Jorge Antonio Gonzaga Santos

ÁCIDOS HÚMICOS E CARVÃO VEGETAL ATIVADO COMO AMENIZANTES EM SOLO CONTAMINADO POR CHUMBO (1)

Soil contamination by Pb poses a significant risk to human health. The municipality of Santo Amaro da Purificacao, Bahia, Brazil, has one of the most severe cases of contamination of this metal in the world. The objective of this study was to evaluate the effect of humic acids and activated charcoal as soil amendments for reducing the toxicity of Pb to corn plants grown in contaminated soil collected near the area of the company responsible for the contamination. Application rates were based on the C content of the materials (humic acid from composting -AHv, commercial humic acid - AHc, and charcoal - CV) and corresponded to 0, 0.75, 1.5, 3 and 7.5 g kg-1 of C in the soil. At 43 days of growth, the plants were cut at ground level, separated into shoots and roots, and Pb contents were determined by nitro-perchloric digestion. The concentrations of chlorophyll a and b were also evaluated to evaluate the effect of the metal on the photosynthetic apparatus. The soil amendments applied to contaminated soil were effective in reducing the stress of Pb in corn plants. The highest efficiency was obtained from AHv, followed by CV and AHc. All the soil amendments tested decreased translocation of Pb to the shoots. This implies a greater fixation of the metal in the soil and, consequently, a reduction in the risk of transfer to the food chain. For this reason, these materials can be recommended as soil amendments for Pb phytostabilization in soils.

Industrial and urban organic wastes increase soil microbial activity and biomass

Microbial processes have been used as indicators of soil quality, due to the high sensitivity to small changes in management to evaluate, e.g., the impact of applying organic residues to the soil. In an experiment in a completely randomized factorial design 6 x 13 + 4, (pot without soil and residue or absolute control) the effect of following organic wastes was evaluated: pulp mill sludge, petrochemical complex sludge, municipal sewage sludge, dairy factory sewage sludge, waste from pulp industry and control (soil without organic waste) after 2, 4, 6, 12, 14, 20, 28, 36, 44, 60, 74, 86, and 98 days of incubation on some soil microbial properties, with four replications. The soil microbial activity was highly sensitive to the carbon/nitrogen ratio of the organic wastes. The amount of mineralized carbon was proportional to the quantity of soil-applied carbon. The average carbon dioxide emanating from the soil with pulp mill sludge, corresponding to soil basal respiration, was 0.141 mg C-CO2 100 g-1 soil h-1. This value is 6.4 times higher than in the control, resulting in a significant increase in the metabolic quotient from 0.005 in the control to 0.025 mg C-CO2 g-1 Cmic h-1 in the soil with pulp mill sludge. The metabolic quotient in the other treatments did not differ from the control (p < 0.01), demonstrating that these organic wastes cause no disturbance in the microbial community.

Biodisponibilidade de chumbo por extratores químicos em solo tratado com ácidos húmicos e carvão ativado

Palavras-chave: Poluicao do solo. Metais pesados. CaCl 2 . Mehlich 1. DTPA. ABSTRACT - Soil contamination by lead in the town of Santo Amaro, in the state of Bahia, Brazil, originated with the installation of a metal plant in the city in the 1960s, and poses a serious risk to the local population. Determination of the available Pb levels in the soil is an important tool in monitoring the risks of this contamination. However, different methods are used to determine the available Pb content of the soil, resulting in differing values for the extractants. The aim of the present work was to compare the efficiency of extraction using Mehlich 1, DTPA and CaCl 2 solutions in the evaluation of Pb availability in soil treated with different soil amendments. The soil sample used in the experiment was collected near the metal plant. The dosages of soil amendments were set up based on the carbon content of the materials (compost humic acid, commercial humic acid and charcoal), being: 0, 0.75, 1.5, 3 and 7.5 g C kg -1 . The available Pb content was extracted by Mehlich 1, DTPA pH 7.3 and CaCl 2 10 mmol L -1 . Soil fractionation was carried out to determine the metal attached to the exchangeable and organic matter fractions of the soil. The addition of AHv reduced the Pb content of the soil by 60, 89 and 47% for extractions carried out with Mehlich 1, CaCl 2 and DTPA respectively. The Pb content of the organic matter fraction was directly proportional to the dosages of soil amendments. The three extractants under evaluation were efficient in predicting the available Pb content.