THE USE OF BIOMARKERS TO MEASURE THE INTERACTIVE EFFECTS OF CHEMICALS

Biomarker assays that pro,ide measures of the toxic effects of chemica ls on key organisms are of particular interest in ecotoxicology and en vironmental risk assessment. Typically, such assays provide measures o f the molecular mechanisms that underlie toxicity (e.g., inhibition of brain acetylcholinesterase activity by organophosphorus insecticides and retardation of the vitamin It cycle by anticoagulant rodenticides) . They are particularly valuable for detecting and quantifying toxicit y where organisms are exposed to mixtures of compounds and for identif ying cases of potentiation. In birds, inhibition of brain acetylcholin esterase activity can provide an index of potentiation of organophosph orus and carbamate insecticides by other pesticides. Inhibition of ser um butyrylcholinesterase also is very useful as a nondestructive assay but is not simply related to inhibition of brain acetylcholinesterase . Assays for DNA damage can indicate where there is an increase in the rate of activation of carcinogens and mutagens due to induction of th e cytochrome P-450 system. Assays for blood levels of retinol (vitamin A) and thyroxine can establish thyroxine antagonism by metabolites of 3,3,4,4-tetrachlorobiphenyl. Assays for changes in levels of clotting protein in serum can give an indication of the effect of mixtures of anticoagulant rodenticides on the vitamin K cycle. The interactive eff ects of mixtures of pesticides in the held are starting to be investig ated by this approach (e.g., a recent study of the combined action of malathion and prochloraz in the red-legged partridge). (C) 1998 Academ ic Press.