Simulating the vapour phase air/water exchange of p,p′-DDE, p,p′-DDT, lindane, and 2,3,7,8-tetrachlorodibenzodioxin

Abstract

Uncertainties in our understanding of gaseous air/water exchange have emerged as major sources of concern in efforts to construct global and regional mass balances of both the green house gas carbon dioxide and semi-volatile persistent, bioaccumulative and toxic chemicals. Hoff et al. (1996) suggested that these uncertainties result from a lack of understanding of the overall gaseous air/water mass transport process as well as imprecision in our ability to perform the necessary physicochemical property measurements of the gaseous species of interest. In this work, nine low to intermediate wind speed-dependent mass transport models were evaluated as to their suitability for simulating air/water gaseous exchange of 2,3,7,8-TCDD, p,p′-DDT, p,p′-DDE and lindane. In addition, two physicochemical property estimation procedures were examined over an environmental temperature range of 0 to 40°C and compared with observations reported elsewhere in the literature. Findings from the work included: (1) the gaseous air/water exchange paradigm published by Mackay and Yeun (1983) appears to be the most robust, (2) models derived from environmental SF6 exchange data may generate upper limits for overall mass transfer coefficients but also may overestimate gaseous air/water exchange for compounds with small Henry’s Law constants, and (3) neither the property estimation procedures outlined by Paasiverta et al. (1999) nor those by Hilal et al. (2003) are suitable for all physicochemical property estimates; instead, combinations of property estimation procedures from both may be most useful.