Arsenic in Mining Areas: Environmental Contamination Routes.

The emission and accumulation of toxic elements such as arsenic in various environmental compartments have become increasingly frequent primarily due to anthropogenic actions such as those observed in agricultural, industrial, and mining activities. An example of environmental arsenic contamination in Brazil exists in the city of Paracatu, MG, due to the operation of a gold mine. The aim of this work is to evaluate the routes and effects of arsenic contamination in environmental compartments (air, water, and soil) and environmental organisms (fish and vegetables) from mining regions as well as the trophic transfer of the element for a risk assessment of the population. In this study, high levels of arsenic were found in the waters of the Rico stream ranging from 4.05 µg/L during the summer season to 72.4 µg/L during the winter season. Moreover, the highest As concentration was 1.668 mg kg-1 in soil samples, which are influenced by seasonal variation and by proximity to the gold mine. Inorganic and organic arsenic species were found above the allowed limit in biological samples, indicating the transfer of arsenic found in the environment and demonstrating a great risk to the population exposed to this area. This study demonstrates the importance of environmental monitoring to diagnose contamination and encourage the search for new interventions and risk assessments for the population.

Degradation of Praguicide Disulfoton Using Nanocompost and Evaluation of Toxicological Effects.

Organophosphates (OPPs) are an important element of modern agriculture; however, because they are being used excessively, their residues are leaching and accumulating in the soil and groundwater, contaminating aquatic and terrestrial food chains. An important OPP called disulfoton is frequently used to eradicate pests from a wide range of crops, including Brazil's coffee crops. Additionally, it does not easily degrade in the environment, and as such, this compound can slowly build up in living organisms such as humans. Moreover, this compound has been classified as "extremely hazardous" by the World Health Organization. This study evaluated the degradation efficiency of disulfoton using a Fenton-like reaction catalyzed by magnetite nanoparticles and determined the toxicity of the by-products of the degradation process using the bioindicator Allium cepa. Further, the removal efficiency of disulfoton was determined to be 94% under optimal conditions. On the other hand, the Allium cepa bioassay showed different toxic, cytotoxic, genotoxic, and mutagenic outcomes even after the remediation process. In conclusion, the Fenton process catalyzed by magnetite nanoparticles presents great efficiency for the oxidation of disulfoton. However, it is important to highlight that the high degradation efficiency of the Fenton-based process was not sufficient to achieve detoxification of the samples.

Bacteria isolated from soils of the western Amazon and from rehabilitated bauxite-mining areas have potential as plant growth promoters.

Several processes that promote plant growth were investigated in endophytic and symbiotic bacteria isolated from cowpea and siratro nodules and also in bacterial strains recommended for the inoculation of cowpea beans. The processes verified in 31 strains were: antagonism against phytopathogenic fungi, free-living biological nitrogen fixation, solubilization of insoluble phosphates and indole acetic acid (IAA) production. The resistance to antibiotics was also assessed. Sequencing of the partial 16S rRNA gene was performed and the strains were identified as belonging to different genera. Eight strains, including some identified as Burkholderia fungorum, fixed nitrogen in the free-living state. Eighteen strains exhibited potential to solubilize calcium phosphate, and 13 strains could solubilize aluminum phosphate. High levels of IAA production were recorded with L-tryptophan addition for the strain UFLA04-321 (42.3 µg mL⁻¹). Strains highly efficient in symbiosis with cowpea bean, including strains already approved as inoculants showed the ability to perform other processes that promote plant growth. Besides, these strains exhibited resistance to several antibiotics. The ability of the nitrogen-fixing bacteria to perform other processes and their adaptation to environmental conditions add value to these strains, which could lead to improved inoculants for plant growth and environmental quality.

Contamination in a brazilian river: a risk of exposure to untreated effluents.

Due to natural or anthropogenic activities, various chemical contaminants, such as toxic metals and organic compounds, enter water systems and can have multiple deleterious effects on many living organisms. The Todos os Santos River (TSR) in Brazil receives a high discharge of untreated effluents from various sources. The purpose of this study was to determine trace element concentrations in water samples from the TSR, evaluate the toxicological effects of these elements by using the (onion) test, and verify the physical-chemical parameters to establish the risk of exposure related to the contaminated river. The samples were taken in 2011 at six selected points (two upstream of an urban area, two in the urban area, and two downstream of the urban area) with physical-chemical parameters evaluated. The concentrations of Al (21.63-1688.84 µg L), P (38.59-1760.87 µg L), and Fe (478.9-8296.3 µg L) were above the maximum levels permitted under Brazilian law (and the World Health Organization); little dissolved O was observed. Based on the test, genotoxic and mutagenic effects may occur in the river and could be due to anthropogenic increases in metal content. These important results have serious implications for the ecosystem as well as the health of the people who use the water.

Leguminous plants nodulated by selected strains of Cupriavidus necator grow in heavy metal contaminated soils amended with calcium silicate.

Increasing concern regarding mining area environmental contamination with heavy metals has resulted in an emphasis of current research on phytoremediation. The aim of the present study was to assess the efficiency of symbiotic Cupriavidus necator strains on different leguminous plants in soil contaminated with heavy metals following the application of inorganic materials. The application of limestone and calcium silicate induced a significant increase in soil pH, with reductions in zinc and cadmium availability of 99 and 94 %, respectively. In addition, improved nodulation of Mimosa caesalpiniaefolia, Leucaena leucocephala and Mimosa pudica in soil with different levels of contamination was observed. Significant increases in the nitrogen content of the aerial parts of the plant were observed upon nodulation of the root system of Leucaena leucocephala and Mimosa pudica by strain UFLA01-659 (36 and 40 g kg(-1)) and by strain UFLA02-71 in Mimosa caesalpiniaefolia (39 g kg(-1)). The alleviating effect of calcium silicate resulted in higher production of dry matter from the aerial part of the plant, an increase in nodule number and an increase in the nitrogen fixation rate. The results of the present study demonstrate that the combination of rhizobia, leguminous plants and calcium silicate may represent a key factor in the remediation of areas contaminated by heavy metals.

Efficient nitrogen-fixing Rhizobium strains isolated from amazonian soils are highly tolerant to acidity and aluminium.

One of the most cultivated and consumed vegetables in Brazil is the common bean, Phaseolus vulgaris L. The symbiosis of this plant species with nitrogen-fixing bacteria that are adapted to the stresses commonly found in tropical soils can increase production. The aim of this study was to evaluate the symbiotic effectiveness of bacterial strains from soils under different land uses in the Amazon region. Further, rhizobia tolerance to acidity and aluminium and the involvement of some possible physiological mechanisms of such tolerance were also investigated. In assessing the efficiency of biological nitrogen fixation, inoculation with strains UFLA04-195, UFLA04-173 and UFLA04-202, belonging to the genus Rhizobium, resulted in greater plant growth, higher shoot nitrogen content and good nodulation compared to the inoculation with the strain CIAT 899 (R. tropici), and to the mineral nitrogen control or Burkholderia fungorum strains that nodulated or not bean plants. These efficient strains grew better at pH 5.0 than at pH 6.0 or pH 6.9; they also tolerated up to 1 mmol l(-1) of Al(3+) and showed an increased production of exopolysaccharides where the growing rates were less (pH 6.0 and pH 6.9). With respect to aluminium, the highest production of EPS produced greater tolerance to this element. Taken together, these results indicate that the strains evaluated in this study were tolerant to acidity and aluminium; they appeared to have developed resistance mechanisms such as EPS production and a resistant cell outer membrane (indicated by resistance to polymyxin and methyl violet). As these strains also gave increased yields of the host species, further studies on whether to recommend these strains as inoculants are already underway.