Research progress in ecotoxicology of climate change coupled with marine pollutions

Abstract

Marine pollution has become a global problem since industrialization. Global climate change has also brought significant changes to the marine environment, especially with the continuously increasing atmospheric CO2 concentration. Lots of studies have solely focused on the influences of climate change or environmental pollutants on marine biota and ecosystem, and made some widely-accepted conclusions. However, in the real environment, marine ecosystem is likely suffering more complex impacts than that exposed to either marine pollution or climate change only. Thus research of climate change coupled with marine pollution is being more and more concerned by the government and scientists, and becomes a hotspot in the field of marine environmental science and global climate change. In the present research, effects of climate change (especially rising sea water temperature, acidification and hypoxia) on the biotoxicity of typical marine pollutants (e.g., heavy metals, POPs), as well as the interactions between climate change and marine pollution were summarized. On the one hand, ocean warming, acidification and hypoxia affect the resistance of marine organisms on pollutants, and further affect their sensitivity to pollutants; on the other hand, ocean warming, acidification and hypoxia affect the physical and chemical properties, environmental behaviors and bioavailability of marine pollutants directly, and thus change pollutants’ toxicity indirectly. Therefore, under the coupled stress of climate change and marine pollution, toxic effects of pollutants may not only be the simple superposition of the two alone, but also more complex synergies. For example, ocean warming changes the distribution of POPs between the water-gas phase significantly, which makes POPs migrate to higher latitudes through the grasshopper effect and increases the exposure risk of polar organisms to POPs. Warming increases the solubility of heavy metals in seawater, but also increases the precipitation of metal oxides and hydroxides (reducing the solubility of metal ions) due to the increased rate of chemical reactions. This paradox is a difficulty in the current quantitative study for effects of ocean warming on metal solubility. Ocean acidification promotes the releasing of Cu2+ in forms of carbonate compound, or makes Cd2+ and Hg2+ dissociate from their compounds in the sea water, while heavy metals in forms of free state are generally more toxic to marine organisms than those in forms of compounds, thus exacerbating the toxicity of heavy metals to marine organisms. Hypoxia promotes the reduction of arsenic from the pentavalent state to the trivalent state. The arsenic in the trivalent state binds to the thiol-containing protein in the marine organism and inactivates the acetylcholine (AChE) enzyme. According to the statistical report of literatures, studies related to climate change coupled with marine pollution had been rarely reported before 2003, and have been receiving more and more attentions since 2003. In terms of content, the studies mainly focus on combined effects of acidification-heavy metals (slightly more), acidification-nanomaterials as well as organic matters (less), hypoxia-heavy metals as well as organic matters (small amounts), and warming-heavy metals (small amounts) on marine organisms; focused on the effects of acidification on the transport of marine pollutants in food chains (small amounts); focused on the ecological risk of POPs and mercury in the polar region under the background of climate change (slightly more). These studies have shown that climate change does affect the environmental behavior and biological toxicity of marine pollutants directly or indirectly. Ocean plays an important role in maintaining the Earth’s system and climate regulation. From the perspective of how to protect the ocean scientifically and utilize marine resources reasonably under coupled stress of climate change and marine pollution, authors proposed that following fields should be considered seriously in future: (1) mechanisms underlying the interaction between climate change and marine pollution; (2) effects of coupled stresses between climate change and environmental pollution on ocean primary productivity and carbonate system; (3) problems related to coastal ecological risks.