Cover page (Title, authors, Date)
Hydrogen Sulfide
Executive summary
Table of contents
Introduction
Hydrogen sulfide gas (H2S) can impact on humans and the environment in many ways over a
variety of scales, although it is at the local scale that is of most immediate concern for
humans.
Hydrogen sulfide bits
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Properties
In low concentrations H2S is identifiable by its pungent odour, and is widely known as rotten
egg gas. The gas is toxic, colourless, and flammable and is heavier than air, which makes it
most likely to accumulate in confined spaces or low lying pits or wells (Snyder et. al. 1995, p.
200).
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Production
The production of H2S occurs as sulphate is reduced to sulphide by bacteria in an anoxic
environment. This process occurs in the built environment in both industrial and waste
services, and is an unfortunate side effect of providing these essential services. Toxic H2S is
also produced in the natural environment, although there tend to be fewer interactions
between humans and H2S in this setting.
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Occurrence
As a proportion of the atmosphere H2S makes up approximately 0.0001ppm (Li, Hsu &
Moore 2009, p. 387). In the natural environment H2S is produced in anoxic environments,
such as enclosed stagnant waters or in active geothermal zones.
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Uses
H2S is a by-product of certain industrial and waste disposal processes, and is generally
considered to be an unwanted hazard. At the micro-scale, it is produced in the human body
and researchers are beginning to understand the benefits it provides to human health in low
concentrations (Li, Hsu & Moore 2009).
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Toxicity
At high concentrations H2S becomes a health problem for people. Safe Work Australia
guidelines limit workers to exposure of 10ppm averaged over the course of an eight hour
day, with an absolute limit of 15ppm at any time (Safe Work Australia 2011). Sustained
exposure at these low levels can lead to illness and irritation. Health impacts become
increasingly more severe as concentrations and exposure rise, with high concentrations at
around 1000ppm leading to almost immediate death (Yalamanchili & Smith 2008).
Waste bits
Waste produced by human society and the manner in which it is stored results in the
production of H2S. The odour, corrosive nature and toxicity of H2S poses a number of
problems for waste disposal, and these need to be managed for the maintenance of
infrastructure and the protection of human health.
Industrial bits
Description of the issue
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Toxicity
According to the National Pollutant Inventory (NPI) (2010) exposure to levels from 5ppm up
to 50ppm begins to cause irritation to the airways and the eyes, at 100ppm it becomes
hazardous to human health when exposed to a sustained dose for over an hour, potentially
resulting in death. Between 100-150ppm olfactory senses become disabled, meaning the
rotten egg smell is no longer present (Yalamanchili & Smith 2008). Above this level even
brief exposure becomes life threatening, with time required to cause death reducing as the
concentration rises. Knockout occurs immediately with inhalation at around 800ppm and
death follows shortly after (Yalamanchili & Smith 2008).
The toxicity of H2S at concentrations above ~ 1000ppm makes it a very efficient killer. This
characteristic of H2S has led to numerous instances where people intending to commit
suicide produce H2S for this purpose (Maebashi et. al. 2011, p. 91). On a larger scale, it has
been theorised that H2S has been partly responsible for the mass extinction event that
occurred at the end of the Permian period. H2S would have contributed in two ways, first in
its role as an ozone depleting gas, and secondly by poisoning the eukaryotic species as the
H2S concentration multiplied (Knoll et. al. 2007).
Waste
Human activities are responsible for the production of a significant quantity of waste. This
waste may occur as refuse, which is generally disposed of and stored as landfill; or
alternatively, human faecal waste, which is stored and often treated before being released
into the environment. One of the consequences of concentrating this waste is the
production of H2S.
Landfill generates a number of environmental challenges, one of which is the production of
gases resulting from the decomposition of waste material. Amongst the hazardous gases
produced by landfill is H2S, which generally occurs in low concentrations (Heaney et. al.
2011, p. 847). The study by Heaney et. al. (2011) suggests that people living in close
proximity to landfill sites may suffer negative physical effects from exposure to H2S and
other landfill related gases. These are apart from the general negative mental reactions to
exposure to unpleasant odorous gases. Although, Heaney et. al. (2011) do not establish
whether the negative physical reactions are brought on by psychological responses to the
malodour. This experience suggests that although there is the potential for illness from
exposure to landfill generated H2S, most negative reactions are resulting from a dislike of
the pungent odour.
The presence of H2S occurring in response to the treatment of sewage is potentially far
more serious than in the landfill scenario. H2S forms during the treatment of waste in an
anaerobic environment, where oxygen phobic bacteria reduce sulfate to sulfide, producing
the toxic gas (US EPA 1991, p. 5). Wastewater is transported and often stored in enclosed
spaces, the resulting limited aeration and the confinement of these spaces both encourage
the production of H2S and allow its concentration to multiply (US EPA 1991, p. 5). The
corrosive nature of H2S damages sewerage infrastructure and produces leakage, this results
in significantly increased maintenance requirements (US EPA 1991). There have been a
number of incidents that have resulted in the deaths of workers in the wastewater industry
due to H2S exposure. In two instances the toxic exposure occurred within the sewer line,
and was worsened by the difficulties in extracting the victim from the confined and toxic
location (Yalamanchili & Smith 2008; Christia-Lotter et. al. 2007). These deaths only
highlight the difficulty in managing H2S emissions whilst providing essential waste services.
Industrial
Management Approach(s)
Waste
Waste is an inevitable by-product of human society, therefore dealing with toxic H2S will be
an ongoing issue. Management solutions for H2S will involve both separating people from
the hazard and attempting to minimise production of the gas. In the case of landfill, ideally
communities will be located with enough separation to avoid the odours from these sites.
Where communities are impacted by malodour this can be managed with liners, capture of
leachate and regular cover with new waste (Heaney et. al. 2011, p. 847). Ultimately whilst
H2S is not attributed to significant negative health effects there will be limits to preventative
measures.
There are a number of approaches for managing the hazard created by the transport and
storage of sewage. In existing wastewater infrastructure managing the production of H2S
may involve chemical measures or aeration. There are a number of chemical procedures for
removing H2S from a sewerage system, these may include Hydrogen Peroxide or Chlorine
(US EPA 1991, p. 4-6). In these cases the sulfide component of the H2S is oxidised by the
chemicals, removing the gas. The US EPA (1991, p. 4-6) also suggests the use of iron salts to
react with the H2S to produce a precipitate that is insoluble. Alternately, measures could be
taken to aerate the sewer, removing the anoxic environment that is essential for the H2S to
form. Aeration could occur by injecting air or oxygen into the sewer (US EPA 1991 p. 4-6).
These methods of reducing the production of H2S would depend on expense and the
available infrastructure.
Building new infrastructure provides an opportunity to mitigate the impacts of H2S on the
sewerage system. Once again, the problem may require a solution that involves adding
chemicals to counter H2S production. The sewerage system can be designed taking account
of this and be constructed with infrastructure such as chemical addition stations, allowing
the most efficient delivery of suppressing chemicals (US EPA 1991, p. 4-7). Alternatively, the
design can ensure the sewerage system remains oxygenated. The methods predominantly
used include ensuring high velocities in the sewer, providing natural ventilation and creating
an environment that encourages turbulence (US EPA 1991, p. 4-10). Whilst this
infrastructure may be beneficial in new developments, the heaviest populations are
concentrated in existing centres, meaning there is less opportunity to build entirely new
sewerage infrastructure. Ultimately, personnel working potentially contaminated
environments will rely on gas monitoring equipment and self contained breathing apparatus
for personal protection.
Industrial
Summary and Conclusions
References
Christia-Lotter, A., Bartoli, C., Piercechi-Marti, M., Demory, D., Pelissier-Alicot, A., Sanvoisin,
A. & Leonetti, G. 2007, ‘Fatal occupational inhalation of hydrogen sulfide’, Forensic
Science International, vol. 169, pp. 206-209.
Heaney, C., Wing, S., Campbell, R., Caldwell, D., Hopkins, B., Richardson, D. & Yeatts, K.
2011, ‘Relation between malodour, ambient hydrogen sulfide, and health in a
community bordering a landfill, Environmental Research, vol. 111, pp. 847-852.
Li, L., Hsu, A. & Moore, P. 2009, ‘Actions and interactions of nitric oxide, carbon monoxide
and hydrogen sulphide in the cardiovascular system and in inflammation – a tale of
three gases!’, Pharmacology & Therapeutics, vol. 123, pp. 386-400.
Maebashi, K., Iwadate, K., Sakai, K., Takatsu, A., Fukui, K., Aoyagi, M., Ochiai, E. & Nagai, T.
2011, ‘Toxicological analysis of 17 autopsy cases of hydrogen sulfide poisoning
resulting from the inhalation of intentionally generated hydrogen sulfide gas’,
Forensic Science International, vol. 207, pp. 91-95.
National Pollution Inventory 2010, Department of Sustainability, Environment, Water,
Population and Communities, Canberra, ACT, Retrieved 20 Oct 12 from
http://www.npi.gov.au/substances/hydrogen-sulfide/health.html
Safe Work Australia 2011, Workplace exposure standards for airborne contaminants,
Retrieved 21 Oct 12 from
http://www.safeworkaustralia.gov.au/sites/swa/AboutSafeWorkAustralia/WhatWeD
o/Publications/Documents/639/Workplace_Exposure_Standards_for_Airborne_Cont
aminants.docx - 22/12/2011
Snyder, J., Safir, E., Summerville, G. & Middleberg, R. 1995, ‘Occupational fatality and
persistent neurological sequelae after mass exposure to hydrogen sulfide’, American
Journal of Emergency Medicine, vol. 13, no. 2, pp. 199-203.
Transportation Safety Board of Canada 2009, Pipeline Investigation Report P09H0006,
Retrieved 12 Oct 12 from http://www.tsb.gc.ca/eng/rapportsreports/pipeline/2009/p09h0006/p09h0006.asp
United States Environmental Protection Agency, 1991, Hydrogen Sulfide corrosion in
wastewater collection and treatment systems, Retrieved 10 Oct 12 from
http://www.epa.gov/nscep/index.html
Yalamanchili, C. & Smith, M. 2008, ‘Acute hydrogen sulfide toxicity due to sewer gas
exposure’, American Journal of Emergency Medicine, vol. 26, pp. 518.e5-518.e7.
Appendices