Mercury in tadpoles collected from remote alpine sites in the southern Sierra Nevada mountains, California, USA.

Amphibians in alpine wetlands of the Sierra Nevada mountains comprise key components of an aquatic-terrestrial food chain, and mercury contamination is a concern because concentrations in fish from this region exceed thresholds of risk to piscivorous wildlife. Total mercury concentrations were measured in whole tadpoles of the Sierra chorus frog, Pseudacris sierra, two times at 27 sites from high elevations (2786-3375 m) in the southern Sierra Nevada. Median mercury concentrations were 14 ng/g wet weight (154 ng/g dry weight), which were generally low in comparison to tadpoles of 15 other species/location combinations from studies that represented both highly contaminated and minimally contaminated sites. Mercury concentrations in P. sierra were below concentrations known to be harmful in premetamorphic tadpoles of another species and below threshold concentrations for risk to predaceous wildlife. Concentrations in tadpoles were also lower than those observed in predaceous fish in the study region presumably because tadpoles in the present study were much younger (1-2 months) than fish in the other study (3-10 years), and tadpoles represent a lower trophic level than these fish. Mercury concentrations were not related to distance from the adjacent San Joaquin Valley, a source of agricultural and industrial pollutants.