Dithiopyr

LC50; Species: Colinus virginianus (Northern Bobwhite Quail) age 10 days; diet >5620 ppm for 8 days /91.5% purity/

LC50; Species: Anas platyrhynchos (Mallard Duck) age 10 days; diet >5620 ppm for 8 days /91.5% purity/

LD50; Species: Colinus virginianus (Northern Bobwhite Quail) age 27 weeks; oral via capsule >2250 mg/kg /91.5% purity/

EC50; Species: Pseudokirchneriella subcapitata (Green Algae); Conditions: freshwater, static; Concentration: 20 ug/L for 5 days (95% confidence interval: 17-24 ug/L); Effect: population abundance /94.3% purity/

For more Ecotoxicity Values (Complete) data for Dithiopyr (11 total), please visit the HSDB record page.

TERRESTRIAL FATE: Based on a classification scheme(1), a Koc range of 1141-3748(2), indicates that dithiopyr is expected to have low to slight mobility in soil(SRC). Research conducted to evaluate the movement of dithiopyr from golf courses found that most of the applied dithiopyr was detected in the top 0-12.5 cm of the rooting media(3). Volatilization of dithiopyr from moist soil surfaces may occur(SRC) given an estimated Henry's Law constant of 1.53X10-6 atm-cu m/mole(SRC), derived from its vapor pressure, 4.0X10-6 mm Hg(4), and water solubility, 1.38 mg/L(4). Despite having a low vapor pressure, dithiopyr belongs to a class of pesticides having important environmental volatility(5). Greenhouse studies found that volatilization can be a primary route of dithiopyr dissipation following herbicidal application with losses >50% after a few days(6-8). Dithiopyr dissipation in the soil environment occurs mostly through a combination of volatilization and biodegradation(4,8). Dithiopyr was found to degrade much faster in non-sterile media versus sterile media(8). Dithiopyr absorbs at wavelengths >290 nm(3) and, therefore, may be susceptible to direct photolysis by sunlight(SRC). One photodegradation study found minimal dithiopyr photolysis on soil (444.4 day half-life)(4), however, a distilled water study found a 1.7 day half-life(8). Field dissipation rates can vary widely depending on conditions. For example, rainstorms or irrigation following application can infiltrate the dithiopyr into the soil greatly decreasing volatilization and photodegradation losses(8). Reported field dissipation half-life rates are 17-61 days(4) and 4-49 days(9).

AQUATIC FATE: Based on a classification scheme(1), a Koc range of 1141-3748(2), indicates that dithiopyr is expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(3) based upon an estimated Henry's Law constant of 1.53X10-6 atm-cu m/mole(SRC), derived from its vapor pressure, 4.0X10-6 mm Hg(4), and water solubility, 1.38 mg/L(4). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 48 and 356 days, respectively(SRC). According to a classification scheme(5), an estimated BCF of 633(SRC), from its log Kow of 4.75(4) and a regression-derived equation(6), suggests the potential for bioconcentration in aquatic organisms is high(SRC). Dithiopyr was found to degrade much faster in non-sterile aqueous media versus sterile media(7) indicating biodegradation may be an important fate process(SRC). Hydrolysis studies indicated that hydrolysis is not an important route of degradation in the environment(4). An aqueous photolysis half-life of 17.6-20.6 days has been reported(4).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), dithiopyr, which has a vapor pressure of 4.0X10-6 mm Hg at 25 °C(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase dithiopyr is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 54 hours(SRC), calculated from its rate constant of 7.1X10-12 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(2). Particulate-phase dithiopyr may be removed from the air by wet and dry deposition(SRC). Dithiopyr absorbs at wavelengths >290 nm(3) and, therefore, may be susceptible to direct photolysis by sunlight(SRC).

IDENTIFICATION AND USE: Dithiopyr is a herbicide used preemergence and early postemergence for selective control of crabgrass and other susceptible annual grasses and broadleaf weeds in established lawns and ornamental turf. HUMAN STUDIES: Worker exposure is monitored by both passive dosimetry and biological monitoring techniques such as urinalysis. ANIMAL STUDIES: Severe dermal irritation has been noted in rabbits. In a 90 day subchronic study in rats the effect was an increase in organ weight and diffused hepatocellular swelling. In a rat and rabbit developmental toxicity study there were no developmental effects at 1000 mg/kg/day. Dithiopyr was not mutagenic in the Ames assays for mutagenicity with Ames (TA) strains of Salmonella typhimurium LT2 at limit of solubility (3,000 mg/plate) with or without activation.

EPA has released the Interactive Chemical Safety for Sustainability (iCSS) Dashboard. The iCSS Dashboard provides an interactive tool to explore rapid, automated (or in vitro high-throughput) chemical screening data generated by the Toxicity Forecaster (ToxCast) project and the federal Toxicity Testing in the 21st century (Tox21) collaboration. /The title compound was tested by ToxCast and/or Tox21 assays/[USEPA; ICSS Dashboard Application; Available from, as of August 9, 2018: http://actor.epa.gov/dashboard/]

Dithiopyr has a reported Koc range of 1141-3748(1) and a single reported Koc value of 1920(2). According to a classification scheme(3), this estimated Koc value suggests that dithiopyr is expected to have low to slight mobility in soil. Dithiopyr has a low potential for leaching into groundwater(4). Vertical mobility of dithiopyr through soil, even in conditions highly susceptible to herbicide leaching, was found not to exceed 24 inches and was often not more than 9 to 12 inches(4). Research conducted to evaluate the movement of dithiopyr from golf courses found that most of the applied dithiopyr was detected in the top 0-12.5 cm of the rooting media at the end of greenhouse experiments and that the highest concentration in runoff from simulated fairways did not exceed 40 ug/L (less than 2% of applied dithiopyr was transported)(5).

/BIOMONITORING/ ChemLawn lawn care specialists were monitored for worker exposure by both passive dosimetry and biological monitoring techniques in the performance of normal duties of mixing/loading and application of Dimension herbicide to turfgrass. Passive dosimetry was performed, utilizing cotton gauze patches, silica gel air sampling absorption media, and hand washes as per US Environmental Protection Agency Pesticide Assessment Guidelines. Biological monitoring was performed by analysis of all urine specimens collected from each specialist from initiation until 72 hr after application of dithiopyr. The mean body dose estimate from urinalysis of the specimens collected over the 72 hr period was 4.60 x 10(-5) mg/kg/lb applied. The passive dosimetry body dose estimates using dermal deposition measurements corrected for skin penetration and simulated inhalation measurements were calculated for the two clothing scenarios observed in the worker tests. The mean body dose estimate for a fully clothed specialist wearing a long-sleeved shirt was 8.09 x 10(-5) mg/kg/lb while for a specialist wearing a short-sleeved shirt the estimate was 3.62 x 10(-4) mg/kg/lb. The lower leg regions, which were protected by long pants and boots, had the highest exposure by passive dosimetry data.

Dithiopyr's production may result in its release to the environment through various waste streams; its use as a herbicide for pre-emergent and early post-emergent control of crabgrass and other annual grasses and weeds(1) will result in its direct release to the environment(SRC). Dithiopyr is used primarily in the professional turf, golf course and ornamental markets and is not currently registered for use in the US for foods or agricultural uses(1).

AEROBIC: Bacterial and fungal populations were shown to effect dithiopyr dissipation rates after herbicidal applications(1); field testing found overall dissipation half-lives to range from 17.3-25.0 days(1). Biological degradation studies conducted in sterile versus non-sterile rooting material and rooting material leachate collected from established golf course greens demonstrated that faster degradation occurred in the non-sterile media(2); for example, at 20 °C, pH 6.8 and dark conditions, the leachate dithiopyr half-life was 515 days in sterile media and 200 days in the non-sterile media(2). Aerobic soil metabolism studies under laboratory conditions found dithiopyr degraded to the normal acid, reverse acid and diacid(3). Field dissipation tests in fields with vegetation found dithiopyr half-lives of 17-61 days(3). Turfgrass field tests reported dithiopyr half-lives of 4-49 days(4).

An estimated BCF of 633 was calculated in fish for dithiopyr(SRC), using a log Kow of 4.75(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is high(SRC), provided the compound is not metabolized by the organism(SRC).

The Henry's Law constant for dithiopyr is estimated as 1.53X10-6 atm-cu m/mole(SRC) derived from its vapor pressure, 4.0X10-6 mm Hg(1), and water solubility, 1.38 mg/L(1). This Henry's Law constant indicates that dithiopyr is expected to volatilize from water surfaces(2). Based on this Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1 m/sec, wind velocity of 3 m/sec)(2) is estimated as 48 days(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(2) is estimated as 356 days(SRC). Dithiopyr's estimated Henry's Law constant indicates that volatilization from moist soil surfaces may occur(SRC). With respect to most compounds, dithiopyr would not be expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure. However, dithiopyr is included in select classes of pesticides that exhibit low to moderate volatility following field application despite having relatively low vapor pressures(3). In one greenhouse volatilization study, up to 70% of dithiopyr applied to crabgrass volatilized within 24 hours at 24 °C and volatilization losses were found to increase with temperature(4). In another greenhouse study, increased volatilization from smooth crabgrass resulted at temperatures of 25-30 °C compared to 10-15 °C(5). A study simulating dithiopyr application to golf course greens found that following application to the rooting media, dithiopyr was primarily lost by volatilization(6). A dissertation review of available literature and actual field testing of the efficacy of dithiopyr in turfgrass environments notes the potential importance of volatilization following field application as a herbicide(7). Volatilization rates of dithiopyr and other turfgrass herbicides can vary greatly under field conditions with dependency on temperature, surface conditions, soil or foliage type, moisture content, soil sorption, and irrigation/rain immediately following application (which reduces volatility)(7).