Long-term effects of aided phytostabilisation of trace elements on microbial biomass and activity, enzyme activities, and composition of microbial community in the Jales contaminated mine spoils Giancarlo Renella * , Loretta Landi, Judith Ascher, Maria Teresa Ceccherini, Giacomo Pietramellara, Michel Mench, Paolo Nannipieri Department of Soil Science and Plant Nutrition, University of Florence, Piazzale delle Cascine 28, I-50144 Florence, Italy Received 19 February 2007; received in revised form 11 June 2007; accepted 26 June 2007 Organo-mineral amendment and revegetation of a gold mine spoil increased microbial activity but did not increase microbial species richness. Abstract We studied the effectiveness of remediation on microbial endpoints, namely microbial biomass and activity, microbial and plant species rich- ness, of an As-contaminated mine spoil, amended with compost (C) alone and in combination with beringite (B) or zerovalent iron grit (Z), to increase organic matter content and reduce trace elements mobility, and to allow Holcus lanatus and Pinus pinaster growth. Untreated spoil showed the lowest microbial biomass and activity and hydrolase activities, and H. lanatus as sole plant species, whereas the presented aided phytostabilisation option, especially CBZ treatment, significantly increased microbial biomass and activity and allowed colonisation by several plant species, comparable to those of an uncontaminated sandy soil. Microbial species richness was only increased in spoils amended with C alone. No clear correlation occurred between trace element mobility and microbial parameters and plant species richness. Our results indicate that the choice of indicators of soil remediation practices is a bottleneck. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Arsenic contamination; Mine spoils; Remediation; Biochemical activity; Microbial diversity; Plant colonisation 1. Introduction Mine spoils of extractory sites represent a permanent threat to surrounding ecosystems and humans, as they are generally contaminated by several trace elements which can be trans- ported through wind erosion and water runoff, or be leached into the groundwater (Vangronsveld and Cunningham, 1998; Eisler, 2004). Mine spoils have generally acidic pH and a low nutrient content. Reduction of the ecological risk asso- ciated to mine spoils can be achieved by amendment with al- kaline minerals and/or organic matter, making trace elements less mobile by either sorption, complexation or precipitation reactions (Adriano et al., 2004). However, in case of As con- tamination, amendments should be carefully used with atten- tion paid to the pH value of remediated spoil, to avoid As leaching, which may occur at pH above 7 (Al-Abed et al., 2007). For the Jales mine spoils, pH correlated with As mobil- ity (Bleeker et al., 2002, 2003). Neutralisation of spoil acidity along with immobilisation of excessive trace elements and input of organic matter may create favourable conditions for growth of trace element-tolerant plants. Such plants are excluders, i.e. trace elements retained in roots, and contribute to reduce trace elements leaching by al- locating organic matter into the spoils, due to litter fall, deposi- tion of root exudates and decaying root material. Fresh input of nutrients should also stimulate microbiological and biochemical * Corresponding author. Tel.: þ39 055 3288 404; fax: þ39 055 333 273. E-mail address: giancarlo.renella@unifi.it (G. Renella). 0269-7491/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2007.06.053 Available online at www.sciencedirect.com Environmental Pollution 152 (2008) 702e712 www.elsevier.com/locate/envpol