Enzyme activities and microbial functional diversity in metal(loid) contaminated soils near to a copper smelter

The monitoring of soil metal(loid) contamination is of global significance due to deleterious effects that metal(loid)s have on living organisms. Soil biological properties such as enzyme activities (EAs) are good indicators of metal(loid) contamination due to their high sensitivity, fast response, and low-cost. Here, the effect of metal(loid) contamination on physicochemical properties and microbial functionality in soils sampled from within 10 km of a Cu smelter is investigated. Soil composite samples were randomly taken within 2, 4, 6, 8 and10 km zones from a mining industry Cu smelter. The EAs of dehydrogenase (DHA), arylsulfatase (ARY), β-glucosidase, urease, and arginine ammonification (AA) were studied as indicators of metal(loid) contamination, which included the ecological dose (ED₅₀) with respect to Cu and As contents. The community level physiological profile (CLPP), functional diversity, and catabolic evenness were evaluated based on the C-substrate utilisation. All EAs decreased in zones with high degrees of metal(loid) contamination, which also had low TOC and clay contents, reflecting long term processes of soil degradation. Positive and strong relationships between EAs and TOC were found. DHA and ARY activities decreased by approximately 85–90% in highly metal(loid) contaminated soils. DHA and AA showed significant ED₅₀ values associated with available Cu (112.8 and 121.6 mg Cu_DTPA kg⁻¹, respectively) and total As contents (30.8 and 31.8 mg As kg⁻¹, respectively). The CLPP showed different metabolic profiles along the metal(loid) contamination gradients. Long-term stress conditions in soils close to industrial areas resulted in the decreasing of general biological activity, catabolic capacity, and functional diversity.