The Environmental Residue Effects Database was evaluated to identify critical body residues of
organic chemicals causing acute baseline neutral
narcosis in aquatic organisms. Over 15 000 records for >400 chemicals were evaluated. Mean molar critical body residues in the final data set of 161 records for 29 chemicals were within published ranges but varied within and among chemicals and species (~3 orders of magnitude), and
lipid normalization did not consistently decrease variability. All 29 chemicals can act as baseline neutral
narcotics, but chemicals and/or their metabolites may also act by nonnarcotic modes of action. Specifically, nonnarcotic toxicity of
polycyclic aromatic hydrocarbons and/or their biotransformation derivatives may be a significant source of variability. Complete testing of the
narcosis-critical body residue hypothesis was confounded by data gaps for key toxicity modifying factors such as metabolite formation/toxicity,
lipid content/composition, other modes of
toxic action, and lack of steady-state status. Such problems impede determination of the precise, accurate toxicity estimates necessary for sound toxicological comparisons. Thus, neither the data nor the chemicals in the final data set should be considered definitive. Changes to testing designs and methods are necessary to improve data collection and critical body residue interpretation for hazard and risk assessment. Each of the toxicity metrics discussed-wet weight and
lipid weight critical body residues, volume fraction in organism
lipid, and chemical activity-has advantages, but all are subject to the same toxicity modifying factors.