Determination of Henry's Law Constants of Organochlorine Pesticides in Deionized and Saline Water as a Function of Temperature

Abstract

The Henry's law constant (H) is an important parameter that is required to estimate the air-water exchange of semi-volatile organic compounds. Henry's law constants for 17 banned/restricted/currently used organochlorine pesticides (OCPs) were experimentally determined using a gas-stripping technique in deionized and saline water (3%) over a temperature range of 5-35 °C. H values (at 25 °C) ranged between 0.066±0.037 Pa m3 mol-1 (endosulfan II) and 62.0±24.2 Pa m3 mol-1 (heptachlor) in deionized water while the range in saline water was 0.28±0.03 Pa m3 mol-1 (γ-HCH) and 135.2±31.3 Pa m3 mol-1 (heptachlor). The increase in dimensionless Henry's law constants (H′) for OCPs over the studied temperature range was between 3 (γ-HCH)-19 times (chlorpyrifos) and 3 (endosulfan II)-80 times (trans-nonachlor) in deionized and saline water, respectively. The calculated enthalpies of phase change (ΔHH) were within the ranges previously reported for OCPs and other organic compounds (23.8-100.2 kJ mol-1). The salting-out constant, ks, ranged between 0.04 (γ-HCH) and 1.80 L mol-1 (endosulfan II) indicating the importance of assessing the H values of OCPs in saline water to accurately determine their partitioning and fate in seawater.