Arylesterase activity in trace element contaminated soils

Arylesterase activity was measured along with microbial biomass C (BC) and respiration, and H2O-soluble and NH4NO3-exchangeable trace elements (TE), in contaminated soils (TECS) from three long-term field trials. The AGIR (AG) soils were contaminated only by inorganic Cd, whereas the Ambarès (AM) and Louis Fargue (LF) soils were contaminated mainly by Mn and Zn, and Cd and Ni, respectively, from past sludge application at different rates. In the AG soils, the arylesterase activity decreased with increasing Cd total concentration and solubility. In the AM soils, the arylesterase activity decreased with increased contamination, whereas in the LF soils the arylesterase activity was increased by sludge additions, with the higher values detected in soils with lower sludge incorporation rates. In the AG and AM soils, arylesterase activity was significantly and negatively correlated with H2O-soluble and NH4NO3-exchangeable TE, whereas in the LF soils it showed a 'hump'-shaped trend with sludge additions and could not be modelled. Multiple regression analysis showed significant interactions between TE, soil pH value and TOC with this enzyme activity. Respiration values of the AG soils generally increased while the BC generally decreased with Cd contamination, while different trends were observed in the AM and LF soils. No trends in the enzyme activity-to-BC ratios were found in relation to soil contamination. Information regarding the inhibition of arylesterase activity in TECS can be important for the management of soils co-contaminated by TE and organic pollutants, in which the detoxification action of arylesterase may be reduced.