Cadmium in forest ecosystems around lead smelters in Missouri.

The development of Missouri's new lead belt within the past decase has provided an excellent opportunity to study the dissemination and effects of heavy metals in a deciduous forest ecosystem. Primary lead smelters within the new lead belt have been identified as potential sources of cadmium as well as lead, zinc, and copper. Sintering and blast furnace operations tend to produce significant quantities of small particulates highly enriched in cadmium and other heavy metals. At one smelter, samples of stack particulate emissions indicate that as ms accompanied by 0.44 lb zinc, 4.66 lb lead, and 0.01 lb copper/hr. These point-source emissions, as well as a number of other sources of fugitive (wind blown) and waterborne emissions contribute to a significant deposition of cadmium in the surrounding forest and stream beds. Mobilization of vagrant heavy metals may be significantly increased by contact of baghouse dusts or scrubber slurries with acidic effluents emanating from acid plants designed to produce H2SO4 as a smelter by-product. Two separate drainage forks within the Crooked Creek watershed permit some comparisons of the relative contributions of cadmium by air-borne versus water-borne contaminants. Cadmium and other heavy metals have been found to accumulate in the forest litter and partially decomposed litter along stream beds. Greater solubility, lower levels of complexation with organic ligands in the litter, and greater overall mobility of cadmium compared with lead, zinc, and copper result in appreciable contributions of dissolved cadmium to the watershed runoff. The present paper attempts to define the principle sources and current levels of heavy metal contamination and summarizes the efforts undertaken by the industry to curtail the problem.