Lead Precipitation Fluxes at Tropical Oceanic Sites Determined From 2øpb Measurements

Concentrations of lead, 21øpb, and 21øpo were measured in rain selected for least influence by local sources of contamination at several tropical and subtropical islands (Enewetak; Pigeon Key, Florida; and American Samoa) and shipboard stations (near Bermuda and Tahiti). Ratios expressed as ng Pb/dpm 2•øpb in rain were 250-900 for Pigeon Key (assuming 12% adsorption for 21øpb and no adsorption for lead), depending on whether the air masses containing the analyzed rain came from the Caribbean or from the continent, respectively; about 390 for the northern Sargasso Sea downwind from emissions of industrial lead in North America; 65 for Enewetak, remote from continental emissions of industrial lead in the northern hemisphere; and 14 near Tahiti, a remote location in the southern hemisphere where industrial lead emissions to the atmosphere are much less than in the northern hemisphere. (The American Samoa sample yielded a higher ratio than Tahiti; the reason for this is not clear but may be due to local Pb sources.) The corresponding fluxes of lead to the oceans, based on measured or modeled 2•øpb precipitation fluxes, are about 4 ng Pb/cm2y for Tahiti, 10 for Enewetak, and 270 for the Sargasso Sea site, and between 110 to 390 at Pigeon Key.