Environmental exposure assessment: Experience under the toxic substances control act

Abstract

The Toxic Substances Control Act (TSCA) has focused governmental attention on the process of assessing the hazards from commercial chemicals. Environmental behavior and impact must be projected before the chemical is released. This requires a knowledge of the environment, relevancy of laboratory data, extent of necessary data and interpretation of those data for future impacts. The responsibility for the data rests with the manufacturer. The key criterion involves a determination of “unreasonable risk.” Six axiomatic principles of risk assessment are identified. This involves an interactive and interdisciplinary thought process that is both iterative and staged. A generalized procedure for exposure assessment has been developed. An initial risk assessment comparing projected environmental concentrations with probable effect levels determines the type and quantity of laboratory test data needed. As examples, three new and three existing chemicals with widely differing properties and uses have been evaluated for their potential environmental impacts.

Fate and persistence of aquatic herbicides

“…An atmospheric half-life with respect to photolysis ranged from 0.5 to 1 d (USEPA 1985; Jori et al 1986). The mand p-xylene isomers are also 80 and 71% biodegradable, respectively, in BOD tests using municipal sewage seed, indicating that xylenes are readily biodegradable (Bridie et al 1979;Daniels et al 1985). However, Bridie et al (1979) found a-xylene to be only 57% biodegradable in BOD tests.…”

“…The predominant fate process is volatilization from water (Klingman et al 1975;Daniels et al 1985). Xylene vapor pressure averages 6 mm Hg at 20°C (Hunter et al 1984;Daniels et al 1985) with H values ranging from 0.017 to 0.022 atm m 3 /mol for o-xylene and p-xylene, respectively (Hunter et al 1984).…”

“…Measured Kow values range from 588 to 1584 for 0-and mxylene, respectively (USEPA 1985). A xylenes BCF of 91 indicates that xylene could bioconcentrate (Daniels et al 1985); however, this is unlikely due to the BCF magnitude and the relatively short xylene persistence in aquatic environments (Jori et al 1986). …”

“…Xylene vapor pressure averages 6 mm Hg at 20°C (Hunter et al 1984;Daniels et al 1985) with H values ranging from 0.017 to 0.022 atm m 3 /mol for o-xylene and p-xylene, respectively (Hunter et al 1984). Compounds with H values greater than 10-5 atm m 3 /mol are expected to volati- (1982) partitioning or distribution model places 77 to 99% of total xylene added to water in the atmosphere (Hunter et al 1984;Daniels et al 1985;Jori et al 1986). Xylenes are photoreactive in both water and air (Jori et al 1986).…”

“…Xylene isomers (xylenes), consisting of 1,2-, 1,3-, and 1 ,4-dimethyl benzenes, are added to water as emulsions (Meister 1986). The water solubility of the xylenes is approximately 200 mg/L (USEPA 1985;Jori et al 1986) with an estimated Kow of 1259 and Koc of 794 (Daniels et al 1985). Measured Kow values range from 588 to 1584 for 0-and mxylene, respectively (USEPA 1985).…”