Environ Monit Assess (2012) 184:2275–2284 DOI 10.1007/s10661-011-2116-5 Bioavailability of copper, cadmium, zinc, and lead in tropical savanna soils assessed by diffusive gradient in thin films (DGT) and ion exchange resin membranes John O. Agbenin · Gerhard Welp Received: 13 November 2010 / Accepted: 26 April 2011 / Published online: 18 May 2011 © Springer Science+Business Media B.V. 2011 Abstract The technique of diffusion gradient in thin films (DGT) for assessing bioavailable metals has not been tested under field conditions. We assessed the relationships of DGT- and cation ex- change resin-membrane-measured concentrations of Cd, Cu, Pb, and Zn with plant uptake of the metals under greenhouse and field conditions. In the greenhouse, the effective concentrations of Cu, Pb, and Zn by DGT correlated significantly with uptake by sorghum (Sorghum bicolor), but cation exchange resin-membrane-measured con- centrations of Cd, Pb, and Zn did not correlate with sorghum uptake. In the field, the DGT- measured concentrations of Cd, Pb, and Zn were J. O. Agbenin Department of Soil Science, Ahmadu Bello University, PMB 1044, Zaria, Nigeria G. Welp Institute of Crop Sciences and Resource Conservation, Division of Soil Science, University of Bonn, Nussalle 13, 53115, Bonn, Germany Present Address: J. O. Agbenin (B ) Department of Crop Science and Production, Botswana College of Agriculture, University of Botswana, Gaborone, Botswana e-mail: joagbenin@yahoo.com not linearly related to uptake Cd, Pb, and Zn by lettuce (Lactuca sativa) except for Cu uptake (r = 0.87, p < 0.05). Similarly, it was only the resin- membrane-extractable Pb that correlated with Pb uptake by lettuce (r = 0.77; p < 0.05). However, fitting non-linear regression models improved the plant metal uptake predictions by DGT-measured bioavailable Cd, Cu, Pb, and Zn under field condi- tions. In conclusion, the DGT technique was fairly predictive of bioavailability in the greenhouse, but not in the field. Keywords DGT device · Cation exchange resin membrane · Effective concentration (CE) · Lettuce · Metal uptake · Sorghum Introduction A standard method for assessing bioavailability of metals in terrestrial ecosystems has not been uni- versally established. Several methods have been reported in literature including extraction with 1.0 M NH 4 NO 3 solution (Prueβ 1997), ion ac- tivities in soil solution (Sauve et al. 1996, 1998), extraction with 0.1 M CaCl 2 solution (Young et al. 2000), and operational speciation of metals (Zeien and Bruemmer 1989). The technique called diffusion gradient in thin films (DGT) was introduced to assess bioavail- ability of trace metals in terrestrial and aquatic