Short-term arsenic mobilization, labilization, and microbiological aspects after gasoline and diesel addition in tropical soils.

The effect of the presence of gasoline and diesel on the speciation and mobility of inorganic arsenic species in tropical topsoils was investigated. Topsoil samples (n = 25) were contaminated with gasoline and diesel (500 mg kg-1) in laboratory and were incubated under unsaturated conditions and regular aeration for 21 days. Speciation analysis and chemical fractionation were performed in the pore water from control, gasoline, and diesel-contaminated soil samples. Arsenic concentrations were compared to microbiological parameters (microbial metabolic quotient and soil basal breathing) and the presence of ArsM-harboring bacteria. The spike of gasoline and diesel to the topsoils increased pore water As3+ (H3AsO3) concentration. Arsenic mobilization was lower compared to previously reported data for other sources of organic matter (biochar, litter, and a mixture of sphagnum peat moss and composted poultry manure). However, gasoline or diesel addition mobilized As fractions that were adsorbed to the solid phase, in approximately 60% of the soils. Methylation presented an important role in the As3+ regulation in control soils, which was no longer observed after gasoline or diesel addition. The quantification of the labile fractions sampled by the diffusive gradients in thin films technique showed that the increased As concentration in the gasoline or diesel-contaminated soils mostly included inert species. Dissolved organic carbon content seems to be an important control mechanism of the labile As concentration. The increase in As mobility seems to pose a more concerning scenario due to As leaching than to plant uptake.

Metals and metalloids in green turtle hepatic tissue (Chelonia mydas) from Santos Basin, Brazil.

Metal and metalloid concentrations in the liver tissue of green turtles (Chelonia mydas) stranded on the Brazilian coast (n = 506) were studied using inductively coupled plasma mass spectrometry and cold vapor atomic fluorescence spectrometry. The influences of occurrence registers (date and location) and biological characteristics (sex, age, and developmental stage) were assessed, as well as the temporal influences of oil exploration and production activities. The mean concentrations of Cd, Cu, Mn, Zn, and Hg were the highest reported for the liver of C. mydas on the Brazilian coast. The mean element concentrations followed the order: Cu > Zn > Cd > Mn > As > Hg > Mo > Pb > V > Ni > Ba > Cr. Further, significant differences (p < 0.05) were observed for Hg between the sexes (males > females) and for As, Cu, Pb, Mo, and V between young individuals and older individuals (≥11 years), suggesting a relationship between the dietary shift inherent to green turtle development. These results were corroborated by the curved carapace length (CCL) data, wherein individuals residing in coastal areas (CCL > 50 cm) presented higher concentrations of Cu, Pb, Mo, Zn, Ba, and V than those in the oceanic stage (CCL < 30 cm). The opposite pattern was observed for As and Hg. The influences of spatial autocorrelation (Moran Index) at a global scale and oil production activities on the element concentrations were not observed. However, five hotspots of high metal concentrations were identified via a local spatial autocorrelation (local indicator of spatial association), existing predominantly in a region of heavy anthropic activity within the sampling area. Further, baseline element concentrations were established at the 95% confidence level. Overall, the developmental stage, which is related to feeding habits, had an expressive influence on element concentrations.

Concentration of essential and toxic elements as a function of the depth of the soil and the presence of fulvic acids in a wetland in Cerrado, Brazil.

The protection of wetlands is essential for sustainable development. The particular hydrology of wetlands creates conditions for the formation of hydric soils. Hydric soils are formed in oxide-reducing environments and perform important removal and re-oxidation of Fe and Mn oxides and hydroxides. They are also characterized by the formation of a superficial horizon enriched by the accumulation of organic matter. The objective of this study was to determine the concentration of essential (Co, Cu, Fe, Mn, Ni, Zn) and toxic (Al, Cd, Pb) elements in the soil solution in a wetland, surrounded by an intense agricultural activity area. The concentrations of the elements were evaluated according to the level of hydromorphy (border to the center) and the depth of the soil. The physical fractionation of these elements was also assessed (total and < 30 kDa), and the results were compared with the chemical speciation of these elements. Despite the high total concentrations of Al and Fe, the concentration of these elements was very low in the < 30 kDa fraction, which suggests that these elements are complexed with organic matter, in the form of hydroxides. Evidence of removal of Fe and Mn from the surface horizon was observed at the center of the wetland, where the highest level of hydromorphy is found. The results showed that the concentration of metals in the fraction < 30 kDa is insignificant, suggesting that the mechanisms of precipitation and/or adsorption to soil colloids play an important role in the regulation of this ecosystem.