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.