United States
Environmental Protection
Agency
Office of Water
Office of Pesticides and
Toxic Substances
Fall 1990
&EPA National Pesticide Survey
DCPA Acid Metabolites
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DCPA Acid Metabolite
What are
DCPA Acid
Metabolites?
How Do
DCPA Acid
Metabolites
Behave in
Soil and
Ground Water
The U.S. Environmental Protection Agency (EPA) has completed its five-year
National Survey of Pesticides in Drinking Water Wells (NPS), a study of the presence
of 127 pesticides, pesticide degradates, and nitrate in community water system (CWS)
wells and rural domestic drinking water wells. The acid metabolites or degradates
(tetrachloroterephthalic acids) of the pesticide DCPA were detected in the Survey.
This fact sheet provides a description of the DCPA acid metabolites, related potential
health effects, a summary of the concentrations of DCPA acid metabolites found by
the NPS in wells, and guidance on both treating and preventing well contamination.
DCPA acid metabolites are the degradates of the pesticide Dacthal, The
chemical name for Dacthal is dimethyl tetrachloroterephthalate (DCPA). Dacthal is the
trade name of a selective herbicide also known by the common names DCPA and
chlorthal dimethyl, the coded number DAC 893, and the discontinued name Fatal.
DCPA was registered for use in 1958. DCPA is used to combat smooth and hairy
crabgrass, witchgrass, green and yellow foxtails, fall panicum, and other annual
grasses. It is also used against certain broadleaf weeds such as carpet weed,
dodder, purslane, and common chickweed. It is presently approved for use on turf,
ornamentals, strawberries, collards, cucumbers, eggplant, garlic, horseradish, kale,
mustard greens, onions, peppers, potatoes, radish, seeded melons, squash, sweet
potatoes, tomatoes, turnips, cotton, soybeans, and field beans.
The behavior of a pesticide breakdown product in the environment is dependent
upon its movement in air, water, and soil as well as the rate at which it is transformed,
or further broken down. Pesticides applied to crops or the soil surface may volatilize
(vaporize) to the atmosphere, be carried off by surface runoff, be carried to ground
water through leaching, or remain in the soil through adsorption (adherence) to soil
particles and undergo little movement in air or water. The parent compound, DCPA, is
tightly bound (adsorbed) by clay particles and organic matter in the soil and has
relatively low solubility in water (0.5 ppm). Thus, DCPA is subject to little leaching into
ground water. However, pesticides may be transformed by reaction with water,
microorganisms, and exposure to sunlight. Microorganisms break down DCPA to form
the acid metabolites. The likelihood that DCPA acid metabolites will migrate into
ground water is influenced by their tendency to be transported (move) from soil to air
and water and to be transformed by these various processes, as well as by the
characteristics of the site, such as soil type, moisture, temperature, and depth to
WPS DCPA Acid Metabolites
Printed on Recycled Paper
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Findings of
the National
Pesticide
Survey
What Health
Effects Might
be Caused by
DCPA Acid
Metabolites
in Drinking
Water?
How is Water
Treated to
Remove
Contami-
nants?
ground water. DCPA acid metabolites have a high potential to be transported, and a
low potential to be transformed.
How Do DCPA Acid Metabolites Get into Ground Water? Migration of DCPA acid
metabolites into ground water could result from the presence of DCPA in the soil due
to agricultural and non-agricultural uses. Non-agricultural uses of DCPA include use
on turf and ornamental plants. DCPA can also reach ground water from direct entry
into a well through accidental chemical spills or improper storage near a well.
Based on the results of the NPS, EPA estimates that DCPA acid metabolites are
present, at or above the analytical detection level of 0.10 [jg/L used in the Survey, in
about 6,010 (6.4%) CWS wells and 264,000 (2.5%) rural domestic wells nationwide.
Considering the precision of the Survey, EPA estimates that the number of CWS wells
with detectable levels of DCPA acid metabolites could be as low as 3,170 or as high
as 8,840, and the number of rural domestic wells could be as low as 129,000 or as
high as 477,000. DCPA acid metabolites are measured in micrograms per liter (/L/g/L)
which is equivalent to parts per billion (ppb). The maximum concentrations of DCPA
acid metabolites detected were 7.2 pg/L in CWS wells sampled by the Survey and 2.4
jug/L in rural domestic wells sampled by the Survey. The median concentrations of
detectable DCPA acid metabolites was 0.34 pg/L in CWS wells and 0.38 [jg/L in rural
domestic wells.
The health-based guidelines established for DCPA apply to the DCPA acid
metabolites as well. The maximum concentrations of these breakdown products
detected in CWS wells and rural domestic wells are well below the Lifetime Health
Advisory Level (HAL) established for DCPA and its acid metabolites of 4,000 fjg/L.
Non-Cancer Effects: EPA has set a Lifetime Health Advisory Level for DCPA in
drinking water at 4000 pg/L A Lifetime HAL represents the concentration of a
contaminant in water that may be consumed over an average human lifetime without
causing adverse health effects. Lifetime HALs are based on health effects that were
found in animals given high doses of pesticides in laboratory studies. This level
includes a margin of safety. Consuming DCPA acid metabolites, however, at high
levels well above the Lifetime Health Advisory Level over a long period of time has
been shown to result in damage to the liver, kidney, and thyroid in animal studies.
Cancer Risk: Data from laboratory studies are inadequate for EPA to determine if
DCPA acid metabolites can increase the risk of cancer in humans.
Standard: EPA sets enforceable standards for public water systems, called Maximum
Contaminant Levels (MCLs). These regulatory standards set achievable levels of
drinking water quality to protect human health. EPA has not established a MCL for
DCPA or its acid metabolites, but plans to list DCPA and its acid metabolites on the
Drinking Water Priority List for future MCL consideration.
DCPA acid metabolites can be detected in drinking water by a laboratory using
an EPA method such as #515.1. If DCPA acid metabolites are detected in well water
and confirmed by retesting to be above 4000 /jg/L, State or County health officials
should be consulted. They may advise periodic retesting to get an accurate overall
picture of the water quality because changes in seasonal precipitation and changes in
pesticide use can cause variations in the amount of chemicals found in water wells.
They also may advise using an alternative drinking water supply (bottled water is an
example of a temporary alternative), treating the water, or drilling a new or deeper well.
You may also be able to treat your well water to remove pesticides and other
contaminants. At present, reverse osmosis appears to be a possible method for
removing DCPA acid metabolites from water. Filtration through activated charcoal has
NPS DCPA Acid Metabolites
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How Can
Water
Contamina-
tion be
Prevented?
Why was the
National
Pesticide
Survey
Conducted?
Where to Go
for More
Information
also been shown to be effective in removing this chemical. However, these
techniques may not necessarily be appropriate or available in every situation. State or
County health officials should be able to provide advice on the best approach to
follow.
Several steps may be taken to prevent pesticides or nitrate from entering wells,
such as eliminating direct entry through the well wall, drilling a new well, or modifying
or reducing pesticide and fertilizer use.
Eliminate Direct Entry Through the Well
If pesticides or nitrate are present in well water, they may be entering the
ground water through the well itself rather than through the soil. If the well is old or
poorly constructed, or if there are visible cracks in the well casing, obtain expert
advice on whether or not improvements can be made to the well, in addition,
investigate simple methods of capping the well or sealing it at the surface to prevent
entry. Do not conduct any mixing activities near the well if you use well water to mix
pesticides because a spill could lead to direct contamination of the well.
Drill a New Well
If the soil surrounding the well is the source of contamination, drilling a new or
deeper well may make sense if water can be drawn from a deeper, uncontaminated
aquifer. Unfortunately, it often is difficult to know the quality of the ground water
without drilling or extensive testing. Seek expert advice before you drill.
Learn More about Pesticide Use
If you use pesticides, whether for agricultural or home lawn and garden
purposes, you should consider attending training courses given by your State or
County agriculture department on how to reduce activities that contaminate ground
water. You may find that you can eliminate or lessen the frequency or quantity of your
pesticide usage by choosing alternative methods of pest control.
EPA conducted this Survey to determine the frequency and concentration of
' pesticides, pesticide degradates, and nitrate in drinking water wells nationwide and to
examine the relationship between the presence of pesticides in drinking water wells
and patterns of pesticide use and ground-water vulnerability. The Survey sampled
566 community water system wells and 783 rural domestic wells for 127 pesticides,
pesticide degradates, and nitrate. The wells were selected as a representative
statistical sample to provide nationwide estimates of the presence of pesticides and
nitrate in drinking water wells, and are not meant to provide an assessment of
pesticide contamination at the local, County, or State level.
This fact sheet is part of a series of NPS outreach materials, fact sheets and
reports. The following additional fact sheets are available through EPA's Public
Information Center (401 M Street SW, Washington, DC 20460, (202) 382-2080):
Survey Design
Survey Analytes
Quality Assurance/
Quality Control
Analytical Methods
Summary Results
Fact Sheet for each
detected analyte
Project Summary
Glossary
How EPA Will Use
The NPS Results
NPS DCPA Acid Metabolites
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Additional information on the Survey and on pesticides in general can be
obtained from the following sources:
U.S. EPA Safe Drinking Water Hotline
1-800-426-4791 (In Washington, DC (202) 382-5533)
Monday-Friday, 8:30 am to 4:30 pm Eastern Time
National Pesticide Telecommunications Network
1-800-858-7378
24 hours a day
U.S. EPA Office of Pesticide Programs (OPP) Docket
401 M Street, SW Room NEG004
Washington, DC 20460
(202) 382-3587
National Technical Information Service (NTIS)
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
Information on regulation of
pesticides in drinking
water
Information on health
effects and safe
handling of pesticides
Background documents
for Survey (available
for review)
Copies of the
NPS Phase I Report
(available 1991)
and
NPS Phase II Report
(when available)
If you are concerned about the presence of pesticides and nitrate in your
private water well, contact your local or State health department. Other experts in
your State environmental agency or agriculture and health departments may also be
helpful to you. If you receive your drinking water from a community water system and
have questions about your water quality, contact your local community water system
owner/operator or the State water supply agency.
Bibliography Meister Publications. Farm Chemicals Handbook. Ohio: Meister Publications, 1990.
U.S. Environmental Protection Agency. Drinking Water Health Advisory: Pesticides.
Michigan: Lewis Publishers, 1989.
U.S. Environmental Protection Agency. Drinking Water Regulations and Health
Advisories. April, 1990.
U.S. Environmental Protection Agency. Health Advisory Summaries, January 1989.
U.S. Environmental Protection Agency. Pesticides in Drinking Water Wells, September
1989.
NPS DCPA Acid Metabolites
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