August, 1987
DICAMBA
Health Advisory
Office of Drinking Water
U.S. Environmental Protection Agency
DRAFT
I. INTRODUCTION
The Health Advisory (HA) Program, sponsored by the Office of Drinking
Water (ODW), provides information on the health effects, analytical method-
ology and treatment technology that would be useful in dealing with the
contamination of drinking water. Health Advisories describe nonregulatory
concentrations of drinking water contaminants at which adverse health effects
would not be anticipated to occur over specific exposure durations. Health
Advisories contain a margin of safety to protect sensitive members of the
population.
Health Advisories serve as informal technical guidance to assist Federal,
State and local officials responsible for protecting public health when
emergency spills or contamination situations occur. They are not to be
construed as legally enforceable Federal standards. The HAs are subject to
change as new information becomes available.
Health Advisories are developed for one-day, ten-day, longer-term
(approximately 7 years, or 10% of an individual's lifetime) and lifetime
exposures based on data describing noncarcinogenic end points of toxicity.
Health Advisories do not quantitatively incorporate any potential carcinogenic
risk from such exposure. For those substances that are known or probable
human carcinogens, according to the Agency classification scheme (Group A or
B), Lifetime HAs are not recommended. The chemical concentration values for
Group A or B carcinogens are correlated with carcinogenic risk estimates by
employing a cancer potency (unit risk) value together with assumptions for
lifetime exposure and the consumption of drinking water. The cancer unit
risk is usually derived from the linear multistage model with 95% upper
confidence limits. This provides a low-dose estimate of cancer risk to
humans that is considered unlikely to pose a carcinogenic risk in excess
of the stated values. Excess cancer risk estimates may also be calculated
using the One-hit, Weibull, Logit or Probit models. There is no current
understanding of the biological mechani ms involved in cancer to suggest that
any one of these models is able to predict risk more accurately than another.
Because each model is based on differing assumptions, the estimates that are
derived can differ by several orders of magnitude.
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II. GENERAL INFORMATION AND PROPERTIES
CAS No. 1918-00-9
Structural Formula
Cl
3,6-Dichloro-2-methoxy-benzoic acid
Synonyms
0 Banes, Banex, Banlen, Banuel D, Banvel, Brush buster, Dianat, Dianate,
Dicambe, Mediben, Mondak, MDBA, Velsicol Compound R
Uses
0 Herbicide used to control broadleaf weeds in field and silage corn,
grain sorghum, small grains, asparagus, grass seed crops, turf,
pasture, rangeland, and non-cropland areas such as fence rows,
roadways and wastelands. For control of brush and vines in non-
cropland, pasture and rangeland areas (Meister, 1983).
Properties (Berg, 1986; CHEMLAB, 1985; Meister, 1983; Windholz et al., 1983;
Worthing, 1983)
Chemical Formula
Molecular Weight
Physical State (at 25"C)
Boiling Point
Melting Point
Density
Vapor Pressure (20°C)
Specific Gravity
Water Solubility (20°C)
Log Octanol/Water Partition
Coefficient
Taste Threshold
Odor Threshold
Conversion Factor
CQH6C1203
221.04
Crystals
114 to 116°C
3.75 x 10~3 mm Hg
6,500 mg/L at 25CC
3.67 (calculated)
Occurrence
Dicamba has been found in 249 of 624 surface water samples analyzed
and in 39 of 275 ground water samples (STORET,- 1987). Samples were
collected at 148 surface water locations and 229 ground water locations
dicamba was found in 12 states. The 85th percentile of all non-zero
samples was 0.15 ug/L in surface water and 0.07 ug/L in ground water.
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The maximum concentration found in surface water was 3.3 ug/L, while
in ground water it was 0.8 ug/L.
Environmental Fate
0 In several aerobic soil metabolism studies, dicamba (acid or salt form
not specified) had half-lives of 1 to 6 weeks in sandy loam, heavy
clay, silty clay, clay loam, sand and silt loam soils at 18 to 38°C
and 40 to 100% of field capacity. Degradation rates decreased with
decreasing temperature and soil moisture (Smith, 1973a,b; Smith, 1974;
Smith and Cullimore, 1975; Suzuki, 1978;1979).
0 For the dimethylamine salt, half-lives in sandy loam and loam soils
ranged from 17 to 32 days (Altom and Stritzke, 1973). Phytotoxic
residues, detected by a non-specific bioassay method, have persisted
in aerobic soil for almost 2 years (Sheets, 1964; Sheets et al.,
1968).
0 Based on soil thin-layer chromatography (TLC), dicamba (acid or salt
form not specified) is highly mobile in sandy loam, silt loam, sandy
clay loam, clay loam, loam, silty clay loam and silty clay soils
(Helling, 1971; Helling and Turner, 1968).
0 The free acid of dicamba and the dimethylamine salt were not appre-
ciably adsorbed to any of five soils ranging from heavy clay to loamy
sand (Grover and Smith, 1974). The dicamba degradation product,
3,6-dichlorosalicylic acid, adsorbed to sandy loam (30%), clay and
silty clay (55%) (Smith, 1973a,b; Smith and Cullimore, 1975).
0 Losses of 12 to 19% of the applied radioactivity from nonsterile soils
indicated that metabolism contributes substantially more to l4C-dicamba
losses than does volatilization (Burnside and Levy, 1965; 1966).
0 Under field conditions, dicamba (acid or salt form not specified) had
half-lives of 1 to 2 weeks in a clay and a sandy loam soil when applied
at 0.27 and 0.53 Ib/A. At either application rate, less than 30 ppb
of dicamba remained after 4 weeks (Scifres and Allen, 1973). In
another study, using a nonspecific bioassay method of analysis,
dicamba phytotoxic residues dissipated within 2 years in loam and
silty clay loam (Burnside et al., 1971).
0 Ditchbank field studies indicated vertical movement of dicamba in
soil; the soil layers at 6 to 12 inches contained a maximum of 0.07 ppm
and 0.28 ppm in canals treated at 0.66 and 1.25 Ib/A, respectively
(Salman et al., 1972).
III. PHARMACOKINETICS
Absorption
0 Atallah and Yu (1980) reported that mice, rats, rabbits and dogs
administered single oral doses of 14C-dicamba (99% purity,
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Oicamba August, 1987
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approximately). 100 mg/kg) excreted an average of 85% of the admini-
stered dose in urine in the 48 hours after dosing.
0 Similar findings were reported for rats by Tye and Engel (1967) (96%
excreted in 24 hours) and by Whitacre and Diaz (1976) (83% excreted
in 24 hours). The data indicate that dicamba is rapidly absorbed
from the gastrointestinal tract.
Distribution
0 The retention of dicamba (99% purity, approximately 100 mg/kg) was
investigated in rats, mice, rabbits and dogs following single doses
by oral intubation (Atallah and Yu, 1980). Tissue levels 16 hours
after treatment were low. Tye and Engel (1967) also found low residue
levels of dicamba in kidneys, liver and blood. The data indicate
that dicamba does not accumulate in mammalian tissues.
Metabolism
0 The metabolism of 14c-dicamba (99% purity) was investigated in mice,
rats, rabbits and dogs after administration of single oral doses at
approximately 100 mg/kg (Atallah and Yu, 1980). Between 97 to 99%
of the dicamba was recovered unchanged in the urine of all four
species* 3,6-Dichloro-2-hydroxybenzoic acid (DCHBA, a metabolite)
was not detected in any urine sample at a level greater than 1% of
the dose. There was also a small amount of unknown metabolites
totaling about 1%.
Excretion
0 Atallah and Yu (1980) investigated the excretion of 14C-dicamba (99%
purity) after a single oral dose (approximately 100 mg/kg) in mice,
rats, dogs and rabbits, and reported that 67 to 93% of the administered
dose was excreted in urine of the four species within 16 hours. The
compound was found to a lesser degree in feces (0.5 to 5.7%) and
various tissues (0.17 to 0.5%) 16 hours postdosing.
IV. HEALTH EFFECTS
Humans ,
0 The Pesticide Incident Monitoring System data base revealed 10
incident reports involving humans from 1966 to March 1981 for
dicamba alone (U.S. EPA, 1981). Six of the ten reported incidents
involved spraying operations. No concentrations were specified.
Exposed workers developed muscle cramps, dyspnea, nausea, vomiting,
skin rashes, loss of voice or swelling of cervical glands. Four
additional incidences resulted in coughing and dizziness in one child
involved in an undescribed agricultural incident. Three children who
sucked mint leaves from a ditch bank previously sprayed with dicamba
were asymptomatic.
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Animals
Short-term Exposure
0 Reported acute oral LD$Q values for technical dicamba [85.8% active
ingredient (a.i.)] range from 757 to 1,414 mgAg (Witherup et al.,
1962) in rats. The acute oral LD$Q in mice has been reported to be
>4,640 mg/kg (Kettering Laboratory, 1962) and 316 mg/kg in hens
(Roberts et al., 1983).
0 An acute inhalation LC50 of >200 mg/L was reported in rats (IRDC, 1973).
0 The neurotoxic effects of dicamba in hens were studied by Roberts
et al. (1983). Technical dicamba (86.2% a.i.) was administered per os
(10 hens/dose) in doses of 0, 79, 158 or 316 mg/kg. Two groups of
ten hens each were dosed at 316 mg/kg. The various groups were
observed for 21 days following treatment. No signs of ataxia were
observed at any dose level tested. Histopathological evaluation of
nervous tissue from 13 hens treated at 316 mg/kg demonstrated
sciatic nerve damage in 6 hens (46%). The authors attributed this
alteration to prolonged recumbency rather than a direct effect of
dicamba. Based on the absence of delayed neurotoxicity and sciatic
nerve damage, a NOAEL of 158 mg/kg is identified for this study.
0 Rats (two/sex/dose) of the CD strain were fed diets containing 658
or 23,500 ppm of technical dicamba (85.8% a.i.) for up to three weeks
(Witherup et al. , 1962). Assuming that 1 ppm in the diet of rats
is equivalent to 0.05 mg/kg/day (Lehman, 1959), these levels correspond
to about 32.9 or 1,175 mg/kg/day. No adverse effects on physical
appearance, behavior, food consumption, body or organ weights, gross
pathology or histopathology were reported. Based on this information,
a NOAEL of 1,175 mg/kg/day (the highest dose tested) is identified.
Dermal/Ocular Effects
0 IRDC (1974) reported an acute LD50 of >2000 mg/kg in rabbit dermal
studies.
0 Heenehan et al. (1978) studied the sensitization potential of technical
dicamba (86.8% a.i.) in albino guinea pigs. The compound was applied
as a 10% suspension to the shaved backs of guinea pigs (five/sex) for
6 hours three times per week for 3 weeks. Following nine sensitizing
doses, two challenge doses were applied. Dicamba was judged to cause
moderate dermal sensitization.
0 Technical dicamba (86.8% a.i.) was applied to the shaved backs of
New Zealand White rabbits (four/sex/dose) in doses of 0, 100, 500 or
2,500 mg/kg/day, 5 days per week for 3 weeks (IRDC, 1979). Slight
skin irritation was observed at 100 mg/kg, and moderate irritation at
500 mg/kg/day and above. No changes were observed in general appearance,
behavior, body weight, organ weight, biochemistry, hematology or
urinalysis.
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9 Thompson (1984) instilled single doses (0.1 g) of technical dicamba
(purity not specified) into the conjunctival sacs of nine New Zealand
rabbits; three eyes were washed and six were not washed. Dicamba was
severely irritating and corrosive to both washed and unwashed eyes.
Long-term Exposure
s
0 Laveglia et al. (1981) fed CD rats (20/sex/dose) technical dicamba
(86.8% a.i.) in the diet for 13 weeks in doses of 0, 1,000, 5,000 or
10,000 ppm. Assuming that 1 ppm in the diet of rats is equivalent to
0.05 mg/kg/day (Lehman, 1959), this corresponds to doses of about
0, 50, 250 or 500 mg/kg/day. No compound-related effects were observed
in general appearance, hematology, biochemistry or in urinalysis valuesp
survival and gross pathology at any dose levels tested. There was an
absence or reduction of cytoplasmic vacuolation of hepatocytes and a
decrease in mean body weight for both sexes (6.3% in females and 7.5%
in males) at 10,000 ppm (500 mg/kg/day). The body weight decrease
was lower (p <0.05) at week 13 when compared to controls. A NOAEL of
5,000 ppm (250 mg/kg/day) can be identified for this study.
0 Male Wistar rats (20/dose) were fed diets containing technical dicamba
at 0, 31.6, 100, 316, 1,000 or 3,162 ppm for 15 weeks (Edson and Sand-
erson, 1965). Assuming that 1 ppm in the diet of rats is equivalent
to 0.05 mg/kg/day (Lehman, 1959), this corresponds to doses of about
0, 1.6, 5, 15.8, 50 or 158 mg/kg/day. Following treatment, general
behavior, physical appearance, food consumption, organ weights, gross
pathology and histopathology were evaluated. However, the authors
presented data only for the evaluation of body and organ weights.
Hematological, urinalysis or clinical chemistry studies were not
reported. No adverse effects were observed in the parameters measured
at 316 ppm (15.8 mg/kg/day) or less. Relative liver-to-body weight
ratios increased (p value not specified) in at 1,000 and 3,162 ppm
(50 and 158 mg/kg/day). Based on these data, the authors identified
a NOAEL of 316 ppm (15.8 mg/kg/day).
0 Davis et al. (1962) fed beagle dogs (three/sex/dose) technical dicamba
(90% a.i.) in the diet in doses of 0, 5, 25 or 50 ppm for 2 years.
Assuming that 1 ppm in the diet of dogs is equivalent to 0.025 mg/kg/day,
(Lehman, 1959), this corresponds to doses of about 0, 0.125, 0.625 or
1.25 mg/kg/day. No compound-related effects were observed on survival,
food consumption, hematology, urinalysis and organ weights. A decrease
in body weight was observed in males at 25 and 50 ppm and in females
at 50 ppm. No individual data except for body weight were reported,
and no statistical evaluations were made. The authors did not present
data on gross pathology. Histopathology was done only on the heart,
lung, liver and kidney. Based on marginal information, a NOAEL of
5 ppm (0.125 mg/kg/day) can be identified.
0 Sprague-Dawley rats (32/sex/dose) were fed technical dicamba (90% a.i.)
in the diet for 2 years in doses of 0, 5, 50, 100, 250 or 500 ppm
(Davis «t al., 1962). Assuming that 1 ppm in the diet of rats is
equivalent to 0.05 mg/kg/day (Lehman, 1959), this corresponds to
doses of about 0, 0.25, 2.'5, 5, 12.5 or 25 mg/kg/day. The authors
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reported no adverse effects upon survival, body weight, food consump-
tion, organ weight, hematologic values or histology at the dose
levels tested. No data were presented for evaluation of pharmacologic
effects, gross pathology, urinalysis or clinical chemistry. Incomplete
histological data were presented. A NOAEL could not be determined for
this study due to insufficient data.
Reproductive Effects
0 Charles River CD rats (20 females or 10 males/dose) were fed diets
containing technical dicamba (87.2% a.i.) in doses of 0, 5, 50, 100,
250 or 500 ppm through three generations (Kettering Laboratory,
1966). Assuming that 1 ppm in the diet of rats is equivalent to
0.05 mg/kg/day (Lehman, 1959), this corresponds to doses of about 0,
0.25, 2.5, 5, 12.5 or 25 mg/kg/day. Fertility index, gestation
index, viability index, lactation index and pup development were
comparable in treated and control rats. A NOAEL of 500 ppm
(25 mg/kg/day) was identified.
Developmental Effects
0 Technical dicamba (87.7% a.i.) was administered per os to pregnant New
Zealand White rabbits (23-27/dose) at doses of 0, 1, 3 or 10 mg/kg/day
from days 6 through 18 of gestation (IRDC, 1978).x No maternal toxicity,
fetotoxicity or teratogenic effects were observed at 1 and 3 mg/kg/day.
There were slightly reduced fetal and maternal body weights and
increased postimplantation losses in the 10 mg/kg/day dose group when
compared to untreated controls. The author did not consider these
differences to be statistically significant. The author identified
a developmental toxicity NOAEL of 10 mg/kg/day (the highest dose
tested). Based on a reduction in body weights and increased post-
implantation losses at the highest dose, a maternal and fetotoxic
NOAEL of 3 mg/kg/day was identified by EPA/OPP.
0 Pregnant albino rats (20-24/dose) were administered technical-grade
dicamba by gavage at dose levels of 0, 64, 160 or 400 mg/kg/day on
days 6 throught 19 of gestation (Toxi Genetics, 1981). No maternal
toxicity was observed up to 160 mg/kg/day. Dicamba-treated dams in
the 400-mg/kg/day dosage group exhibited ataxia and reduced body
weight gain; they consumed less food during the dosing period when
compared with controls given vehicle alone (p <0.05). No fetotc :icity
or developmental effects were observed at the dose levels tested.
Based on these findings, a NOAEL for maternal toxicity of 160 mg/kg/day
is identified. The NOAEL for fetotoxic and developmental effects is
400 mg/kg/day (the highest dose tested).
Mutagenicity
0 Moriya et al. (1983) reported that dicamba (up to 5,000 ug/plate)
exhibited no mutagenic activity against Salmonella typhimurium
(TA 98, TA 100, TA 1535, TA 1537 and TA 1538) or Escherichia coli
(WP2 her) either with or without metabolic activation.
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0 An increased number of chromosomal aberrations (p <0.01) were reported
in mouse bone marrow cells exposed to 500 mg/kg dicamba (Kurinnyi
et al., 1982). No other details were presented.
Carcinogenicity
0 Sprague-Dawley rats (32/sex/dbse) were administered dicamba (90% a.i.)
in the diet for two years at doses of 0, 5, 50, 100, 250 or 500 ppm
(Davis et al., 1962). Assuming that 1 ppm in the diet of rats is
equivalent to 0.05 mg/kg/day (Lehman, 1959), this corresponds to
doses of about 0, 0.25, 2.5, 5, 12.5 or 25 mg/kg/day. The treated
rats did not differ from the untreated control animals with respect
to the incidence, types and time of appearance of tumors.
V. QUANTIFICATION OF TOXICOLOGICAL EFFECTS
Health Advisories (HAs) are generally determined for one-day, ten-day,
longer-term (approximately 7 years) and lifetime exposures if adequate data
are available that identify a sensitive noncarcinogenic end point of toxicity.
The HAs for noncarcinogenic toxicants are derived using the following formula:
HA = (NOAEL or LOAEL) x (BW) = /L ( /L)
(UF) x ( L/day)
~"^~~ \
where:
NOAEL or LOAEL = No- or Lowest-Observed-Adverse-Effect-Level
in mg/kg bw/day.
BW = assumed body weight of a child (10 kg) or
an adult (70 kg).
UF = uncertainty factor (10, 100 or 1,000), in
accordance with NAS/ODW guidelines.
L/day = assumed daily water consumption of a child
(1 L/day) or an adult (2 L/day).
One-day Health Advisory
No information was found in the available literature that was suitable
for determination of the One-day HA value for dicamba. Accordingly, it is
recommended that the Ten-day HA value of 0.3 mg/L (calculated below) for a
10 kg child be used at this time as a conservative estimate of the One-day HA.
Ten-day Health Advisory
The developmental toxicity study by IRDC. (1978) has been selected to
serve as the basis for the Ten-day HA value for dicamba. In this study,
pregnant rabbits administered technical dicamba (87.7 % a.i.) by gastric
intubation at dosage levels of 1, 3 or 10 mg/kg/day from days 6 through 18
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of gestation showed slightly reduced maternal body weights at 10 mg/kg/day.
Similarly, fetal body weights were slightly reduced, and postimplantation
losses were increased in the 10-mg/kg/day dose group.
Based on these data, a maternal and fetal toxicity NOAEL of 3 mg/kg/day
is identified. A rat study (Toxi Genetics, 1981) of comparable duration deter-
mined higher maternal and fetal NOAELs (160 and 400 mg/kg/day, respectively).
Hie Ten-day HA for a 10-kg child is calculated as follows:
Ten-day HA = (3 mg/kg/day) (10 kg) = o.3 mg/L (300 ug/L)
(1 L/day) (100)
where:
3 mg/kg/day = NOAEL, based on absence of body weight loss and post-
implantation losses.
10 kg = assumed body weight of a child.
1 00 = uncertainty factor, chosen in accordance with NAS/ODW
guidelines for use with a NOAEL from an animal study.
1 L/day = assumed daily water consumption of a child.
Longer-term Health Advisory
No studies found in the available literature were suitable for
determining a Longer-term HA value for dicamba. One 13-week rat study (Laveglia
et al., 1981) and one 15-week rat study (Edson and Sanderson, 1965) reported
NOAELs (250 mg/kg/day and 15.8 mg/kg/day, respectively) that were higher than
the NOAEL (3 mg/kg/day) of the rabbit study (IRDC, 1978) selected to derive
the Ten-day HA value. It is therefore recommended that the Reference Dose
(RfD) derived below in the calculation of the Lifetime HA (0.0013 mg/kg/day)
be used at this time as the basis for the Longer-term HA values. As a result,
the Longer-term HA is 13 ug/L for the 10-kg child and is 50 ug/L for the
70-kg adult.
Lifetime Health Advisory
The Lifetime HA represents that portion of an individual's total exposure
that is attributed to drinking water and is considered protective of noncar-
cinogenic adverse health effects over a lifetime exposure. The Lifetime HA
is derived in a three step process. Step 1 determines the Reference Dose
(RfD), formerly called the Acceptable Daily Intake (ADI). The RfD is an esti-
mate of a daily exposure to the human population that is likely to be without
appreciable risk of deleterious effects over a lifetime, and is derived from
the NOAEL (or LOAEL), identified from a chronic (or subchronic) study, divided
by an uncertainty factor(.s). From the RfD, a Drinking Water Equivalent Level
(DWEL) can be determined (Step 2). A DWEL is a medium-specific (i.e., drinking
water) lifetime exposure level, assuming 100% exposure from that medium, at
which adverse, noncarcinogenic health effects would not be expected to occur.
The DWEL is derived from the multiplication of the RfD by the assumed body
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August, 1987
weight of an adult and divided by the assumed daily water consumption of an
adult. Ihe Lifetime HA is determined in Step 3 by factoring in other sources
of exposure, the relative source contribution (RSC). The RSC from drinking
water is based on actual exposure data or, if data are not available, a
value of 20% is assumed for synthetic organic chemicals and a value of 10%
is assumed for inorganic chemicals. If the contaminant is- classified as a
Group A or B carcinogen, according to the Agency's classification scheme of
carcinogenic potential (U.S. EPA, 1986), then caution should be exercised in
assessing the risks associated with lifetime exposure to this chemical.
The 2-year dog study by Davis et al. (1962) has been selected to serve
as the basis for deriving the Lifetime HA for dicamba. In this study, beagle
dogs were administered technical dicamba at dietary levels of 0, 5, 25 or
50 ppm (0, 0.125, 0.625 or 1.25 mg/kg/day). A decrease in body weight was
observed in males at 25 and 50 ppm and in females at 50 ppm. A NOAEL of
25 ppm (0.125 mg/kg/day) was identified.
The Lifetime HA is derived from this NOAEL as follows:
Step 1: Determination of the Reference Dose (RfD)
Rf D = 0.125 mg/kgyday = 0. 001 3
0.125 mg/kgyday
(100)
where:
0.125 mg/kg/day = NOAEL based on the absence of body weight loss.
100 = uncertainty factor, chosen in accordance with NAS/ODW
guidelines for use with a NOAEL from an animal study.
Step 2: Determination of the Drinking Water Equivalent Level (DWEL)
DWEL = (0.0013 mg/kg/day) (70 kg) = 0.046 mg/L (46 ug/L)
(2 L/day)
where:
0.0013 mg/kg/day = RfD.
70 kg = assumed body weight of an adult.
2 L/day = assumed daily water consumption of an adult.
Step 3: Determination of the Lifetime Health Advisory
Lifetime HA = (0.046 mg/L) (20%) = 0.009 mg/L (9 ug/L)
where:
0.046 mg/L = DWEL.
20% = assumed relative source contribution from water.
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Evaluation of Carcinogenic Potential
e One study on the carcinogenic!ty of dicamba in rats has been reported;
it revealed no evidence of carcinogenicity (Davis et al., 1962).
0 The International Agency for Research on Cancer has not evaluated the
carcinogenicity of dicamba.
0 Applying the criteria described in EPA's guidelines for assessment of
carcinogenic risk (U.S. EPA, 1986), dicamba is classified in Group D:
not classified. This category is used for substances with inadequate
evidence of carcinogenicity in animal studies.
VI. OTHER CRITERIA, GUIDANCE AND STANDARDS
0 The NAS (1977) has calculated an ADI of 0.00125 mg/kg/day based on a
NOAEL of 1.25 mg/kg/day from a 2-year feeding study in dogs and .an
uncertainty factor of 1,000. Assuming a body weight of 70 kg and a
20% source contribution factor, they calculated a Suggested-No-Adverse-
Reaction-Level (SNARL) of 0.009 mg/L.
0 Residue tolerances from 0.05 to 40 ppm have been established for a
variety of agricultural products (U.S. EPA, 1985a).
VII. ANALYTICAL METHODS
Analysis of dicamba is by a gas chromatographic (GC) method applicable
to the determination of certain chlorinated acid pesticides in water
samples (U.S. EPA, 1985b). In this method, approximately 1 L of
sample is acidified. The compounds are extracted with ethyl ether
using a separatory funnel. The derivatives are hydrolized with
potassium hydroxide, and extraneous organic material is removed by
a solvent wash. After acidification, the acids are extracted and
converted to their methyl esters using diazomethane as the derivatizing
agent. Excess reagent is removed, and the esters are determined by
electron capture (EC) GC. The method detection limit for dicamba has
been estimated to be 0.2'7 ug/L.
VIII. TREATMENT TECHNOLOGIES
Available data indicate granular-activated carbon (GAC) adsorption
to be a possible removal technique for dicamba.
Whittaker et al. (1982) report that a reduction of pH from 7 to 3
increased the extent of dicamba GAC adsorption. No system performance
was reported.
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IX. REFERENCES
Atallah, Y.H., and C.C. Yu.* 1980. Comparative pharmacokinetics and
metabolism of dicamba in mice, rats, rabbits and dogs. MRID 00128088.
Altom, J.D., and J.'R. Stritzke. 1973. Degradation of dicamba, picloram, and
four phenoxy herbicides in soils. Weed Sci. 21:556-560.
Berg, G.L. 1986. Farm Chemicals Handbook. Willoughby, OH: Meister
Publishing Co.
Burnside, O.C., and T.L. Levy. 1965. Dissipation of dicamba. Unpublished
study prepared by the University of Nebraska, Department of Agronomy,
submitted by Velsicol Chemical Corporation, Chicago, 111.
Burnside, O.C., and T.L. Levy. 1966. Dissipation of dicamba. Weeds
14:211-214.
Burnside, O.C., G.A. Wicks and C.R. Fenster. 1971. Dissipation of dicamba,
picloram, and 2,3,6-TBA across Nebraska. Weed Sci. 19:323-325.
CHEMLAB. 1985. The Chemical Information System, CIS, Inc.
Davis, R.K., W.P. Jolly, K.L. Stemmer et al.* 1962. The feeding for two
years of the herbicide 2-methoxy-3,6-dichlorobenzoic acid to rats and
dogs. MRID 00028248.
Edson, E.F., and D.M. Sanderson. 1965. Toxicity of the herbicides 2-
methoxy-3,6-dichlorobenzoic acid (Dicamba) and 2-methoxy-3,5,6-tri-
chlorobenzoic acid (tricamba). Food Cosmet. Toxicol. 3:299-304.
Grover, R., and A.E. Smith. 1974. Adsorption studies with the acid and
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