E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/93
TRADE OR OTHER NAMES
Trade names for products containing the compound include Dacthal,
DAC 893, and Dacthalor. It may be formulated with several other
herbicides such as methazole and propachlor. Its only restrictions
apply in Washington State which requires supplemental labeling for
Dacthal W-75 (9).
DCPA also known as chlorthal dimethyl is a phthalate preemergent
herbicide used on annual grasses and certain annual broadleaf weed
species in a wide range of vegetable crops. About one-half of the use
of this compound in the United States is for homes and gardens.
While there is no toxicological concern for DCPA per se, the
technical product may contain very small amounts of dioxin (2, 3, 7, 8,
TCDD) and HCB as impurities which are of considerable toxicological
concern (8). There are also many gaps in the available information on
the herbicide and EPA has stated that no new uses will be approved until
some of the gaps are filled in.
DCPA is classified as a general use pesticide.
DCPA is a slightly toxic compound that carries the signal word
CAUTION on the label. The compound has a very low toxicity to mammals.
Therefore, LD50 values are difficult to obtain. The LD50 figures for
DCPA in rats range from greater than 3000 mg/kg to 12,500 mg/kg. DCPA
in rabbits and beagle dogs has an LD50 of greater than 10,000 mg/kg.
The dermal LD50 for rabbits is greater than 10,000 mg/kg. DCPA is not a
skin sensitizer and it is only a mild eye irritant.
The lowest dose that caused observable effects in rats was 758
mg/kg/day over a month of exposure. Dogs given 800 mg/kg/day a month
showed some adverse effects in the liver. In longer term studies with
rats (90 days), similar doses (about 750 mg/kg) caused no adverse
effects in the animals at the highest dose tested (10). In a two year
study with rats, a dose of around 50 mg/kg/day was responsible for
chronic toxic effects. Changes were noted in the adrenal weights of the
females and in the kidney weights of the males (10).
Rats fed moderate doses of DCPA (500 mg/kg/day) showed no changes
in fertility, gestation, live births or lactation (2). The study was
conducted over one full generation. It is unlikely that the compound
would present a reproductive threat to humans.
Pregnant rabbits fed moderate doses (up to 300 mg/kg) of DCPA on
days 8 to 16 of gestation had no maternal effects and there were no
skeletal or organ abnormalities in the offspring (10). It is unlikely
that the compound presents a significant risk of birth defects in
humans. However, more research is needed in this area.
No mutagenicity was seen in any one of a number of tests (mutation
frequency and activity, cytogenetic tests, DNA repair and dominant
lethal tests) (10). Strong evidence indicates that the compound is not
Based on gross and microscopic examination, no carcinogenic effects
were noted in rats in a two-year study where diets contained up to 500
mg/kg/day of DCPA. However, there is not enough information to draw any
firm conclusion about the carcinogenic risk to humans. The EPA has
stated that the compound currently is not classifiable (10).
Humans given 25 or 50 mg oral doses showed no evidence of
abnormalities in blood, liver, kidney and urine analysis. A 3 mg dose
in a rabbit eye produced mild irritation which was gone in 24 hours.
Fate in Humans and Animals
Much of the compound that is ingested is not absorbed. Cows
excreted nearly all of a small dose of DCPA within five days and dogs
absorbed only small amounts (3%) of the compound. The remaining amount
was eliminated within four days. The half-life of the parent compound is
about five minutes.
Dairy cows had some DCPA or metabolites in their milk. Diets up to
200 ppm for 24 days gave 0.26 ppm in milk, while 30 to 90 ppm for 9 or
23 days gave residues of 0.036 ppm and 0.066 ppm in milk. Residues in
other tissues were generally less than 1 ppm (6).
DCPA appears to be moderately toxic to some young wildfowl and
practically non-toxic to the young of other species and to adult birds.
The LD50 in young bobwhite quail is 5500 mg/kg. Young mallards and young
quail were more sensitive to the herbicide than adult birds. Diets
containing about 250 mg/kg caused heavy mortality in the first five days
to younger ducks. Older birds had a higher survival rate at this level
over a 100-day period (3). The total consumption of DCPA for the study
was nearly 40,000 mg/kg.
DCPA is slightly toxic to practically non-toxic to fish depending
on the species. For example it is non-toxic to blue gill sunfish and
slightly toxic to rainbow trout. The compound is practically non-toxic
to estuarine and marine organisms (invertebrates and some fish). The
available data suggest that DCPA poses no hazard to endangered aquatic
When exposed to rates of 100 g/bee, DCPA was not toxic. At 229.63
g/bee there was only three percent mortality. Thus, DCPA is only
slightly toxic to bees.
The half-life of DCPA is from 14 to one hundred days in most soils,
However, moisture is essential for degradation. In one study there was
no apparent buildup of pesticide residues in soil even after repeated
application. The DCPA concentration declined slowly to 75 or 80% in 28
days. Later sampling showed a continued decline of DCPA and its
breakdown products. No actual half-time was found for one of its
breakdown products (diacid), but it is thought to be about a year.
There is virtually no degradation of DCPA in water ranging from
moderately acidic to moderately alkaline (pH 5.0 to pH 9.0). The half-
life due to sunlight action in water is greater than one week.
Plants may produce the same two breakdown products that are seen in
soils with the proportion varying in different species. DCPA affects
the seed and pre emergence stage, but has little effect on crops or
weeds after they have emerged. Limited information suggests that plants
may remove the chlorine molecules of DCPA (6). In one study pine trees
took up nearly 1% of the soil applied chemical. The majority of the
compound taken up by the trees remained in the root system where it was
The metabolite, tetrachloro-terephthalic acid (TTA or diacid), is
much more water soluble than the parent compound and is subject to
leaching in some soils. This metabolite has been detected below the
health advisory level in groundwater in the onion growing areas of
Eastern Oregon (5). It has been detected in several other states in the
US as well (10).
|NOEL (rat): ||50 mg/kg/day
|DWEL: ||2.0 mg/l
|HA: ||4.0 mg/l lifetime
|ADI: ||0.5 mg/kg/day (ppm) (EPA)
|RfD: ||0.5 mg/kg/day (EPA)
|LEL: ||500 mg/kg/day (rat)
|CAS #: ||1861-32-1
|Chemical name: ||dimethyl 2,3,5,6-tetrachlorobenzene-1,4dicarboxylate
|Chemical class/use: ||phthalate herbicide
|Solubility in water: ||0.5 mg/l
|Solubility in other solvents: ||benzene 25 g/100 g; toluene 17 g/100 g; acetone 10 g/100g; carbon tetrachloride 7 g/100 g
|Melting Point: ||155-156 degrees C
|Vapor Pressure: ||12.5 x 10 to the minus 6 power mm Hg
|Partition Coefficient: ||4.95 (octanol/water)
ISK Biotech Corp.
5966 Heisley Rd
PO Box 8000
Mentor, OH 44060-8000
Review by Basic Manufacturer:
Comments solicited: October, 1992
SDS Biotech Corporation (1986). DCPA (Dathal) Supporting Data,
Tetrachloroterephthalic Acid, Volume I, SDS-954, Painesville, OH.
U.S. Environmental Protection Agency (1987). Health Advisory,
Office of Drinking Water.
Beste, C.E., Chairman (1983). Herbicide Handbook of the Weed
Science Society of America. Weed Science Society of America, Champaign,
Midwest Research Institute (1975). Initial Scientific and
Minieconomic Review No. 14, DACTHAL, Kansas City, MO.
Malheur County Sanitarian (1985) News Release, October 7, Vale, OR.
Food and Drug Administration (1986). The FDA Surveillance Index.
Bureau of Foods, Dept of Commerce, National Technical Information
Service, Springfield, VA.
Forest Service (1987). Pesticide Background Statements, Vol III
Nursery Pesticides, U. S. Dept. of Ag., Agriculture Handbook N. 7.
Walker, Mary M. and Lawrence H. Keith. (1992). EPA's Pesticide
Fact Sheet Data Base. Lewis Publishers. Chelsea, MI.
The Farm Chemicals Handbook. (1992). Meister Publishing.
Health Advisories for 50 Pesticides. 1988. United States
Environmental Protection Agency. Dacthal.