Adsorption of chlordane onto humic acids from soils and pig slurry E. Loredo*, V. D'Orazio, G. Brunetti, N. Senesi Istituto di Chimica Agraria, University of Bari, Via Amendola 165/A, 70126 Bari, Italy Abstract Adsorption of trans- and cis-chlordane onto humic acids (HAs) isolated from soils and a pig slurry was measured using a batch equilibrium method followed by gas chromatographic analysis. Experimental data for adsorption of either chlordane isomers onto any HA examined were best ®tted by a Langmuir-type isotherm. The adsorption capacity of pig slurry HA for chlordane was slightly lower than that of soil HAs. FT-IR, ¯uorescence and ESR spectroscopic data excluded the formation of strong chemical bonds between chlordane and HA, thus suggesting that chlordane can be adsorbed to HA only by physical (hydrophobic) mechanisms, involving to some extent ¯uorophore groups of the HAs. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Chlordane; Humic acid; Adsorption isotherms; Spectroscopic techniques 1. Introduction Chlordane is an organochlorine, broad-spectrum, nonsystemic insecticide that has been used for several decades in many countries in land applications against ants, coleopterus pests, cutworms and termite control, in seed treatment and in residential applications (Nomeir and Hajjar, 1987; Buser and MuÈller, 1992). Similar to most other chlorinated hydrocarbon insecti- cides, such as DDT, aldrin, dieldrin and others, chlor- dane is highly toxic and has a long half-life in soil (Bennett et al., 1974). Because of its persistence and bioaccumulation at all trophic levels, chlordane is con- sidered one of the most dangerous contaminants in the environment (Ware, 1988). Technical chlordane is a complex mixture of about 20 chemically similar components containing seven, eight or nine chlorine atoms, the main constituents being the alpha, or cis-isomer and the gamma, or trans-isomer of chlordane, which are present in the mixture in the proportion of 19 and 24%, respectively (Nomeir and Hajjar, 1987). Chlordane is nonpolar and has a low water solubility and high lipophilic nature. The main processes it undergoes in soil are adsorption onto soil particles and uptake and bioaccumulation in micro- and macroorganisms. These phenomena aect markedly its fate and behaviour in soil, including bioactivity, persistence and mobility. Adsorption of chlordane has been studied on var- ious substrates by various authors. In particular, adsorption capacities of chlordane onto activated car- bon Filtrasorb 1 300 were measured to be 100, 42 and 18 mg of product per g of carbon at equilibrium con- centrations of 100, 10 and 1 mg L 1 , respectively (Dobbs and Cohen, 1980). Sorption and desorption of cis- and trans-chlordane onto various sediments and their size-fractions was found to be directly related to organic matter content and the trans-isomer showed a higher anity to sediments than the cis-isomer Organic Geochemistry 30 (1999) 443±451 0146-6380/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0146-6380(99)00029-7 * Corresponding author.