By Michael K. Saiki, Darell G. Slotton, Thomas W. May, Shaun M. Ayers,
and Charles N. Alpers
U.S. GEOLOGICAL SURVEY
Data Series 103
Sacramento, California 2004
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This report summarizes results of total mercury measurements
in skinless fillets of sport fishes collected during August 2000, September–October
2002, and July 2003 from Lake Natoma, a small (8,760 acre-feet) afterbay for
Folsom Dam on the lower American River. The primary objective of the study was
to determine if mercury concentrations in fillets approached or exceeded guidelines
for human consumption. The Food and Drug Administration (FDA) human-health action
level for methylmercury in commercially caught fish is 1.0 µg/g (microgram per
gram); the U.S. Environmental Protection Agency (USEPA) human-health criterion
for methylmercury residue in fish tissue is 0.30 µg/g. Wet weight concentrations
of total mercury in skinless fillets were as high as 0.19 µg/g in bluegill (Lepomis
macrochirus), 0.39 µg/g in redear sunfish (L. microlophus), 1.02
µg/g in largemouth bass (Micropterus salmoides), and 1.89 µg/g in channel
catfish (Ictalurus punctatus). Maximum concentrations of mercury in
other fish species varied from 0.10 µg/g in rainbow trout (Oncorhynchus
mykiss) to 0.56 µg/g in white catfish (A-meiurus catus). Altogether,
1 of 86 largemouth bass and 11 of 11 channel catfish exceeded the FDA human-health
action level. In addition, 1 of 20 redear sunfish, 26 of 86 largemouth bass,
2 of 3 spotted bass (M. punctulatus), 1 of 1 brown bullhead (A.
nebulosus), and 1 of 1 white catfish exceeded the USEPA human-health criterion.
These results indicate that some fish species inhabiting Lake Natoma contain
undesirably high concentrations of mercury in their skinless fillets.
Purpose and Scope
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