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

Abstract

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); E. verrucosus: 115 nM (12.9 μg L); 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; E. verrucosus: 0.26 ± 0.07 μg g), 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.

Investigation of cellular stress response related heat shock proteinhsp70/Hsp70 and multixenobiotic transporterabcb1in Siberian freshwater amphipods upon cadmium exposure

“…Eulimnogammarus vittatus , however, was from the examined species least sensitive to CdCl 2 although the body sizes of the individuals were clearly below those of E. verrucosus and it can be assumed that the cadmium uptake rate was accordingly higher. It was previously found that the occurrence of toxic effects by CdCl 2 in E. verrucosus was in addition to a in comparison to E. cyaneus lower cadmium uptake rate further depressed by a reaction to CdCl 2 exposure with metabolic depression [47]. This was not examined here but it seems conceivable that the in comparison low toxic sensitivity of E. vittatus to CdCl 2 may be due to particularly pronounced metabolic depression as a reaction to CdCl 2 exposure.…”

“…Body size has previously been shown to be an important determinant of cadmium uptake by aquatic insects [46]. Along those lines, cadmium uptake rates during CdCl 2 exposures were higher in the concurrently toxicologically more sensitive E. cyaneus than in E. verrucosus that differed by 10- to 50-fold in freshweight [47]. In the present study, G. lacustris individuals that were similar in size to E. cyaneus individuals showed toxic sensitivities that were accordingly in the same range as for E. cyaneus (Table 1).…”

“…Although metabolic depression by cadmium may have decreased activity on a physiological level it appeared to have no effect on the transcription activity. Thus, hsp70 was significantly induced in E. verrucosus that previously showed a metabolic depression response to CdCl 2 exposure but not in E. cyaneus that does not respond to CdCl 2 with metabolic depression [47] in the 6 and 24 hr CdCl 2 treatments at LC50 (Fig. 3).…”

“…Provided that across the gammarid species equal internal, toxicologically relevant cadmium concentrations cause equal levels of toxic effects, as was indicated earlier [47], the LCx values can be regarded as approximate measures of the respective internal cadmium concentrations. Hence, across the species the degrees of hsp70 transcript and Hsp70 protein induction appear to be approximately equal at corresponding internal cadmium levels.…”

The interplay between chemical speciation and physiology determines the bioaccumulation and toxicity of Cu(II) and Cd(II) to Caenorhabditis elegans

“…Models for the prediction of metal biouptake, e.g., the biotic ligand model and the free ion activity model, assume that only free metal ions are available for biouptake (Brown & Markich, 2000;Campbell, 1995;Jakob et al, 2017;Paquin et al, 2002;Slaveykova & Wilkinson, 2005), and attempts have been made to use metal ion characteristics as predictors of toxic effects (Renner, 1997;Tatara, Newman, McCloskey, & Williams, 1997;Tatara, Newman, McCloskey, & Williams, 1998). Recent work with C. elegans showed that toxicological responses to metal ions were strongly time dependent (unpublished data), yet the results reported herein show that metal speciation in the exposure medium is largely invariant with time ( Figure 1).…”