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Pesticides from neighbouring states and from across the Pacific Ocean have been identified in the air at an observatory in the Cascade Range in Oregon. The measurements reveal the influence of historic and current use pesticides locally and remotely on the overall pesticide burden. Environmentalists, scientists and agriculturalists are all too aware of the long-term effects of pesticides as they seep away to pollute streams and watercourses. Once they enter the natural water system, they can be transported hundreds of miles down rivers to affect adjacent regions and countries. If that were not enough, pesticides can also enter the atmosphere and travel great distances to contaminate distant countries. The recent detection of pesticides in the once-pristine Arctic region is evidence of this mode of transport. Pesticides can become airborne during application, by volatilisation from the soil, and by wind erosion of the soil particles containing sorbed pesticides and they are not the only compounds to do so. Recent studies by scientists based in Oregon, US, showed that combustion byproducts and other semivolatile organic compounds (SOCs) are also susceptible to air travel. Polycyclic aromatic hydrocarbons from the incomplete combustion of organic matter and fuels, industrial chemicals such as the polychlorobiphenyls and consumer-based chemicals like the fluoroalcohols have all been detected in the air in the Western USA. Some of them originated in Asia and had travelled across the Pacific Ocean. Now, the same group have extended their detective work to pesticides. Staci Simonich, Toby Primb, Glenn Wilson and David Schmedding from Oregon State University and Carol Higginbotham from the Central Oregon Community College at Bend tested a total of 69 samples. They had been collected from April 2004 to May 2006 at the Observatory on the dormant volcano named Mount Bachelor in the Oregon Cascade Range of mountains, 2763 m above sea level. Mount St. Helens, which erupted in 1980, is also in this mountain range, in Washington State. Sampling was carried out on quartz fibre filters for particulates and XAD-2 sorbent sandwiched between two polyurethane foam plugs for the SOCs. They were spiked with isotopically labelled internal standards then subjected to accelerated solvent extraction. The extracts were analysed by GC/MS with electron ionisation and negative chemical ionisation, both in selected ion monitoring mode. This procedure gave recoveries of 48-95% and detection limits were 0.39-114 and 0.0001-4.6 pg/m3 for the EI and NCI methods, respectively. The data were inserted into a model for calculating the airborne back trajectories of the analytes over the previous 10 days to ascertain their transport patterns. This was linked to potential source regions of pesticide air mass, which were based on the percentage of cropland and estimated pesticide usage. Several regions in Oregon, Washington state and California were identified as source regions, plus two large areas in Asia. A large swathe covering Japan, the Koreas and part of China, and a second area in Eastern Russia (Siberia) were implicated. For the historic use pesticides hexachlorobenzene (HCB) and alpha-hexachlorocyclohexane (alpha-HCH), elevated concentrations were measured at times during the sampling period. They were banned in North America more than 20 years ago and their presence in the air over Oregon was largely attributed to Asian origins. Their levels correlated with other markers of Asian air and with known trans-Pacific air transport events, particularly in the spring. Their potential sources include an alpha-HCH facility in China that was not closed down until 2000. However, there was also a contribution from regional fires in the USA and Canada, which would revolatilise the pesticides. Current use pesticides such as endosulfan, dacthal, metribuzin and chlorpyrifos all had elevated concentrations which correlated episodically with their seasonal applications in the spring, summer and autumn in the western US. The increases are indicative of their broad use across the region but there were also contributions linked to fires for some of them. For some current use pesticides trans-Pacific transport was also implicated. For instance, the highest gamma-HCH levels were noted during a springtime transport event but the second highest peak occurred following fires in western Oregon. The results reveal significant contamination of the air in the western US from Asian pollution plumes, in line with the trans-pacific transport of other pollutants. These long-distance transfers must have important consequences for air quality in western North America, along with the more local agricultural effects.
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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