PT12 Metals and Bioaccumulation
Exhibit Hall
8:00 AM - Tuesday
(PT144) An examination of metal exposure history on Cd bioaccumulation and subcellular distribution in an aquatic insect.
Cain, D1, Buchwalter, D1, Luoma, S1, 1 U.S. Geological Survey, Menlo Park, CA, USA
ABSTRACT- Species inhabiting metal-contaminated environments can acquire tolerance through a variety of mechanisms. Species of the caddisfly Hydropsyche are known to be moderately tolerant of metals, although the underlying mechanisms are unclear. We examined potential tolerance mechanisms by comparing uptake, efflux, and the subcellular distribution of Cd between populations of Hydropsyche californica that had different exposure histories. Specimens were obtained from a site chronically contaminated by mining and from a nearby uncontaminated site. The insects were continually exposed to solute Cd (0.53 
M) labeled with 109Cd for 6 days, and then transferred to clean water for 9 days to follow loss. The subcellular distribution of Cd was determined in samples from each population at the end of the uptake and loss phases. Uptake, efflux and the resulting body concentrations of Cd were similar between populations. After 6 days of exposure, Cd was largely distributed between cell debris and cytosolic proteins. Total cytosolic Cd concentrations were the same in both populations, but Cd bound to metallothionein-like proteins (MTLP) accounted for 89% of the cytosolic Cd in the contaminated population and 60% in the uncontaminated population. Consequently, the concentration of Cd bound to non-MTLPs (representing potentially metal-sensitive sites) was more than 3-fold higher in the uncontaminated population (27 ng/g wet wt.) than the contaminated population (7 ng/g). Insects rapidly eliminated the accumulated Cd (t1/2 = 0.6 day) from all subcellular fractions, and after 9 days of loss Cd concentrations in MTLPs and non-MTLPs were similar in the populations. Results indicated that differences in metal exposure history did not affect biokinetics, but inter-population differences in Cd tolerance might be expected as a consequence of Cd binding to induced MTLPs.
Key words: biokinetics, Cd, subcellular distribution, metal tolerance