β-HCH mobilization in polluted wetland soils as influenced by dissolved organic matter

The β isomer of 1,2,3,4,5,6-hexachlorocyclohexane (β-HCH) which is formed during synthesis of the pesticide lindane shows high mobility in polluted soils despite its low water solubility. Therefore, we studied the correlation between the quantity and quality of dissolved organic matter (DOM) and the mobilization and transport of β-HCH in two soil profiles used as grassland and in incubation experiments. From our results we conclude that β-HCH was mobilized and transported to deeper soil horizons probably by coupling between β-HCH and DOM. The interaction of β-HCH with DOM as indicated by the measured high partition coefficient between β-HCH and DOM (logKDOC = 4.39) was much higher than would be expected from the physicochemical properties of β-HCH. As suggested from synchronous fluorescence spectroscopy data, the capacity of DOM to bind β-HCH increases as the more extended aromatic regions of DOM are accessible in the aqueous extracts. The addition of lime and fresh organic matter to the grassland soils did not affect the measured coupling between β-HCH and DOM. Long drying periods increased the coupling up to 9.9 μg β-HCH per mg DOC. Water-logging destroyed the binding between DOM and β-HCH despite increasing DOC contents. Our main conclusion is that qualitative differences in DOM due to changed environmental conditions can drastically change the coupling of hydrophobic organic pollutants to DOM and greatly affect polltant mobilization and translocation.