A SIMPLIFIED RADIOCHEMICAL TECHNIQUE FOR MEASUREMENTS OF NET MERCURY METHYLATION RATES IN AQUATIC SYSTEMS NEAR GOLDMINING AREAS, AMAZON, BRAZIL

Current Hg-0 emissions from goldmining activities in the Amazon basin reach 100 tons . xyear(-1), but very little is known about Hg methylat ion rates in local aquatic systems. Simplified versions of the Furutan i and Rudd (1980) radiochemical method were tested and applied in the determination, by in-situ incubations, of specific net Hg methylation rates in water and surface sediments of the Madeira river goldmining a rea. Efficiency for Me(203)Hg extraction from water and sediment was i n the 75.3-96.77% range, depending on sample type and extraction proce dure. Methylation was not detectable in water but rates in surface sed iments ranged from 10(-5) to 10-1%. g(-1) h(-1), the higher rates bein g found in sites in a reservoir area. Methylation was absent or strong ly depressed in sterilized sediments. The effect of delays between sam pling, incubation and extraction on methylation rates and Me(203)Hg re covery was documented. Despite their limited spatial and temporal rang e, these data are further evidence that concerns about the potential t oxicological impacts of Hg emissions in the Amazon basin are justified .