Effects of Different Sewage Sludge Concentrations on the Soil Microorganism Sensibility and Metals Accumulation during Helianthus annuus L. Cultivation

The agricultural use of sewage sludge have been presented as an alternative both to reduce the volume of this environmental liability as to obtain a product to be used in agricultural soils as fertilizer. However, when the household sewage is also composed of water from the industrial area, the sludge is richer in potentially toxic elements. Hence, the present study aimed to evaluating the effects of different concentrations of sewage sludge on soil microbial activity and contents of Cd, Cu, Cr, Pb and Zn in soil, plant and seed. The experiment was conducted at the greenhouse during the crop season of 2012 to 2013, with evaluations of soil total organic carbon, microbial biomass carbon, metabolic quotient and heavy metals in soil, plant and seed. According to the results, application of 20 Mg ha-1 of sewage sludge promoted higher microbial activity, lower metabolic quotient and in increased production of dry plant matter. Resulted in 480.77 µg g-1of microbial carbon and 9.75% of soil organic carbon. Heavy metal contents in seeds were 1.29, 14.26, 1.52 and 80.57 mg kg-1 of Cd, Cu, Pb and Zn, respectively, with the lead content above the maximum extent recommended in food by WHO (Word Health Organization).