Ocean as source or sink for legacy persistent organic pollutants

Abstract

With the phase-out of legacy persistent organic pollutants (POPs), the ocean's role is evolving, potentially acting as both a reservoir and a source. This study investigates the air-sea fluxes of the first banned POPs, such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), using literature from Web of Science up to 2023. OCP and PCB concentrations in air and seawater show significant spatiotemporal variability. In air, α-HCH and p,p'-DDE dominate, with concentrations decreasing over time and varying with latitude. In seawater, α-HCH and p,p'-DDTs show higher levels in the Northern Hemisphere and significant temporal decreases. PCB concentrations differ notably between low- and high-chlorinated compounds, with distinct spatial patterns. HCHs exhibit distinct flux patterns, with volatilization in equatorial regions and deposition in higher latitudes. DDTs mainly show deposition trends, except in Southeast Asia where recent increases in volatilization are observed. PCBs generally demonstrate deposition, with regional and seasonal variations. Time significantly impacts fluxes due to changes in human activity and regulations. High-chlorine PCBs are more affected by distance from the sea surface, while temperature increases POPs volatilization.

Keywords: Boosted regression tree model; Legacy persistent organic pollutants; Sea-air fluxes; Source-sink transformation.