Combined effects of acidification and emerging contaminants on immune parameters of the mussel Mytilus galloprovincialis.

From the beginning of the Industrial Revolution, human activities have had an increasing influence on terrestrial and aquatic environments. Presently, greenhouse gas emissions and deforestation are indicated as the main cause of global climate changes (GCCs). CO2 levels in the atmosphere influence both global heat balance and carbonate chemistry in the oceans. In the marine environment, the increment of atmospheric CO2 levels leads to increasing temperature and seawater acidification. Marine organisms have to face not only reduced pH, but they are also exposed to many anthropogenic substances, whose fate and effects under GCC scenarios are totally unknown. Among emerging environmental contaminants, pharmaceuticals give cause for increasing concern. In this study, the combined effects of sea water acidification, as predicted in climate change scenarios, and Diclofenac, a non-steroidal anti-inflammatory drug, were investigated for the first time in the mussel Mytilus galloprovincialis. A flow-through system was used to carry out a three weeks exposure of mussels. In the first week, animals were exposed to three pH values (8.1; 7.7; 7.4) only. Thereafter, mussels were maintained for 7 and 14 days at the three experimental pH values and exposed simultaneously to environmentally relevant concentrations of Diclofenac (0, 0.05 and 0.5 μg/L). Each experimental condition was tested in two replicate tanks. Haemolymph was collected after 7, 14 and 21 days of exposure and 3 pools of haemolymph from 7 mussels each per pH value or pH/Diclofenac combination were prepared. Total haemocyte count (THC), pinocytotic activity and haemocyte proliferation were measured. At reduced pH values, THC significantly decreased after 7 and 21 days of exposure, whereas no significant effects of Diclofenac (alone or in combination with pH) were observed. Exposure of mussels to low pH values generally increased pinocytotic activity of haemocytes. Interestingly, exposure to reduced pH and Diclofenac increased significantly haemocyte proliferation, after 14 and 21 days respectively. Results obtained demonstrated that exposure of mussels to reduced pH is a more stressful condition than exposure to Diclofenac, for the immune parameters measured at least. In any case, further studies will be performed to assess effects of seawater acidification and contaminants on other mussel responses, both physiological and biochemical.