Leg deformities of oribatid mites as an indicator of environmental pollution Tapio Eeva a, ⁎, Ritva Penttinen b a Section of Ecology, University of Turku, FIN-20014 Turku, Finland b Zoological Museum, University of Turku, FIN-20014 Turku, Finland abstract article info Article history: Received 4 March 2009 Received in revised form 29 April 2009 Accepted 11 May 2009 Available online 29 May 2009 Keywords: Acidification Bio-indicator Environmental pollution Heavy metals Oribatid mites Skeletal abnormalities Oribatid mites have often been used as indicators of the degree of environmental pollution but few studies have assessed the effects of pollution at individual level. One possible indicator of environmental stress at individual level is structural malformations of exoskeleton. We studied whether a number of leg deformities in soil oribatid mites could be used as an indicator of the degree of heavy metal pollution or acidity in nature. For this purpose we collected soil samples in a well known pollution gradient of a Finnish Cu-Ni smelter. Heavy metals are common pollutants in the area. Ten focal oribatid species were inspected under microscope for deformations in their legs (missing, broken or deformed leg). Of the focal species only one (Chamobates cuspidatus) showed an increasing trend along the pollution gradient in the proportion of leg abnormalities but there were clear differences in proportions among species. We consider that leg deformities are not a good indicator of heavy metal exposure in the studied species. Our data suggest, however, that they may indicate spatial variation in soil pH. We also tested for the possible effects of pollution on oribatid species number and abundances. There were pollution-related differences in relative abundances of mites but not in the number of species. We discuss the relationship between soil pH, calcium requirements and skeletal malformations of oribatid mites. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Oribatid mites have been used successfully as bioindicators of environmental pollution. Many studies have measured their responses to environmental pollution at community level (Seniczak et al., 1997; Zaitsev and Van Straalen, 2001; Skubala and Kafel, 2004). Soil dwelling oribatid mites are a good choice for such studies because of their relatively restricted home range, important role in detrital food webs and their high abundance in various habitats. In general, heavy pollution exposure decreases both abundance and species diversity, but species vary in their sensitivity to pollution and some species may even benefit from moderate pollution levels (Seniczak et al., 1997). Several studies have measured directly the accumulation of pollutants, in most cases heavy metals, in oribatid mites (Ludwig et al., 1992b; Roth, 1993; Janssen and Hogervorst, 1993; Siepel, 1995; Heck et al., 1995; Zaitsev and Van Straalen, 2001; Skubala and Kafel, 2004). These studies have shown that oribatid mites easily accumu- late environmental pollutants, such as heavy metals, but again there is a clear variation among species according to their diet. For example, copper has been shown to accumulate effectively in oribatid species (Skubala and Kafel, 2004). Van Straalen et al. (2001) found that among seven different soil invertebrate groups oribatid mites showed the highest heavy metal concentrations. There are at least three reasons for high heavy metal levels in oribatids. First, many pollutants easily accumulate in soil, which is the matrix for many oribatid species. Second, fungal hyphae, which are known to effectively accumulate heavy metals, are the main food source for many of the species (Siepel, 1995). Third, their relatively high calcium requirement promotes the simultaneous uptake of heavy metals (Roth, 1993). Very few studies, however, have assessed the effects of environ- mental pollution on mites at individual level. One possible indicator of environmental stress at individual level is structural malformations of exoskeleton. Only a few studies have tried to quantify the number of anomalies as a possible indicator of pollution exposure. Dubinina and Alekseev (1994) found that increased exposure to NiCl 2 increased the number leg abnormalities in one of the oribatid species, Oppiella nova. Köhler et al. (2005) noticed that lead treatment from the larval stage onwards caused leg malformations in Archegozetes longisetosus. Oribatid mites are known to use calcium to harden their cuticle (Norton and Behan-Pelletier, 1991). On the other hand, heavy metals are known to interact with calcium metabolism in animals (Goyer, 1997). Therefore, possible mechanisms linking heavy metal exposure and skeletal defects include the interference of heavy metals with calcium. We studied whether a number of leg deformities in oribatid mites could be used as an indicator of the degree of heavy metal pollution in nature. For this purpose we collected soil samples in a pollution gradient of a copper smelter and determined the number of leg deformities in ten potential indicator species. Since soil acidity may affect the availability of calcium we also measured organic soil pH to be used as a potential explaining variable in the analyses. As focal species we selected ten common species of relatively large body size, Science of the Total Environment 407 (2009) 4771–4776 ⁎ Corresponding author. Fax: +358 2 3336550. E-mail address: tapio.eeva@utu.fi (T. Eeva). 0048-9697/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2009.05.013 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv