Distrito garimpeiro de alta floresta, um estudo de caso: descontaminação de solos de áreas degradadas

Abstract

The region f Alta Floresta - Mato Grosso - Brazil, like all the others that had been object of gold prospecting, presents a great number of lots of soil contaminated with mercury in high concentrations. These lots can act like source of contamination of surround areas, as well as, source of biota and local underground water contamination. The decontamination of polluted lots of soils using conventional technologies ex situ (acid washing, eletrorrecuperation, etc) become economically not practicable by the dimension of the lots and by the necessary treatments systems (transport, reagent, installation if compared with the relative low costs of acquisition of soils the bioremediation reveal gradually as a technological solution of costs much cheaper and ecologically recommendable “once” the opposite of ex situ, does not include revolviment of soils layers, degradation of rizosferic micro biota or drastic alteration of physic chemical properties. The use of plants with hyperacumulator properties, microorganisms with capacity to process compositions f heavy metals or, specially, the consortment of hyperacumulator with rizosferic microorganisms, has been investigated by many researchers in several parts of world as an alterna- tive to control the problem of soil pollution by heavy metals and others contaminants, considering the soils properties (pH, Eh, chemistry and mineralogical compositions, texture, etc) and of the contaminants (concentration, speciation, toxicity, etc). The natives plants identified as hyperacumulators of heavy metals are, ordinary, endemical can, therefore, be adapted to very climatical and pedogenicals conditions. Among the hyperacumulators, the studies has been got down to Brassicacea family, giving emphases to Brassica juncea e Thlaspi caerulescens that have high capacity to absorb and con- centrate heavy metais from metaliferous soils. For mercury were identified some sorts that can have until 25% of its dried weigh of the metal and their among them the Achillea millifolium and Andropogon paniculatus. The microorganisms then, have generically the skill to metabolize heavy metals and others dangerous compounds. From its isolated or combined come up the transformation of polluters in inert elements or compounds or less damaging (e.g. Organical compounds whose final product include water and CO»), the extract of the contaminate of the ecosystem, as happen with the mer- cury vaporizations into less damaging forms, as it's the case of mercury metilation and the others heavy metals. When it's working in the rizosferic zone, in combinations with the roots, can increase, decrease or impair the phitoextraction of metals from the soil. To the mercury a group of codified microorganisms with the mer operon, specially of Pseudomonas genre, present the ability to resist to combined environment with mercury, metabolize mercury compounds as well as above the metal in their practicable or not practicable cells. All this components and mechanisms have been tested with the aim to effect bioremedia- tion processes of soils and others ecossistemic niches, in the searching of viabilizing technologies of practicable technique environmental reparation, economical and ecological. In Brazil there are not almost no efforts in this way, knowing as “efforts” the identification or adaptation and improvement (bigger green mass production and bigger capacity of phytoextraction) of hyperacumulators sorts to ours soil conditions and climate, objecting the recuperation four soils chemically impacted. This work tried to investigate the conditions and proceedings related to the decontamination of soils with the use biotechnologies, the properties of the soils of the Alta Floresta, near the prospected areas and, based them, the possibility of recuperation of these soils under such technologies. From the observation done (kind of soil, mercury concentrations, lots size, etc) concluded that the option of bioremediation is more practicable for the area in question.