Abstract
In order to investigate the ecotoxicological effects of nano-ZnO particles and seawater acidification on marine bivalves, the thick shell mussels, Mytilus coruscus were subjected to joint treatments with different nano-ZnO concentrations (0 [control], 2.5 [medium] and 10 mg L-1 [high]) under two pH levels (7.7 [low]and 8.1 [control]) for 14 days. The results showed that respiration rate (RR), absorption efficiency (AE), clearance rate (CR), O:N ratio and scope for growth (SFG) were significantly reduced with nano-ZnO concentration increase, but ammonium excretion rate (ER) was increased. Low pH significantly reduced CR, RR, SFG, and O:N ratio of the mussels especially under high nano-ZnO conditions, and significantly increased ER. Principal component analysis (PCA) showed consistent relationships among most tested parameters, especially among SFG, RR, O:N ratio and CR under the normal pH and 0 nano-ZnO conditions. Therefore, seawater acidification and nano-ZnO interactively impact the ecophysiological responses of mussels and cause more severe effects when they appear concurrently.
Highlights
Since the beginning of industrial revolution, large amounts of fossil fuels have been burned and the green vegetation has been reduced greatly worldwide, resulting in dramatic increased carbon dioxide (CO2) emissions (Caldeira and Wickett, 2003; Intergovernmental Panel on Climate Change [IPCC], 2014)
The salinity remained at 25.1 ± 0.3 psu, the water temperature remained at 20.1 ± 0.3◦C, the normal pH was kept at 8.10 ± 0.02, and the low pH was kept at 7.69 ± 0.02 (Table 1)
The particle diameter of ca. 15–25 nm and spheroid irregular shapes of nano-ZnO were found by TEM and SEM, respectively (Supplementary Figures S1A,B)
Summary
Since the beginning of industrial revolution, large amounts of fossil fuels have been burned and the green vegetation has been reduced greatly worldwide, resulting in dramatic increased carbon dioxide (CO2) emissions (Caldeira and Wickett, 2003; Intergovernmental Panel on Climate Change [IPCC], 2014). The absorption of CO2 in the ocean slows down the trend of rising atmospheric carbon dioxide concentration, but the continuous absorption of CO2 changes the carbon dioxide-carbonate system of seawater, resulting in increased concentrations of hydrogen ions, CO2 and bicarbonate in seawater, and decreased carbonate concentration, ocean acidification (OA) Due to the widespread use of zinc oxide nanoparticles, coastal waters and the ocean would become an ultimate sink of these environmental contaminants (Yung et al, 2014). Muller et al (2014) pointed out that long-term exposure of Mytilus galloprovincialis to nano-ZnO cause accumulation of zinc in mussel tissues, affecting the energy budget. Nano-ZnO has attracted some attention in ecotoxicological research, there is little research on the combined physiological effects of nano-ZnO associated with additional environmental stressors on marine bivalves. It is necessary to explore the combined effects of nano-ZnO and OA on marine species
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