Algal Blooms Reduce the Uptake of Toxic Methylmercury in Freshwater Food Webs

Mercury accumulation in fish is a global public health concern, because fish are the primary source of toxic methylmercury to humans. Fish from all lakes do not pose the same level of risk to consumers. One of the most intriguing patterns is that potentially dangerous mercury concentrations can be f...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2002-04, Vol.99 (7), p.4419-4423
Main Authors: Pickhardt, Paul C., Folt, Carol L., Chen, Celia Y., Klaue, Bjoern, Blum, Joel D.
Format: Article
Language:English
Subjects:
Algae
Algal blooms
Animals
Biological Sciences
Biomass
Daphnia - metabolism
Eutrophication
Fish
Food Chain
Food chains
Fresh Water
Freshwater fishes
Isotopes
Lakes
Mercury
Methylmercury Compounds - metabolism
Nutrients
Particulate matter
Phytoplankton
Water Pollutants, Chemical - metabolism
Water tanks
Zooplankton
Zooplankton - metabolism
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Summary:Mercury accumulation in fish is a global public health concern, because fish are the primary source of toxic methylmercury to humans. Fish from all lakes do not pose the same level of risk to consumers. One of the most intriguing patterns is that potentially dangerous mercury concentrations can be found in fish from clear, oligotrophic lakes whereas fish from greener, eutrophic lakes often carry less mercury. In this study, we experimentally tested the hypothesis that increasing algal biomass reduces mercury accumulation at higher trophic levels through the dilution of mercury in consumed algal cells. Under bloom dilution, as algal biomass increases, the concentration of mercury per cell decreases, resulting in a lower dietary input to grazers and reduced bioaccumulation in algal-rich eutrophic systems. To test this hypothesis, we added enriched stable isotopes of Hg to experimental mesocosms and measured the uptake of toxic methylmercury CH3 200Hg+and inorganic201Hg2+by biota at several algal concentrations. We reduced absolute spike detection limits by 50-100 times compared with previous techniques, which allowed us to conduct experiments at the extremely low aqueous Hg concentrations that are typical of natural systems. We found that increasing algae reduced CH3Hg +concentrations in zooplankton 2-3-fold. Bloom dilution may provide a mechanistic explanation for lower CH3Hg +accumulation by zooplankton and fish in algal-rich relative to algal-poor systems.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.072531099