Toxicological properties of a major release of untreated wastewaters into the St. Lawrence River to quagga mussels Dreissena bugensis

Abstract

Before maintenance work could be carried out on the sewage system in the city of Montreal (Quebec, Canada), 5 billion litres of untreated wastewater had to be released directly into the St. Lawrence River over a five-day period in November 2015. The purpose of this study was to examine the toxicity of untreated wastewaters on quagga mussels. Water samples were collected at various points from the most densely populated downtown area and downstream points: 0 km, 5 km, 12 km, 16 km and 19 km. A river water sample was collected at the opposite shore as a reference site, and aquarium (dechlorinated tap) water was used for controls. Mussels were exposed for four days at 15 oC to these wastewaters, then examined for biotransformation (CYP1A1 and glutathione S-transferase activities), energy expenses (mitochondria activity and triglycerides), estrogenicity (alkali-labile phosphates) and damage (lipid peroxidation and DNA strand breaks). The data revealed that exposure to the released wastewaters produced changes to all the above biomarkers. CYP1A1 activity, DNA damage and triglyceride levels were the most responsive biomarkers for optimal site classification as determined by discriminant function analysis. CYP1A1 activity, lipid peroxidation and alkali-labile phosphate levels were significantly correlated with distance from downtown, suggesting that population density influenced more directly those effects. In conclusion, exposure to untreated wastewaters could lead to adverse toxic effects in quagga mussels. Mussels could be at risk from the release of untreated wastewaters events given that high-intensity precipitation could also result in the release of untreated wastewaters in these times of climate change.