Dietary mercury exposure and bioaccumulation in larvae of the southern leopard frog, Rana sphenocephala.
JASON UNRINE & CHARLES JAGOE
Savannah River Ecology Laboratory. University of Georgia, P.O. Drawer
E. Aiken. SC 29803, USA; E-mail: unrine@srel.edu
Abstract: We investigated dietary mercury exposure and
bioaccumulation in larvae of the southern leopard frog, Rana sphenocephala.
Aufwuchs, an important dietary source for many larval amphibians
was collected from three reservoirs, a constructed wetland used for groundwater
treatment and from mercury-enriched mesocosms in South Carolina, USA to
determine the relationship between inorganic mercury and methylmercury
in aufwuchs. Four experimental diets were formulated with mercury
enriched aufwuchs, trout pellets, rabbit pellets. agar, and gelatin
to concentrations that bracketed those observed in aufwuchs from
the field and reported in the literature from sites contaminated primarily
by atmospheric deposition. The diets were fed to southern leopard frog
larvae in the laboratory for the entire larval period (60-254 d) and metamorphs
and tadpoles that died before metamorphosis were analyzed for inorganic
and methylmercury content by GC-CY AFS. We found that methylmercury concentration
increased with total mercury concentration in aufwuchs .but the proportion
of methylmercury to total mercury decreased with increasing total mercury
concentration. In the feeding experiment, bioaccumulation factors were
low and were inversely related to exposure concentration for both methylmercury
and inorganic mercury. Methylmercury was transferred from diets to larvae
4.7 times more efficiently than inorganic mercury suggesting that subcellular
fractionation of Hg in algal cells that constituted the aufwuchs
used to formulate experimental diets governed relative assimilation efficiencies
of the two mercury species.
Key words: amphibian. diet. exposure. bioaccumulation
factor. aufwuchs .
SREL Reprint #2776
Unrine, J. M. and C. H. Jagoe. 2004. Dietary mercury exposure and bioaccumulation in larvae of the southern leopard frog, Rana sphenocephala. Paper 83. In 7th International Conference on Mercury as a Global Pollutant, edited by Milena Horvat, Nives Ogrinc, and Jože Kotnik. Jožef Stefan Institute, Ljubljana, Slovenia.
