Influence of soil zinc concentrations on zinc sensitivity and functional diversity of microbial communities K. Lock * , C.R. Janssen Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, 9000 Gent, Belgium Received 16 July 2004; accepted 28 December 2004 Zinc sensitivity of microbial communities and functional diversity decrease with increasing zinc concentration in the pore water. Abstract Pollution induced community tolerance (PICT) is based on the phenomenon that toxic effects reduce survival of the most sensitive organisms, thus increasing community tolerance. Community tolerance for a contaminant is thus a strong indicator for the presence of that contaminant at the level of adverse concentrations. Here we assessed PICT in 11 soils contaminated with zinc runoff from galvanised electricity pylons and 11 reference soils sampled at 10 m distance from these pylons. Using PICT, the influence of background concentration and bioavailability of zinc on zinc sensitivity and functional diversity of microbial communities was assessed. Zinc sensitivity of microbial communities decreased significantly with increasing zinc concentrations in pore water and calcium chloride extracted fraction while no significant relationship was found with total zinc concentration in the soil. It was also found that functional diversity of microbial communities decreased with increasing zinc concentrations, indicating that increased tolerance is indeed an undesirable phenomenon when environmental quality is considered. The hypothesis that zinc sensitivity of microbial communities is related to background zinc concentration in pore water could not be confirmed. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Pollution induced community tolerance; Zn; Bioavailability; Metallo-region 1. Introduction Due to natural variability and the presence of other parameters interfering with the effect of the studied con- taminant, it is still hard to demonstrate toxic effects of a specific contaminant on the structure and functioning of an ecosystem and to assess the connection between the presence of this contaminant and the effects observed in the field. Blanck et al. (1988) suggested to study pollution induced community tolerance (PICT) as a measure for toxicity at the community level of an ecosystem. The concept of PICT is based on the principle that toxicity decreases the survival of the most sensitive organisms, resulting in an increased tolerance of the community. An increased tolerance of a community is therefore a good indicator for the presence of the contaminant at harmful concentrations (Posthuma, 1997). In the context of metal contamination, three different mechanisms are suggested as causes of the increased tolerance: (1) an immediate, toxic effect killing sensitive species, (2) a selection for metal tolerance due to different competitive abilities of surviving organisms, and (3) acclimatisation/adaptation of organisms developing in these polluted soils due to physiological and/or genetic changes. The presence of PICT can be considered as evidence for toxic effects on organisms under field conditions, metal resistance is therefore an undesirable phenomenon when quality of the environment is considered. * Corresponding author. Tel.: C32 9 2643710, fax: C32 9 2643766. E-mail address: koen_lock@hotmail.com (K. Lock). 0269-7491/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2004.12.038 Environmental Pollution 136 (2005) 275e281 www.elsevier.com/locate/envpol