Advances in Environmental Research 8 (2003) 69–76 1093-0191/03/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1093-0191(02)00136-3 The transport of Cu and Zn from agricultural soils to surface water in a small catchment H. Xue *, P.H. Nhat , R. Gachter , P.S. Hooda a, b a c ¨ Swiss Federal Institute for Environmental Sciences and Technology (EAWAG), Limnological Research Center, a CH-6047 Kastanienbaum, Switzerland Vietnamese Institute for Tropical Technology and Environmental Protection (VITEP), 56 Troung Quoc Dzung Street, b Phu Nhuan District, Ho Chi Minh City, Viet Nam Center for Earth and Environmental Science Research, Kingston University, Kingston upon Thames, Surrey KT1 2EE, UK c Received 28 January 2002; received in revised form 1 November 2002; accepted 13 November 2002 Abstract Long-term manure-borne copper and zinc inputs (18–324 mg Cu m yr and 100–800 mg Zn m yr ) to y2 y1 y2 y1 grassland soils resulted in their catchment in water concentrations that often exceeded the surface water quality criteria (2 mg Cu l and 5 mg Zn l ). This paper compares retention and release of Cu and Zn by two types of y1 y1 soil, a mineral soil (MS) and a dark colored soil rich in organic matter (OS). On the basis of dry soil mass, the OS has a higher retentionyaffinity for Cu and Zn than the MS, but much less Zn accumulated in the MS when compared on an areal basis. This is largely because of the much smaller bulk OS density and larger dissolved metal concentrations in the OS drainage than that for the MS. However, because of the greater water retention capacity of the OS, elevated metal concentrations in the soil solution do not necessarily cause greater loss to water. It is concluded that artificially drained OS can contribute significantly to the observed elevated Cu and Zn concentrations of the river, especially during relatively dry weather conditions when the contribution of water seeping from OS to the total river water discharge becomes increasingly important.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Water quality; Soil; Metal release; Copper; Zinc 1. Introduction Copper (Cu) and zinc (Zn) are essential nutrients to all organisms, their elevated concentrations, however, may cause toxicity. When metals such as Cu and Zn are introduced into a natural environment, or migrate from one compartment to another, environmental conditions can change their speciation, bioavailability and toxicity (Baker and Senft, 1995; Chen et al., 1995; Selim and Amecher, 1997), with potential implications for the wider environment. Acid-mine drainage (Jeong et al., 1999), urban runoff (Davis et al., 2001), leaching and runoff from municipal *Corresponding author. Tel.: q41-41-349-21-11; fax: q41- 41-349-21-68. E-mail address: xue@eawag.ch (H. Xue). or industrial waste amended soils (Unlu, 1998; Gove et al., 2001) and landfill leachate (Christensen et al., 2001) can introduce metals to receiving surface- and ground- waters. However, agricultural runoff as a source of surface water contamination with heavy metals has not received much attention. Metals such as Cu and Zn are often added to livestock forage due to their anti-microbial and growth promoting properties, with significant concentrations of these met- als ending up in the manure (Xue et al., 2000). Long- term intensive application of livestock manure, with high Cu and Zn concentrations, can lead to the accu- mulation of manure-borne metals in the soils and could also result in elevated metal concentrations in the drainage (Xue et al., 2000). It is therefore important to understand the factors that affect the mobility of metals