Selective sorption and desorption of DOM in podzol horizons - FTIR and Py-GC/MS of leachates from a column experiment.

The sorption of dissolved organic matter (DOM) depends on its interaction with the soil matrix. In hydromorphic podzols, DOM reacts mainly with aluminium (Al), which is responsible for the formation of the Bh-horizon in the subsoil. In this work, we investigated whether the retention of DOM in the soil during the podzolization process is selective in relation to the molecular composition of DOM. A column experiment was conducted to study the selective retention of sorption and desorption processes under controlled conditions. Materials used in the column experiment were representative for Brazilian coastal podzols under tropical rainforest. Materials were collected from this tropical coastal podzol ecosystem, and included soil from E- and Bh-horizons, and DOM from a stream (Stream), peat water (Peat), litter (Litter) and charred litter (Char). To evaluate selective retention of DOM, both the initial DOM and its leachates were analyzed by Fourier transform infrared spectra absorption (FTIR) and pyrolysis gas-chromatography/mass spectrometry (Py-GC/MS). The results showed preferential retention of DOM associated with biopolymers for soil columns with E-horizon material (E), E with Al nitrate (E-n), E with kaolinite (E-k) and E with gibbsite (E-h), except for Char. The composition of leachates after percolation through B horizon columns was mainly determined by desorption, and had a relatively large contribution from phenolic and carboxylic groups associated with Al and low molecular weight aromatic and N-containing pyrolysis products, while products from macromolecular materials such as cellulose were selectively retained in the columns for all DOM types. DOM from the Stream (taken during the rainy season) resembled that of desorbed OM from the B columns, reinforcing substantial desorption in the field as well. Our results suggest that sorption and desorption of OM in the hydromorphic Bh-horizon is continuous and that the selectivity of sorption is dependent on DOM source.

Respiratory bioaccessibility and solid phase partitioning of potentially harmful elements in urban environmental matrices.

Studies regarding the role of geochemical processes in urban environmental matrices (UEM) and their influence on respiratory bioaccessibility in humans are scarce in humid tropical regions, especially in Brazil. Contaminated UEM are potentially hazardous to humans if particles <10 µm in diameter are inhaled and reach the tracheobronchial region. In this study, we evaluated samples collected in Brazilian UEMs with a large environmental liability left by former mining industries and in a city with strong industrial expansion. UEM samples were classified into soil, sediment and mine tailings according to the characteristics of the collection sites. The respiratory bioaccessibility of potentially harmful elements (PHE) was evaluated using artificial lysosomal fluid (ALF, pH 4.5), and the BCR-sequential extraction was performed to evaluate how the respiratory bioaccessibility of the PHE was related to the solid phase partitioning. The bioaccessible fraction (BAF) ranged from 54 to 98% for Cd; 21-89% for Cu; 46-140% for Pb, 35-88% for Mn and; 41-84% for Zn. The average BAF of the elements decreased in the following order: Soil: Cd > Pb > Mn > Zn > Cu; Tailing: Pb > Cd > Zn > Mn > Cu; and Sediments: Pb > Mn > Cd > Zn > Cu. BCR-fractions were useful to predict the PHE bioaccessibility (R2 = 0.79-0.98), thus suggesting that particle geochemistry and mineralogy can influence PHE behaviour in the pulmonary fluid. Therefore, this approach provides a combination of quantitative and qualitative data, which allows us to carry out a more realistic assessment of the current situation of the potentially contaminated site and possible alternatives for decision making by the stakeholders.

Human intestinal Caco-2 cell line in vitro assay to evaluate the absorption of Cd, Cu, Mn and Zn from urban environmental matrices.

The Caco-2 cell line is derived from a human colon adenocarcinoma and is generally used in toxicity assays. The ingestion of soil or dust is a significant route of human exposure to potential harmful elements (PHE), and assays of bioaccessibility or bioavailability can be used to measure the potential hazard posed by exposure to toxic substances. The in vitro digestion (UBM method) and Caco-2 cell model were used to investigate the bioaccessibility and absorption by intestinal cells of the PHE in four matrices (two urban soils and two soils with lead (Pb)-mining tailings) along with the guidance material for bioaccessibility measurements, BGS 102. The gastrointestinal (GI) compartment was simulated, and the resulting material added to Caco-2 cells. In the GI, the average bioaccessibility was 24% for cadmium (Cd), 17% for copper (Cu), 0.2% for Pb, 44% for manganese (Mn) and 6% for zinc (Zn). The poor reproducibility was attributed to the pH (6.3) and the highly complex GI fluid that formed PHE precipitates and complexes. In 2 h, Caco-2 cells absorbed 0.2 ng mg-1 of cellular protein for Cd, 13.4 ng mg-1 for Cu, 5 ng mg-1 for Mn and 31.7 µg mg-1 for Zn. Lead absorption was lower than the limit of quantification (< 2 µg L-1). Cd was presented in the cell monolayer and could interfere in the intracellular accumulation of Cu, Mn and Zn. The use of in vitro assays allowed for an estimation of the absorption of Cd, Cu, Mn and Zn from environmental matrices to be made, and except for Mn, it had a positive correlation with bioaccessible concentration, suggesting a common association of these elements in the cellular environment.

Bioconcentration factors and the risk concentrations of potentially toxic elements in garden soils.

Empirical models describe soil-plant transfers to explain the variations in the occurrence of potentially toxic elements (PTE) in soils and to estimate the Bioconcentration Factor (BCF). In this study, results were selected based on data in the literature on soils of humid tropical and temperate regions to evaluate soil-plant transfer models, to calculate the BCF and to derive risk concentrations of Cu, Cr, Pb, Ni and Zn present in the exposure pathway leading to the consumption of contaminated vegetables. The Cetesb (Environmental Agency of the State of Sao Paulo, Brazil) mathematical model was used to derive the risk posed by soil concentrations in urban and rural exposure scenarios. The results of the pseudo total contents of PTE in the soil and the contents absorbed by plants were compared and the BCFs were calculated by the use of geometric means, including a correction factor appropriate to each particular type of soil. Differences were observed between BCFs calculated for each climate region: humid tropical (HTR) and temperate (TE), which the first one presented the highest values to BCF in leaves and the lowest BCF values for root, except Ni, compared to second one. The soil concentrations with the highest risk were found in humid tropical regions as compared with those found in temperate regions, except for Ni. The obtained BCFs may contribute to any future revisions of guideline values as well as help other state environmental agencies to establish their own guideline values.