Copper Dynamics in the Aquatic Environment Under Ocean Acidification and Contamination by Microplastics

Abstract Microplastics are pollutants that cause great concern due to their known effects on biota and growing accumulation in the oceans. Microplastics can act as vectors of copper (Cu) ions, potentially altering their dynamics and bioavailability in the marine environment through adsorption processes, which are influenced by several factors, including pH. Given that ocean acidification is a current process that can be further aggravated through many processes, including an increase in anthropogenic CO 2 emissions, one of the aims of this study was to evaluate the behaviour of Cu (II) in the presence of photodegraded microplastics (polyethylene terephthalate (PET) in two different reduced pH scenarios according to the Shared Socioeconomic Pathway predicted for 2100 by IPCC. The other aim was to verify chemical changes in the carbonate system and Cu (II) speciation in both reduced pH scenarios predicted for 2100 by IPCC, focusing on inorganic complexation. At the moderate acidification (pH 7.88) treatment, the concentration of dissolved Cu (II) decreased after a 48-h exposition to PET microplastics compared to the initial concentration, primarily due to inorganic complexation and adsorption onto natural particles rather than adsorption onto microplastics, which exhibited a limited capacity to adsorb Cu 2+ under the experimental conditions. Conversely, in the intense acidification treatment (pH 7.59), the concentration of dissolved Cu (II) increased, likely due to the release of previously complexed Cu (II) and the reduced adsorption capacity of the microplastics, as Cu 2+ competes with the increased H + concentrations for the sorption sites on the surfaces of microplastics. These results indicate that under a more intense acidification scenario, the capacity of microplastics to act as vectors of Cu (II) could be insufficient, potentially increasing the concentration of free ionic-Cu and increasing its availability and consequent toxicity to marine biota.