SEHIC TTHM Drinking Water Measure
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TTHM DRINKING WATER INDICATOR:
Distribution of the total population and percent of population served
by level of Total Trihalomethanes (TTHMs) in finished water
(users of public water supplies only).
Measurement
Units
Geographic
Area
Population in number of persons and % of population served by public water systems
TTHM concentration in ug/L
Other factors as categories (e.g. state, year, quarter, season, source type, disinfection process)
Scope: State level, perhaps county or sub-county level depending on ability to locate water systems.
Measures Of
Frequency
Time Period
Year, Quarter, Season
Significance
&
Background
TTHMs represent four different compounds (chloroform, chlorodibromomethane,
bromodichloromethane, bromoform) that arise as a result of chlorinating drinking water containing
organic acids. Chlorination is used to inactivate microbiological contaminants and provide a residual
level is used for continued protection. TTHMs are one indicator of a class of chemicals, disinfection
byproducts (DBPs), created from the reaction of chlorine with organic material.
2000 to most recent year with complete data
Concern regarding the carcinogenic potential of TTHMs and DBPs in community water supplies was
raised in the early 1980’s when they were linked to bladder and colon cancer. More recent evidence
suggests that TTHMs and DBPs may impact fetal growth and development of young children leading
to fetal growth restriction and certain birth defects. There is also some evidence to suggest that
individuals’ genetic makeup can also increase their susceptibility and potential for developing cancer.
TTHMs are formed from the reaction of total organic carbon (humic acids) and chlorine during
treatment and/or distribution; the formation rate is primarily a function of concentrations of the
precursors and time of reaction. Sources of organic matter in the source water can be both natural or
man-made from non-point sources such as agricultural run-off. Consequently, TTHM levels can vary
widely at different times of the year, and at different points in the distribution system.
The potential for population exposure to TTHMs is high as many public water supply systems rely on
surface water which is more likely to have significant levels of dissolved organic material; all PWS
using surface water provide disinfection and chlorination is a common method of disinfection. Efforts
to reduce TTHM formation within public water supplies must balance the importance of controlling
microbial risks in drinking water.
Rationale
Understanding the distribution of the population served water from public water supplies with various
levels of TTHMs provides practitioners with an understanding of the potential numbers, and
proportion, of populations being exposed to varying levels of TTHMs. Understanding this distribution
is important for public health as current research indicates that there may health risks corresponding
to water levels below the MCL. Further the current MCL for TTHMs is an engineering based standard
that corresponds to a 1 * 10-4 lifetime cancer risk. Because of this generating the distribution of
concentrations is preferable to a measure that is a simple proportion of the population served water
over the MCL or some other health-based reference value that might be revised at a later date. The
potential for population exposure to TTHMs is significant as community water supplies supply water to
85% of the US population. Even in the states which have the highest proportion of the population not
served by CWS, over 60% are served by CWS.
The measure allows for comparisons of the population distribution of potential TTHM exposures
between states, over time, by season, and potentially across demographic groups. Being able to
examine such comparisons on a population basis, rather than on the number of water systems,
provides useful information for prioritizing public health efforts, directing research, and potentially
identifying groups at higher risk. Potential vulnerable populations would include women of
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childbearing age, and children.
As the potential for TTHM creation is based on both the organic composition of the raw water (which
varies by season), the type of treatment train, and the type(s) of disinfection processes used,
generating the measure stratified by source type (surface, ground, purchased), season, and type of
disinfection, may provide insight into the underlying factors that drive the distribution of potential
exposure at the population level.
Limitations Of
Measure and
Data
In the future, if new scientific evidence strongly suggest that there are health concerns at levels below
the MCL, this population based indicator can be used to retrospectively identify populations at greater
or lower risk based on their historical exposures. In addition we can use this indicator in conjunction
with other health effect/outcome indicators to examine if there is a correlation between health effects
and exposures to TTHMs at concentrations lower than the MCL. Such correlations would be useful in
directing further research.
Estimates of the potential for exposure to populations are only applicable to populations on
community water supplies; TTHM data are generally not available for unregulated small water systems
private domestic wells. While many of these systems use chlorination, users would not be expected to
face potential exposures as groundwater is usually low in organic material.
Estimates of the population served by each CWS as reported yearly by the water purveyor may not be
accurate as they are usually based on the number of residential connections and an assumed average
number of residents per connection. In some cases a connection to an multi-family unit may be
counted as a single connections.
Demographic information about specific populations, needed to generate distributions for
demographic sub-populations, is not collected or reported by purveyors. Using demographic data
from the US Census or other population-based surveys requires a method for linking a specific water
system to a population unit of analysis (e.g. block group). This requires knowledge of the extent of the
distribution system for each water system, or some geographic aggregation of water systems. The
extent of distribution systems is generally not available.
The measurements are taken at ‘representative’ points to the distribution system and do not measure
the actual concentrations coming out of residential taps. The concentration of TTHMs can change
during distribution; this variability in concentrations within a distribution system is not captured.
TTHMs are a surrogate for a range of DBPs, each with different toxicities For example, chloroform is
carcinogenic. Therefore some detail on potential toxicity may be lost by combining concentrations of
all TTHMs.
The indicator provides annual or quarterly averages; extreme values on the low or high end of the
distribution are lost. While the risk of cancer may be more strongly associated with long-term average
exposures, risks of adverse reproductive effects may be associated with short-term or high-level
exposures during critical developmental stages.
The monitoring requirements for TTHMs will change under the Stage 2 Disinfectants and Disinfection
Byproducts Rule (e.g., location-specific running averages will be used and monitoring locations will be
chosen based on where the highest levels of TTHMs and HHAs are observed). This may affect our
ability to make meaningful comparisons over time using this measure.
The actual levels of exposure depend on a number of behavioral and household factors (e.g.
consumption of bottled water, showering and bathing habits). These factors can be responsible for
large variations in actual exposures given a set level of TTHMs at the service connection. While
reference values are available for these factors, there are regional and demographic differences in the
behaviors and factors that are not taken into account. While this limits this indicator as a measure of
exposure, it is still a valuable measure of potential exposure, and to identify regions or water systems
which may need to be targeted for improvement.
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Data
Resources
State water quality and water system data collected to satisfy requirements of the SDWA.
Technical
Capacity
Low to moderate technical capacity required. Accessing and extracting data may be most difficult part.
Related Sets
Of Indicators
EPA Draft Report on the Environment (Exhibit 2-7), Healthy People 2010, CSTE,
U.S. EPA: America’s Children and the Environment, 2nd ed. Washington, DC: U.S. EPA, Office of Children’s
Health Protection, 2003.
Secretariat - Commission for Environmental Cooperation. Children’s Health and the Environment in North
America. A First Report on Available Indicators and Measures. January 2006.
Drinking
Water (2)
Additional
Data To
Collect
(a) Percentage of children (households) without access to treated water (b)
Percentage of children living in areas served by public water systems in
violation of local standards
FOR DISTRIBUTIONS BY DEMOGRAPHIC FACTORS:
geographic boundaries of PWS, spatially linked to US Census data, including demographic
characteristics for each block/block group.
FOR ESTIMATE OF TTHM FORMATION POTENTIAL:
Source water type, total organic carbon; treatment type; levels of chlorine
References
FOR ESTIMATES OF EXPOSURE:
Consumption patterns (consumption of bottled water, volume consumed at home, type of drink
hot/boiled); showering, bathing, swimming frequency and duration for demographic sub-groups..
N. J. Ashbolt. 2004. Risk analysis of drinking water microbial contamination versus disinfection by-products
(DBPs). Toxicology. 198(1-3):255-262.
R. A Howd. 2002. Can we protect everybody from drinking water contaminants? International Journal of
Toxicology 21:389–395.
M. Koivusalo and T. Vartiainen. 1997. Drinking water chlorination by-products and cancer. Reviews in
Environmental Health 12(2):81-90.
M. J. Nieuwenhuijsen, M. B. Toledano, N. E. Eaton, J. Fawell and P.Elliott. 2000. Chlorination disinfection
byproducts in water and their association with adverse reproductive outcomes: a review. Occupational and
Environmental Medicine 57:73-85.
M. B. Toledano, M. J. Nieuwenhuijsen, N. Best, H. Whitaker, P. Hambly, C. de Hoogh, J. Fawell, L. Jarup, and
P. Elliott. 2005. Relation of trihalomethane concentrations in public water supplies to stillbirth and birth weight
in three water regions in England. Environmental Health Perspectives 113:225–232.
Porter CK, Putnam SD, Hunting KL, Riddle MR. 2005. The effect of trihalomethane and haloacetic acid
exposure on fetal growth in a Maryland county. American Journal of Epidemiology 162(4):334-344.
http://www.epa.gov/ogwdw/disinfection/stage2/basicinformation.html
http://www.epa.gov/ogwdw/disinfection/stage2/pdfs/assesment_stage2_occurance_main.pdf
http://www.epa.gov/ogwdw/disinfection/stage2/pdfs/bibliography_stage2_frnotice122304_updated3.pdf
General
feedback
Growing concern regarding the security of public water supplies limits readily available data on public
water supply distributions. Better information regarding the distribution of public water supplies and
changes in flow over time would provide better data for estimating exposure as well as determining
population served by community water supplies at various concentrations.
How the measure can be used for prevention/intervention efforts: Would need to be tracked over time,
and results of changes in population distributions and any associated health outcomes sent to the
EPA’s Office of Water.
Risk of adverse effects from DBPs must be measured against risk of waterborne infectious diseases
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from inadequate disinfection. As levels of DBPs decrease, risk of waterborne infections may
increase. It is impossible to eliminate DBPs totally, as they are formed from naturally occurring
reactants that continually leach out of the soil.
Data quality and data control are primary concerns in the derivation and use of this indicator which
may limit the ability to make comparisons across states and to ensure the validity and accuracy of the
measures. This indicator is derived from individual state level environmental monitoring data bases
used to address provisions of the national safe drinking water act (SDWA). The quality of data varies
by state, by sampling year, and by location. A primary reason for the potential inconsistencies of data
quality is that the source database was not designed, nor is it currently managed with environmental
public health indicator development in mind. Different parameters are deemed more important for
regulatory purposes than for public health risk assessment. At the same time, this is currently the
most extensive source of drinking water monitoring data available in all fifty states and is currently the
only source of comparable state level data available to all practitioners.
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Distribution of the total population and percent of population served by level of Total
Trihalomethanes (TTHMs) in finished water (users of public water supplies only)
How-to Guide
1) From state agency responsible for administering the SDWA, obtain TTHM data for all community
water systems (CWS, not TNTC or TNC) for the time period 2000 - most recent complete year of
data. Request data that has undergone QC review and a description of the QC process. Request
the following data elements:
a. For each system:
i. System ID
ii. Water System Name
iii. Location (county and city)
iv. Resident Population Served (not total)
v. Treatment(s), method of disinfection if noted
b. For each source:
i. Source ID
ii. Source Water Type
c. For each sample analyzed for TTHM
i. Sample date
ii. Concentration
iii. Data quality code
iv. Limit of detection
2) Calculate mean TTHMs levels for each CWS (i.e. within each System ID)
a. Assign all TTHM observations that are less than the level of detection (LOD) a value
equal to half the detection limit. The detection limit may vary between samples. Include
samples that are marked as ‘estimates.’
b. Calculate quarterly means as the arithmetic mean of all observations within each
calendar quarter within each year (e.g., Jan 2001 – Mar 2001). If there are no
observations in a quarter, set the value to missing. Document the % of observations each
quarter which were < LOD.
c. Calculate annual means as the arithmetic mean of the four quarterly means for each
year. Document the % of observations in each year which were < LOD.
d. Calculate the seasonal mean as the arithmetic mean of all observations occurring within
a calendar quarter, regardless of year. Document the % of observations in each season
which were < LOD.
3) Calculate population served by mean level of TTHM.
a. For a each year, assign each CWS a TTHM level category based on the annual mean
TTHM level. A CWS may be assigned a different category for different years if mean
TTHM levels were different. The cut-off TTHM values are (in ug/L):
i. 0-20
ii. >20-40
iii. >40-60
iv. >60-80
v. >80-100
vi. >100
vii. missing data
b. For each year sum the total residential population reported by each CWS in each TTHM
level category.
c. For each year, calculate the % of population in each TTHM level category by dividing the
total population assigned to that category by the total of all population value reported for
that year.
d. Repeat a), b) and c) for quarterly, or seasonal mean TTHM values.
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4) Create a frequency distribution for each year by plotting the total population, or % of population,
(y-axis) within each TTHM level category (x-axis).
Variations: Plot by quarter (season)
Plot by source water type
Plot by demographic characteristics, if possible to link to population data
Regional analyses within state
Regional analyses within a state
SAMPLES:
Percent of Total Population Served by Community
Water Supplies
Percent of Total Population
90
80
70
60
50
40
30
20
10
0
0-20
20-40
40-60
60-80
80-100
100+
Total
TTHMs Concentration Level (ug/l)
Indicator: Estimated population served by community
water supplies by TTHM Levels for STATE X
Population (in 1000s)
60
50
40
30
20
10
0
0-20
20-40
40-60
60-80
80-100
100+
TTHM Concentration Levels (ug/l)
Notes: NJ population served data from DEP does not match fed SDWIS database.
* Community water system includes-municipal and non-municipal does not include transient or nontransient water supplies (NEED TO GET EPA’s Definition)
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