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Air-Water Distribution of the Endosulfan Isomers

Environmental Chemistry Laboratory, Natural Resources Institute, USDA-ARS, Beltsville, MD 20705;
National Biological Service, Great Lakes Science Center, 1451 Green Rd., Ann Arbor, MI 48105.

^* Corresponding author (crice{at}asrr.arsusda.gov).

ABSTRACT

The objective of this study was to experimentally characterize the air/water partitioning of the two major isomeric forms of commercially applied endosulfan. Henry's law constants (HLCs) or air/water partitioning constants for technical endosulfan (6,7,8,9,10-hexachloro-1,4,-5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzo-dioxathiepin-3-oxide) and its two major isomers, endosuifan I and endosulfan II, were experimentally determined using a wetted wall column (WWC) method. The HLC values for the isomers were significantly higher than their literature HLC values. The HLCs for salt water were higher than distilled water suggesting that the salt ions reduced the solubilities of the chemicals. The HLC of endosulfan I was log linearly related to change in temperature; however, no such relationship could be established for endosulfan II. When pure endosulfan II (99% endosulfan II and 1% endosulfan I) was allowed to equilibrate in the WWC apparatus, the ratio of endosulfan II to endosulfan I in the gas phase became 8:92 at 20°C. These results suggested that the II form of endosulfan was converting to the I form. This apparent conversion was observed to be temperature dependent. Air/water transfer of the endosulfan isomers was similar when either N or air was used as the gas phase. The ratio of endosulfan I to endosulfan II observed in the gas phase when HLC experiments with technical endosulfan were performed (91:9) were similar to ratios of the two isomers that are observed in field-collected air samples.

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