Influence of natural organic matter on the sorption of biocides onto goethite .1. gamma-BHC and atrazine

The influence of three fractions of aquatic natural organic matter (NOM) isolated from Redwater Creek (RWC) on the sorption of gamma-BHC and atrazine onto goethite has been studied. The NOM fractions used were the total unfractionated Redwater Creek NOM, the hydrophobic add fraction and the total hydrophilic fraction. All three fractions when coated onto goethite increased the sorption of gamma-BHC over that observed with uncoated goethite. Sorption followed the Freundlich adsorption equation. The effective capacity of the NOM-coated goethite for gamma-BHC was over three orders of magnitude greater than for uncoated goethite at pH 5. pH had a large influence on gamma-BHC sorption in both the coated and uncoated systems. Between pH 4 and 5.5, gamma-BHC sorption was greatest for the hydrophobic add coated goethite, while above pH 5.5 goethite coated with unfractionated Redwater Creek NOM exhibited the greatest sorption. The more polar hydrophilic compounds had the least effect of the NOM fractions on gamma-BHC sorption by goethite over the pH range investigated. It is speculated that pH may change the conformation of the NOM associated with the goethite surface, and thus influence the microenvironment into which the gamma-BHC can partition. Atrazine did not adsorb onto coated or uncoated goethite under the conditions used in these experiments. Other workers have reported sorption of atrazine sorption to soils and sediments, bur it appears that either the higher absolute amount of NOM, and/or the type of NOM (e.g. greater proportion of humus), associated with these solids were the reason for the atrazine sorption.