Uptake of Waterborne Methylmercury by Rainbow Trout (Salmo gairdneri) in Relation to Oxygen Consumption and Methylmercury Concentration

Oxygen consumption and uptake of waterborne methylmercury were measured for rainbow trout (Salmo gairdneri) forced to swim at sustained swimming speeds at 10 and 20 °C. The concentrations of methylmercury used (< 8 μg Hg∙L−1) did not affect oxygen consumption. The log of mass specific oxygen consumption increased linearly with relative swimming speed. Standard metabolic rates were significantly different (P < 0.05) at 10 and 20 °C (111 and 192 mg O2∙kg−1∙h−1, respectively) but the rate of increase in oxygen consumption with swimming speed was not significantly different between temperatures. The rate of methylmercury uptake was positively correlated with both oxygen consumption and methylmercury concentration. Multiple linear regression equations relating the logs of rate of methylmercury uptake, rate of oxygen consumption, and methylmercury concentration at 10 and 20 °C were contiguous and a single equation described the relationship at both temperatures. The efficiency of methylmercury uptake relative to oxygen was ~0.25 at both temperatures. Assuming an oxygen percent utilization of 33%, the percent utilization of methylmercury from water was ~8%.Key words: methylmercury, uptake, respiration, oxygen consumption, rainbow trout, bioaccumulation, pollutant

Tissue Uptake, Subcellular Distribution, and Metabolism of 14CH3HgCl and CH3203HgCl by Rainbow Trout, Salmo gairdneri

Uptake, whole tissue, and subcellular distribution of methylmercury (MeHg) by rainbow trout, Salmo gairdneri, was studied during, and in three 2-wk intervals following, a single 24-h exposure to 14CH3HgCl and CH3203HgCl. Gel permeation chromatography of cytosol fractions was performed on select tissues. Gills contained approximately 10 times as much MeHg as any other tissue after 24-h exposure whereas concentrations were lowest for brain and skeletal muscle. In the 2-wk period following exposure, gill MeHg concentrations decreased to levels comparable with most other tissues; methylmercury in most other tissues increased and then decreased during the subsequent 4-wk period. Methylmercury levels in brain, skeletal muscle, and gonad were highest at 6 wk. During the 6-wk interval following MeHg exposure, the percent of mercury as inorganic mercury (Hg++) increased in gill, kidney, and liver and to a lesser extent in all other tissues except skeletal muscle. Total MeHg was greatest in cytosol fractions and usually made up from 50 to 80% of the total tissue mercury. In liver cytosol a methylmercury binding metallothionein-like species accounted for up to 40% of the total methylmercury bound. Inorganic mercury (Hg++), probably derived from demethylation of methylmercury, was associated with a metallothionein-like protein detected in gill tissue but no more than 6% of the total mercury in the soluble fraction was bound to this protein(s). Mercury binding to metallothionein-like proteins in kidney and splenic fractions was minimal in spite of relatively large amounts of mercury in the cytosol from these tissues. Metallothionein may act as a binding scavenger for methylmercury and inorganic mercury in fish. Key words: methylmercury, uptake by trout, tissue distribution, subcellular distribution, metallothionein, detoxification