THE METHYLMERCURY TO TOTAL MERCURY RATIO IN SELECTED MARINE, FRESH-WATER, AND TERRESTRIAL ORGANISMS

Total and methylmercury concentrations were determined in muscle and o rgan tissue from a wide variety of marine and terrestrial organisms sp anning several trophic levels. Sediment and water samples from many of the tissue sampling sites were also analyzed to assess the degree of mercury contamination to which the animals were exposed. The methylmer cury to total mercury ratios were examined to determine whether this r atio is indicative of elevated exposure to organic or inorganic mercur y and how it varies relative to tissue type and position in the food c hain. As an ancillary study, a subset of these tissues was analyzed as 1) wet tissue, and 2) freeze-dried, ball-milled tissue to determine w hether the form of sample preparation can adversely affect mercury ana lysis. Results indicate that the methylmercury to total mercury ratios generally approach unity only in muscle tissue of higher food chain c arnivorous fish residing in waters that are relatively uncontaminated with respect to inorganic,mercury species. Herbivorous terrestrial mam mals and low food chain marine organisms tend to have very low methylm ercury to total mercury ratios. Marine animals placed higher on the fo od chain, such as crabs and lobsters, exhibit somewhat higher methylme rcury to total mercury ratios and can exhibit a large variation in thi s ratio between organ tissue and muscle tissue of the same animal. The samples analyzed as both wet and freeze-dried, ball-milled tissue ind icate that freeze-drying and ball-milling in no way result in mercury loss or contamination and, in fact, result in better replicate analyse s and create a sample sufficiently stable to be archived for several y ears without refrigeration.