Linking Cd Accumulation and Effect in Resistant and Sensitive Freshwater Invertebrates

There has been recent discussion within the field of environmental toxicology as to the viability of using the bioaccumulation of a chemical toxicant to predict toxic effects. Current literature has shown this concept to carry some merit, although there is a major flaw in that with many cases, namely those involving sensitive species, body burdens cannot be reliably linked to effects (Adams et al. (2010)). Bearing this issue in mind the goal of this thesis was to assess the viability of using bioaccumulation as a measure of effect in a different way. The proposed idea utilized Cd accumulation in a resistant species the California blackworm (Lumbriculus variegatus), to predict effect in a sensitive species the freshwater amphipod Hyalella azteca. In this study L. variegatus accumulated cadmium in a dose dependent manner with body burdens increasing with both exposure duration and exposure concentration regardless of water hardness. In both hard (120 mg/L as CaCO3) and soft water (22 mg/L as CaCO3) exposures at concentrations as high as 200 ug Cd/L there were no lethal effects observed, demonstrating the ability of this organism to store and detoxify accumulated Cd within cellular debris or with metallothionein (MT) like proteins. Steady-state accumulation was not reached despite chronic exposure durations of 87 and 28 days for hard and soft water exposures respectively. In hard water exposures L. variegatus suffered significant reductions in reproduction at exposures over 100 μg Cd/L, with an almost 8-fold reduction at exposure over 200 μg/L. These effects may be related to the accumulation of Cd inside sensitive organelles or the binding of Cd to important heat denaturable proteins and enzymes (Wallace et al., 2003). Hyalella azteca was sensitive to Cd exposure, resulting in 100% mortality at concentrations above 10 μg Cd/L in hard water and 1.4 μg Cd/L in soft water. In contrast to the resistant species, H. azteca was able to quickly (10 days in hard water; 14 days in soft water) accumulate Cd to a steady state body burden. Through extrapolation of steady state concentrations and modelling, it was possible to relate lethal concentrations in the sensitive species to estimated body burdens in the resistant species. Although this study exists only as a proof of principle, this concept, if applied to contaminated fresh waters could be used to quickly determine deleterious toxic effects in sensitive members of an ecosystem. This would be accomplished through the use of a resistant species as a bioindicator. A researcher would need to go out into the field and collect samples of the indicator species from a contaminated site, then return to lab and analyze the samples for their total body burden. Based on the average of these body burdens, the researcher could predict negative effects in the ecosystem’s sensitive species. However, this concept is still in its infancy and the observed relationships need to be reproduced in different water chemistries for confirmation prior to further development