The critical body residue (CBR), estimated from aquatic toxicity QSARs and bioconcentration‐log Kow relationships, appears to be relatively constant, at about 4 mmol L−1 of fish, for the acute toxicity of a variety of hydrophobic narcotic organic chemicals examined by the U.S. Environmental Protection Agency (Duluth, MN) in tests with the fathead minnow. However, for hydrophilic chemicals (log Kow < 1.5) the bulk of the toxicant is in the water phase rather than the organic/lipid phase of the organism, so the whole‐body residues in these cases should be similar to the LC50 water concentration. Over the log Kow range of – 1.5 to 6, acutely toxic whole‐body residues for narcotics can be approximated by the QSAR‐derived equation: CBR (mM) = 2.5 mM + 50/Kow. Estimates obtained by this method are in reasonable agreement with the limited literature data available for acutely toxic whole‐body residues of hydrophobic narcotic organic chemicals. Elimination half‐lives estimated from nonlinear curve fitting to time‐toxicity information were relatively constant for the Duluth bioassay data at approximately 3 h. Despite the relatively high variability of this type of kinetics data, the literature information for small aquatic organisms, from both toxicity‐and bioconcentration‐based tests, was in a similar range. It appears that QSARs created with raw aquatic bioassay data occur primarily as a result of the influence of chemical‐physical properties on the partitioning process. Log Kow appears to have little to do with the inherent potency of the neutral, narcotic organic chemicals examined.

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A residue‐based one‐compartment, first‐order‐kinetics model (1CFOK) was used to investigate the toxicity of mixtures of organic chemicals to the American flagfish, Jordanella floridae. Four sets of chemicals (chloroethanes, chloroethylenes, chlorobenzenes, and chlorophenols) were used to examine within‐set mixtures. Component chemicals of the mixtures appeared to be simply additive at threshold LC50. Kinetics rate constants and critical body residue (CBR) data estimated from single chemical toxicity test data, along with bioconcentration factor information calculated from log Kow, were used to model the time course of toxicant action of the mixtures and compare them against independently observed mixture toxicity test results. Agreement between observed and modeled information was good, in terms of both threshold toxicity estimates and the time course of toxicant action.

The paper examines the significance of toxicant kinetics information obtained from aquatic toxicity bioassays and bioconcentration tests. The data, bioconcentration kinetics and acute mortality versus exposure-duration information for juvenile American flagfish (Jordanellafloridae) exposed to 1,4-dichlorobenzene, are interpreted in terms of a one-compartment, first-order kinetics model. The output of the model is used to formulate a testable hypothesis regarding the comparison of toxicant kinetics derived from both bioconcentration test exposures and toxicity bioassays. The model's estimates of the toxicant body burden attained at mortality are compared with theoretical and observed body burdens from literature sources. The use of a simple, deterministic residue-based, one-compartment, first-order kinetics model to evaluate existing data, as well as to formulate hypotheses to direct experimental designs, is examined.