Enantiomeric Signatures Of Organochlorine Pesticides In Asian, Trans-pacific, And Western U.s. Air Masses

摘要

The enantiomeric signatures of organochlorine pesticides were measured in air masses from Okinawa, Japan and three remote locations in the Pacific Northwestern United States: Cheeka Peak Observatory (CPO), a marine boundary layer site on the Olympic Peninsula of Washington at 500 m above sea level (m.a.s.l); Mary's Peak Observatory (MPO), a site at 1250 m.a.s.l in Oregon's Coast range; and Mt. Bachelor Observatory (MBO), a site at 2763 m.a.s.l in Oregon's Cascade range. The enantiomeric signatures of composite soil samples, collected from China, South Korea, and the western U.S. were also measured. The data from chiral analysis was expressed as the enantiomeric fraction, defined as (+) enantiomer/(sum of the (+) and (-) enantiomers), where a racemic composition has EF = 0.5. Racemic a-hexachlorocyclohexane (a-HCH) was measured in Asian air masses at Okinawa and in Chinese and South Korean soils. Nonracemic α-HCH (EF = 0.528 ± 0.0048) was measured in regional air masses at CPO, and may reflect volatilization from the Pacific Ocean and regional soils. However, during trans-Pacific transport events at CPO, the a-HCH EFs were significantly more racemic (EF = 0.513 ± 0.0003, p < 0.001). Racemic a-HCH was consistently measured at MPO and MBO in trans-Pacific air masses that had spent considerable time in the free troposphere. The a-HCH EFs in CPO, MPO, and MBO air masses were negatively correlated (p = 0.0017) with the amount of time the air mass spent above the boundary layer, along the 10-day back air mass trajectory, prior to being sampled. This suggests that, on the West coast of the U.S., the α-HCH in the free troposphere is racemic. Racemic signatures of cis- and frans-chlordane were measuredrnin air masses at all four air sampling sites, suggesting that Asian and U.S. urban areas continue to be sources of chlordane that has not yet been biotransformed.