Diagnóstico e estudo da variabilidade espacial da contaminação por metais pesados em solos e águas superficiais de área de destruição de munição

Abstract

The production of weapons and ammunition, and their later disposal in the environment, without adequa te control of these materials, has increased considerably the concentrations of heavy metals in the soil, causing serious environmental contamination problems. This study aimed to evaluate the level of contamination of soil and surface water by heavy metals in an destruction of ammunition area and its surroundings, and also to map the spatial variability of the concentrations of heavy metals in the study area. It was adopted a sampling system that followed a grid with spacing of 5 x 5 meters, defining 30 sampling points. At each point samples were taken at 5 depths, at each 20 cm, up to 1.00 m. In order to evaluate the area under the influence of the local destruction of ammunition, it was also sampled the soil in the surrounding area, as well as in a transect parallel to the main drainage channel. Along the way, in addition to sampling soil, samples of bottom sediments and surface water were also taken. The soil samples were air dried, sieved to reach soil less than 2.0 mm size, and subjected to extraction procedures with aqua regia (HCl:HNO3, 3:1), to determine pseudototal extraction and sequential (BCR method) forms in the geochemical fractionation method. The extracts were analyzed by atomic absorption spectrophotometry, using the equipment Varian AA-600. To assess the contamination of lead, cadmium and copper in soil from the destruction of ammunition area, the guidelines proposed by CETESB (2005)/CONAMA (2009) were used. In the studies of spatial variability the following geostatistical techniques were applied: descriptive statistics, variography and kriging; using the Geostat software. A spatial dependence was observed in the data, concluding that the spatial variability of concentrations of heavy metals in the area was not simply random and, yes, entirely or in part, the metals values adjusted to the models. The results showed that for lead, about 37% of the samples were above the intervention value, 49% above the prevention value and below the intervention, and only 14% samples were below the prevention value. Similarly, the results showed that 67% of the samples for both cadmium and copper had concentrations above the prevention value and below the intervention value, and only 33% were below the prevention and above the quality reference value. However, in the samples from bottom sediments, concentrations of lead, cadmium and copper were higher only in sites closest to the area of ammunition destruction, thus confirming that the contaminated area is restricted to that area and its proximity. The analysis of surface water showed lead and manganese concentrations higher than the standards for effluent discharges into water bodies, being of 0.5 mg L-1 and 1.0 mg L-1, respectively, only at the site in the destruction of ammunition area exit.