Bromine in soil — An indicator of automobile exhaust lead pollution?

Abstract

Soil Br concentrations, determined by neutron activation analysis, ranged from ‘natural’ levels of 11 to 18 ppm to values of up to five times as high in Glasgow roadside and park surface soil. Elevated Br concentration in soil is shown to be a useful qualitative indicator of automobile exhaust Pb pollution, although care must be exercised in sample selection to avoid erroneous interpretation of data. The excess Br originates from ethylene dibromide used to scavenge Pb from automobile engines in which tetraethyl Pb is used as an anti-knock agent.

Bromine was found to be enhanced to a lesser extent than Pb in contaminated Glasgow soil. The postemission and post-deposition chemistry of exhaust-emitted PbBrCl and its decomposition products are invoked to explain the differing distribution patterns dPb and Br in soil and street dirt. One street-dirt Br concentration of 182 ppm was considered atypical in view of a mean street-dirt Br level of 15 ± 7 ppm, indistinguishable from ‘natural’ levels, for which removal of Br as soluble bromide by rain-waterrun-off is considered chiefly responsible.