The Link between Continental and Marine Geochemistry as shown by Mercury and Arsenic Anomalies in Sediments from Southern Tuscany and Tyrrhenian Sea

Abstract

Presenting and discussing new data stressing the link between marine and continental trace element geochemistry is the aim of this paper.

• 1. Among the maps from geochemical exploration surveys, applied to environmental issues, it is worth mentioning the one that shows the distribution of Hg in the stream sediments from Tuscany, where 1,000 samples were examined from an area of 20,000 km² (1966). Fifteen years later huge Hg anomalies were picked up in marine sediments from Tyrrhenian sea and 20 years later Hg contents in local fisheries were frequently found to be higher than the allowed Maximum Admissible Concentration (MAC) values.

• 2. Data on the anomalous As contents, in both continental and marine environments, are presented. In particular, the new maps of As distribution in the stream sediments of southern Tuscany, as well as in marine sediments from the Piombino channel, show huge and wide anomalies. These last data are impressive, because the average value of all the 57 samples is as high as 66 mg/kg (vs an average value for the Earth’s crust of about 2 mg/kg) and the samples collected around Elba Island have an average value as high as 252 mg/kg, with peaks of over 400 mg/kg. The isoconcentration curves clearly identify the origin of the dispersion aureole on the eastern coast of the Island. With reference to As distribution, two very extensive and distinct aureoles can be distinguished: one originating from the mining sector of eastern Elba Island (high arsenopyrite content in sulfide deposits) and the other located in mainland Tuscany and represented by multiple dispersion sources.

The need for urgently initiating research in two related complementary areas to get more information on the As aureoles and on their effects on the biota is also discussed.