Uptake, bioaccumulation, and elimination of elemental mercury by Blacknose dace (Rhinichthys atratulus)

Blacknose dace (Rhinichthys atratulus) were exposed to Hg° in a controlled laboratory environment. Gill exposure, not uptake through food, was the primary focus of these experiments. Muscle tissue of all fish was tested for total mercury content. Selected fish were analyzed for methyl and total mercury to determine percent methylmercury in muscle tissue.

The fish in all experiments achieved elevated inorganic mercury levels in muscle tissue. Tissue concentration in the fish rose rapidly for the first several days then appeared to reach a plateau after 5-10 days. Uptake coefficients were high and varied little with exposure concentration, ranging from 4-14 hour^-1 when determined using a two compartment model. Apparent elimination coefficients calculated using the same model varied little with exposure concentrations, ranging from 0.0034 -0.0069 hour^-1 The experimentally determined elimination rate coefficient was 0.00032 hour^-1, almost 20 times slower than the mean rate coefficient estimated from the uptake curves.

Fish analyzed for total and methyl mercury concentrations in tissue were found to contain ≥ 90% inorganic mercury rather than ≥ 90% methylmercury which is usually the case in fish from natural environments. These findings make the process of in vivo methylation in blacknose dace seem very unlikely.

Regardless of the uptake and elimination patterns, the fish in all experiments achieved elevated inorganic mercury levels in muscle tissue. Little depuration was seen in the elimination experiment. This is very significant in regard to fish in East Fork Poplar Creek where high levels of inorganic mercury both in the form of Hg° and other species are found in the headwaters.