Systematic review of alternative materials that improve retention of potentially toxic metals in soil/clay liners in waste disposal areas.

When soils available for the construction of liners do not display the characteristics necessary for a good performance, mixtures with other materials can be employed for achieving the desired quality. Several researchers have addressed those mixtures from either a geotechnical or a gas diffusion perspective, emphasizing low hydraulic conductivity. However, in recent years, growing attention has been drawn to the ability of liners to mitigate contamination. The literature lacks studies on the use of amendments for soil liners or cover systems to retain potentially toxic metals, which are important inorganic contaminants. This paper provides a systematic review of the literature considering publications available on Web of Science and SpringerLink databases between January 1st, 2012, and December 5th, 2022. The aim of the review was to identify the types of soils and amendments studied as liners or cover systems for such retention of potentially toxic metals, the methodologies of application of the alternative materials in the soils, and the research gaps and perspectives in the field. Seventeen papers that addressed 31 materials as amendments were retrieved. The most studied amendment was coal fly ash, and 17 amendments were residues or by-products, which indicates concerns over waste destination and sustainability. Among the potentially toxic metals analyzed are Pb, Cu, and Cd. Gaps such as lack of pilot, field-scale, and long-term studies, as well as perspectives for future research (e.g., different liner configurations, concomitant mixtures of two or more materials in the soil, and focus on the sustainability of amendments), were identified.

Assessment of the mobility, bioaccessibility, and ecological risk of Pb and Zn on a dirt road located in a former mining area-Ribeira Valley-Brazil.

The inadequate transportation of foundry slags during the construction of a mining waste landfill accounted for the presence of slags in the dirt road that connects the working district of Vila Mota to the city of Adrianópolis. The objectives of this work were to assess the lead (Pb) and zinc (Zn) contamination of the dirt. Three samples separated by 2 km were collected along a dirt road (samples: Adrianópolis, Deposit, and Plant). The conducted assays were physico-chemical parameters, pseudototal concentration, three sequential extraction procedures, and bioaccessibility assay. The laboratory data was used as input in the calculation of contamination indices risk assessment code (RAC) and potential ecological risk (Eri). The dirt road presented high concentrations of Pb (mean 1426.5 mg kg-1) and Zn (mean 4964.8 mg kg-1). The BCR SEP (Bureau Community of Reference Sequential Extraction Procedure) method was more adequate in extracting the soluble-exchangeable fraction, and this fraction was correlated with the gastric phase. The bioaccessible fraction is mainly present in the stomach fraction and is transported to the intestinal phase. Using BCR SEP method to calculate the contamination indices, sample Deposit yielded very high risk when calculating RAC and Eri for Pb (72.9% and 639.5, respectively). For Zn, high risk was obtained with RAC and very high risk for Eri (42.5% and 344.2, respectively). The high content of Pb and Zn on the dirt road presents a risk to the population that uses this road, since the soil particles are easily transported, deposited on the dermis, and inhaled.

Soil contamination assessment for Pb, Zn and Cd in a slag disposal area using the integration of geochemical and microbiological data.

Improper disposal of mining waste is still considered a global problem, and further details on the contamination by potentially toxic metals are required for a proper assessment. In this context, it is important to have a combined view of the chemical and biological changes in the mining dump area. Thus, the objective of this study was to evaluate the Pb, Zn and Cd contamination in a slag disposal area using the integration of geochemical and microbiological data. Analyses of soil organic matter (SOM), pH, Eh, pseudo-total concentration of metals, sequential extraction and microbial community by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) were conducted. Metal availability was evaluated based on the geoaccumulation index (I geo), ecological risk ([Formula: see text]), Risk Assessment Code (RAC) and experimental data, and different reference values were tested to assist in the interpretation of the indices. The soil pH was slightly acidic to neutral, the Eh values indicated oxidized conditions and the average SOM content varied from 12.10 to 53.60 g kg-1. The average pseudo-total concentrations of metals were in the order of Zn > Pb > Cd. Pb and Zn were mainly bound to the residual fraction and Fe-Mn oxides, and a significant proportion of Cd was bound to the exchangeable and carbonate fractions. The topsoil (0-20 cm) is highly contaminated (I geo) with Cd and has a very high potential ecological risk ([Formula: see text]). Higher bacterial diversity was mainly associated with higher metal concentrations. It is concluded that the integration of geochemical and microbiological data can provide an appropriate evaluation of mining waste-contaminated areas.