Tuesday, January 15, 2008

Toxic Metal Pollution From Medieval Mining Persists 800 Years Later

Study looks at patterns of heavy-metal contamination of a site in southern France

Scientists have tracked down the source of high levels of heavy metal pollution at a site in southern France: medieval metallurgical workshops. Sandrine Baron, Jean Carignan, and Alain Ploquin of the Center for Petrographic and Geochemical Research in Nancy, France, report that the lead, antimony, arsenic, copper, and zinc residues left behind there more than 800 years ago still pose a potential health threat (Environ. Sci. Technol., DOI: 10.1021/es0606430). Mont-Lozère Massif, the site of medieval workshop remnants that they studied, is in the Cévennes National Park, where people fish, hunt, farm, and camp.

Heavy metals are distributed in the environment because of natural and anthropogenic mechanisms. The trick for Baron's team was to figure out to what extent each mechanism contributed. While it's not surprising that large quantities of heavy metals have staying power in soil and rocks, this study is one of the first to systematically attribute present-day pollution levels to an ancient source of man-made pollution. The study "certifies the responsibilities of the polluters and the origin of the toxicity," Baron points out.

The team examined leftover slag—the by-product of smelting ore to purify mined metals—and the background content of the metals in surrounding soil and granite. By comparing the lead-isotope ratios found in the slag to those found in rock and soil, Baron's team illustrated that binary mixing between slag and granite was the primary method of dispersion and verified that the medieval pollution contributed at least 40% of the lead found in the granite.

Studies of old metallurgical pollution allow the understanding of modern pollution because we can observe the long-term effect of heavy metals in the environment.

Here is the full article.