A method for the determination of uptake and clearance rate constants during the bioconcentration of toxicants in fish is described and validated. The procedure is limited to stable lipophilic compounds and requires the exposure of fish to an aqueous solution of toxicant under static conditions and measurement of toxicant loss from water with time. The rate constants are obtained from the time-concentration profile with the use of an iterative computer program. Bioconcentration factors obtained for pentachlorobenzene, two isomers of tetrachlorobenzene, and 1,4-diiodobenzene were consistent either with previous determinations or with expectations based on the octanol-water partition coefficient. The measurements with pentachlorobenzene were made over a 100-fold range of chemical concentration. No dependence of the bioconcentration factor on chemical concentration was observed, in accordance with a simple first-order uptake and depuration model, but in contrast to reported data on chlorinated diphenyl ethers and brominated toluenes.
An acclimated shake flask CO2 evolution test was used to study the biodegradability of 14 commercial phthalate esters that are commonly used as plasticizers. Both CO2 evolution (ultimate biodegradation) and loss of parent phthalate esters (primary biodegradation) were measured. With only a few exceptions, primary biodegradation was 90% or higher, and ultimate biodegradation was in excess of 55% of theoretical results in 28 days. The results showed that all of the commercial phthalate esters were susceptible to biodegradation by mixed populations of microorganisms from natural sources. The results also provide considerable insight into the utility and reproducibility of a standard biodegradation test that is being recommended for widespread screening of chemicals.
The activated sludge biodegradability of 12 commercial phthalate esters was evaluated in two test systems: (i) a semicontinuous activated sludge test and (ii) an acclimated 19-day die-away procedure. Both procedures demonstrated that phthalate esters are rapidly biodegraded under activated sludge conditions when loss of the parent phthalate ester (primary degradation) is measured.
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