the diet and the pore water of the sediments used to contaminate the diet will be documented, 
allowing comparison of water concentrations that directly cause toxic effects with the water 
concentrations needed to result in toxic concentrations in diet. If these experiments demonstrate 
significant toxic effects from diet that might substantially increase risk from water alone, 
additional experiments will be conducted with metal exposure both via water and diet to further 
evaluate the relative importance of these two routes. 
2. Dietary Metals Effects on Zooplankton. 
This will include experiments in which zooplankton (freshwater cladocerans and saltwater 
copepods) are dironically exposed to metals dissolved in water and incorporated into food, both 
separately and combined. Methods will build on those of Hook and Fisher (2001) and Kim et al. 
(2000) and will address the reasons for the discrepancies between these studies and the relative 
importance of these different routes of exposure under conditions expected in natural systems. 
Experiments will be designed to supplement and complement related research in progress 
elsewhere. 
Products 
FY03 Journal article regarding importance of dietary exposure to chronic metal toxicity to 
juvenile fish. 
FY04 Journal article regarding importance of dietary exposure to chronic metal toxicity to 
cladocerans. 
APM 4D FY06 Report evaluating importance of dietary route of exposures to aquatic risk 
assessments for metals (MED). 
Benefits of Products 
The existing controversy over dietary exposure to metals is influencing regulatory decision¬ 
making in several Regions and programs. In addition to the Superfund process and Natural 
Resources Damage Assessment (NRDA) litigation on the CFR, similar issues have been raised 
regarding the assessment of mining impacts on the Coeur d’Alene River in Idaho. With respect 
to State WQS, ORD staff have been contacted by State representatives concerned that shifting 
standards from total to dissolved will increase metal loadings and thereby increase risk from 
metal toxicity via other pathways such as dietary and sediment exposure. In the consultation of 
Region 9 and OW by the Department of Interior on the California Toxics Rule (CTR), the issue 
of dietary exposure to metals figured prominently in the draft Biological Opinion (BO), with DOI 
citing uncertainty regarding dietary uptake as reason for using total, rather than dissolved, metals 
as a measure of compliance. Enhancing understanding of combined waterborne and dietary 
exposures to metal mixtures will improve the ability of environmental managers in the EPA and 
elsewhere to make informed decisions on the assessment of ecological risk from metals in 
aquatic systems. 
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