RESUMO
Sewage sludge usage as agricultural soil amendment is a well-known practice employed worldwide. However, certain components may pose risks to the soil ecosystem. For a better verification of the potential adverse effects on the soil biota, biological assays have become an indispensable tool for an accurate understanding of the residue's behavior on soil, as well as its potential toxicity. Accordingly, to properly assess the effects of natural tropical soil (Oxisoil) amended with sewage sludge, we conducted toxicological tests with edaphic organisms (Enchytraeus crypticus and Folsomia candida) and microbial biomass (through respirometric assessment). Results indicate that E. crypticus and F. candida present similar reproduction sensitivity behavior to sewage sludge. For the microbiological analysis, the results suggest that microbial activity was stimulated by sludge application. For further evaluation of respiration of the microbial community and CO2 stabilization values behavior, Ford-Walford modeling was applied and presented limit values for sludge application in soil for 1.5 g kg-1 and 15.0 g kg-1 of, approximately, 55 mg and 88 mg, respectively. CO2 releases were faster and reached stability within 18 weeks for the soil with higher sludge content (15.0 g kg-1 of dry soil). In contrast, CO2 releases were slower for the soil with lower sludge content (1.5 g kg-1 of dry soil), and until the experiment's final period (21 weeks) respiration behavior did not reach stability. This study indicates that the stabilized sewage sludge, at the considered recommended application rate, presents a low toxicity risk for the studied bioindicators, being suitable for agricultural use.
Assuntos
Microbiota , Poluentes do Solo , Animais , Solo , Esgotos , Dióxido de Carbono , Poluentes do Solo/toxicidade , Monitoramento AmbientalRESUMO
Zinc (Zn) is an essential micronutrient for plants and an important component for maintaining soil quality. Commonly found in the soil due to anthropogenic activities, such as industrialization and application of organic waste as fertilizers, in high concentrations, Zn may induce soil toxicity, affecting important communities, such as edaphic fauna. Despite its high concentrations found in the environment, Zn bioavailability can be affected by the type of soil, organic matter content and pH. In this work, Zn had its toxicity evaluated in a natural tropical soil, sampled in São Paulo-Brazil, for two soil invertebrates (Folsomia candida, Enchytraeus crypticus) and two seeds (Lactuca sativa and Phaseolus vulgaris), through ecotoxicological tests. The invertebrate E. crypticus was exposed to Zn concentrations of 10.0 (T1); 100.0 (T2); 150.0 (T3); 200.0 (T4); 400.0 (T5) mg Zn kg-1 of dry soil, while F. candida, L. sativa and P. vulgaris were exposed to Zn concentrations of 100.0; 200.0; 400.0; 800.0 (t6); 1600.0 (t7); and 2000.0 (t8) mg Zn kg-1 of dry soil. The outcome evaluated were seed germination, for L. sativa and P. vulgaris, and reproduction, for F. candida and E. crypticus. The EC50 obtained for E. crypticus, F. candida, L. sativa, and P. vulgaris were 261.5, 1089.7, 898.5, and 954.5 mg Zn kg-1 of dry soil, respectively, being E. crypticus the most sensitive organism, and only at the highest Zn's concentrations the organisms' reproduction and seeds' germination showed a statistically significant inhibitory effect (p < 0.05). Therefore, this work's results showed that Zn does not present significant toxicity for the tested soil organisms and seeds and that at 100 mg Zn kg-1 of dry soil it can be beneficial to F. candida and E. crypticus' reproduction and L. sativa's germination. These results imply that the presence of Zn in low concentrations, both in soil and biofertilizers, such as sewage sludge, not only is not a concern, but it can even benefit certain crops and functions of edaphic organisms, which may contribute to the engagement of sustainable agricultural practices and the quest for food security.
Assuntos
Artrópodes , Besouros , Oligoquetos , Phaseolus , Poluentes do Solo , Animais , Esgotos , Lactuca , Zinco , Brasil , Monitoramento Ambiental , Solo/química , Poluentes do Solo/análiseRESUMO
Biodegradation of solid waste is a process that depends on the characteristics of waste and soil, and these characteristics may create a waterproof barrier in the landfill, changing its performance. Some residues, such as waste foundry sand (WFS), whose final destination is the sanitary landfill, can create waterproofing and alter the performance of the landfill. This study was carried out to test this hypothesis by evaluating two prototypes composed of layers of organic residues, one covered by a mixture of 30% clay soil + 70% WFS and the other covered only with clay soil, monitored for 24 months. The generated leachate was analyzed regarding the parameters of chemical oxygen demand (COD), pH and electrical conductivity. In addition, after the monitoring period, semi-undeformed samples were collected for quantification of microorganisms and physical-chemical analysis (pH, electrical conductivity, moisture content and images with scanning electron microscopy). In the soil prototype, there was the formation of a waterproofing barrier in its deepest layer (soil3). Factors such as the clay-mineral portion, moisture content (33,18%) and amount of microorganisms influenced this formation (650.000 and 15.000 CFU/g bacterial and fungal biomass, respectively), showing that WFS avoids the formation of this waterproofing barrier, as indicated for covering organic waste in landfills.