Comparative analysis of sediment quality indices using different reference values in an environmental protection area in Southeastern Brazil

Contamination of aquatic ecosystems by potentially toxic elements (PTEs) is a concerning environmental issue, given their persistence, toxicity potential, and ability to accumulate in living organisms. Several studies have been conducted to assess the contamination of aquatic ecosystems by PTEs, using pollution and ecological risk indices that rely on the concentration of these elements in aquatic sediments. However, many of these studies use global reference values for calculating the indices, which can lead to misleading interpretations due to substantial variations in PTEs concentrations influenced by the geological characteristics of each region. Therefore, the use of regional reference values is more appropriate when available. This study aimed to investigate variations in the results of five indices, employing global, regional, and quality reference values, based on sediment samples collected from rivers in the Ipanema National Forest, a protected area in Brazil exposed to various anthropogenic pressures. The results revealed that elements such as Al, Fe, and Mn exceeded the limits allowed by legislation in water samples, while As and Cr surpassed the limits in sediment samples. Comparative analysis highlighted significant discrepancies in the results of the indices when global reference values were used compared to regional and quality reference values, especially for As and Ba. Thus, this study underscores the importance of establishing specific regional values for an accurate assessment of sediment quality and the risks associated with contamination by PTEs in different regions worldwide.

Responses of Chironomus sancticaroli to the simulation of environmental contamination by sugarcane management practices: Water and sediment toxicity

Sugarcane management practices include the application of pesticides, including the herbicide 2,4-D and the insecticide fipronil. In addition, a by-product from the ethanol industry, called vinasse, is commonly applied to fertilize sugarcane areas. The potential risks of these practices to the edge-of-field aquatic ecosystems were assessed in the present study. This was done by contaminating mesocosms with (single and mixtures of) both pesticides and vinasse and evaluating the effects on the midge Chironomus sancticaroli through in-situ and laboratory bioassays. To this end, outdoor mesocosms were treated with fipronil (F), 2,4-D (D), and vinasse (V) alone and with the mixture of fipronil and 2,4-D (M), as well as with both pesticides and vinasse (MV). C. sancticaroli was deployed in mesocosms before contamination in cages, which were taken out 4- and 8-days-post-contamination. Water and sediment samples were also taken for laboratory bioassays on the first day of contamination, as well as 7-, 14-, 21-, 30-, 45-, and 75-days post-contamination. The responses assessed in subchronic assays (8-day) were survival, growth, head capsule width, development, and mentum deformities. Low survival occurred in the in-situ experiments of all treatments due to the low oxygen levels. In the laboratory tests, effects on survival occurred for F, V, and M over time after exposure to both water and sediment. All organisms died post-exposure to water samples from the MV treatment, even 75-days-post-contamination. Impairments in body length and head capsule width occurred for F, V, and M for water and F, V, M, and MV for sediment samples over time. All treatments increased mentum deformities in exposed larvae for any of the sampling periods. The negative effects observed were more significant in the mixture mesocosms (M and MV), thus indicating increased risks from management practices applying these compounds together or with a short time interval in crops.

The environmental importance of iron speciation in soils: evaluation of classic methodologies

Iron is an essential mineral and one of the most abundant in soils, presenting itself in the environment as ferrous and ferric ions. As each oxidation state of iron has a different role in the environment, its speciation in environmental studies is important. The determination of ferrous iron received great attention from soil chemists because of its important role in agriculture, in redox processes, and as an electron acceptor in the catalysis of organic matter. Methodologies with the use of colorimetric reagents to determine ferrous iron are divergent and not very clear. In this study, we compared two colorimetric reagents (1,10-phenanthroline and ferrozine) to determine the total concentration of iron, ferrous and ferric ions in soil, using simple and low-cost methodologies. The determination of ferrous and total iron with 1,10-phenanthroline colorimetric reagent, following published instructions, did not correlate with ferrozine method, presenting an erroneous quantification. After neutralizing the extract of 1,10-phenanthroline with NaOH, both colorimetric methods allowed to quantify with precision and high yield the amount of ferrous and total iron extracted from the soil. The oxidation states of iron have a different contribution and importance to the environment. In this sense, the improvement of a widely used methodology is crucial for the better study of iron speciation in soil.

Spatial modeling applied to environmental monitoring: identifying sources of potentially toxic metals in aquatic system

Aquatic contamination by potentially toxic metals is a problem that has been aggravated, especially due to the quantity and the diversity of sources. Locating these sources is not always an easy task, especially because of the wide variety of possibilities. In this context, the application of geostatistical methods may represent an excellent tool to find out sources of metal contaminants in aquatic systems. Thus, the objective of this work was to elaborate an approach to identify sources of potentially toxic metals (Zn, Ba, Pb, Cr, Mn and Fe), by relating their spatial-temporal variations with the local land use patterns, along a longitudinal profile of the Pirapora River, located in the State of Sao Paulo, Brazil. For this purpose, water samples were collected at different points, taking into consideration each specific land use pattern and quantifying the metals contents by microwave plasma atomic emission spectrometry. In this work, thirteen land use patterns have been identified: mining, forestry, abandoned pasture, water, urban area, human occupation, floodplain, bare soil, temporary crop, roads, forest, streets and pasture. The results revealed temporal variations for the metals Ba, Cr, Fe, and Pb and spatial for Zn and Mn, making possible to correlate the presence of these two latter metals with mining and forestry, the most proeminent activities in the region. Overall, this work proposes a model which brings together geoprocessing and analytical methods, in order to correlate spatial-temporal variations of potentially toxic metals with specific land use patterns of a determined region, aiming the environmental monitoring.

Natural organic matter residue as a low cost adsorbent for aluminum

The contamination of aquatic and terrestrial environments by potentially toxic metals is highlighted by the possible impacts that their high availability can have on the environment. Thus, the development of alternative absorbents that can be used in the remediation of contaminated areas is of great environmental interest. Humin, one of the fractions of natural organic matter, is a promising alternative in studies on the retention of different metals that are environmentally toxic. In this study, the influence of the organic and inorganic humin constituents that are involved in the retention of aluminum species was evaluated. After extraction and calcination to obtain the ashes (inorganic constituents), humin and ash samples were structurally characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. Interaction studies between aluminum-humin and ash-humin were performed in the pH range of 4.0-8.0 and with various contact times. The results of the characterization of humin and ash showed different functional groups present in the structures of these materials. Based on the results of the interaction between humin-aluminum and ash-aluminum, it can be inferred that both the organic and inorganic components of humin are efficient at absorbing aluminum. However, the adsorption isotherms showed that humin and the ashes have different adsorption behaviors. Humin is the only fraction of natural organic matter with a significant inorganic constituent content; it is the fraction least used by researchers in this field and is often discarded as waste. In light of this, the results obtained in this work highlight the importance of humin as a natural adsorbent material. Humin may be promising for the removal of aluminum species in contaminated environments due to the presence of organic and inorganic constituents.