Residue‐based interpretation of toxicity and bioconcentration QSARs from aquatic bioassays: Neutral narcotic organics

Abstract

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.

Toxicity of nitromusks in early lifestages of South African clawed frog (Xenopus laevis) and zebrafish (Danio rerio)

“…This may possibly be due to the use of higher number of embryos in these assays, leading to an increased statistical power for the detection of differences between the control and nitromusk treatment groups. The concurrently high wholebody concentrations determined via GC-ECD analysis (0.004-0.02 mmol/kg wet weight; Table 1), suggest that the observed mortality may not be due to a specific toxicity mechanism of the nitro-musks tested but rather the result of generalized narcosis, as previously demonstrated for various other organic compounds in fish and amphibians (0.2 -0.8 mmol/kg wet weight; McCarty et al, 1992). This hypothesis is also corroborated by studies of Adema and Langerwerf (1985), who reported musk xylene mediated mortality (LC 50 of 400 mg/l) in zebrafish exposed for 14 days using DMSO as the solvent for musk xylene.…”

Toxicokinetics and Bioconcentration of Polycyclic Aromatic Hydrocarbons in Freshwater Isopods

“…Bioconcentration factors and first-order elimination rate constants for persistent neutral organic compounds in aquatic organisms usually exhibit strong (double logarithmic) relationships with Kow (46)(47)(48)(49)(50)(51)(52). The relationship proposed by Mackay (48) for (wet weight) BCFs in fish commonly is considered a benchmark for the equilibrium partitioning theory (50,(52)(53).…”

“…The relationship proposed by Mackay (48) for (wet weight) BCFs in fish commonly is considered a benchmark for the equilibrium partitioning theory (50,(52)(53). The slopes of the wet weight bioconcentration QSARs (quantitative structure-activity relationships) calculated for freshwater isopods show a close resemblance to this benchmark relationship and are in good agreement with slopes documented (Table A-5, SI) for the bioconcentration of PAHs in daphnids and marine mollusks (13,49).…”

Chronic Toxicity Thresholds for Sediment-Associated Benzo[a]pyrene in the Midge (Chironomus dilutus)

“…Acute bioassays are useful for analyzing the hazards of highly toxic chemicals and contamination at high levels, but do not test key life-stage events, such as moulting and reproduction, during which organisms' susceptibility to toxicants may increase, and thus they do not show the long-term effects of contaminant exposure at low levels. Alternatively, chronic exposure to low levels of PAHs in sediment is more environmentally relevant (McCarty et al 1992). Fewer data, however, are available regarding toxicity in benthic invertebrates after chronic exposure to PAHs in sediment.…”