CHLOROTHALONIL BINDING TO AQUATIC HUMIC SUBSTANCES ASSESSED FROM GAS PURGE STUDIES

Fate of the fungicide chlorothalonil (TClN) binding to dissolved organ ic acid fractions was quantified using gas-purge desorption studies. B inding studies were conducted to measure the dissolved organic carbon partition constant (K-DOC) with aquatic fulvic and humic acid fraction s purified from cranberry bog water. Desorption studies at DOC concent rations up to 50 mg L(-1) resulted in mean log K-DCC values of 4.63 (s .d.=0.5, n=8) and 4.81 (s.d.=0.7, n=7) for fulvic and humic acids, res pectively. These values deviated from reported K-OC (organic carbon) v alues by 0.5 to 1.5 orders of magnitude. The relationship between K-OC and K-DOC did not conform to accepted ratios of 10:1 to 3:1, although these studies were conducted with the strong hydrophobic fraction of DOC. Binding was rapid suggesting hydrophobic partitioning or weak Van Der Waals forces as binding mechanisms. The strong binding potential for TClN to aquatic humic substances corresponds to increased solubili ty in the aqueous system. Sorption to DOC suggests a possible transpor t mechanism which may result in elevated concentrations of TClN in cra nberry bog systems.