Henry's Law coefficients of chloropicrin and methyl isothiocyanate

Henry's Law coefficients were measured for the first time for chloropicrin and methyl isothiocyanate (MITC) at 25 degrees C in deionized water, in 0.10 M NaCl, in 0.20 M NaCl, and in pH 4.0 and 8.0 buffered solutions. For chloropicrin, the Henry's Law coefficient was 2.1 +/- 0.3 atm M-1, and did not show significant pH dependence or dependence on ionic strength. For MITC, the coefficient was much smaller, 0.06 +/- 0.05 atm M-1. The Henry's Law coefficient for MITC did show dependence on ionic strength, increasing to 0. 14 +/- 0.05 atm M-1 at 0.20 M, but did not appear to depend on pH. MITC has a much stronger tendency to remain in solution than chloropicrin. The transport of chloropicrin from solution to the atmosphere is likely to be significant environmentally, while MITC shows a much lower rate of volatilization. When transferred to the atmosphere, oxidation and photochemical reactions are likely to dominate the transformation of both chloropicrin and MITC, rather than heterogenous reactions. (C) 2007 Elsevier Ltd. All rights reserved.