TA6 Atmospheric Transport and Fate
202 Oregon Ballroom
8:00 AM - 12:00 PM, Tuesday
() Soil-air exchange of organochlorine pesticides in southern Mexico.
Wong, F1, Bidleman, T2, Alegria, H3, Salvador-Figueroa, M4, 1 Meteorol. Service of Canada, Downsview, ON, Canada2 Centre for Atmospheric Research Experiments, Egbert, ON, Canada3 California Lutheran University, Thousand Oaks, CA, US4 University of Chiapas, Tapachula Chiapas, Mexico
ABSTRACT- Mexico is known for its long history of organochlorine pesticide (OCP) usage in malaria control and agricultural practices. An air sampling campaign was conducted in 2003 to investigate the OCP pattern in Chiapas, southern Mexico. High volume air samples were collected at a mountain site (MN) which located at 1300 m altitude, and a suburban site, Tapachula (TP), which located 5 km away from the city centre. Total DDT levels at MN were four times higher than at TP. Moreover, increased fractions of p,p'-DDT/sum-DDTs were found at MN (74%) than TP (53%). Enantiomer fractions of o,p'-DDT at MN ranged from 0.497-0.504 and at TP ranged from 0.499-0.503. The predominance of fresh DDT and racemic EFs in air reflect recent local use of DDT or regional-scale air transport from neighbouring countries. Soil samples collected near the two sites also showed higher p,p'-DDT/sum-DDTs at MN. Soil/air fugacity ratios were estimated using the octanol-air partition coefficients. Fugacity ratios of the DDTs for most soil samples were <1 which indicates net deposition of DDT to the soil. Toxaphene concentrations in air were higher at TP than MN. Chromatographic profiles of octachlorobornanes in both air and soil showed depletion of Parlar congeners 39 and 42. Contrary to DDT, these results suggest that emission of old residues from soil, rather than current usage, is the source of toxaphene in air.
Key words: Mexico, Pesticides, Air, Soil