Uptake Kinetics and Subcellular Compartmentalization Explain Lethal but Not Sublethal Effects of Cadmium in Two Closely Related Amphipod Species

Eulimnogammarus cyaneus and Eulimnogammarus
verrucosus, closely related amphipod species endemic to Lake
Baikal, differ with respect to body size (10- to 50-fold lower fresh
weights of E. cyaneus) and cellular stress response
(CSR) capacity, potentially causing species-related differences in
uptake, internal sequestration, and toxic sensitivity to waterborne
cadmium (Cd). We found that, compared to E. verrucosus, Cd uptake rates, related to a given exposure concentration, were
higher, and lethal concentrations (50%; LC50) were 2.3-fold lower
in E. cyaneus (4 weeks exposure; 6 °C). Upon
exposures to species-specific subacutely toxic Cd concentrations (nominal
LC1; E. cyaneus: 18 nM (2.0 μg L–1); E. verrucosus: 115 nM (12.9 μg L–1); 4 weeks exposure; 6 °C), Cd amounts in metal sensitive tissue
fractions (MSF), in relation to fresh weight, were similar in both
species (E. cyaneus: 0.25 ± 0.06 μg g–1; E. verrucosus: 0.26 ± 0.07
μg g–1), whereas relative Cd amounts in the
biologically detoxified heat stable protein fraction were 35% higher
in E. cyaneus. Despite different potencies in detoxifying
Cd, body size appears to mainly explain species-related differences
in Cd uptake and sensitivities. When exposed to Cd at LC1 over 4 weeks,
only E. verrucosus continuously showed 15-36% reduced
oxygen consumption rates indicating metabolic depression and pointing
to particular sensitivity of E. verrucosus to persisting
low-level toxicant pressure.