Application of the narcosis target lipid model to algal toxicity and deriving predicted-no-effect concentrations.
The marine environment is contaminated with many organic compounds, some of which induce deleterious responses in biota. Biological impact can be assessed by measuring the physiological responses of mussels, though the task of establishing which of the bioaccumulated compounds cause the observed effects is complex. To facilitate this task, quantitative structure-activity relationships (QSARs) for the physiological responses are being established. In this paper, the responsiveness of ciliary feeding to alkanes and benzene-substituted alkanes is described and compared with a QSAR established previously for aromatic compounds. Most of the test compounds with aqueous solubilities greater than 70 micrograms dm-3 were toxic to feeding activity when bioaccumulated to similar concentrations, whereas compounds of lower solubility were less toxic. The only exceptions were the polyaromatic hydrocarbons pyrene and fluoranthene, which were less toxic than predicted from their solubility. These data are consistent with the hypothesis that the toxicity cut-off is due to solubility-related phenomena, the effect perhaps being enhanced for aromatic hydrocarbons dosed near to their solubility limits, by sequestration of crystals within the mussel tissues. These observations indicate that many organic contaminants detected by chemical analysis of mussels have no direct effect on filter feeding, whereas the less frequently determined volatile compounds are toxic.