Common and particular biochemical responses of Unio tumidus to herbicide, pharmaceuticals and their combined exposure with heating
The priority list of freshwater pollutants is increasingly amended by pharmaceuticals. Their impact on the aquatic biota can be modulated by the presence of typical pollutants, like pesticides, and/or abnormal heating. The aim of this study was to elucidate potentially hazardous impact of combined environmental factors on the freshwater mussels by analysing various sets of biochemical markers. We treated the bivalve molluscs of Unio tumidus with non-steroidal anti-inflammatory drug diclofenac (Dc, 2 nM), calcium antagonist and antihypertensive drug nifedipine (Nf, 2 nM) or organophosphonate glyphosate-based herbicide Roundup MAX (Rn, 79 nM of glyphosate) at 18oC as well as with the mixture of these substances at 18oC (Mix) or 25oC (MixT) during 14 days. The concentrations used were correspondent to the environmentally relevant levels. The biomarkers of stress and toxicity were evaluated in digestive gland, except the lysosomal membrane stability measured in hemocytes. All exposures caused an oxidative stress due to the decreased SOD and GST activities and decreased GSH/GSSG ratio, increased levels of thiobarbituric acid-reactive substances and protein carbonyls (with exceptions of Dc and MixT treatments). Diclofenac increased lysosomal cathepsin D activity. Nifedipine increased lysosomal membrane stability and caspase-3 activity. Roundup caused a dramatic distortion of metallo-thiolome due to highly increased levels of GSH and metallothionein-related thiols (MTSH) as well as depletion of Zn, Cu and Cd in the composition of metallothioneins, and decreased Zn/Cu molar ratio in the tissue. The particular toxicity of Rn was also attested by decreased lysosomal membrane stability and cholinesterase activity, and by the highest value of integrated biomarker index. Generally, compound-specific effects were expressed in U. tumidus responses to the mixture of pharmaceuticals and herbicide at both temperatures. Multi-marker approach and integrative analysis proved to be a useful tool for understanding possible future risks to freshwater mussels under a combination of xenobiotics and warming climate.