Association of organotin compounds with aquatic and terrestrial humic substances

Organotin-humic substance (OT-HS) binding constants (K-doc) were determined by equilibrium-binding studies using dialysis techniques. The OT-HS bindin g was characterized by linear isotherms. The K-doc values measured in this study were several orders of magnitude greater than would be predicted base d only on nonpolar interactions with HS las estimated by K-ow). Binding of tri-n-butyltin (TBT) by Aldrich humic acid decreased with increasing salini ty and pH, indicating that ionic interactions predominate in TBT-HS binding . Thus, the binding of OT by HS observed in this study occurs primarily thr ough complexation, with secondary contributions from nonpolar interactions. The effects of the physicochemical properties of HS (e.g., molecular weigh t, % aromaticity, oxygen content) on TBT-HS binding was examined with HS fr om a range of sources, including a commercial humic acid and HS from aquati c and terrestrial sources. Although binding of organic contaminants by HS h as been correlated with various structural features of HS, no meaningful re lationship between any of the HS properties examined in this study and the extent of TBT-HS binding was found.