Quantitative structure-activity relationships for the effect of hydrophobic organic chemicals on rate of feeding by mussels ( Mytilus edulis)

Abstract

The effect of hydrophobic organic chemicals on the rate of feeding by mussels ( Mytilus edulis) was investigated. The effect was expressed as the toxicant concentration in water required to reduce feeding rate by 50% (WEC 50). A quantitative structure-activity relationship (QSAR) was derived in which WEC 50 was negatively correlated with log 10 octanol-water partition coefficient (log K ow) and positively correlated with aqueous solubility, indicating that hydrophobicity has a major influence on toxicity. QSARs calculated between bioconcentration factor, and log K ow and aqueous solubility showed, that hydrophobicity influences toxicity largely through its effect on bioconcentration. This observation was confirmed by expressing toxicity as the toxicant concentration in mussel tissue required to reduce feeding rate by 50% (TEC 50). For the compounds tested which have log K ow values< 4.6, TEC 50 was relatively constant, irrespective of molecular structure. Compounds with log K ow values > 5 could be accumulated to much greater concentrations before feeding rate was affected, indicating that there is a ‘molecular weight cut-off’ in the toxicological response. These observations are characteristic of a non-specific narcotic mode of toxic action. The application of the reported QSARs to interpreting results derived from combined chemical contamination and biological effects environmental monitoring studies with mussels is discussed.