Organolead Compounds in Natural Systems

Abstract

Most organolead compounds with alkyl groups attached to a central lead atom are many times more toxic than inorganic lead compounds. The widespread use of tetraethyllead and tetramethyllead as antiknock agents in gasoline, and consequently their emission or discharge into the environment, is therefore of considerable importance. It is thought that alkylleads in an estuarine environment were responsible for the death in 1979 of a large number of coastal birds. There are relatively little data on the fate, toxicity or accumulation of these compounds in natural systems, such as bivalve molluscs. These animals are an essential part of the diet of coastal birds and may have accumulated alkyllead to concentrations that were acutely toxic to the birds. Data reported in this thesis indicate the approximate concentrations of the most environmentally abundant alkylleads that are toxic to two estuarine bivalves and two algae. It is observed that high concentrations may accumulate in bivalves, which may be acutely toxic to birds. In addition, the relative toxicities of a number of alkyllead compounds are established in an attempt to resolve conflicting reports of tetraethyllead toxicity in the literature. Our results suggest that tetraethyllead is not toxic in its pure form, but that the ionic triethyllead and trimethyllead are highly toxic. Evidence is presented suggesting that triethyllead may be adsorbed onto tetraethyllead molecules both in solution and in cytoplasm, causing a reduction in overall toxicity. It is also likely that certain unicellular algal cells may be capable of metabolising alkyllead compounds via dealkylating mechanisms.