Oceanic Sink and Biogeochemical Controls on the Accumulation of Polychlorinated Dibenzo-p-dioxins, Dibenzofurans, and Biphenyls in Plankton.

Abstract

Polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), and dioxin-like polychlorinated biphenyls (dl-PCBs) were measured in plankton samples from the Atlantic, Pacific and Indian Oceans collected during the Malaspina circumnavigation cruise. The concentrations of PCDD/Fs and dl-PCBs in plankton averaged 14 and 240 pg gdw-1, respectively, but concentrations were highly variable. The global distribution of PCDD/Fs and dl-PCBs was not driven by proximity to primary sources in continents, but significantly correlated with plankton biomass. These trends are consistent with the interactions between atmospheric deposition, biomass dilution, and settling fluxes of organic matter in the water column, as key processes driving the POPs plankton phase concentrations in the global oceans. The application of a model of the air-water-plankton diffusive exchange of PCDD/Fs and PCBs reproduce in part the influence of biomass on plankton phase concentrations, and suggest future modelling prioritiesThe estimated oceanic sink (Atlantic, Pacific and Indian Oceans) due to settling fluxes of organic matter bound PCDD/Fs and dl-PCBs is of 400 Kg y-1 and 10500 kg y-1, respectively. This oceanic sink is 3 and 8 times lower, for PCDD/Fs and dl-PCBs respectively, than the atmospheric inputs due to gross diffusive absorption and dry deposition. These important atmospheric inputs, among other observations, confirm that atmospheric deposition supports and drives the accumulation of dl-PCBs and PCDD/Fs in plankton from the oligotrophic oceans.