[Lo-Feature] November 1999 L&O Featured Article now available

[Everett Fee]

The featured article in the November issue of L&O is:

"Cadmium sources and exchange rates for Chaoborus larvae in nature" 
by Catherine Munger, Landis Hare, and Andr E9 Tessier. It will appear 
in Limnology and Oceanography 44(7): 1763-1771,1999.

This article is freely available at the Web address:

          http://aslo.org/lo/toc/vol_44/issue_7/1763.pdf

Instructions for reading PDF files are located on the ASLO web page:

          http://aslo.org/help/loonline.html

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Introductory comments by Helene Cyr (L&O Associate Editor)

Predicting the fate of heavy metal contaminants in aquatic environments 
is a pressing environmental and economic challenge.  One set of 
successful models focuses on metal speciation in water to determine 
their availability and toxicity to aquatic organisms (Hare and Tessier 
1996). Several studies, however, are now suggesting that these 
relationships may be indirect. In particular, evidence is mounting that 
animals can take up a significant proportion of contaminants from their 
food, rather than solely from the  surrounding water (Reinfelder et al. 
1998; Wang and Fisher 1998).  The  experiments necessary to tease 
out the relative importance of the aqueous  medium and of an animal 
92s food as sources of contaminants are complicated,  and the task of 
testing these ideas in situ has been daunting.

In this month's L&O featured article Munger, Hare, and Tessier (1999) 
propose a relatively simple approach to this problem.  Reciprocal 
transplantation of predaceous phantom midge larvae between low- and 
high-contamination lakes allows them to measure in situ rates of 
cadmium uptake and depuration.  Most importantly, by offering different 
concentrations of prey to the transplanted predators, they demonstrate 
that contaminated prey contribute most of the cadmium taken up by 
phantom midge larvae. Their results show that, contrary to the implicit 
assumptions of most laboratory experiments and models, food is a very 
effective vector of cadmium contamination in Chaoborus.

The story is likely to get even more complicated as the importance of 
food web dynamics is explored further.  Predators are selective, and 
prey differ in degree of contamination. Metal assimilation by a predator 
will also probably vary with its feeding rate, the quality of its food, the 
partitioning of metals in its prey, and the digestive physiology of the 
predator (Wang and Fisher 1999), all of which are highly variable.  Thus, 
despite this breakthrough, it is unclear how much information on the 
intricacies of food webs will be needed to significantly improve current 
models of contaminant transfers.

References

Hare, L. and A. Tessier. 1996. Predicting animal cadmium 
concentrations in lakes. Nature 380: 430-432.

Munger, Catherine, Landis Hare, and Andr E9 Tessier. 1999. Cadmium 
sources and exchange rates for Chaoborus larvae in nature. Limnology 
and Oceanography 44: 1763-1771.

Reinfelder, J.R. et al. 1998. Trace element trophic transfer in aquatic 
organisms: a critique of the kinetic model approach. Science of the Total
Environment 219: 117-135.

Wang, W.X. and N.S. Fisher. 1998. Accumulation of trace elements in 
a marine copepod. Limnology and Oceanography. 43: 273-283.

Wang, W.X. and N.S. Fisher. 1999. Assimilation efficiencies of 
chemical contaminants in aquatic invertebrates: a synthesis. 
Environmental Toxicology and Chemistry 18: 2034-2045.
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Everett Fee
Editor-in-Chief, Limnology & Oceanography
343 Lady MacDonald Crescent
Canmore, Alberta  T1W 1H5  CANADA
office: 403/609-2456, fax: 403/609-2400
<lo-editor@aslo.org>
http://www.ucalgary.ca/~efee
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