Long-term effects of heavy metals and microelements on nematode assemblage Ga ´bor Bakonyi a, *, Pe ´ter Nagy a , Imre Ka ´da ´r b a Department of Zoology and Ecology, Szent Istva ´n University, H-2103 Go ¨do ¨llo ˝, Pa ´ter K. u. 1, Hungary b Research Institute for Soil Science and Agricultural Chemistry of the Hungarian Academy of Sciences, H-1025 Budapest, Herman O. u. 15, Hungary Received 15 September 2002; accepted 12 December 2002 Abstract Effects of Cd, Cr, Se and Zn at a maximum rate of 270 mg kg 1 were studied on a nematode assemblage after 6  /10 years of application. Winter wheat, sunflower, sorrel, barley and rape were grown on the experimental field. Cd had a moderate effect on nematodes in spite of the fact that this element significantly decreased plant biomass. Cr was harmful to plants only in the first year of the study. However, Cr decreased Aporcelaimellus density and maturity index, increased Pratylenchus density and bacterial /fungal ratio, changed the c-p structure and feeding type composition. Se proved to be very toxic at a concentration of 11 mg kg 1 (NH 4 -acetate /EDTA soluble form). Some advantageous effects of Zn were found in the first year. These disappeared later on. Remarkable between-year fluctuations of the nematode assemblage composition were observed. # 2003 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Soil pollution; Heavy metals; Microelements; Nematode assemblage 1. Introduction Heavy metals and microelements from different sources, mainly from industry, traffic, wet or dry deposition, sewage sludge, fertilisation, and pesti- cide application pollute agroecosystems. Besides the crop plants other components of the system, as nematode assemblage are also affected (Bongers and Bongers, 1998; Bongers and Ferris, 1999; Yeates and Bongers, 1999; Ferris et al., 2001). There is relatively little information on the long- term effects of heavy metals and microelements on the nematode assemblage of the agroecosystems. Weiss and Larink (1991) examined the effect of heavy metal contaminated sewage sludge on agricultural field. They found that a mixture of heavy metals in sewage sludge increased nematode density. This was a consequence of growth of bacterial (especially Rhabditid) and fungal feeder nematode populations. On the other side, density * Corresponding author. Tel.:  /36-28-522-085. E-mail address: bakonyi@fau.gau.hu (G. Bakonyi). Toxicology Letters 140 /141 (2003) 391 /401 www.elsevier.com/locate/toxlet 0378-4274/03/$ - see front matter # 2003 Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0378-4274(03)00035-3