appendix B. Mercury was found as a trace constituent of gas produced in Central Oman in
2001. Efforts have been made to measure the concentrations of mercury in various hydrocarbon streams associated with the production and processing systems. Details of the analytical measurements are contained in Appendix B. It is anticipated that the concentration of mercury in produced fluids will increase in the future due to increased production from newer fields having higher mercury concentrations.
A secondary purpose of this guideline document is to provide some quantity of background information for use by HSE personnel. The selected information in the Appendices covers several aspects of toxicology, mercury safety plans, medical treatment and other areas that are considered essential reading prior to formulation of company polices and operational procedures. A good overview of health and safety concerns, in a question and answer format, is contained in Appendix C. Although this report is directed to the managerial level, it should serve as a reasonably comprehensive reference document for those employees tasked with implementation of policy.
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2.0 HEALTH, SAFETY and ENVIRONMENTAL POLICY
If mercury is a constituent of processed hydrocarbons, then plans for dealing with its consequences should be inc orporated into a company’s existing HSE policy framework and into work procedures for specific jobs in which contact with mercury in hydrocarbons is possible.
Such incorporation should be based on sound technical information with acknowledgement of the limitations of current understanding. A mercury-specific process hazard management strategy is an integral part of a comprehensive process safety and environmental protection program.
Some key elements of company HSE policies affected by mercury’s presence in processed fluids typically include:

Risk Assessment

Worker Health and Safety

Environmental protection

Training of personnel

Analytical Basis
2.1 Risk Assessment
Risks associated with producing, transporting or processing petroleum or natural gas containing mercury fall in several categories. Of primary importance is the risk to workers who handle fluids or repair and maintain equipment. Mercury is highly toxic and has a propensity to accumulate in and contaminate storage tanks, pipelines and processing equipment. Assessing health risks to workers is a reasonably straightforward exercise if a concerted effort is made to acquire the analytical information necessary to make sound judgments.
Aside from worker health and safety, there are clear economic risks associated with mercury in process feeds. The economic risks derive from mercury’s lowering of product quality, potential negative interactions with equipment (corrosion and embrittlement of metals) and the liabilities derived from its pronouncedly detrimental impact on the environment. Having mercury in process feeds causes difficulties with normally routine repair and maintenance activities and leads to generation of waste streams that may be difficult to dispose of. Mercury also can damage equipment under certain circumstances.
Steps can be taken to minimize risks from an understanding the toxicological, chemical and physical properties of mercury and mercury compounds, determination of the possible exposure pathways in the work place and adopting policies and procedures that mitigate worker exposure and dispersal of mercury to products and the environment.
Both human-related and economic risks generally are proportional to the concentration (total) of mercury in processed hydrocarbons. In general, the risks associated with mercury can be categorized according to total mercury concentrations acquired by routine analytical procedures having documented quality assurance. The arbitrary categories are as follows:

Less than 10 ppb liquid (<5
 g/m 3 gas) – Low Risk

Between 10 and 100 ppb liquid (5-50
 g/m 3 gas)
– Medium Risk

Greater than 100 ppb liquid (>50
 g/m 3 gas) – High Risk
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In the low risk category, speciation of mercury compounds is not essential given the analytical uncertainties. HSE policy in this category should focus on monitoring the total amount of mercury in key process streams to ensure that the concentration does not increase over time.
In addition, workplace monitoring should be directed to process locations known to concentrate mercury (cryogenic process sections for example).
In the medium risk category, limited operational speciation of the chemical forms of mercury is required to determine the percentage of elemental mercury in the measured total concentration.
If the elemental form comprises over 75 percent of the total, then the policies adopted for worker health and safety should be directed to avoidance of inhalation and dermal absorption of the elemental form. In the medium risk category, the locations of possible accumulation of mercury also are more numerous and the monitoring requirements in the work place need to be more frequent and detailed. At this level some attention must be paid to the possibility that organic mercury may be present in liquid process fluids.
Having total mercury concentrations in excess of 100 ppb requires detailed speciation of compounds, frequent monitoring and stringent controls on activities that could expose workers to mercury vapors and dermal contact with fluids. Environmental protection is more difficult in this category and numerous process streams require scrutiny for mercury content.
2.2 Worker Health and Safety (see Appendices D – F)
Mercury is poisonous to humans and can cause neural damage or even death from either acute or chronic exposure. Because of the subtleties of mercury poisoning, toxic influences to neural function can go unnoticed for very long periods of time, if they are detected at all. Chronic, low level exposures may require years to diagnose unless exposure risks are apparent and efforts are made to biologically evaluate those potentially affected. Chronic mercury toxicity is extremely difficult to diagnose from symptoms in their early stages. At the point of conclusive symptomatic diagnosis, neurological impairment is usually at an advanced stage and remediative therapies are mostly ineffective.
The discovery of significant quantities of mercury in fossil fuels is not a recent occurrence and, in spite of the fact that mercury is abundant in some major fields, major health deficiencies have not been documented in large classes of workers in the petroleum industry. This fact is reassuring, however, workers can be exposed to mercury and mercury compounds in activities such as equipment cleaning, repair and inspection, during hot work on contaminated equipment and piping, and in a variety of other activities. Acute high-level exposures that produce obvious detriment in workers are rare but can occur under certain circumstances (vapor monitor malfunction, vessel entry, non-monitored hot work, equipment maintenance).
Avoiding exposure to mercury, in most maintenance and inspection activities, is readily accomplished if some fairly simple steps are taken to identify those situations in which exposure is possible, and by provision of commonly available equipment for worker protection from inhalation or dermal absorption. Incidents of inadvertent exposure are more likely in situations that are not routine or that involve unsupervised or contract personnel. With proper procedures and plans, protection of workers can be achieved without tremendous expense or operational impediment.
Policies designed to ensure the health and safety of workers should be based on a thorough chemical analysis of process streams that provides concentration of total mercury and some information on concentrations of the chemical forms of mercury. Computational methods can supplement analytical data to predict locations of accumulation. Atmospheric monitoring of mercury vapor in work areas is essential to identify potentially hazardous conditions. With this
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Procedural details should address PPE logistics to make sure that protective equipment is readily available when needed and easily replaced.
2.3 Environmental Protection
Mercury is universally detrimental to the environment and discharges should be minimized or eliminated to the extent possible. The trend in mercury discharge regulations, whether to air, water or solid waste streams is toward greater restriction. Producers and processors of petroleum that contains mercury should be aware of its presence and should take prudent steps to ensure environmental impacts are as minimized and well within existing regulations.
Mercury, unlike many other pollutants, does not degrade to benign forms over time. Thus one cannot rely on naturally occurring processes to mitigate the impact of mercury on the local environment. Spilled elemental mercury, for example, will remain in soil for hundreds of years without major degradation.
A major effort is underway internationally to reduce anthropogenic mercury discharges to the environment. There are a myriad of reasons as to why this is the case but the major reasons stem from the toxicity of methylmercury to humans and piscivorous mammals in general and to inorganic mercury’s toxicity to aquatic organisms. No attempt is made in the present context to review the geochemistry of mercury that leads to the conclusion that the mercury originating from human activities should be substantially reduced or eliminated. Rather, the reader is referred to any of the major reviews on the subject for a thorough discussion (U.S. EPA Mercury
Study Report to Congress, United Nations Environment Programme (Chemicals), Global
Mercury Assessment).
It is undisputed, however, that the majority of the mercury that enters the global mercury cycle from human activities comes from combustion of waste and fuels. Discharges of mercury to water and surface mercury waste accumulations are severely restricted and regulated by governments because of mercury’s toxic and persistent nature. It is incumbent upon companies to account for mercury in all produced waste streams and in products sold commercially, to comply with regulations that apply to emissions and to adopt policies that protect the environment, even in the absence of applicable guidelines.
2.4 Training
Training is important to ensure worker health and safety and to ensure that the plant environment is not contaminated by mercury. Workers should be trained to anticipate situations in which they could be exposed, provided appropriate personal protection equipment (PPE), trained in the use of PPE and taught to recognize the symptoms of exposure. Workers should attend training courses that provide the basic technical information concerning mercury in hydrocarbons and provide the safety information that workers need to avoid inhalation of mercury vapor and contact with organic mercury. The major topics in such training courses should include:

Basic chemistry of mercury.

Origin and consequence of mercury in plant feeds.

Toxicology of mercury (how to recognize intoxication).

Personal protection to prevent inhalation and dermal absorption.
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
Confined space procedures.

Mercury vapor monitoring.

Waste handling procedure.

Operation and calibration of mercury vapor analyzers.

Sampling and analysis for mercury.

Company policy review.

Medical screening requirements.
2.5 Analytical Program
HSE policy should be based on a thorough understanding of the amounts and types of mercury in process fluids, treatment fluids and waste streams. Accurate analytical data are best acquired by establishing a routine monitoring scheme in which the mercury concentrations of critical streams are tracked over time. In complicated processes, mercury concentrations seldom are uniform and are subject to numerous influences to variability. Sampling and analysis variations can be large and typically produce numbers biased lower than actual, especially when wet chemical methods such as digestion of organic matrices is required as part of the procedure. The temporal variation in mercury concentration at a particular process location is affected by fluid homogeneity, temperature/pressure changes and numerous other factors.
The concentration of organic mercury is important to HSE policy because the organic mercury species are many times more toxic than the elemental form and they have the added characteristic of the ability to be absorbed through the skin easily. If organic mercury is known to be present at concentrations above a few ppb then substantially more emphasis must be placed on avoiding contact with process fluids. Conclusive analysis for dialkylmercury is extremely difficult to accomplish. One reason for this fact is that the concentration of dialkylmercury in crude oil or gas condensates is typically low in the rare cases that it is successfully analyzed. It is further postulated that the dialkyl forms of mercury are unstable in samples such that they may not be detected, even though they might be present in fluids.
If organic mercury cannot be ruled out as a major constituent, and if the total concentration of mercury is above approximately 100 ppb (in liquids), then a major dilemma is encountered that can be difficult to resolve without significant expenditure of time, effort and money. It is nonetheless prudent to attempt to resolve the uncertainty by analytical tests that determine the concentration of organic forms exactly or at least to bracket the possible concentration by measuring exactly the concentration of other forms.
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References
Mercury Study Report to Congress, US EPA, EPA-452R/R-97-004 (1997).
United Nations Environment Programme (Chemicals), Global Mercury Assessment , Geneva,
Switzerland, December 2002.
Wilhelm, S. M., “Mercury In Petroleum; Processing And Regulatory Issues”, Proceedings of
ASME/ETCE 2001, 23rd Energy Sources Technology Conference and Exposition, February 5 –
7, 2001, Houston, TX.
Wilhelm, S. M.
, 2001, “An Estimate Mercury Emissions to the Atmosphere from Petroleum”,
Environ. Sci. Tech, 35,24:4704 (2001) .
Wilhelm, S. M., “Avoiding Exposure to Mercury During Inspection and Maintenance Operations in Oil and Gas Processing”, Process Safety Progress, Fall (1999).
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3.0 HEALTH AND SAFETY
3.1 Routes of Worker Exposure
Exposure to mercury and its compounds poses a potential health risk to workers involved with inspection and maintenance activities in facilities that process hydrocarbons containing significant amounts. The risks of exposure to mercury are often underestimated for a variety of reasons. Foremost is the fact that the exact amount of mercury present in processed petroleum often is not known with certainty. Secondly, the specific quantities of mercury compounds that may be present in hydrocarbon liquids seldom are known at all. Thirdly, monitoring for mercury vapor in work environments is not a routine procedure for many processing facilities. Lastly, mercury toxicity is gradual and produces no immediately apparent impairment that easily can be associated with occupational exposure. Superimposed on the risk issues are several aspects of the chemistry of mercury that make it illusive both to quantitative analysis and to detection in work environments. The combination of the cited factors increases the likelihood that workers will be inadvertently exposed to mercury and those exposed will be adversely affected.
The major mercury-specific considerations for heath and safety of workers in petroleum processing involve exposure of workers to mercury vapor and dermal absorption of elemental and/or dialkylmercury. Comprehensive health and safety plans to prevent exposure to mercury are best predicated on a complete understanding of the concentrations of mercury and mercury compounds in process fluids. Computations that predict deposition of mercury in equipment can assist identification of hazardous locations of mercury accumulation. A thorough mercury vapor detection and monitoring program for plant atmospheres is necessary to confirm and quantify exposure risk.
Elemental mercury is readily absorbed into the blood stream via the lungs. Dermal absorption efficiencies for elemental mercury in vapor are typically low (less than 3 percent of the absorbed dose) but nonetheless to be strictly avoided. The major inhalation scenarios are short duration (one or two work shifts) inhalation of vapor having a high mercury concentration and chronic inhalation of moderate to low level concentrations. A typical short duration situation is a welder who repairs or cuts pipe that has mercury adsorbed on the interior pipe wall corrosion products. Here the vapor concentrations can be very high due to volatilization by the torch or arc. Maintenance workers who repair equipment in plant areas dedicated to such activities can be chronically exposed unless such areas are well ventilated and periodically monitored fro mercury vapor.
3.2 Exposure Limits
The American Conference of Governmental Industrial Hygienists (ACGIH) mercury vapor threshold limit value (TLV) is 0.025 mg/m 3 (TWA for a normal 8-hour workday and a 40-hour workweek). The current US Occupational Safety and Health Administration (US OSHA) permissible exposure limit (PEL) for mercury vapor is 0.1 milligram per cubic meter (mg/m 3 ) of air. The PEL is a ceiling limit (U.S. EPA 1996) and exposure for any length of time above this limit must be strictly avoided.
Mercury vapor is not classified as a human carcinogen. The minimum risk level for chronic inhalation of mercury vapor is 0.0002 mg/m 3 . An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse (noncancer) health effects over a specified duration of exposure (greater than one year). The U.S.
EPA reference concentration (RfC) for inhalation is calculated to be 0.0003 mg/m 3 (TWA).
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There are no accepted norms for limits of exposure (maximum concentration in fluids) to organic mercury as might occur in activities associated with hydrocarbon production and processing.
3.3 Personal Protective Equipment (see Appendix I)
The strategies for preventing worker exposure to mercury are reasonably straightforward and can be implemented without major expense or operational impediment. This assessment is predicated on the assumption that the magnitude of the exposure risk has been quantified by chemical analysis to determine the exact concentrations of mercury species that are present and work environments have been subjected to a vapor-monitoring program to determine mercury vapor sources and concentrations.
Protection from inhalation exposure can be accomplished using cartridge respirators or bottled breathing air. Cartridge respirators use impregnated (by a chemical reactive to mercury) activated carbon to scavenge mercury from air. The mercury is scavenged both by adsorption on the carbon and reaction to form a non-volatile species (HgS or HgI
2
). In the US, permitted respirators are those that have been approved by the Mine Safety and Health Administration or by the National Institute for Occupational Safety and Health. Cartridge respirators do not function adequately when the mercury vapor concentration is above 1.0 mg/m 3 . Tethered or bottled breathing air is required when vapor concentrations are higher than can be tolerated by respirators. In addition to respirator or breathing air selection, a complete respiratory protection program should be instituted which includes regular training, maintenance, inspection, cleaning, and evaluation.
NIOSH Recommendations for Elemental Mercury (Concentrations In Air):
Abbreviations: SAR = supplied-air respirator; SCBA = self-contained breathing apparatus; IDLH
= immediately dangerous to life or health.

UP to 0.5 mg/m 3 : Chemical cartridge respirator with cartridge(s) to protect against mercury compounds*; or SAR.

UP to 1.25 mg/m 3 : SAR operated in a continuous-flow mode; or powered air- purifying respirator with cartridge(s) to protect against mercury compounds
(canister)*.
NOTE: These recommendations are based on the NIOSH exposure limit of 0.05 mg/m 3 (timeweighted average). The IDLH concentration for mercury is 10 mg/m
3
.
The ability of respirators to prevent inhalation of dialkylmercury is not known with certainty. The primary uncertainty is sorbent capacity although reactivity is suspect as well. Little data are available concerning the ability of sorbents to scavenge vapor-phase organic mercury associated with petroleum processing operations.
Workers should be provided with and required to use impervious clothing, eye protection and other appropriate protective clothing necessary to prevent skin contact with liquids that may contain mercury and/or dialkylmercury. If clothing becomes contaminated, workers should change into uncontaminated clothing immediately. The possibility of contamination of laundry facilities, living quarters on platforms and control rooms must be carefully scrutinized. Personal hygiene (Appendix H) is likewise important and especially if liquid hydrocarbons are known or suspected to contain dialkylmercury.
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Gloves and other protective clothing that are resistant to hydrocarbons are generally sufficient to prevent dermal absorption of elemental mercury. The ability of dialkylmercury to cross polymeric barriers is less known and is likely much more facile than might be normally estimated (the fatal laboratory exposure of a researcher was due to the facile transport of dimethylmercury through latex gloves; Bayney, 1997). Although chronic dermal exposure to oil and condensate is common for some maintenance workers, the incidence of mercury intoxication from such exposures is thought to be very low (no clearly defined cases are known). This infers that organic mercury is not prevalent in petroleum at high concentrations.
The exact magnitude of risk is only quantitatively defined by determining the exact amount of dialkylmercury in hydrocarbon liquids and estimation of dermal absorption efficiencies. Absent precise risk definition, increased emphasis on dermal protection is needed in those situations where the concentration of total mercury in processed hydrocarbons is greater than 10 ppb.
Purging equipment to remove hydrocarbon vapor is a common practice and it is often assumed that, when vessels have been purged to reduce the hydrocarbon concentration to a safe level, the mercury concentration is acceptable as well. This assumption is usually incorrect if the amount of mercury deposited in the vessel is substantial. Mercury adsorbs readily on equipment surfaces and, more importantly, is highly soluble in the hydrocarbon surface layers that always exist in process vessels. The amount of mercury that accumulates in surface layers can be large and can evaporate slowly, thus providing a significant vapor concentration long after successful purging to reduce the hydrocarbon level.
If mercury precipitation or condensation has occurred to produce actual pools of elemental mercury in equipment, then no amount of purging will suffice to reduce the mercury level to a safe level. Precipitation and condensation of elemental mercury occurs primarily in cryogenic heat exchangers and cold separators. Maintenance and inspection activities performed on equipment containing liquid mercury require extensive precautions to prevent worker exposure and to prevent transferring the mercury to locations outside the contaminated vessel. Full breathing apparatus and chemical suits are usually required to protect workers. In some situations, it is prudent to subject the equipment containing precipitated mercury to some form of decontamination treatment prior to extensive maintenance or inspection activities.
One operation seldom scrutinized is hot work on steel vessels or piping that has been exposed to gas or liquids that contain substantial quantities of mercury. Mercury reacts with steel corrosion products to produce a surface layer that is high in mercury content. Welding, torch cutting and other types of hot work readily vaporize the mercury contained in the corrosion product layer. The local concentrations in hot work areas can be very large, exceeding 50 mg/m 3 in some cases. The higher than vapor pressure concentrations are achieved by adsorbed mercury in smoke. Cartridge respirators are not sufficient to scavenge mercury vapors at these concentrations. Use of breathing apparatus in conjunction with eye and face protection for welding requires special equipment that may not be readily available in some work locations.
Recommended personal protection for mercury in air concentrations is outlined in Figure 1. The recommendations assume normal PPE (eye protection, hydrocarbon protection, coveralls, work boots) are used at a minimum. The recommendations in the figure consist of additional requirements over and above normal PPE.
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Figure 1
– PPE Decision Tree
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3.4 Diagnosis and Treatment of Exposed Workers (see Appendix G)
Chronic occupational exposure to mercury is rarely diagnosed unless a specific program is in place to monitor mercury concentrations in the blood or urine of at-risk workers over time.
Absent a biological monitoring program, medical diagnosis is extremely difficult unless affected individuals exhibit significant and readily apparent symptoms. For most petroleum workers, acutely toxic environments are infrequently encountered and chronic exposures require years to manifest. Also important is the fact that large oil and gas fields containing high concentrations of mercury are rare in the US and Europe. High mercury concentrations are found in the Gulf of Thailand, Indonesia, China, North Africa (Algeria), parts of South America
(Venezuela) and in a few fields in the Middle East. In many of these locations, the risk factors are compounded by logistical impediments to detection of mercury in produced hydrocarbons and to biological monitoring of accumulated mercury levels in at-risk groups.
Workers who may be exposed to mercury in the work place should be monitored in a systematic program of medical surveillance designed to detect the magnitude of occupational exposure relative to an individual background mercury level. When the concentration of mercury in processed hydrocarbons is known to be high, periodic biological monitoring of workers for mercury exposure should be part of a comprehensive safety program, especially if a robust mercury vapor monitoring program is not implemented.
Workers who are routinely and frequently engaged in activities that involve mercury in the work environment can be monitored for mercury in blood or urine at a frequency dictated by a quantitative assessment of risk. It should be noted that such situations are rare in the oil and gas industry but nonetheless can occur in some circumstances. Analysis of blood and urine are the most common diagnostic tools for the discovery and quantification of occupational exposure. Reference levels (background level for populations not occupationally exposed) for mercury (total) in blood, urine and scalp hair are compiled in Table 3.1. Assessment of worker exposure requires testing for mercury in blood or urine at a frequency that is dictated by the exposure risks. The concentrations of mercury in blood and urine decrease with time but not in the same manner.
The quantitative assessment of worker exposure to mercury of occupational origin requires distinction between dietary mercury (ingested monomethyl mercury) and work place absorption
(inhaled elemental mercury and dermally absorbed dialkyl mercury). To accomplish the process of discrimination using analytical procedures, it is important to understand the metabolic pathways and toxicokinetics to be in position to interpret data.
About 80 percent of inhaled elemental mercury enters the blood stream where it is slowly oxidized (to Hg +2 ). The rate of oxidation is sufficiently slow that mercury distributes to body tissues because the dissolved elemental form (Hg 0 ) can cross tissue barriers, including the blood/brain barrier. In brain tissue, Hg 0 reacts to cause neurologic impairment and is retained in brain tissue as a mercury-thiol species. Hg 0 is slowly oxidized in blood. After a few days of exposure the un-oxidized Hg 0 is associated with red blood cells and Hg +2 resides mostly in plasma. The Hg +2 does not cross tissue barriers easily and is eliminated from the body via urine, feces, perspiration and saliva. Elimination via feces is dominant during the first two days following exposure but the urinary pathway dominates after that period. The concentration of mercury in blood reflects the absorbed dose, the rate of oxidation (which controls the rate of excretion) and the rate of tissue absorption. Following an acute dose, the blood concentration peaks rapidly (minutes) and then decreases slowly with a half-life of 2-4 days. Urinary mercury peaks in about 10 days (from an acute exposure) and has a half life of about 50 days.
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Measurement of mercury in urine is the recommended biologic monitor for workers exposed to metallic and inorganic mercury. Ideally, the collection should be over 24 hours, but this is seldom feasible. Spot urine samples may also be taken, but care must be taken to always collect them at the same time of day. Overnight samples may also be collected; this collection extends from the time the employee goes to bed through the first urination of the morning.
Samples must be collected in containers provided by the laboratory, since a preservative must be added. At least 25 milliliters of urine must be collected. Great care must be taken to prevent contamination of the sample containers or the urine with mercury from the skin or workplace air.
When results are interpreted, the urine values should be corrected for grams of creatinine in the sample, and should be expressed as
 g Hg/gram creatinine. In persons not occupationally exposed to mercury, urine levels rarely exceed 5
 g/g creatinine.
While many laboratories indicate that only levels above 150
 g/L should be considered toxic, there is strong evidence that early signs of mercury intoxication can be seen in workers excreting more than 50 µg Hg/L of urine (standardized for a urinary creatinine of 1 gram/L). This value of 50
 g/g creatinine is proposed by many experts as a biological threshold limit value for chronic exposure to mercury vapor, and in 1980 this was endorsed by a World Health
Organization study group.
Exposed individuals with levels above 50
 g/g creatinine should be placed in a non-exposed job until the reason for their over exposure has been identified and corrected and their urine levels have fallen below the biologic threshold limit value.
Table 3-1 - Reference Values for Total Mercury Concentrations in Biological Media
(General Population)
Matrix
Whole blood
Concentration
1 –8 µg/L
Reference
WHO (1990)
Fish Consumption
No fish meals
2 meals/week
2-4 meals/week
2.0 µg/L
4.8 µg/L
8.4 µg/L
Urine
Scalp hair
4 –5 µg/L
2 µg/g
WHO (1990)
WHO (1990)
Fish Consumption once/mo once/2 wk once/wk
1.4 µg/g
1.9 µg/g
2.5 µg/g
11.6 µg/g once/day
At least 90 percent of ingested monomethyl mercury (CH
3
Hg + ) from fish is absorbed by the body and is transported by the blood to tissues. As opposed to mercuric ion, CH
3
Hg + readily crosses tissue barriers. In brain tissue, CH
3
Hg + is slowly demethylated and retained by neural tissue. Both CH
3
Hg + and demethylated Hg +2 are reactive to cause neurological impairment. The primary elimination pathway for CH
3
Hg + is feces. CH
3
Hg + from blood crosses the intestinal barrier, is demethylated by gut organisms and leaves the body as Hg +2 . Insignificant amounts of
CH
3
Hg + are eliminated from the body via urine. The half-life of ingested CH
3
Hg + in blood is
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3
Hg + in blood reflects the average amount ingested over time because of the long half-life. Blood mercury levels always contain a background CH
3
Hg + concentration that derives from diet. The background monomethyl mercury concentration in blood is superimposed on any occupational contributions and can be dominant for individuals who consume large quantities of fish (Watanabe 1994).
The concentration of mercury in blood reflects exposure to organic mercury as well as metallic and inorganic mercury; thus it can be influenced by the consumption of fish containing methylmercury. Samples should always be taken at the same time of day near the end of the work week after several months of steady exposure. The blood should be collected in mercuryfree heparinized tubes after careful skin cleansing.
In unexposed individuals, the amount of mercury in blood is usually less then 2 µg/100 ml.
According to some experts, an average airborne concentration of 50 µg/m 3 meter corresponds to a mercury concentration in blood of about 3-3.5 µg/100 ml. Early effects of mercury toxicity have been found when the blood concentration exceeds 3 µg/100 ml. Any worker exceeding this level should be placed in a non-exposed job until dietary and workplace exposures have been evaluated and blood levels have returned to baseline.
Analysis of urine is a better indicator of Hg 0 inhalation exposure than is analysis of total Hg in blood, especially for working populations that have moderate to high fish diets. Since little
CH
3
Hg + is eliminated via urine, the urine Hg concentration (normalized to creatinine) more closely correlates with inhalation exposure. Constant dose rate inhalation exposures can be quantified to some extent but many variables must be considered for precise estimation.
Urinary levels of about 50 µg/g creatinine are seen after occupational exposure (continuous) to about 40 µg Hg/m 3 of air. An exposure of 40 µg mercury/m 3 of air will correspond to about 15-
20 µg Hg/liter of blood for an individual who does not consume significant amounts of fish. At a urinary mercury excretion level of 100 µg/g creatinine, there is a high probability of developing neurological signs of mercurial intoxication.
The amount of mercury in hair reflects mostly CH
3
Hg + ingestion as the incorporation of mercury into hair takes place primarily via the methylated form and not from mercuric ion. As hair can absorb some mercury vapor from work environments, the correlation of occupational exposure with scalp hair concentration is tenuous at best.
The toxicokinetics of dialkylmercury have not been studied sufficiently to have definitive data on the mechanisms of transport and elimination. Dialkylmercury is readily absorbed dermally and readily crosses tissue barriers. Hence its interactions with the body are likely more similar to
CH
3
Hg + than to Hg 0 . This would mean that the contribution of dialkyl mercury to the total concentration of mercury in blood would reflect the dose, equilibria with tissue and demethylation rate. By analogy with CH
3
Hg + , little dialkyl mercury should eliminate via urine.
Monitoring total mercury in blood should be the better method for determination of occupational exposure to dialkylmercury.
Dialkylmercury is estimated to be many times more toxic than elemental mercury on an equivalent (weight) dose basis but exact quantification of toxicokinetics awaits focused studies.
The current OSHA standard for dialkylmercury is 0.01 mg/m 3 of air averaged over an eight-hour work shift, with a ceiling level of 0.04 mg/m 3 . The derivation of these limits is suspect and they should not be relied on. The concentrations of organic mercury in unprocessed petroleum are generally assumed to be lower than for elemental and the exposure pathways for organic mercury are more hindered in petroleum occupations.
Medical monitoring is the periodic evaluation of exposed workers to insure that they are experiencing no adverse effects of potentially hazardous workplace exposures. For mercury,
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Confidential Draft medical monitoring serves as a backup for a program of routine air and biological monitoring, which are the primary means for insuring that exposure levels are below those associated with adverse health effects. Medical monitoring is seldom required if a rigorous air monitoring is in place and random biological monitoring does not reveal affected individuals.
A medical monitoring program, if required, should be designed to detect adverse effects of exposure as early as possible, at a stage where there are still reversible, so that exposures can be controlled and serious permanent adverse effects prevented. An initial medical examination should be performed on all employees exposed to potentially hazardous levels of mercury. The purpose of this examination is to provide a baseline for future health monitoring.
The examination should include a complete medical history and symptom questionnaire, with emphasis on the:

nervous system (target organ for chronic exposure).

kidneys (target organ for acute and chronic exposure).

oral cavity (target organ for chronic exposure).

lungs (target organ for acute exposure).

eyes (affected by chronic exposure).

skin (since mercury is a known skin sensitizer).
Signs and symptoms of the earliest signs of mercury intoxication should be elicited; these include personality changes, weight loss, irritability, fatigue, nervousness, loss of memory, indecision, and intellectual deterioration. Complaints of tremors and loss of coordination should also be sought. Physical examination should focus on the target organs described above. A baseline handwriting sample should be obtained. Laboratory evaluation should include at minimum a complete urinalysis.
This examination should be repeated annually. Results should be compared with the findings on the baseline examination for changes suggestive of mercury toxicity. Handwriting samples should be compared to the baseline sample for evidence of tremor. Interim evaluations should be conducted if symptoms suggestive of mercury intoxication are occurring.
The occupational risk from exposure to dialkylmercury, at present, is unknown due to the lack of detailed information on the precise concentrations in crude oil and gas condensate and due to the lack of definitive studies to measure dermal absorption efficiencies. Absent quantified risk assessments, precautions to avoid contact with hydrocarbons containing high levels of total mercury are warranted.
Estimation of the potential risk to oilfield workers due to dialkylmercury compounds in petroleum liquids is uncertain both because of the lack of data on prevalent concentrations and the lack of data on dermal absorption efficiency. Inhalation of large amounts of dialkylmercury in petroleum work environments is less likely than for elemental mercury due to its lower volatility. This is offset by the higher toxicity of the dialkyl species and may not be operative in situations involving hot work or closed space entry in warm vessels. Dermal exposure to condensate containing dialkylmercury is suspected to be a significant health risk because dermal absorption of organic mercury is much more facile than dermal absorption of elemental mercury based on solubility and chemical modeling. Data are lacking on the precise rates and efficiencies in both animals and humans. It is known that workers are routinely exposed to liquid hydrocarbons that
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Confidential Draft reportedly contain significant amounts of dialkylmercury. Chronic health deficiencies have not been reported suggesting that either the amount of dialkylmercury is over estimated or the rate of dermal absorption is low (or both). A recent case of exposure (and death) of a laboratory worker suggests the former hypothesis is more likely (Blayney 1997).
Ingestion of mercury is not a typical occupational hazard for workers, but ingested mercury is often a major contributing dose factor for those whose diets contain a high percentage of fish.
The mercury compound in fish is monomethyl mercury that is bio-accumulated and bioconcentrated in piscivorous populations. The predatory marine fish species (shark, tuna, swordfish, barracuda, marlin, mackerel) accumulate high concentrations, as do all predatory fresh water species (pike, bass). Mercury in fish that constitute a major portion of dietary intake can contribute significantly to the total concentrations in blood (but not in urine). The combination of dietary and occupational mercury can cause total exposure to exceed the threshold for chronic detriment. High fish diets also can obfuscate monitoring programs based on blood analysis for worker exposure to the extent that occupational intake can be overestimated.
Mercury and its compounds are neurotoxins. Inhalation of mercury vapor, ingestion of ionic mercury or dermal absorption of mercury compounds ultimately results in neurological dysfunction. The period of time between exposure and exhibition of symptoms varies considerably depending upon the type (absorbed mercury species) and magnitude of exposure.
Chronic exposure to mercury vapor results in psychological anomalies (excitability, memory loss, insomnia, and depression) and physical symptoms (weakness, fatigue, anorexia, weight loss). Tremors may develop in more advanced cases. Compromise of renal function is seen in acute, high dose cases.
3.5 Vapor Monitoring
Health and safety plans require monitoring the work atmospheric environment. This can be accomplished in a variety of ways.
Air Monitoring - Atmospheres inside vessels and in the proximity of opened vessels and piping should be analyzed for mercury vapor to assist decisions on worker protection. Since the local concentration of mercury vapor varies considerably depending upon temperature and air convection, rapid and numerous analyses are useful to understand the source and concentration of mercury vapor over time. Atmospheres in work areas are typically characterized using portable vapor analyzers. Monitoring concentrations of mercury vapor in plant equipment is not a routine operation in most processing plants unless there is a historical recognition of mercury in processed hydrocarbons and prior discovery in closed space atmospheres.
Determination of airborne mercury vapor also can be made using absorber tubes (Hydrar or
Hopcalite). Samples are collected at a measured flow rate (0.2 liter/minute) until a known volume (4 – 100 liters) is collected. Analysis is conducted by cold vapor atomic absorption spectroscopy. This method (OSHA ID-140, NIOSH 1994b) suffers form the fact that the cold vapor analytical technique is seldom logistically convenient to work locations and the time to make a determination can be long. Determination of airborne mercury vapor can be made using absorber tubes (Draeger) that give a visual indication of approximate mercury concentration in air. The Draeger tubes are only semi-quantitative and for this reason, portable vapor analyzers are more prevalently used.
The most common portable monitoring instrument for mercury vapor in air is the Jerome mercury analyzer, which can be used to examine mercury concentrations in work areas, vessels and ambient atmospheres. The Jerome mercury analyzer (Figure 2) operates by
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Confidential Draft flowing a known gas volume across a gold detector wire. Mercury in the gas volume is absorbed (amalgamates) with the gold changing its resistance, as measured by a Wheatstone bridge. The gold sensitivity is better than 95 percent for elemental mercury and better than 75% percent for organic mercury (reportedly). Hydrogen sulfide interferes with the Jerome detector to some extent and its use in situations where sour gas is prevalent is limited. Similarly, high humidity and some types of hydrocarbons affect the performance of the instrument requiring frequent regeneration and recalibration.
Figure 2 – Jerome Mercury Analyzer (Arizona Instruments)
AIR
PUMP
DETECTOR
.0 2 5
Figure 3 – Jerome Schematic
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The ambient mercury vapor background for non-contaminated (rural) sea level atmospheres is less than approximately 0.005 ug/m 3 . The atmospheric mercury concentration in urban industrial settings can vary between 0.005 and 0.20 ug/m 3 . In most gas plants that process mercury-laden gas and that also operate gas flares, the background atmospheric mercury concentration will depend on the proximity to the flare and prevailing wind.
Air monitoring programs for mercury vapor should include areas other than strictly work areas if the concentration of mercury in processed hydrocarbons is above 10 ppb. Offshore production and processing platforms are particularly at risk because of the likelihood of transferring mercury between maintenance and other areas on shoes and clothes. Contamination of laundry is especially problematic and difficult to remediate. Storage areas for waste that contains mercury require continuous monitoring programs to avoid vapor accumulations.
Extraordinary cleanliness and hygiene are beneficial to prevent transferring mercury from maintenance areas to living quarters on platforms or plant control rooms.
Passive Vapor Monitoring - Methods for determining personal exposure levels to inorganic mercury vapor are available. And consist of passive air samplers (PMS) that are relatively simple to use and also eliminate the need for sampling pumps. Passive samplers are designed to be analyzed using standard laboratory equipment. The PMS measures worker exposure levels as a time-weighted average over a broad range of mercury concentrations and sampling times. The PMS has been (OSHA) verified according to sampling rate, desorption efficiency, precision and accuracy, storage stability, reverse diffusion, face velocity dependence, and comparison of methods.
Mercury vapor enters the sampler by positive, controlled diffusion so that a known sample volume is taken for a given period of time. Mercury is completely adsorbed onto the solid sorbent. The sorbent capsule is then taken to a qualified laboratory where the sorbent is dissolved in acid and analyzed by flameless atomic absorption. The sampler holder is cleaned and reused.
Field testing and chamber studies have shown that reasonable accuracy and precision can be achieved without interference from moisture or other gases, including chlorine. The sampling rate varies with ambient temperature changes that affect the diffusion rate. This effect is small, but may be significant if sampling at unusually high or low temperatures. The sampling rate will remain substantially constant over a range of wind velocities but is affected by ambient pressure, which must be noted.
References
Blayney, M. B., Winn J. S., Nierenberg, D. W., "Letters; Chemical Safety - Handling
Dimethylmercury", Chemical and Engineering News, May 12, 1997.
Hathaway, G. J., Proctor, N. H., Hughes, J. P., and Fischman, M. L., “Proctor and Hughes'
Chemical Hazards of the Workplace”, Van Nostrand Reinhold, New York, NY (1991).
Hunter, D., The Diseases of Occupations , 5th ed., London, English Universities Press (1969).
OSHA Method No. ID-140, Occupational Safety and Health Administration, Inorganics Division,
OSHA Technical Center, Salt Lake City, Utah.
National Research Council, 2000, Toxicological Effects of Methylmercury , National Academy
Press, Washington, DC.
Nierenberg, D. W., "Letters: More on Working with Dimethylmercury," Chemical and
Engineering News, June 16, 1997.
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U. S. Occupational Safety a nd Health Administration, “Guideline for Mercury Vapor”, US OSHA
(1996).
U. S. Occupational Safety and Health Administration, “Occupational Health Guideline for
Organo (Alkyl) Mercury”, US OSHA (1996).
U.S. Environmental Protection Agency, “Mercury Study Report to Congress”, US EPA, EPA-
452R/R-97-004 (1997).
Watanabe, C. and Satoh, H.
, “Evolution of Our Understanding of Methylmercury as a Health
Threat”, Workshop on Risk Assessment Methodology for Neurobehavioral Toxicity
(SGOMSEC), June 1994, Rochester, New York.
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4.0 ENVIRONMENTAL ISSUES
Mercury in produced petroleum and natural gas has the potential to enter the biosphere and thus to contribute to global pools. Such contributions are not beneficial in any respect. It is incumbent upon those responsible for environmental protection policy in companies involved with production and processing of fossil fuels to recognize the potential impact of discharge of mercury from activities derived from energy production.
Combustion of fossil fuels has been identified as the major anthropogenic source of mercury emissions to the atmosphere. The mercury in combusted fuels originates from petroleum and coal, but coal accounts for the vast majority. Emissions are proportional to concentrations in the various fuels. The average amount of mercury in coal is approximately 100 ppb. The concentration of mercury in crude oil and natural gas is highly dependent on geologic location and varies between approximately 0.01 ppb and 10 ppm (wt.). Eventually, the mercury in combusted hydrocarbons contributes to the atmospheric mercury cycle where it distributes, by recently identified mechanisms and pathways, to marine and lacustrine ecosystems. The causes and consequences of mercury deposition to marine environments have been reviewed in Volume 4 of the U.S. EPA Mercury Report to Congress .
Mercury and its common chemical forms are designated as persistent, bioaccumulative and toxic (PBT) pollutants, which are defined as those substances that are persistent (months to years) in the environment, accumulate and concentrate in biota and that are toxic to organisms.
Mercury and its compounds are thus the subjects of numerous regulations that originate from both federal and regional agency jurisdictions. The statutes that regulate mercury discharges to the environment include provisions based on both human and aquatic life concerns.
The geochemical mechanisms by which mercury cycles in the environment are generally known in concept but some aspects of the cycle are incompletely understood in detail. The level of understanding, however, has improved markedly over the last few years and many of the aspects of the cycle can be described with a fair degree of confidence. The term cycle is used because of the movement of mercury between major pools at significant rates of flux.
Major pools are air and water. Geologic mercury is not considered a pool but contributes to the cycle. The movement is coincident with chemical transformations of mercury that are produced by physical, chemical and biologic forces. While the total amount of mercury in the world as a whole is constant, the amount in the biosphere is not. The amount of mercury mobilized and released into the biosphere has increased markedly over time, especially from human activities since the beginning of the industrial age.
Contributions of mercury to the biosphere originate from both natural and anthropogenic sources. The natural sources are volcanic activity; erosion of terrain; dissolution of mercury minerals in oceans, lakes and rivers; and a variety of other avenues that are not related to human activities. Mercury also enters the biosphere from industrial activities through its use as a raw material and from combustion of fossil fuels and waste. The use of mercury as an ingredient in manufactured products has been reduced in recent years and likely will be completely discontinued within the next decade or two.
The atmosphere is considered important because it is the mobilizing pathway for mercury deposition to remote regions not contiguous with industrial activities and thus provides the avenue for introduction of mercury to otherwise pristine environments. The estimate of the total annual global input to the atmospheric pool from all sources including natural, anthropogenic, and oceanic emissions is approximately 5,000 Mg.
Most of the mercury in the atmosphere exists as elemental mercury vapor, which can circulate in the atmosphere for more than a year and thus can be transported to regions far from the
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(evasion). From land, mercury re-enters the atmosphere from the transpiration of plants or as mercury adsorbed to mobilized particles. As it cycles between the atmosphere, land, and water, mercury undergoes numerous chemical and physical transformations, some of which are not completely understood in a quantitative fashion.
While most of the mercury in the atmosphere is elemental, most of the mercury in water, soil, sediments, or plants and animals is in the form of inorganic mercury salts and organometallics
(mostly methylmercury). Bacteria in sediments produce most of the methylated form of mercury but the exact mechanisms have yet to be completely defined. Although its concentration is a very small percentage of the amount in water, methylmercury concentrates in the aquatic food chain. Predatory organisms at the top of the aquatic food web acquire and accumulate the methylmercury in their diets and present elevated concentrations. While the concentration at the bottom of the aquatic food chain may be at the low parts per trillion level, at the top, fish tissue can present mercury concentrations in excess of 1 ppm. Bioconcentration factors are thus on the order of 10 4 to 10 5 .
Inorganic mercury (oxidized and elemental) is less efficiently absorbed and more readily eliminated from the body than methylmercury and, therefore, does not tend to bioaccumulate in fish or other organisms. Inorganic mercury (mercuric ion, mercury complexed to inorganic ligands) is toxic to organisms, however, and is the dominant toxic species in water. Although environmentally important, the toxicity of inorganic mercury is secondary in consideration to its role as the species that is acted on by bacteria to produce methylmercury that concentrates in the aquatic food chain. It is the rising amount of methylmercury in fish and the known effects of inorganic mercury on aquatic organisms that are the principal reasons to reduce the human contribution to the mercury cycle. Since natural emissions are largely outside the domain of human influence, attention is focused on man’s contribution and on ways to minimize it.
Mercury in produced hydrocarbons may escape to the environment by several avenues of egress. These avenues may be generally categorized as wastewater, solid waste streams and air emissions. Wastewaters originate in production operations in the form of produced water and in refining and gas processing as wastewater. Solid waste streams are generated in production, transportation and in refining. Air emissions originate from fugitive emissions from process equipment and from combustion, with combustion thought to be vastly dominant as a possible avenue by which mercury in oil and gas may be transferred from produced hydrocarbons to the environment.
It is useful, therefore, to examine the major pathways (solids, liquids and gas) and to further categorize mercury emissions by industry segment, meaning production, transportation, and processing systems. Mercury in combusted fuels is examined in detail as this is considered to be the dominant avenue of transfer of mercury in fossil fuels to the atmosphere based on the existing data and based on the analogy to coal combustion recently developed.
The industry distinguishes between upstream and downstream operations. The upstream category refers to primary production and whatever processing is necessary to place the produced fluids in the transportation system. Downstream operations are refining and gas processing that produce salable products. Natural gas is transported exclusively via pipeline in the U.S. while crude oil is transported by a variety of ways with pipelines and tankers conveying the overwhelming majority.
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4.1 Mercury Emissions to Water
The main wastewater streams that derive from petroleum production and processing are produced water from both oil and gas production and refinery wastewaters. Very minor amounts of water (relative to produced water and refinery wastewater) derive from gas processing and these are mainly water from separators at gas plants (essentially produced waters) and condensed water from dehydration. No wastewater streams originate from transportation systems other than the very small amounts that come from pipeline pigging operations and tanker ballast.
Produced Water
Normal production operations of both crude oil and natural gas involve primary separation of water, gas and oil. Separated water (referred to as produced water when separated close to the well) is either discharged (to an ocean, lake or stream or evaporation pond) or re-injected
(usually to the formation it came from). Re-injection is utilized to enhance oil recovery (EOR) or to comply with regulatory requirements stemming from environmental concerns.
Produced water is the largest waste stream in the oil and gas industry. Produced water varies greatly in composition and salinity, depending on the geologic source of the water, type of production, and the treatment of the water once brought to the surface. The salinity of produced water ranges from essentially fresh water to brines that are several times more saline than seawater. Some countries allow surface discharge of produced water, but many do not.
Produced water originating on offshore platforms usually is discharged to the ocean unless the platforms are located in sensitive areas or the water is unusually hazardous due to a particular characteristic (salinity, hydrocarbon content, toxicity). In sensitive coastal areas of the U.S., produced water is closely regulated with permit requirements that severely limit options for discharge thus necessitating treatment or re-injection.
Only limited data are available concerning mercury in produced waters and essentially none concerning speciation. Produced waters may contain suspended HgS, elemental Hg 0 and/or oxidized forms but the relative amounts in any produced waters are not reported relative to the forms that occur in co-produced hydrocarbons. HgS and Hg 0 are the dominant forms found in produced water associated with gas production in the Gulf of Thailand (Frankiewicz and
Tussaneyakul 1997). Gas condensates originating in the Gulf of Thailand contain between 100 and 1000 ppb total mercury (mostly elemental).
Total mercury concentrations in produced waters were only recently reported as, prior to approximately 1990, analytical methods were insufficient to detect the low ppb and ppt levels typically now found. Tables 4-1 and 4-2 summarize the available data.
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Table 4-1 – Mercury in Produced Waters
Location
Gulf of Mexico
Gulf of Mexico
Ocean
Ocean
Gulf of Mexico Coastal LA
North Sea
North Sea
North Sea
North Sea
North Sea
Gulf of Mexico
Brent
Northern
Central
UK
Dutch
Coastal
Discharge Rate
(10 9 L/y)
0.64
0.40
1.74
140
THg
(ppb)
<0.010
<0.010
0.007 - 27;
Mean 7.08; SD 11.26
<3
<3
<3
<1
4
<0.01 – 0.2, n = 37
Reference
Ray 1998
Ray 1998
Meinhold et al. 1996
Jacobs et al. 1992
Jacobs et al. 1992
Jacobs et al. 1992
Jacobs et al. 1992
Jacobs et al. 1992
Trefry et al. 1996
Table 4-2 - Mercury Concentrations in Produced Water
(Southern CA, year 1990; Raco 1993)
Platform No. Volume
Samples (10 6 L/y)
THg
(ppb)
Elly
Edith
Hogan
Hillhouse
A
B
C
Habitat
2
1
2
1
2
2
2
1
1
176
225
361
1184
726
836
21
<1
<1
<1
<1
0.5
2.5
<1
<1
Irene
Grace
Gail
Gilda
4
2
5
2
608
139
273
704
0.5
1
1.6
<1
5,254
Data from National Pollutant Discharge Elimination System discharge monitoring reports submitted to US EPA Region 9, San
Francisco.
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Wastewater
Speciation of mercury in wastewater is largely unknown. Post-biological treatment waters from municipal sewage treatment (similar in process to refinery biological water treatment) generates mercury compound speciation such that less than 5 percent (of the total mercury concentration) exists as monomethylmercury, less than 0.01 percent as dialkylmercury, less than 0.1 percent as Hg 0 , possibly 10-30 percent suspended particulate Hg, less than 10 percent labile Hg(2+), and between 60 and 90 as organochelated Hg(2+). The concentration of total mercury in effluents from (municipal) sewage treatment facilities is in the range of 5-20 ng/L (Bloom and
Falke 1996).
The mean and range of mercury concentration in oil refinery wastewater cannot be stated with certainty. Very little information is available in the published literature that speaks directly to this issue. The EPA study of refinery effluents from the early 80’s (Ruddy 1982) provides a mean close to 1 ppb but the methodology to arrive at this number is poorly documented. The advances in mercury analysis procedures that have occurred since that time may allow a more accurate estimate in the future, but now it can only be stated that the mean is likely less than 1 ppb and that the level varies from refinery to refinery and with the amount of mercury in processed crude.
4.2 Mercury Emissions to Air
The primary opportunities for atmospheric emissions of mercury in oil and gas production and processing operations are fuel combustion, mercury in fugitive emissions and gas flares at primary production operations. Flared gas typically originates from gas co-produced with oil production in situations where economics dictate that flaring is less expensive than collection and transport. For refineries, volatile and particulate mercury emissions to the atmosphere are postulated come mostly from the fuels that are used to fire refinery process heaters and possibly some (unknown) amount from fugitive emissions (mostly process vents).
4.3 Mercury Emissions via Solid Waste Streams
Most solid wastes directly associated with exploration and crude oil or natural gas production are not considered hazardous wastes. These categories include drilling fluids and other wastes directly related to production. For this reason, such wastes are infrequently scrutinized for metals content and data are scarce upon which one might estimate the totals for this category.
Drilling wastes primarily consist of the extracted cuttings and drilling mud from the boreholes of exploratory wells (also workovers and injection wells). Data on mercury content of drilling wastes are not generally reported but TCLP test results typically do not identify this category of waste as characteristically toxic due to mercury content. The reason for this fact is that subterranean mercury (as would be in the cuttings from drilling operations) is found almost exclusively as HgS or as a substitutional element in minerals (mostly pyrites). In addition most of the mercury in drilling muds comes from the mineral ingredients (barite) used to make the mud, not from the drill cuttings, except in rare situations. In these mineral forms mercury is not water soluble and thus not extractable by TCLP.
Mulyono et al. (1996) reported analysis of four water-base drilling muds (Indonesia) as having mercury concentrations between 144 and 2141 ppb (mean 750 ppb). These concentrations were for fresh mud and the concentrations did not change after use. Approximately 20 percent of the mercury was nitric acid extractable.
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References
Bloom, N. S. and A. Falke, 1996, The Importance of Chemical Speciation in the Assessment and Treatment of Hg, As, and Se Contaminated Waste Streams, Pacific Northwest Pollution
Control Association Conference, Boise, ID, October 27-30.
Frankiewicz, T. C and S. Tussaneyakul, 1997, Upgrading production facilities on the Funan platform to remove hydrocarbons and heavy metals from produced water, Proceedings:
Offshore Technology Conference, May 1997, pp. 299-310.
Jacobs, R., Grant, R., Kwant, J., Maequine, J., and E. Mentzer, 1992, The Composition of
Produced Water from Shell Operated Oil and Gas Production in the North Sea, in Produced
Water, Technological and Environmental Issues and Solutions , Ray, J., ed., Plenum Press,
New York, NY.
Meinhold, A., DePhillips, M., and S. Holtzman, 1996, Final Report: Risk Assessment for
Produced Water Discharges to Louisiana Open Bays, Brookhaven National Laboratory Report
No. BNL-62579 for U.S. DOE, Brookhaven, NY.
Mulyono, M., Desrina, R., Priatna, R., Sudewo, B., and M. Sawolo, 1996, Heavy Metals in
Water Base Drilling Muds Used in Several Locations of Oil Fields in Indonesia, SPE paper No.
35980.
Petrusak,R., Freeman, B., and G. Smith, 2000, Baseline Characterization of U.S. Exploration and Production Wastes and Waste Management, SPE Paper No. 63097 presented at the SPE
Annual Technical Conference and Exhibition, Dallas, TX, October.
Raco, V., 1993, Estimated Discharges from Offshore Oil Platforms in the Southern California
Bight (Santa Barbara Channel and Santa Maria Basin) in 1990, Southern California Coastal
Water Research Project Annual Report 1992-93, Los Angeles, CA.
Ray, J. P., 1998, Findings of the Offshore Operators Committee Produced Water
Bioaccumulation Study, SPE Paper No. 46838, Society of Petroleum Engineers, Dallas, TX.
Ruddy, D., 1982, Development Document for Effluent Limitations Guidelines, New Source
Performance Standards, and Pretreatment Standards for the Petroleum Refining Point Source
Category, EPA/440/1-82/014 (NTIS PB83-172569), Office of Water Regulations and Standards,
Washington, DC.
Stephenson, M., 1992, A Survey of Produced Water Studies, Produced Water: Technological and Environmental Issues and Solutions , Ray, J., ed., Plenum Press, New York, NY.
Trefry, J., Trocine, R., Naito, K., and S. Metz, 1996, Assessing the Potential for Enhanced
Bioaccumulation of Heavy Metals from Produced Water Discharges to the Gulf of Mexico, in
Produced Water 2, Environmental Issues and Mitigation Technologies, Reed, M. and Johnsen,
S., eds., Plenum Press, New York, NY.
U.S. EPA, 1996, 1995 Updates: Water quality criteria documents for the protection of aquatic life in ambient water, EPA/820/B-96/001 (NTIS PB98-153067), Office of Water, Washington,
DC.
U.S. EPA, 1996, Waste Minimization for Selected Residuals in the Petroleum Refining Industry,
Office of Solid Waste and Emergency Response, EPA/530/R-96/009 (NTIS PB97-121180),
Washington, DC.
U.S. EPA, 1997, Mercury Study Report to Congress, EPA/452/R-97/003 (NTIS PB98-124738),
Office of Air Quality Planning and Standards, Research Triangle Park, NC and Office of
Research and Development, Washington, DC.
Wilhelm, S. M., 2001, An Estimate of Mercury Emissions from Petroleum, in press, Environ, Sci.
Tech .
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5.0
TRAINING (see Appendix J)
Worker training is essential to ensure the safety and heath of workers and contractors. Training is also essential to ensure compliance with environmental policy. Workers should be trained to anticipate situations in which they could be exposed, provided appropriate personal protection equipment (PPE), trained in the use of PPE and taught to recognize the symptoms of exposure.
Workers should attend training courses that provide the basic technical information concerning mercury in hydrocarbons and provide the safety information that workers need to avoid inhalation of mercury vapor and contact with organic mercury. The major topics in such training courses should include:

Basic chemistry of mercury.

Origin and consequence of mercury in plant feeds.

Toxicology of mercury (how to recognize intoxication).

Personal protection to prevent inhalation and dermal absorption.

Confined space procedures.

Mercury vapor monitoring.

Waste handling procedures.

Operation and calibration of mercury vapor analyzers.

Sampling and analysis for mercury.

Company policy review.

Medical screening requirements.
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6.0 CONCLUSIONS and RECCOMMENDATIONS
Companies that process oil and natural gas that contains mercury should adopt HSE policies that identify mercury as a special hazard and concern. Clear instructions should be provided to responsible parties on the procedures to be followed to protect the health and safety of workers and the environment. The policy and enumerated procedures should address at a minimum, the following issues:

Risk Assessment - The assessment of risk entails examination of risks to people, to equipment and a thorough examination of liabilities associated with failure to comply with environmental regulations. Risk assessments should be formal, comprehensive, quantitative and continuous. Assessment of risk is impossible absent a thorough and current knowledge of the concentrations of mercury in process streams, treatment fluids and effluents. In addition, assessment of risk can only be accomplished form a thorough understanding of the chemistry of mercury and its chemical compounds.

Worker Health and Safety – The major points that need to be addressed to ensure worker health and safety are monitoring of the work place for mercury vapor and personal protective equipment (and a clear policy for its utilization). Biological monitoring of individuals deemed at risk should be considered as an option in extreme circumstances. The health and safety policy is heavily impacted by the presence of organic mercury in process streams, thus a concerted effort should be made to identify organic mercury in processed hydrocarbons.

Environmental Protection – Avenues of egress of mercury from production and processing facilities should be critically examined and monitored for mercury content. In certain circumstances, process effluents should be treated to remove and segregate mercury compounds so as to meet local regulations and/or international norms.

Training - Worker training is essential to ensure the safety and heath of workers and also is essential to ensure compliance with environmental policy. Information concerning mercury and methods to avoid exposure should be a well-defined segment of the overall safety program.
The above enumerated guidelines certainly apply to PDO but, in addition, the following particular recommendations are offered.
1. PDO should modify the “Permit to Work System” to provide procedures specific to mercury that may be found in the work place. An additional section on mercury (similar to the section on NORM) should be added. The sections that require modification are:
 Welding (gas and arc)
 Confined space entry
 Handling hazardous substances
 Cutting pipe systems
 Shot-blasting
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2. Some PDO policy documents need to be modified to add information and procedures specific to mercury. The following documents should be examined:
 Health, Safety and Environment Specification, Occupational Health, SP-1231-
R1 (February 2002) – A section on mercury needs to be added. The section should identify methods to anticipate work situations that could bring people in contact with vaporous mercury and/or dissolved mercury in fluids. Specification of PPE, monitoring methods and medical requirements are essential.
 HSE Management Procedure: Hazards Management, PR-1055 (Dec. 1998) – An environmental assessment specific to mercury should be conducted. Occupational activities that are potentially hazardous due to the presence on mercury in produced fluids and/or equipment should be identified.
 HSE Management Procedure - Objectives and Targets, PR-1056 (December
1998) – It may be useful to identify the corporate HSE policy guideline document for mercury and to state a generation plan for dealing with mercury contamination of the gas process.
3. Continued acquisition of analytical data on a routine basis is necessary to predict product and process contamination.
4. The anticipated acquisition and implementation of mercury removal systems for LPG and gas will certainly improve product quality but they it will not improve the level of contamination by mercury of the CPP. Continued attention to monitoring, decontamination and waste issues is required.
5. Environmental impacts associated with mercury should be quantitatively assessed.
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