Ocean Acidification

Ocean acidification threatens calcifying organisms by reducing seawater pH and carbonate ion availability, while plastic pollution may intensify this effect through chemical and microbial processes, exacerbating impacts on calcification. Here, we investigated, for the first time, the biogeochemical mechanisms of plastic-pollution-induced ocean acidification and the role of plastic as a modifier of the seawater carbonate system. Microcosm experiments were conducted using naturally weathered plastic particles incubated in seawater under irradiated and dark conditions. The experiment comprised two seven-day phases: (1) an abiotic phase evaluating the physicochemical effects of plastic degradation and (2) a biotic phase assessing microbial contributions to plastic-induced acidification. Variations in pH, dissolved CO₂, Ωarag, and Ωcalc were monitored as acidification indicators. During the abiotic phase, plastic increased dissolved CO₂ concentrations threefold under irradiation (27.08 µmol kg⁻¹) compared with the dark treatment (9.65 µmol kg⁻¹), reducing pH, Ωarag, and Ωcalc. By the end of this phase, irradiated plastic reached pH = 7.6, Ωarag = 2.16, and Ωcalc = 3.25, corresponding to values associated with impacts on calcifying organisms and considered terminal for coral reef development. During the biotic phase, no significant changes were observed, likely due to limited dissolved organic carbon release, indicating that UV-driven abiotic processes, rather than microbial activity, predominated in CO₂ release. The observed chemical changes matched end-of-century projections under high-emission scenarios, highlighting that plastic pollution may intensify reductions in carbonate ion concentration and calcium carbonate saturation states, accelerating calcifier mortality and biodiversity loss.

da Silva V. É. D. A., Wanderley B., Longo G. O. & Longhini C., 2026. Plastic pollution as a pathway to ocean acidification and disruption of the seawater carbonate system. SSRN. Article.