HENRYS LAW CONSTANTS FOR PESTICIDES MEASURED AS A FUNCTION OF TEMPERATURE AND SALINITY

A wetted wall column device was used to determine air-water distributi on coefficients [Henry's law constants (HLCs)] for pesticides: chlorpy rifos, trifluralin, endosulfans I and II, methyl parathion, metolachlo r, and 2,4-D. The measured HLCs were all significantly higher than val ues calculated from published vapor pressure and solubilities except t hose for technical endosulfan and 2,4-D. With 2,4-D, however, the HLC was higher under acidic conditions. The effects of temperature and sal inity were investigated using chlorpyrifos, trifluralin, and endosulfa n I. Simulated seawater increased the HLCs from 1.5 to 2.4 times, whic h suggests a salting out effect. Natural water HLC values that were de termined on Chesapeake Bay and Bering/Chukchi Sea water samples of mic rolayer and subsurface water were all lower than predicted values even after correction for temperature and salinity. Therefore, some as yet undefined factors in the aqueous phase appear to be responsible for t hese lowered HLCs. There was generally a linear increase in the log HL C versus increase in temperature for all of the pesticides in both dis tilled water and salt water except for trifluralin, which was curvilin ear in simulated seawater.