Avaliação de estratégias para remediação de solo contaminado por chumbo e bário provenientes de resíduos de perfuração de poço de prospecção de petróleo

Abstract

This study begun with a field survey in a one hectare area of petroleum drill waste (rocks and mud came from perforation) in Santa Maria do Oeste, in Paraná state, Brazil. It was verified different levels of metal contamination in the area, according to the surface position and with depth, with barium and lead over the investigation standard according to legislation. The highest level contaminated material was collected and used in a laboratory and greenhouse experiment at the campus of the Universidade Federal Rural do Rio de Janeiro, initiated on December, 2007, and completed on June, 2010. The objective was to evaluate the efficiency of remediation by washing contaminated soil (in situ and ex-situ) as well as phytoremediation. The waste washing ex-situ was simulated such as the contaminant would be removed from soil using a rotating device, with soil mixed with an ethylenediaminetetraacetic acid (EDTA) solution in the proportion of 1:10. Removal of lead and calcium increased proportionally to concentration of extractor (from 100 to 1500 mmol L-1). Removal of barium increased considerably above 600 mmol L-1. Iron and manganese showed little influence by different concentration of extractor. The soil washing in-situ was simulated by addition of two solutions of EDTA, with concentration of 150 and 300 mmol L-1, and the control (water). The material was incubated in plastic columns, for three weeks, after that volumes of 100 mL of deionized water were added weekly for three weeks, and after that samples were taken daily up to a total of ten. The leached was collected and the barium and lead content were analyzed, also other metals that could interfere with the extraction. The fractions (exchangeable, iron bound, organic matter bound, and residual) that metals were associates in the waste, before and after washing, were also determined. It was found, in the higher EDTA concentration, a small extraction of barium, while lead had about 20% of the total in soil extracted. The phytoremediation was carry on with two species, Brachiaria decumbens cv. Basilisk, an herbaceous plant, and Cordia africana, an arboreal. The plants growing up in vases with 4 kg of substratum were irrigated with deionized water and Hoagland nutrient solution (25% of ionic power). Two treatments were used in the phytoextraction induced with EDTA, in the concentration of 6 mmol L-1 (with one single application, and 3 dosages of 2 mmol L-1), plus the control. After 150 days for Brachiaria and 270 days for Cordia, the plants were collected, and analyzed (root and shoots) for heavy metal content. EDTA was effective to induce metal absorption, except for barium and calcium, where lead concentrated in the roots and barium in leaves (with highest concentration for EDTA applied in one dose). For Cordia, barium distributed equally in the plant sections, and lead concentrated in the roots.