Trends in detoxification enzymes and heavy metal accumulation in ground beetles (Coleoptera: Carabidae) inhabiting a gradient of pollution

Abstract

Non-specfic carboxylesterase and glutathione S-transferase activity was measured in the ground beetle, Pterosthicus oblongopunctatus (Coleoptera: Carabidae), from five sites along a gradient of heavy metal pollution. A previous study determined that beetles from the two most polluted sites (site codes OLK2 and OLK3) were more susceptible to additional stressors compared with beetles from the reference site (Stone et al., Environ. Pollut. 113, 239–244 2001), suggesting the possibility of physiological impairment. Metal body burdens in ground beetles from five sites along the gradient ranged from 79 to 201 μg/g Zn, 0.174 to 8.66 μg/g Pb and 1.14 to 10.8 μg/g Cd, whereas Cu seemed to be efficiently regulated regardless of metal levels in the soil. Beetle mid- and hindguts were homogenized and the soluble fraction containing glutathione S-transferase (GST) and carboxylesterase (CaE) was assayed using kinetic analyses. Significantly higher levels of GST were found only in female beetles from the most polluted sites (OLK2 and OLK3; P=0.049, P<0.001, respectively) compared with the reference site (OLK7). In addition, OLK3 females had significantly higher levels of CaE compared with the reference beetles ( P=0.01). Male beetles did not differ in enzyme activity along the metal gradient. Overall, obvious trends in detoxification enzymes were not detected in ground beetles in association with metal body burdens.