RESUMOExistem poucos estudos sobre os solos sob cultivo de subsistência em assentamentos rurais do norte da Amazônia. Os objetivos deste trabalho foram a caracterização de solos da Colônia Agrícola do Apiaú, Roraima, e a avaliação das alterações em algumas propriedades químicas resultantes dos sistemas de manejo adotados pelos agricultores, bem como os impactos da ação de queimadas nos solos. As áreas estudadas foram: pastagens, cultivo de banana e de milho, mata queimada e não queimada. As amostras de solos foram submetidas a análises químicas e mineralógicas. Foram encontrados Latossolos, Argissolos e Gleissolos, todos possuindo mineralogia caulinítica e expressivos teores de Ti, evidenciando elevado grau de intemperismo. Os Argissolos e Gleissolos possuem baixos teores de Fe. Os baixos teores de cátions trocáveis indicam a baixa fertilidade natural, com elevada saturação por Al no complexo sortivo na maioria dos solos. A pobreza química resultou em pouca variação química entre os diferentes solos. Comparativamente, a área cultivada com banana mostrou os maiores teores de cátions trocáveis e de P disponível no horizonte superficial, conseqüência da mineralização dos restos culturais pela ação do fogo e maior proximidade de afloramentos de rocha. A pobreza química extrema nos Argissolos refletiu-se na má qualidade da pastagem degradada. Os baixos teores totais de Zn, Cu e Mg indicaram sua baixa reserva e possível deficiência.

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Recebido em 21/6/07; aceito em 26/10/07; publicado na web em 15/5/08Acid drainage results from exposition of sulfides to the atmosphere. Arsenopyrite is a sulfide that releases arsenic (As) to the environment when oxidized. This work evaluated the As mobility in six sulfidic geomaterials from gold mining areas in Minas Gerais State, Brazil. Grained samples (<2 mm) were periodically leached with distilled water, during 70 days. Results suggested As sorption onto (hydr)oxides formed by oxidation of arsenopyrite. Low pH accelerated the acid generation, dissolving Fe oxihydroxides and releasing As. Presence of carbonates decreased oxidation rates and As release. On the other hand, lime added to a partially oxidized sample increased As mobilization.Keywords: arsenopyrite; acid mine drainage; contamination. INTRODUCTIONAcid mine drainage (AMD) results from a set of chemical, electrochemical and microbiological reactions, risen from exposure of sulfide bearing geological materials to the atmospheric oxygen and water.1 Under such conditions there is a net generation of sulfuric acid, decreasing pH of the drainage water and increasing solubility and leaching of toxic elements as heavy metals and metalloids.2-4 Consequently, there are increasing risks for toxic metals and metalloids incorporation in biological systems and so, bioaccumulation and biomagnification processes in the trophic chain.Arsenopyrite is a sulfide (AsFeS) commonly found in gold mine areas. 5,6 Its oxidation produces arsenic and sulfur oxiacids (e.g. H 3 AsO 3 , H 3 AsO 4 , H 2 SO 4 ). Arsenic is toxic at low concentrations and sulfuric acid is responsible by the pH drop. 7 The rate of sulfides oxidation depends on several factors, including the amounts of arsenopyrite (e.g. AsFeS), grain size distribution, temperature and the exposure time of the material to the atmospheric water and oxygen. Catalytic action of the Acidithiobacillus aggravates the problem under acid medium, at pH < 3, which stimulates bacterial activity. 8Ingestion of water is considered the main source for As contamination. The most noticeable reports are mass contamination cases that took place in Bangladesh, 9,10 Taiwan 11,12 and Chile. 13 In Brazil, the Iron Quadrangle is one of the affected regions in Minas Gerais State. Most impacted areas are close to gold mines, as in Nova Lima, Raposos, Mariana and Santa Bárbara districts. [14][15][16] Several researchers showed that As adsorption onto iron oxides decreases as the pH increases. [16][17][18][19][20] On the other hand there are reports of increasing As (III) sorption as the pH increases from 3 to the neutral, when the adsorbent is a sulfide as troillite (FeS) or pyrite (FeS 2 ). 21 Release of As from arsenopyrite structure, by oxidation, also decreases at increasing pH, mainly due to the drop of bacterial activity. 8,9 Face to the need for controlling As dispersion in the environment, this research was performed in order to study the mobility of As in samples of sulfidic materials from gold mine areas in different geological sc...

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The Cu, Ni and Zn accumulations in leaves and roots of lettuce (Lactuca sativa L) grown in soil amended with natural and contaminated cattle manure vermicompost were evaluated. The vermicompost residues containing relatively high metal concentrations used in this work were obtained from a previous experiment, in which vermicompost was applied to removing metals from electroplating wastes. Sequential lettuce cultivations were conducted in pots containing the residual substrates from the first cultivation by adding metal-enriched vermicompost residues. In general, the Cu, Ni and Zn concentrations in leaves and roots of lettuce plants grown in vermicompost enriched with these metals were higher than in the treatment using the natural vermicompost. The metal concentrations in leaves from treatments with natural vermicompost were below the critical concentrations of toxicity to plants. However, the metal concentrations in leaves of the third cultivation in which metal-enriched vermicompost was applied were greater than the upper limit that causes plant toxicity, but no visual damage was observed in the plants. Treatment with Zn-enriched vermicompost resulted in toxicity symptoms, but plant damage did not result in the death of the plant. The chemical fractionation of Cu, Ni and Zn in residues from lettuce cultivation was evaluated by using a sequential extraction procedure and metal concentrations were increased in the different chemical fractions according to the increase of vermicompost dose.