Characteristics of pesticide use in a pesticide applicator cohort: the Agricultural Health Study.

Data on recent and historic pesticide use, pesticide application methods, and farm characteristics were collected from 35,879 restricted-use pesticide applicators in the first 2 years of the Agricultural Health Study, a prospective study of a large cohort of private and commercial licensed pesticide applicators that is being conducted in Iowa and North Carolina. (In Iowa, applicators are actually "certified," while in North Carolina they are "licensed"; for ease of reference the term license will be used for both states in this paper.) Commercial applicators (studied in Iowa only) apply pesticides more days per year than private applicators in either state. When the types of pesticides being used by different groups are compared using the Spearman coefficient of determination (r2), we find that Iowa private and Iowa commercial applicators tend to use the same type of pesticides (r2=0.88). White and nonwhite private applicators tended to use the same type of pesticides (North Carolina r2=0.89), as did male and female private applicators (Iowa r2=0.85 and North Carolina r2=0.84). There was less similarity (r2=0. 50) between the types of pesticides being used by Iowa and North Carolina private applicators. A greater portion of Iowa private applicators use personal protective equipment than do North Carolina private applicators, and pesticide application methods varied by state. This heterogeneity in potential exposures to pesticides between states should be useful for subsequent epidemiologic analyses using internal comparison groups.

Factors associated with self-reported, pesticide-related visits to health care providers in the agricultural health study.

To investigate factors associated with pesticide-related visits to health care providers (i.e., doctor or hospital visits), responses to self-administered questionnaires received from 35,879 licensed restricted-use pesticide applicators participating in the Agricultural Health Study were analyzed. (In Iowa, applicators are actually certified, whereas in North Carolina they are licensed; for ease of reference, the term license will be used for both states in this paper.) The cohort reported a total of more than 10.9 million pesticide-application days. These applications were associated with one or more pesticide-related health care visits by 2,214 applicators (7.0% of the applicator cohort for whom health care visit data were available). The odds of a pesticide-related health care visit were increased for commercial applicators compared to private applicators [odds ratio (OR = 1.77; 95% confidence interval (CI), 1.52-2.06) and for applicators who used insecticides 70 times or more in their lifetime compared to those who used insecticides less frequently (OR = 1.43; CI, 1.26-1.63). After adjusting for the number of applications in a logistic regression model, significantly higher odds of health care visits were observed among North Carolina applicators compared to Iowa applicators (OR = 1.35; CI, 1.17-1.52), among applicators who mixed their own pesticides (OR = 1.65; CI, 1. 22-2.23), and among applicators who personally repaired their pesticide application equipment at least once per year (OR = 1.12; CI, 1.06-1.25). Significantly lower odds were found among female versus male applicators (OR = 0.68; CI, 0.46-0.99) and among applicators who graduated from high school versus those who did not (OR = 0.82; CI, 0.71-0.94 for high school graduates and OR = 0.79; CI, 0.68-0.91 for those with at least some college). Several methods of pesticide application to crops, seed, or stored grain were also associated with significantly elevated odds ratios of health care visits. These observations suggest that several steps can be taken to reduce the number of health care visits resulting from occupational exposure to pesticides. The implications of this pattern of pesticide-related health care visits may have etiologic implications for cancer and other chronic diseases.

Degradation of propanil by bacterial isolates and mixed populations from a pristine lake.

The microbial transformation rates of propanil, a commonly used herbicide, were investigated using water from a pristine lake in northeast Georgia. Microbial degradation rates were measured using natural water microflora, the natural water microflora amended with five bacterial species (Aerobacter aerogenes, Aeromonas hydrophila, Acinetobacter calcoaceticus, Proteus mirabilis, and Aeromonas salmonicida) isolated from the same lake, and the five isolates individually. Transformation rate constants for propanil were compared for the mixed microbial assemblages and isolates at similar initial bacterial concentrations (approximately 5.0 x 10(-3) bacteria/mL). Degradation started within 60 hours and was completed by 160 hours in all experiments. The mean first-order rate constant for natural microflora was -(4.80 +/- 0.620) x 10(-3) h-1. Natural waters amended with the bacterial isolates yielded rate constants ranging from -(0.39 +/- 0.186) x 10(-3) h-1 to -(2.13 +/- 0.029) x 10(-3) h-1 with an overall mean of -(1.63 +/- 0.242) x 10(-3) h-1. After 660 hours following the first amendment of propanil, (i.e., 500 hours after propanil degradation was complete), each sample was again amended with propanil. Subsequent degradation rates ranged from -(21.3 +/- 0.186) x 10(-3) h-1 to -(64.2 +/- 0.786) x 10(-3) h-1 and the mean rate constant was -(37.5 +/- 0.922) x 10(-3) h-1. No significant differences were observed between first-order rate constants among isolates following the first or the second addition of propanil. After the second spike, however, the average of rate constants was approximately 20 times greater than that following the first spike. Rates for the individual isolates varied greatly from one isolate to another, ranging from virtually no degradation with A. calcoaceticus to -(21.6 +/- 0.332) x 10(-3) h-1 for the composite treatment of all isolates.

Microbial degradation of seven amides by suspended bacterial populations.

Microbial transformation rate constants were determined for seven amides in natural pond water. A second-order mathematical rate expression served as the model for describing the microbial transformation. Also investigated was the relationship between the infrared spectra and the second-order rate constants for these amides. Second-order rate constants (k2) ranged from a low of 2.0 X 10(-14) to a high of 1.1 X 10(-9) liters organism-1 h-1 for niclosamide (2',5-dichloro-4'-nitrosalicylanilide) and propachlor (2-chloro-N-isopropylacetanilide), respectively. The mechanism of degradation (i.e., microbially mediated hydrolysis) of the amides was consistent with that of other organic chemicals previously studied in a variety of natural waters. Preliminary investigations indicate that temporal variations in measured second-order rate constants are small. A simple linear regression of the infrared carbonyl-stretching frequency with log K2 gave a correlation coefficient (r2) of 0.962.

Microbial transformation of esters of chlorinated carboxylic acids.

Two groups of compounds were selected for microbial transformation studies. In the first group were carboxylic acid esters having a fixed aromatic moiety and an increasing length of the alkyl component. Ethyl esters of chlorine-substituted carboxylic acids were in the second group. Microorganisms from environmental waters and a pure culture of Pseudomonas putida U were used. The bacterial populations were monitored by plate counts, and disappearance of the parent compound was followed by gas-liquid chromatography as a function of time. The products of microbial hydrolysis were the respective carboxylic acids. Octanol-water partition coefficients (K(ow)) for the compounds were measured. These values spanned three orders of magnitude, whereas microbial transformation rate constants (k(b)) varied only 50-fold. The microbial rate constants of the carboxylic acid esters with a fixed aromatic moiety increased with an increasing length of alkyl substituents. The regression coefficient for the linear relationships between log k(b) and log K(ow) was high for group 1 compounds, indicating that these parameters correlated well. The regression coefficient for the linear relationships for group 2 compounds, however, was low, indicating that these parameters correlated poorly.

Effect of phenol molecular structure on bacterial transformation rate constants in pond and river samples.

Microbial transformation rate constants for a series of phenols were correlated with a property of the substituents, van der Waal's radius. Transformation products were the corresponding catechols, with the exception of p-hydroxybenzoic acid, the product of p-acetylphenol. A different product suggested a different pathway; p-acetylphenol, therefore, was deleted from the data base.

Structure-activity relationships in microbial transformation of phenols.

The second-order rate constants for the microbial transformation of a series of phenols were correlated with the physicochemical properties of the phenols. The compounds studied were phenol, p-methylphenol, p-chlorophenol, p-bromophenol, p-cyanophenol, p-nitrophenol, p-acetylphenol, and p-methoxyphenol. Phenol-grown cells of Pseudomonas putida U transformed these compounds. Microbial transformation rate constants ranged from (1.5 +/- 0.99) x 10 liter . organism . h for p-cyanophenol to (7.0 +/- 1.3) x 10 liter . organism . h for phenol. Linear regression analyses of rate constants and electronic, steric, and hydrophobic parameters showed that van der Waal's radii gave the best coefficient of determination (r = 0.956). Products identified by thin-layer chromatography and liquid chromatography indicated that the phenols were microbially oxidized to the corresponding catechols.

Second-order model to predict microbial degradation of organic compounds in natural waters.

The reliability of second-order rate constants for assessing microbial degradation kinetics in natural waters was examined by using three compounds that undergo hydrolytic degradation. The butoxyethyl ester of 2,4-dichlorophenoxyacetic acid was studied in water samples from 31 sites, malathion was examined in water from 14 sites, and chlorpropham was studied in samples from 11 sites. The coefficient of variation for rate constants for each compound was less than 65% over all sites. Additional studies indicated that the rate conformed to second-order kinetics; that is, the rate was proportional to both bacterial and xenobiotic concentrations.