Distribution and air-sea exchange of organochlorine pesticides in the North Pacific and the Arctic

Surface seawater and boundary layer air samples were collected on the icebreaker Xuelong (Snow Dragon) during the Fourth Chinese Arctic Research Expedition (CHINARE2010) cruise in the North Pacific and Arctic Oceans during 2010. Samples were analyzed for organochlorine pesticides (OCPs), including three isomers of hexachlorocyclohexane (HCH), hexachlorobenzene (HCB), and two isomers of heptachlor epoxide. The gaseous total HCH (ΣHCHs) concentrations were approximately four times lower (average 12.0 pg m−3) than those measured during CHINARE2008 (average 51.4 pg m−3), but were comparable to those measured during CHINARE2003 (average 13.4 pg m−3) in the same study area. These changes are consistent with the evident retreat of sea ice coverage from 2003 to 2008 and increase of sea ice coverage from 2008 to 2009 and 2010. Gaseous β‐HCH concentrations in the atmosphere were typically below the method detection limit, consistent with the expectation that ocean currents provide the main transport pathway for β‐HCH into the Arctic. The concentrations of all dissolved HCH isomers in seawater increase with increasing latitude, and levels of dissolved HCB also increase (from 5.7 to 7.1 pg L−1) at high latitudes (above 73°N). These results illustrate the role of cold condensation processes in the transport of OCPs. The observed air–sea gas exchange gradients in the Arctic Ocean mainly favored net deposition of OCPs, with the exception of those for β‐HCH, which favored volatilization. Key Points Air‐sea exchanges were first measured in Arctic Beta‐HCH suggests a net deposition process HCB is considered the closest to equilibrium