PERSISTENT ORGANIC POLLUTANTS IN THE ARCTIC, ATLANTIC AND PACIFIC OCEANS

Abstract

Persistent organic pollutants (POPs) are a group of compounds that are persistent, toxic, bioaccumulative and undergo long range transport. Polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) are three groups of POPs. They were widely used as dielectric and coolants fluids, pesticides and flame retardants, respectively. Polycyclic aromatic hydrocarbons (PAHs), normally produced by incomplete combustion of carbonaceous materials, were not in the list but have similar properties as POPs. Even though restrictions and bans over POPs started decades ago (PCBs and OCPs in the 1970s and BDEs in the 2000s), POPs are still detected in the environment and could negatively affect human and wildlife health. Previous studies of POPs monitoring were mostly focused on land or coastal areas; POPs data in remote oceans are lacking. In this study, polyethylene passive samplers (PEs) were used for measuring POPs in the Atlantic and Pacific. The Atlantic study involved deep ocean measurements, while the Pacific study used surface seawater and atmosphere measurements. Deep ocean measurements were conducted by deep moorings at two locations, in the North and Tropical Atlantic Ocean. Results revealed the presence of POPs in the deep ocean with concentrations up to 10 pg L-1 for PCBs, OCPs and BDEs. Oceanic current study suggested that the concentration maximum around 800 m at the Tropical Atlantic site could be potentially originated from the Mediterranean Sea. Mass balance calculation indicated that deep ocean is an important storage for POPs (4.8-26 % of the global HCB environmental burdens). The Pacific study measured both gas-phase and dissolved phase POPs in the Pacific. Atmospheric and oceanic concentrations of PCBs were detected at the magnitude of 1 pg m-3 and 0.1 pg L-1 respectively, except for PCB-8 which was detected at concentrations 10 times higher. HCB dominated in the gas phase (~300 pg m-3), while α -HCH dominated in the dissolved phase (~100 pg L-1). Large variations of BDEs and PAHs concentrations in either phase were found and were higher than most reported values. Close to equilibrium state of PCBs and OCPs were found in the oligotrophic Pacific. Absolute air-water exchange fluxes were <0.4 ng m-2 day-1 for PCBs and <4.5 ng m-2 day-1 for OCPs. Net air-water exchange gradients strongly favored gas-phase deposition of PBDEs into the water, while mixed gradients were found for PAHs.