Effects of Photoirradiation on the Adsorption of Dissolved Organic Matter to Goethite

Previous research has shown that intermediate and high molecular weight components of dissolved organic matter (DOM), as well as components rich in aromatic moieties, are preferentially adsorbed to mineral surfaces. It has also been shown that photoirradiation degrades DOM, decreasing the overall amount of dissolved organic carbon (DOC) in solution, as well as decreasing the average molecular weight and UV light absorbing properties of DOM molecules in solution. Our results show that the decrease in molecular weight and UV light absorbance of adsorbed irradiated DOM, as well as the percent adsorption of irradiated DOM was greater than from either irradiation or adsorption alone. The coupled decrease in UV light absorbance upon irradiation and adsorption may have dilatory environmental ramifications if water which was exposed to sunlight interacts with mineral surfaces and is then flushed into streams or lakes. This would result in a larger amount of UV light penetrating through the water column, possibly threatening the health of sensitive organisms and ecosystems.