Soil Use and Management (1999) 15, 230^232 Remediation of a long-term copper-contaminated soil using a polyacrylate polymer A. de Varennes & M.O. Torres Abstract. We investigated whether a polyacrylate polymer could be used to remediate a soil which had been con- taminated with copper for many years. Perennial ryegrass was grown in a loamy sand containing 230 mg ammo- nium-acetate-EDTA extractable Cu kg 71 and amended with 0, 0.1 and 0.2% of polymer. Growth of perennial ryegrass was stimulated in the polymer-amended soil, especially in the soil with 0.1% of polymer. After plant growth for 177 days, the amount of water extractable copper present in the unamended soil was 17 times that of the original soil. In the soil amended with 0.1% of polymer the level of copper after plant growth was only 0.11 times the amount present in the unamended soil.When the soil was incubated with polymer in the absence of plants, the level of water extractable copper was not reduced. The polymer seems to compete with plants for copper, and to prevent the increase of copper in soil solution brought about by root exudates. Keywords: Remediation, copper, polluted soils, polymers INTRODUCTION M any soils have been contaminated with copper, mainly due to the application of copper-containing fungi- cides (Merry et al., 1983; Magalha¬ es et al., 1985; Semu & Singh, 1996). In previous work, we showed that a polyacrylate polymer could be used to remediate a sandy soil artificially contaminated with copper (Torres & de Varennes, 1998). Growth of perennial ryegrass was stimulated in the polymer- amended soil. Copper concentration in the shoots was smal- ler in plants cultivated in the amended soil.Water-extractable copper was considerably reduced in the contaminated poly- mer-amended soil. However, when contamination of the soil and addition of the polymer are simultaneous, a greater pro- portion of the added copper probably remains in an inorganic form and in solution, compared with a soil that has been con- taminated with copper over decades.The fact that in the pre- vious experiment the beneficial effect of the polymer became apparent only three months after sowing, suggests that most of the added copper remained in the soil solution during this period, and therefore available to plants (Torres & de Varennes, 1998). In soils with long-term contamination, an appreciable fraction of copper will be associated with organic matter forming stable chelates.The concentration of copper in solution is very low, and mostly in the form of solu- ble organic complexes (Srivastava & Gupta, 1996). Therefore, in order to remove copper from solution in these soils the polymer will have to compete for copper with organic ligands. We studied the effects of a polyacrylate polymer on water- soluble copper in a soil from a long-established vineyard, to investigate if this type of polymer could be used to remediate soils contaminated with copper for many years. MATERIALS AND METHODS Polymer The polymer used was supplied by Hoechst Marion Roussel, Lda. with Na as counter ion. The unswollen particles are insoluble in water, and contain 150 mg of Na g 71 of polymer, and only trace levels of copper (c. 0.04 mg Cu g 71 of polymer). Effect of the polymer on Cu availability in soil and on plant growth A loamy sand from a region where vineyards have been estab- lished for several decades was used.The soil, with the charac- teristics shown in Table 1, was passed through a 5-mm sieve and received a basal dressing of 50 mg N, 125 mg K, and 65 mg P kg 71 of soil.These nutrients were supplied as ammo- nium nitrate, potassium sulphate, and calcium dihydrogen phosphate, respectively.The polyacrylate polymer was added at 0, 0.1 or 0.2% (dry wt. basis). Four replicate pots were filled with 2 kg of soil, and 60 seeds of perennial ryegrass ( Lolium perenne L. cv.Victorian) were sown per pot on 16 January 1998. They were thinned to 45 plants per pot 21 days later. Four cuts were carried out 94, 122, 150 and 177 days after sowing. The first three cuts were made 5 cm above the soil surface, to allow plant regrowth. After each of these cuts 50 mg N kg 71 of soil was added as ammonium nitrate. At the time of the Department of Agricultural and Environmental Chemistry, Instituto Superior de Agronomia,Tapada da Ajuda, 1399 Lisboa Codex, Portugal. E-mail: adevarennes@isa.utl.pt Table 1. Characteristics of the soil used in the experiment. Texture Loamy sand Sand (%) 85 Silt (%) 10 Clay (%) 5 Organic matter (%) 1.1 pH in water 6.2 P 2 O 5 (mg kg 71 )öRiehm >200 K 2 O (mg kg 71 )öRiehm 148 Cu (mg kg 71 )öAA-EDTA 230 Cu (mg kg 71 )öwater 0.43 AA-EDTAöammonium-acetate-EDTA extraction. 230 Remediation of a Cu-contaminated soil with a polymer