Dimethrin

LC50 Perca flavescens 28 ug/l/96 hr. Static bioassay without aeration, pH 7.2-7.5, water hardness 40-50 mg/l as calcium carbonate and alkalinity of 30-35 mg/l.

LC50 Lepomis macrochirus 38 ug/l/96 hr. Static bioassay without aeration, pH 7.2-7.5, water hardness 40-50 mg/l as calcium carbonate and alkalinity of 30-35 mg/l.

LC50 Ictalurus punctatus 1,140 ug/l/96 hr. Static bioassay without aeration, pH 7.2-7.5, water hardness 40-50 mg/l as calcium carbonate and alkalinity of 30-35 mg/l.

LC50 Pimephales promelas 62 ug/l/96 hr; flow through toxicity test.

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 31,000(SRC), determined from a structure estimation method(2), indicates that dimethrin is expected to be immobile in soil(SRC). Volatilization of dimethrin from moist soil surfaces is expected to be an important fate process(SRC) given an estimated Henry's Law constant of 7.6X10-5 atm-cu m/mole(SRC), using a fragment constant estimation method(3). However, adsorption to soil is expected to attenuate volatilization(SRC). Dimethrin is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 1.7X10-5 mm Hg(SRC), determined from a fragment constant method(4). Although biodegradation data for dimethrin are not available, the pyrethroid class of insecticides is readily degraded by environmental microorganisms(5,6) and based upon its structure, dimethrin is also expected to readily biodegrade(5,6).

AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 31,000(SRC), determined from a structure estimation method(2), indicates that dimethrin 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 7.6X10-5 atm-cu m/mole(SRC), developed using a fragment constant estimation method(4). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 15 hours and 13 days, respectively(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column. The estimated volatilization half-life from a model pond is 160 years if adsorption is considered(5). According to a classification scheme(6), an estimated BCF of 520(SRC), from an estimated log Kow of 6.57(7) and a regression-derived equation(8), suggests the potential for bioconcentration in aquatic organisms is high(SRC). However, bioconcentration studies on compounds which are structurally similar suggest that bioconcentration may be lower than that indicated by the regression-derived equations due to the ability of aquatic organisms to readily metabolize this class of compounds(9). Although biodegradation data for dimethrin are not available, the pyrethroid class of insecticides is readily degraded by environmental microorganisms(10,11) and based upon its structure, dimethrin is also expected to readily biodegrade(10,11).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), dimethrin, which has an estimated vapor pressure of 1.7X10-5 mm Hg at 25 °C(SRC), determined from a fragment constant method(2), will exist in both the vapor and particulate phases in the ambient atmosphere(SRC). Vapor-phase dimethrin 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 4 hours(SRC), calculated from its rate constant of 1.1X10-10 cu cm/molecule-sec at 25 °C(SRC) determined using a structure estimation method(3). Particulate-phase dimethrin may be removed from the air by wet and dry deposition(SRC).

Using a structure estimation method based on molecular connectivity indices(1), the Koc for dimethrin can be estimated to be 31,000 (SRC). According to a classification scheme(2), this estimated Koc value suggests that dimethrin is expected to be immobile in soil(SRC).

The clinical manifestations of inhalation exposure to pyrethrins can be local or systemic. Localized reactions confined to the upper respiratory tract include rhinitis, sneezing, scratchy throat, oral mucosal edema, and even laryngeal mucosal edema. Localized reaction of the lower respiratory tract include cough, shortness of breath, wheezing, and chest pain. An asthma like reaction occurs with acute exposures in sensitized patients. Hypersensitivity pneumonitis characterized by chest pain, cough, dyspnea, & bronchospasm may occur in an individual chronically exposed. /Pyrethrum and synthetic pyrethroids/

The allergenic properties of pyrethroids /with early pyrethrum preparations/ are marked in comparison with other pesticides. Many cases of contact dermatitis and respiratory allergy have been reported. Persons sensitive to ragweed pollen are particularly prone to such reactions. Preparations containing synthetic pyrethroids are less likely to cause allergic reactions than are the preparations made from pyrethrum powder. /Pyrethroids/

Although environmental biodegradation data specific to dimethrin are not available, the pyrethroid class of insecticides is readily degraded by environmental microorganisms(1,2); based upon its structure, dimethrin are also expected to readily biodegrade(1,2).

An estimated BCF of 520 was calculated for dimethrin(SRC), using an estimated log Kow of 6.57(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). However, bioconcentration studies on compounds which are structurally similar suggest that bioconcentration may be lower than that indicated by the regression-derived equations due to the ability of aquatic organisms to readily metabolize this class of compounds(4).

The Henry's Law constant for dimethrin is estimated as 7.6X10-5 atm-cu m/mole(SRC) using a fragment constant estimation method(1). This Henry's Law constant indicates that dimethrin 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 15 hours(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 13 days(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column(SRC). The estimated volatilization half-life from a model pond is 160 years if adsorption is considered(3). Dimethrin's Henry's Law constant(1) indicates that volatilization from moist soil surfaces may occur(SRC). Dimethrin is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 1.7X10-5 mm Hg(SRC), determined from a fragment constant method(3).

... Male and female albino rabbits (two/sex/dose) and male albino Wistar-CWL rats (five/dose) were given a single dose of 10 or 15 ml/kg (9.8 or 14.7 mg/kg) of technical grade dimethrin (98% pure) by gavage. Albino guinea pigs (four/sex) received a single dose of 10 ml/kg (9.8 mg/kg) by gavage. No effects were observed in rats or rabbits during a 2 wk observation period. ... In guinea pigs, the only effect ... was a refusal to eat or drink for 24 hr following dosing.

... 10 ml/kg (9.8 mg/kg) of technical grade dimethrin (98% pure) /was administered / to 15 male albino Wistar-CWL rats by gavage, 5 days/wk for 3 wk. This corresponds to an average daily dose of 7 mg/kg. No adverse effects, as judged by general appearance, behavior and growth, were observed. At necropsy, no gross abnormalities were observed.

... Single or multiple (3 consecutive days) instillations of 0.1 ml of undiluted dimethrin (98% pure) into the conjunctival sac of eight albino rabbits caused no visible irritation or chemosis and no injury of the cornea as detectable by means of fluorescein staining. When 0.2 ml of dimethrin was applied to the penile mucosa of five albino rabbits on two occasions 6 days apart, no irritation or sloughing of the mucosa was observed during a 1 week observation period.

... Dimethrin (98% pure) /was applied/ to the skin of albino rabbits (five/dose) 5 days/wk for 13 wk (65 applications). Doses admin were 0.5 ml/kg undiluted dimethrin or 0.5 ml/kg of a 50% soln of dimethrin in cottonseed oil (= to 0.25 ml/kg of dimethrin); controls received 0.5 ml/kg of cottonseed oil only. No evidence of any cutaneous reaction was observed. Occasionally, a slight, nonpersistent erythema was observed in all groups of rabbits. At necropsy, all organs from treated animals were indistinguishable from controls. No histopathological differences between control & treated animals were observed.

For more Non-Human Toxicity Excerpts (Complete) data for DIMETHRIN (6 total), please visit the HSDB record page.

The rate constant for the vapor-phase reaction of dimethrin with photochemically-produced hydroxyl radicals has been estimated as 1.1X10-10 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 4 hours at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). The rate constant for the vapor-phase reaction of dimethrin with photochemically- produced ozone has been estimated as 4.3X10-16 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 38 minutes at an atmospheric concentration of 7X10+11 hydroxyl radicals per cu cm(2). Reaction with nitrate radicals with vapor-phase dimethrin may also be an important degradation mechanism in air(SRC). A base-catalyzed second-order hydrolysis rate constant of 4.0X10-2 l/mole-sec(SRC) was estimated using a structure estimation method(3); this corresponds to half-lives of 5.5 years and 200 days at pH values of 7 and 8, respectively(3).