William C. Steen

Reliability of reporting on life-style and agricultural factors by a sample of participants in the Agricultural Health Study from Iowa.

Repeat interviews from 4,088 Iowa pesticide applicators participating in the Agricultural Health Study provided the opportunity to evaluate the reliability of self-reported information on pesticide use and various demographic and life-style factors. Self-completed questionnaires were administered 1 year apart when participants returned to county agricultural extension offices for pesticide certification or training. Percentage agreement for ever-/never-use of specific pesticides and application practices was quite high, generally ranging from 70% to more than 90%, and did not vary by age, educational level, or farm size. Agreement was lower (typically 50–60%) for duration, frequency, or decade of first use of specific pesticides. Level of agreement regarding pesticide use in this population is similar to that generally found for factors typically used in epidemiologic studies such as tobacco use and higher than typically reported for diet, physical activity, and medical conditions.

Phthalate ester hydrolysis: Linear free energy relationships

Abstract Alkaline hydrolysis rate constants were measured for dimethyl, diethyl, di- n -butyl, di- iso -butyl, and di-(2-ethylhexyl) phthalate esters in water. A linear free energy relationship (LFER) was established for estimating alkaline hydrolysis rate constants for other phthalate esters. Dimethyl phthalate hydrolyzes to phthalic acid with the mono ester as an intermediate. The rate ratio for the second-order-alkaline hydrolysis rate constants of the diester to the monoester is 12. Water solubilities for dimethyl, diethyl, di- n -butyl, di- n -octyl and di-(2-ethylhexyl) phthalate esters were measured and compared with literature values.

Partitioning of selected polychlorinated biphenyls to natural sediments

Abstract The partitioning of two polychlorinated biphenyl mixtures (Aroclor 1016 and 1242) and two tetrachlorobiphenyl isomers (2,5,3′,4′ and 2,6,2′,6′ tetrachlorobiphenyl) between water and four natural sediments was evaluated in laboratory investigations. For both Aroclor mixtures, the extent of adsorption was comparable on all four natural sediments studied. For individual isomers, partitioning was comparable with that observed for the mixtures. Both particle size distribution and total organic carbon were important factors in determining the extent of partitioning for the two isomers; but in the case of the mixtures, there was no correlation with organic content.

Use of linear free energy relationships and an evaluative model to assess the fate and transport of phthalate esters in the aquatic environment

Linear free energy relationships for selected phthalate esters were used to estimate the rate constants for hydroysis, biolysis, sediment-water partition coefficients, and biosorption required for modeling. The fate and transport behavior of dimethyl, diethyl, di-n-butyl, di-n-octyl, and di-(2-ethylhexyl) phthalate esters were assessed by use of an evaluative model, the Exposure Analysis Modeling System (EXAMS). Four EXAMS environments were defined: a pond, an oligotrophic lake, a eutrophic lake, and a river using environmental parameters representative of the Southeastern United States. Results suggest that higher molecular weight esters are not significantly transformed and that export from the ecosystem is the dominant process.

Biosorption of hydrophobic organic pollutants by mixed microbial populations

Abstract In recognition of the need to estimate biosorption for natural microbial populations, the variability of partition coefficients for two hydrophobic pollutants to natural populations from a variety of aquatic systems was investigated. Biosorption partition coefficents for pyrene [2.46(±0.6) × 10 4 ] and phenanthrene [6.34(±1) × 10 3 ] were nearly constant over 14 different microbial sources, consisting of sediments and soils from eight states. For these condensed ring aromatics, semi-empirical equations were developed relating biosorption partition coefficients to octanol/water partition coefficients and to water solubility and melting point. Concepts and relationships developed for these materials should extend to other families of hydrophobic compounds.

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 propanil in aquatic systems

Abstract Second-order microbial degradation rate constants were developed for the herbicide propanil in lake and water samples from the Union of Soviet Socialist Republics. Variations in calculated second-order rate constants were attributed to differences in bacterial counting methods used. Rate constants determined for propanil transformation in waters investigated in the USSR were similar to those established for natural water systems throughout the United States.