ATMOSPHERIC CONCENTRATIONS AND CHEMISTRY OF ALKYLLEAD COMPOUNDS AND ENVIRONMENTAL ALKYLATION OF LEAD

The atmospheric chemistry of alkyllead compounds was investigated by determining the ratio of alkyllead to total lead in a variety of different air masses. Maritime air was found to contain significantly more alkyllead relative to total lead than continental or urban air. The presence of gas-phase trialkyllead in the rural atmosphere was confirmed, with trialkyllead becoming progressively more important relative to other lead species with increasing distance from urban source areas. On the basis of estimates of the atmospheric lifetimes of the various lead species, it is concluded that these enhanced alkyllead ratios are explicable in terms of the atmospheric chemistry of the various species, with pollutant tetraalkyllead decomposing in the atmosphere to the relatively stable trialkyllead derivatives. It is therefore probably not necessary to invoke the hypothesis of the natural alkylation of lead to explain these enhanced ratios. Notwithstanding this, evidence is also presented from experiments using intertidal sediments both with and without the addition of a labeled lead tracer that indicates that lead (II) nitrate can be inefficiently alkylated by a sediment system.