Host-parasite interaction as a toxicity test endpoint using asymmetrical exposures

Interspecific relationships frequently determine the effect a pollutant can have on an organism, and this is especially true in closely interacting species such as hosts and parasites. The high spatial and temporal variability of contaminant concentrations combined with the movement of aquatic biota can further influence the consequences that are associated with contamination. We used a full factorial design for the exposed and unexposed partners of the relationship between the parasitic larvae (glochidia) of the European freshwater mussel (Anodonta anatina) and its host fish (Squalius cephalus) to identify the sources of variation in the sublethal endpoints of species interaction (the intensity of parasite attachment, the spatial position of glochidia on the host body, and encapsulation success). We used the water-borne human pharmaceutical compounds methamphetamine (a central nervous system stimulant) and tramadol (an opioid) at environmentally relevant concentrations (˜ 6.7 and 3.8 nmol L^-1 of methamphetamine and tramadol, respectively) as a proxy for contaminant exposure because these compounds are emerging aquatic stressors that are known for high spatial and temporal variability in their detected concentration levels. The relationship between the bivalve and the fish species was influenced by the preceding contact with both methamphetamine and tramadol, but this effect was highly asymmetric. Our experimental design enabled us to identify the specific changes in the relationship outcome that are elicited by the exposure of individual partners, such as the significant increase in glochidia infection success rate from 59.6 ± 3.9% to 78.7 ± 2.8% (means ± s.e.) that was associated with host exposure to methamphetamine. Additionally, the significant interaction effect of the exposure was demonstrated by the lowered proportion of glochidia attached to gills after the coexposure of both partners to tramadol. The impact of pharmaceuticals on wild aquatic host-parasite relationships provides an example of the risks that are associated with the unintentional discharge of biologically active compounds into freshwater habitats. Given the increasing evidence showing the ecological impact of waste pharmaceuticals, the use of multitrophic interaction endpoints after joint and unilateral exposures provides an important step towards the realistic risk assessment of these compounds.

Acute effects of salinity exposure on glochidia viability and host infection of the freshwater mussel Anodonta anatina (Linnaeus, 1758)

Freshwater mussels of the Unionida are globally in decline and knowledge of the sensitivity of their vulnerable life stages to stressors is crucial for their conservation. Increasing salinity, e.g., due to road deicing, has been proposed as an important stressor, but its impact on the complex interaction between mussel larvae and their obligate attachment to fish hosts remains largely unknown. This study tested the acute toxicity effects of environmentally relevant chloride concentrations on larvae of European Anodonta anatina mussel as well as the impacts on attachment rates of the larvae to their fish host. Chloride concentrations above 727 mg⋅L(-1) significantly affected glochidia viability and the 24h EC50 value was determined at 2,505 mg⋅L(-1). Successful attachment of glochidia to the host fish Phoxinus phoxinus was negatively correlated with increasing chloride concentration and became significant at concentrations > 2,909 mg⋅L(-1). Comparable responses could be observed by separately counting fin and gill attached glochidia, while gill attachment showed the highest correlation with overall attachment rates. These results indicate a potential threat from short-term elevated chloride concentrations during runoff events on sensitive life stages of freshwater mussels. Consequently, we propose additional chloride sensitivity tests on other mussel species as well as the reduction of salt peak input loading into freshwater bodies through a 3R-principle (restriction of use, retention of runoff for peak concentration avoidance and replacement by alternatives) in areas where endangered mussels occur.

CAPSULE

Freshwater mussels of the Unionoida are globally in decline and knowledge on the sensitivity of the most vulnerable larval stages to salinity is crucial for their conservation.

Multi-biomarkers approach in different organs of Anodonta cygnea from the Dnister Basin (Ukraine)

The aim of this study was to compare environmental quality in two sites in western Ukraine-rural (R) and urbanized (U)-with the usage of the resident bivalve mollusk Anodonta cygnea. The study was realized during three seasons. The metal uptake and a set of biochemical markers were determined. For each season, Cd and metallothioneins (MTs) contents in the digestive gland and gills of the mollusc were higher at the U site, reflecting its chronic pollution. The oxidative stress in the mollusk was observed at the U site during spring and at the R site during summer and autumn according to the differences in Mn-superoxide dismutase and catalase activities, O (2) (*-) production, lipid peroxidation, and glutathione levels. The elevated vitellogenin-like protein levels in the hemolymph and the ethoxyresorufin-O-deethylase activity in the digestive gland in summer-autumn suggested pollutions by organic substances at the R site. The acetylcholinesterase activity was similar in both groups. The centroid grouping analysis of biomarkers and morphological and water indexes demonstrated the clear differentiation of general response in each group in spring and, at the R site, in summer and autumn but its similarity at the U site in summer and autumn.