Long-term effects of untreated wastewater on soil bacterial communities

For 46 years (1957-2002), irrigation with wastewater has increased the amount of heavy metal and organic contaminants in soils and altered bacterial communities in Shenyang, northeastern China. There has been characterization of the different heavy metal and petroleum contaminants in two types of land uses (cornfields and paddy fields). The Nemerow composite indices of heavy metal contaminants have been higher in cornfields (1.17-4.73) than those in paddy fields (0.57-1.64). Molecular-based techniques and biochemical-based techniques were used to analyze soil microbial diversity in our study. The metabolic activity of soil microbe communities was higher in paddy sites than that in cornfields. Organic pollutants such as saturated and polycyclic aromatic hydrocarbons have significantly affected soil bacterial compositions. Heavy metals differed in how they disturbed the microbial communities. Arsenic (As) and lead (Pb) shifted the community composition and decreased microbial diversity; copper (Cu) reduced bacterial abundance in soil; and cadmium (Cd) and chromium (Cr) lowered the metabolic capabilities of bacteria.