Mercury toxicity is an environmental concern in diverse aquatic systems because
methylmercury enters the water column in a number of ways and then biomagnifies
through food webs. Piscivorous fish at the top of many freshwater food webs
can then extend that trophic transfer and potential for neurotoxicity to
wildlife and humans. Mining activities, particularly those associated with the
San Francisco Bay region, can generate both point and non-point mercury
sources. Largemouth bass and hybrid striped bass from Guadalupe Reservoir
(GUA), California and Lahontan Reservoir (LAH), Nevada were analyzed at SSRL's
Beam Line 9-3 to determine predominant chemical species of mercury accumulated
by high-trophic-level piscivores that are exposed to elevated mercury in both
solution and particulate phases in the water column. Both GUA and LAH are
affected either directly or indirectly by the legacy of gold and silver mining
in the Sierra Nevada during the 19th century.
The results, based on mercury x-ray absorption spectroscopy data, demonstrated
that mercury was accumulated almost exclusively as methylmercury-cysteine
complexes in the muscle tissues of piscivorous freshwater fish from both GUA
and LAH. This result, consistent with observations for several marketed marine
fish species, suggested that speciation of bioaccumulated mercury at high
trophic levels was consistent over a wide range of ionic strengths and mercury
sources. In terms of management implications, the dominance of methylmercury
cysteine complexes in muscle tissues of fish obtained from such contrasting
environments and exposure conditions suggest that one may be able to greatly
simplify toxicological models for fish consumption over wide-ranging aquatic
habitats by assuming that piscivorous fishes, a food source for wildlife and
humans, consistently accumulate mercury as cysteine complexes in their tissues.
Kuwabara, J.S., Arai, Yuji, Topping, B.R., Pickering, I. J., and George, G.N.
(2007). Mercury speciation in piscivorous fish from mining-impacted
reservoirs: Environmental Science and Technology 41, 2745-2749.
To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/ch3hg_trophictrans.html