Pyrimethanil

SRP: At the time of review, criteria for land treatment or burial (sanitary landfill) disposal practices are subject to significant revision. Prior to implementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices.

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 835(SRC), determined from a log Kow of 2.84(2) and a regression-derived equation(3), indicates that pyrimethanil is expected to have low mobility in soil(SRC). Volatilization of pyrimethanil from moist soil surfaces is expected to be an important fate process(SRC) given an estimated Henry's Law constant of 2.5X10-6 atm-cu m/mole(SRC), using a fragment constant estimation method(4). Pyrimethanil is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 1.65X10-5 mm Hg(2). The half-life of pyrimethanil in laboratory soil column experiments was reported in the range of 27-82 days(2). The half-life in soils determined from field experiments was in the range of 7-54 days(2).

AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 835(SRC), determined from a log Kow of 2.84(2) and a regression-derived equation(3), indicates that pyrimethanil is expected to adsorb to suspended solids and sediment in water(SRC). Volatilization from water surfaces is expected(3) based upon an estimated Henry's Law constant of 2.5X10-6 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 14 and 158 days, respectively(SRC). According to a classification scheme(5), an estimated BCF of 31(SRC), from its log Kow(2) and a regression-derived equation(6), suggests the potential for bioconcentration in aquatic organisms is moderate. Biodegradation may occur based on laboratory and field studies conducted in soils(2).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), pyrimethanil, which has a vapor pressure of 1.65X10-5 mm Hg at 25 °C(2), is expected to exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase pyrimethanil 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 2 hours(SRC), from its estimated rate constant of 2X10-10 cu cm/molecule-sec at 25 °C(3). Particulate-phase pyrimethanil may be removed from the air by wet and dry deposition(SRC). Based on absorption spectra of structurally similar compounds(4) pyrimethanil may absorb light greater than 290 nm and undergo direct photolysis in the environment(SRC), but the kinetics of this reaction are unknown.

The fate of four new fungicides (cyprodinil, fludioxonil, pyrimethanil, and tebuconazole) from the treatment on vine to the production of wine was studied. The influence of clarifying agents (bentonite, charcoal, potassium caseinate, gelatin, and polyvinylpolypyrrolidone) on residue concentrations in wine was also studied. The fungicide residues on grapes showed different decay rates after treatment, with first-order kinetics and half-lives ranging from 8 to 57 days. Grape processing into wine caused considerable residue reduction with cyprodinil (ca. 80%), fludioxonil (ca. 70%), and tebuconazole (ca. 50%) and no reduction with pyrimethanil. The two wine-making techniques employed (with and without maceration) had the same influence on the residue concentrations in wine, except for fludioxonil which showed maximum residue reduction with vinification with maceration. Among the clarifying agents tested, only charcoal showed effective action on the elimination of residue content in wine, proving complete elimination, or almost, of fungicide residues.

The Koc of pyrimethanil is estimated as 835(SRC), using a log Kow of 2.84(1) and a regression-derived equation(2). According to a classification scheme(3), this estimated Koc value suggests that pyrimethanil is expected to have low mobility in soil.

The alkaline comet assay was used to assess DNA damage in mononuclear leukocytes of farmers before and after a 1-day spraying period with selected pesticides under usual conditions. Two blood samples were collected, one in the morning of the day of spraying (S0) and the second in the morning of the day after (S1). Here, we assessed variations in DNA damage levels between these two sampling times. Four groups of farmers were formed, according to exposure to: (a) various fungicide-insecticide mixtures (including chlorothalonil; group 1, n = 8), (b) the herbicide isoproturon (group 2, n = 11), (c) fungicide triazoles (group 3, n = 14), and (d) a fungicide (chlorothalonil)-insecticide mixture (group 4, n = 8). An increase in DNA damage levels was observed at S1 for groups 1 and 4, who were exposed to similar pesticides. This increase was correlated with area sprayed between S0 and S1 and with the number of spraying tanks used over this 1-day period. No effect was observed on cell viability or on hematological parameters for these two groups. No statistically significant modification of DNA damage level was observed the day after spraying for groups 2 and 3, when each was observed as a whole. However, some farmers presented significantly more DNA damage after exposure, and others presented less damage. In these two groups, a significant decrease of neutrophils was observed at S1, and a decrease of red blood cells was observed in group 3. In parallel, a significant loss of lymphocyte viability was observed in these two groups. A 1-day spraying period seems to be sufficient to significantly modify DNA damage levels in mononuclear leukocytes, but the correlation of this change with pesticide-related exposure parameters depends on the kind of pesticide concerned.

An estimated BCF of 31 was calculated for pyrimethanil(SRC), using a log Kow of 2.84(1) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is moderate.

The Henry's Law constant for pyrimethanil is estimated as 2.5X10-6 atm-cu m/mole(SRC) using a fragment constant estimation method(1). This Henry's Law constant indicates that pyrimethanil 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 14 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 158 days(SRC). Pyrimethanil's Henry's Law constant(1) indicates that volatilization from moist soil surfaces may occur(SRC). Pyrimethanil is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 1.65X10-5 mm Hg at 25 °C(3).

The rate constant for the vapor-phase reaction of pyrimethanil with photochemically-produced hydroxyl radicals has been estimated as 2X10-10 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 2 hours at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). Based on absorption spectra of structurally similar compounds(3) pyrimethanil may absorb light greater than 290 nm and undergo direct photolysis in the environment(SRC), but the kinetics of this reaction are unknown. Pyrimethanil is a weak base with a pKa value of 3.52(2), suggesting it may partially exist in the protonated form in acidic waters.