Assessing relative sensitivity of marine and freshwater bivalves following exposure to copper: Application of classical and novel genotoxicological biomarkers.

Determination of relative sensitivity of biota following exposures to contaminants including metals is important for environmental protection. Copper (Cu), although biologically essential can be highly toxic to biota if present at higher concentrations in the natural environment. Given its ubiquitous presence within coastal and inland water bodies, we compared Cu-induced genotoxicity in two ecologically important mussel species, the freshwater Dreissena polymorpha (DP) and marine Mytilus galloprovincialis (MG), along with its tissue specific accumulation. Novel biomarker in terms of induction of gamma H2AX (γ-H2AX) foci, along with comet assay and induction of micronuclei (MN) were used to determine DNA damage response (DDR) in these two species following exposure to a range of Cu concentrations (18, 32, 56 µg L-1) for 10 days. Concentration-dependent increases in Cu concentration in gill tissue, as determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), were paralleled by a greater degree of genotoxicity. An induction of γ-H2AX foci was present in all Cu exposure concentrations, proving this technique to be a sensitive and suitable biomarker of genotoxicity in bivalves. The multi-biomarker approach adopted here suggests firstly that in parallel with MG, which is widely used to assess the health of marine and coastal environment, DP is also suitable representative of inland water bodies, and that there is a similar mechanism of action for the induction of genotoxicity between the two species, following exposure to Cu. Secondly, for genotoxicity assessment a battery of responses could simultaneously be assessed in these two bivalve species. Finally, for adequate protection of the environment it is vital to adopt a multi-biomarker, multi-species approach to determine adverse biological effects to gain a holistic understanding of the real threat posed by contaminants to hydrosphere.

Toxic effect and physiological disruption of sodium phosphate to the quagga mussel (Dreissena bugensis).

Phosphorous is an essential nutrient for all forms of life; however, the question of toxicity to aquatic species remains largely unanswered, despite many systems that exceed natural phosphorus loads. This study determined the ecotoxicological threshold concentration of phosphorus to the freshwater bivalve Dreissena bugensis using a 96-h bioassay. Sublethal, medial lethal, and lethal levels of sodium phosphate to D. bugensis were found to be 125, 260, and 476 ppm. Physiological biomarkers such as the oxygen consumption and filtration rate were estimated by exposing D. bugensis to five different sublethal concentrations (25, 50, 75, 100, and 125 ppm) of sodium phosphate for 96 h. Both oxygen consumption and filtration rate gradually declined with increasing exposure concentrations and durations, which was significant (α < 0.05) for 75, 100, and 125 ppm of sodium phosphate concentrations. Based on the feeding rate and oxygen consumption endpoints, the no-observed effect concentration and the low observed effect concentration were 25 and 75 ppm, respectively. Maximum acceptable toxicant concentration of sodium phosphate was 43.3 ppm. Measured environmental concentration (MEC) of total phosphorus (0.015 ppm; n = 6) was obtained from seasonal field assessments in Saginaw Bay during the years 2008 to 2010. An assessment factor of 1000 was used for calculating the predicted no effect concentration (PNEC) of 0.025 ppm. Risk quotient (RQ) of "0.6" was therefore established using MEC/PNEC (real risk) ratio. Binary ecological classification (RQ < 1) suggested that there is no appreciable risk of phosphorus to D. bungensis in the Saginaw Bay of Lake Huron of Laurentian Great Lakes.

Impacts of microcystins on the feeding behaviour and energy balance of zebra mussels, Dreissena polymorpha: a bioenergetics approach.

Microcystins are produced by bloom-forming cyanobacteria and pose significant health and ecological problems. To investigate the impacts of these biotoxins on the physiology of the zebra mussels, Dreissena polymorpha, a series of short-term feeding experiments were conducted in the laboratory. We used five microalgal diets consisting of single-cell suspensions of the green algae, Chlorella vulgaris, the diatom, Asterionella formosa, the cryptophyte, Cryptomonas sp. and two strains of the toxic cyanobacterium, Microcystis aeruginosa (strains CCAP 1450/06 and CCAP 1450/10). A sixth diet was a mixture of the diatom and the CCAP 1450/10 cyanobacterial strain. The low-toxicity strain CCAP 1450/06 contained 7.4 microg l(-1) of the MC-LR variant while the very toxic strain CCAP 1450/10 contained 23.8 microg l(-1) of MC-LR and 82.9 microg l(-1) of MC-LF. A flow-through system was designed to measure the following feeding parameters: clearance, filtration, ingestion and absorption rates. Ultimately the scope for growth (SFG) was determined as a net energy balance. We observed that mussels cleared the cyanobacterial species containing MC-LF (mean+/-95% confidence interval) at a significant lower rate (498+/-82 ml h(-1) g(-1) for the single cell suspension and 663+/-100 ml h(-1) g(-1) for the mixture diet) than all of the non-toxic species and the cyanobacterium containing MC-LR (all above 1l h(-1) g(-1)). The same pattern was observed with all the feeding parameters, particularly absorption rates. Furthermore, MC-LF caused an acute irritant response manifested by the production of 'pseudodiarrhoea', unusually fluid pseudofaeces, rich in mucus and MC-LF-producing Microcystis cells, ejected through the pedal gape of the mussels. This overall response therefore demonstrates selective rejection of MC-LF-producing cyanobacteria by zebra mussels, enhancing the presence of the very toxic MC-LF-producing M. aeruginosa in mixed cyanobacterial blooms and in the benthos. Finally, we observed that the SFG (mean+/-95% confidence interval) of mussels feeding on M. aeruginosa containing MC-LF was significantly lower (34.0+/-18.8 J h(-1) g(-1) for the single cell suspension and 83.1+/-53.0 J h(-1) g(-1) for the mixture diet) than for mussels ingesting non-toxic diets, except for C. vulgaris (all above 200 J h(-1)g(-1)). This reveals a sublethal, stressful effect of microcystins (particularly MC-LF) on the feeding behaviour and energy balance of the zebra mussel.