Evidence of recent lead pollution in deep north-east Atlantic sediments

Abstract

Today, the global lead emissions into the atmosphere from anthropogenic sources are about 200 times higher than in the past¹ and dominate other lead pathways to the ocean. Exhaust from leaded gasoline is the major source of pollutant lead in the atmosphere², and subsequently in the marine environment due to atmospheric deposition by wet and dry removal processes^3,4. This pollution has already perturbed the biogeochemical cycle of lead in the open ocean^2,3,5–7 especially in the north Atlantic. In surface waters, where lead is introduced mainly in the dissolved state, its residence time is relatively short (less than 5 years), as it is rapidly scavenged by, and transported with, participate matter^5,7. The mean residence time of lead in the ocean is estimated to be ∼100 yr^5,8. One can therefore expect to see some pollutant lead in the deep ocean surficial sediments. Here, we report lead concentrations in two short cores from the north-east Atlantic. Lead concentrations in surficial sediments (21.0 and 15.0 p.p.m. in the top cm) are higher than in the uppermost 10 cm of the cores (6.0 and 2.8 p.p.m.), and are likely to be enhanced from anthropogenic sources. The quantity of lead stored in these surficial sediments (5.7 and 2.5 µg cm⁻²) is of the same order as the amount of pollutant lead present in the dissolved state in the water column.