Batch test methodology applied at a site contaminated with hexachlorocyclohexane Available to Purchase

The batch equilibrium test allows the construction of adsorption isotherms, for estimating parameters, like the partition coefficient (K _d) and the retardation factor (R _d). These parameters are essential for decision making for remediation of a contaminated site. This paper presents part of the geo-environmental investigation of a contaminated site, located in Santo André, São Paulo, Brazil. The adsorption capacity of hexachlorocyclohexane (HCH) isomers by the local natural soil, using the batch equilibrium test, was studied. The test methodology consisted of the preparation of a pollutant solution and the determination of the punctualK _d, sorption degree (S) and adsorption percentage (%A) values. The results obtained varied because of the very low concentrations of HCH obtained for the pollutant solution. The HCH isomers were less adsorbed by the soil than expected, presenting low K _d (0·70–2·07 ml/g) and R _d (4·51–11·99) values. δ-HCH and γ-HCH were the most adsorbed by the studied soils. The β-HCH isomer tended to have lower soil retention results when compared with the others isomers. Desorption behaviour was observed in some of the soil–solution ratios used during the tests. The environmentally conservative isotherms are not recommended for this kind of contaminant.