Spatial distribution and factors influencing the accumulation of toxic metals in soils in mountain agroecosystems, Rio De Janeiro, Brazil.

The concentrations of toxic metals (TM) were analyzed in 498 samples of agricultural soils used for intensive vegetable cultivation in the watershed of Barracão dos Mendes, Brazil. The goal of this study was to characterize the distribution of these elements and the main natural and anthropogenic factors affecting their accumulation. In general, the average concentrations of TM were higher than the reference quality values for cultivated soils in the region, with the exception of Cr, Co, Ni and Mn, and the average concentration of Cd was ten times greater. Three sources of variation in the distribution of TM concentrations were identified: one related to topographic relief, another related to lithology, and one related to the massive use of agrochemicals. These factors contributed to TM accumulation in the soil; moreover, the transport of toxic metal-enriched clay by runoff resulted in higher concentrations of these elements in the lower parts of the slope. The long-term application of massive amounts of fertilizers and pesticides resulted in the accumulation of Cr, Cu, Zn, Ni, Pb and Cd in the vegetable cultivation soils and promoted the enrichment of macronutrients, mainly P and K. Moreover, the spatial distribution of TM in the agricultural soils of this mountain agroecosystem was affected by intensive vegetable cultivation, which altered the natural TM distribution dynamics determined by variations in topographic relief and lithology. In intensive cultivation areas, the TM distribution was also influenced by soil management practices such as tillage along the slope direction and massive mineral and organic fertilization.

Cadmium and lead transfer factors to kale plants (Brassica oleracea var. acephala) grown in mountain agroecosystem and its risk to human health.

The aim of the present study is to assess soil Cd and Pb contamination in kale (Brassica oleracea var. acephala) production sites in mountain agroecosystem, as well as its potential risk to human health. The study was carried out within 24 kale-production sites located in mountainous region of Rio de Janeiro (Brazil). Soil, plant, and fertilizer samples were collected in all assessed properties. Pseudo-total and bioavailable soil Cd and Pb content and their concentration and amount accumulated in plants were analyzed. The recorded results were used to calculate the pollution index. Risks to human health associated with kale consumption were assessed by comparing the limits set by the Brazilian regulating agency and by calculating estimated daily intake (EDI), noncarcinogenic target hazard quotient (THQ), and carcinogenic risk factor (CRF). Soil Cd and Pb enrichment was observed. Inappropriate management adopted in the assessed sites and terrain slope and the intensive use of mineral (phosphate and potassium) and organic (poultry litter) fertilizers were the main factors contributing to increase soil Cd and Pb pseudo-total and bioavailability contents. Most Cd and Pb contents in leaves, in natura, exceed the maximum values set by the Brazilian regulating agency. The present EDI, THQ, and CRF results recorded for these metals were within the tolerable ranges.

Variability factors of heavy metals in soils and transfer to pasture plants of Mayabeque in Cuba.

Studies to assess variability factors of heavy metals in soils are essential to understand their behavior in the environment and for the assessment of contaminated areas. In this context, this research aimed to study the factors that influence the variability of heavy metal levels and their bioavailability in pasture areas in the Alturas de Nazareno region, Mayabeque, Cuba, as well as the transfer to plants. Forty-five points were distributed in a natural pasture and at two depths (0-20 and 20-40 cm) as a function of relief and soil type. Pseudo-total heavy metal contents were determined according to method 3051A of USEPA, geochemical fractionation according to the Community Bureau of Reference method, and plant digestion according to method 3052 of USEPA. Soil samples were separated into two groups, according to cluster analysis. The type of soil associated with the pH and Ca attributes were the factors that most influenced the variability of the total and bioavailable levels of metals in natural pasture soils in the region of Alturas de Nazareno. Group 1 showed the lowest heavy metal contents and the highest pH and calcium values, which were predominantly associated with carbonate soils. Group 2 had the highest contents of heavy metals and Fe, corresponding mainly to the soil Ferralítico Rojo. The concentration of metals in plants was directly related to their bioavailable content in the soil, where G2 represents the group with the highest risk of transferring metals to the food chain.

Lead and Cadmium Transfer Factors and the Contamination of Tomato Fruits (Solanum lycopersicum) in a Tropical Mountain Agroecosystem.

The objectives of this study was to diagnose Cd and Pb contamination in soil and to identify the main factors that contribute to the transfer of these elements to tomato plants and fruits and contamination levels of the fruits in tropical mountain conditions. Contamination of the study area soils by Cd and Pb was verified. This contamination stemmed from the intensive use of agricultural inputs, mainly organic fertilizers and soluble mineral fertilizers. The relief of the terrain and inadequate soil management influenced the spatial distribution of these two metals. The Cd concentration in tomato fruits was very low, but the Pb contamination detected in approximately 80% of the fruit samples was considerably higher than the limits that pose a danger to human health. The translocation of Pb to the tomato fruits was associated with the use of organic fertilizer, mainly poultry litter.

Potential of water lettuce (Pistia stratiotes L.) for phytoremediation: physiological responses and kinetics of zinc uptake.

Two greenhouse experiments were carried out to evaluate the phytoremediation potential, physiological responses and zinc (Zn) uptake kinetics of water lettuce (Pistia stratiotes L.). The phytoextraction experiment evaluated four doses of Zn (0.7 mg L-1 - represented the Zn in the nutrient solution, 1.8, 18 and 180 mg L-1 - corresponded to ten, hundred and a thousand times, respectively, the maximum permitted content for fresh water) at four different culture times (24, 48, 72 and 168 h). The Zn uptake kinetics of water lettuce were evaluated at two concentrations of Zn (1.8 and 18 mg L-1). The water lettuce attained the highest percentage removal at the lowest evaluated doses (0.7 and 1.8 mg L-1), reaching a maximum value of approximately 72% removal (when cultivated in 1.8 mg L-1 of Zn after 168 h of culture). The Zn uptake increased with culture time, increasing the synthesis of carotenoids at all doses evaluated. The highest doses of Zn resulted in a reduction in photosynthetic efficiency. The results showed a high potential of water lettuce to absorb and tolerate Zn, accumulating preferably in the roots, demonstrating that these plants are able to absorb large quantities of Zn in contaminated solution.

Relation between changes in organic matter structure of poultry litter and heavy metals solubility during composting.

Poultry litter (PL) is widely used as fertilizer because of its rich N, P and Ca content. When PL is applied to previously untreated soil, it is a potential contaminant. Composting is an alternative for stabilizing organic and mineral components. This study aimed to elucidate the structural changes and its influence on the solubility of heavy metals in poultry litter during the first 30 d of composting, which is the period when the most intense transformations occur. For this analysis, the transformation dynamics of the organic structures and the availability of mineral elements were studied via spectroscopic characterization, total heavy metal content determination and chemical fractionation at three composting times (0, 15, and 30 d). During composting, the material's aromaticity increased, while its aliphaticity decreased, and the hydrophobicity index increased as the polarity decreased. These results indicate that during the first 30 d, PL composting occurs via transformation of the most labile structures (carbohydrate, peptide and fatty acid fragments), thereby preserving the most stable and least functionalized structures. Composting increased the concentrations of Cu, Cr, Pb and Zn and the transformation of CAlk-O and CAlk-di-O associated with peptides and carbohydrates and favored solubilizing and leaching a water-soluble fraction rich in these compounds. The labile fractions of Fe and the humified organic matter fractions of Cu, Fe, Mn, Zn, and Al increased. The structural changes reduced heavy metal solubility, thus indicating that after 30 d of composting, the heavy metal contamination risk is low.

Soil heavy metal content on the hillslope region of Rio de Janeiro, Brazil: reference values.

The increasing concern regarding the preservation of soil quality suggests the adoption of quality reference values as a first step in environmental monitoring actions. In this context, the objective of this study was to establish soil quality reference values for Al, Zn, Mn, Cd, Fe, Pb, Ni, Cr, and Cu and to correlate several soil properties with the occurrence of these elements in the hillslope region of Rio de Janeiro State. Sixty-two samples were collected at depths of 0-20 and 20-40 cm and analyzed using the USEPA method 3051A. After clustering analysis, the samples were separated into three groups. Classification functions were obtained based on the variables pH - Mg - Fe - Mn, i.e., the variables that were best related to heavy metal content. We determined to establish the quality reference values for the 75th percentile of the three groups. The relief forms of the area, which facilitate the transport of soil fine-particle fractions and accumulation in lowlands, were revealed to be one of most important factors in understanding the distribution of soil heavy metals.

Spatial variability and solubility of barium in a petroleum well-drilling waste disposal area.

The petroleum industry generates a range of wastes which is often are disposed in soil close to the well location, negatively affecting soil and water quality. The objective of this study was to evaluate the solubility and map the spatial variability of barium in a potentially contaminated area. The study area consisted of a petroleum well-drilling waste disposal site located in the municipality of Mato Rico-PR. A large georeferenced sampling grid was organized. Soil samples were collected at depths of 30, 60, 90, and 120 cm for determination of the "pseudo-total" concentrations and geochemical fractionation of barium. The barium concentrations showed spatial dependence, which permitted the use of geostatistical interpolators. Regarding depth, the depth of 0-30 cm showed the largest contaminated area; however, higher concentrations of barium were found at the depth of 60-90 cm. The results of geochemical fractionation showed that the analyzed samples contained percentages higher than 99% in the non-labile fraction (residual). These results indicate clearly that the barium was in a condition of low solubility, even for samples that had the highest concentrations, presenting low-environmental risk.

Quality reference values of trace elements in Brazilian organosols.

Determination of the natural background levels of trace elements in organosols and the proposal of quality reference values (QRVs) for these elements are essential for monitoring these soils because they are fragile and subject to change more intensely and rapidly than other soil classes. Given the above information, the objectives of this study were to determine the QRVs of trace elements for organosols and to correlate some soil properties with the occurrence of these elements. Forty organic soil horizon samples from different regions of Brazil were selected to determine the pseudo-total content of trace elements. The samples were separated into three groups according to a cluster analysis. The soil variable Fe and C contents had the strongest influence on the trace element contents in the organosols and were therefore used in the group classification functions. QRVs were proposed according to the 75th percentiles of the groups. The classification functions are a suitable tool for the allocation of new samples into previously established groups and may potentially be used to estimate the degree of organosol degradation.