Pollution attenuation by soils receiving cattle slurry after passage of a slurry-like feed solution. Column experiments Avelino N u~ nez-Delgado a,b, * , Eugenio L opez-Perıago b , Francisco Dıaz-Fierros-Viqueira b a Department of Edafoloxıa e Q.A. (Soil Science and Agricultural Chemistry), Escola Polit ecnica Superior, Campus Univ. S/N, 27002 Lugo, Spain b Department of Edafoloxıa e Q.A. (Soil Science and Agricultural Chemistry), Fac. Farmacia, Campus Univ. S/N, 15706 Santiago de Compostela, Spain Received 3 October 2000; received in revised form 11 February 2002; accepted 24 February 2002 Abstract Designing soil filtration systems or vegetated filter strips as a means of attenuating water pollution should take into account soil purging capacity. Here we report data on laboratory column trials used to investigate the capacity of a Hortic Anthrosol to at- tenuate contamination due to downward leaching from cattle slurry applied at the surface. The columns comprised 900 g of soil to a depth of about 20–25 cm, and had been used previously in an experiment involving passage of at least 5 pore volumes of an ion- containing cattle slurry-like feed solution. For the present experiments, the columns were first washed through with distilled water (simulating resting and rain falling after passage of the feed solution), and then received a single slurry dose equivalent to about 300 m 3 ha 1 . The columns were then leached with distilled water, with monitoring of chemical oxygen demand (COD) and ion contents in outflow. The results indicated that the pollution-neutralising capacity of the soil was still high but clearly lower than in the earlier experiments with the feed solution. Furthermore, the time-course of COD showed that organic acids were leached through the column even more rapidly than chloride (often viewed as an inert tracer) enhancing the risk of heavy metals leaching and subsequent water pollution. Resting and alternate use of different soil-plant buffer zones would increase the lifespan of purging systems that use soil like the here studied one. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Cattle slurry; Removal from slurry; Diffuse pollution; Soil columns; Solute transport 1. Introduction Laboratory column studies are essential for under- standing the dynamics of penetration of soil by con- taminants, and for investigating the factors––such as dispersion and retardation––that affect this process (van Genuchten and Wierenga, 1986; Leij and van Genuch- ten, 2000). Some such studies use laboratory-prepared feed solutions (Toran and Palumbo, 1992), while others use real contaminants, such as refuse tip leachates (Hoeks et al., 1979), wastewater (Powelson and Gerba, 1994) and pesticide-contaminated solutions (Jiann-Yuan and Shian-Chee, 1997). Cattle slurry is a potential cause of water, soil and air pollution (Ackerman and Taylor, 1985; Amberger, 1987; Boutin et al., 1988; Castilho et al., 1993; Larsen et al., 1994). In Galicia (Northwest Spain), more cattle slurry is produced than can be used as fertiliser (Carballas et al., 1990; Dıaz-Fierros et al., 1993). Open-air slurry storage ditches are widely used, but in view of the re- gion’s high rainfall (about 1400 mm per annum) these must be emptied regularly once the underlying soil has become saturated, particularly in spring and autumn (Dıaz-Fierros et al., 1993). During periods of heavy rainfall (and thus saturation soil water content), over- flow is common, leading to massive loss of contaminants in surface runoff; furthermore, slurry contaminants that enter the soil during such periods are poorly retained because of saturation and low microbial activity (Dıaz- Fierros et al., 1990; Carballas et al., 1990; Dıaz-Fierros et al., 1993). In view of this, our group has performed studies of cattle slurry composition (Dıaz-Fierros et al., 1983; Dıaz-Fierros et al., 1987; Dıaz-Fierros et al., 1988; Bioresource Technology 84 (2002) 229–236 * Corresponding author. Fax: +34-982-241-835/+34-981-594-912. E-mail address: edavelin@usc.es (A. N u~ nez-Delgado). 0960-8524/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0960-8524(02)00050-0