Contamination study of forest track soils located in a recreational area and filled with steel industry waste 30years ago

Evaluation of testing approaches for constituent leaching from electric arc furnace (EAF) slags

Increased usage of electric arc furnace (EAF) slags as soil amendments and surface aggregates raises concerns regarding heavy metal release. However, no standardized leaching characterization approach exists for EAF slags and other industrial materials. This study compares test results for three EAF slags using several testing approaches: (i) total content analysis, (ii) single-batch extractions (i.e., TCLP, SPLP, and in-vitro bioaccessibility assay), and (iii) evaluation for the fine fraction (<2 mm) and ingestion fraction (<250 μm). Test results were compared to the pH-dependent liquid-solid partitioning (LSP) and percolation column testing. Constituent screening based on total content identified As, Cr, Fe, Li, Mn, Sb, Se, Tl and V as constituents of potential concern (COPCs); however, pH-dependent LSP curves indicated that only Fe, Mn, and possibly Cr have the potential to exceed regional residential soil screening levels. Additional COPCs (Al, Ba, Cd, Cu, Cr(VI), Hg, Mo, Ni, Pb, and Sn) exceeded example thresholds at one or more of three plausible release conditions. LSP curves and column test results indicated that most COPCs are in equilibrium at test conditions. Although leaching evaluation indicated the potential for concentrations greater than thresholds, assessments incorporating test results with scenario-specific parameters provide a more precise basis for evaluating COPC release. This study demonstrates that the applicability of single-batch extraction tests is limited to conditions simulated by the test, while a well-defined LSP curve is representative of leaching over conditions of all single-batch tests. Therefore, pH-dependent and percolation column testing provides a baseline characterization to support environmental decision making.

From leaching data to release estimates: Screening and scenario assessments of electric arc furnace (EAF) slag under unencapsulated use

Electric arc furnace (EAF) slag is the non-metallic byproduct of the primary U.S. steelmaking process. Much of the slag is marked for secondary uses as aggregates. EAF slags used as construction fill or residential groundcover are directly exposed to the environment, raising concerns of potential leaching impacts. Leaching data of EAF slags as function of eluate pH (Method 1313) and liquid-to-solid ratio (Method 1314) were used to refine an initial list of constituents of potential concern to those with potential to leach at concentrations greater than project thresholds, and to estimate release from EAF slags when used as unencapsulated groundcover. Screening assessment identified 11 of over 20 constituents requiring further assessment. Scenario-based assessments results showed that constituents with high available content and low leaching concentrations (Al, Cr, Co, Mn, Se) are persistent in contacting water over the assessment period while those with limited available content (As, Ba, Mo, V) were depleted. Aging decreased the release of Se while increasing Tl release, likely through a combination of hydration, carbonation, and cracking processes. Increasing fill depth and infiltration rates did not alter leaching concentrations; however, liquid-solid ratio for each assessment interval changed thereby impacting cumulative release.

Spatial distribution and source apportionment of DTPA-extractable metals in soils surrounding the largest Serbian steel production plant

Despite presenting a practical approach for the characterization of the environmental risk of potentially toxic elements (PTEs) derived from steel production facilities, the analysis of the spatial distribution of bioavailable PTEs concentrations in the soil is frequently overlooked in the management of polluted sites. In this study, the diethylenetriaminepentaacetic acid (DTPA)-extractable forms of PTEs were investigated in soils surrounding the largest Serbian steel production plant. The correlation and geostatistical analysis indicated their pronounced variability suggesting the anthropogenic origin of most investigated elements, apparently from the steel production facility. The detailed visualization of variables and observations derived by self-organizing maps (SOMs) revealed the homologies in PTEs' distribution patterns, implying the common origin of some elements. These observations were confirmed by principal component analysis (PCA) and positive matrix factorization (PMF). The аpplied approach supports a comprehensive assessment of contaminated sites' ecological and health risks and provides a basis for soil remediation.

Temporal-spatial distribution and diastereoisomer pattern of hexabromocyclododecane in the vicinity of a chemical plant

Hexabromocyclododecane (HBCD) is an effective brominated flame-retardant additive, which is mainly produced in the coastal area of China. This study collected soil samples from a HBCD production plant and its surrounding area in Weifang, Shandong Province, China, and analyzed the temporal-spatial distribution of HBCD and its diastereoisomers in soil. The analysis results showed that the concentration of HBCD in soil near the plant was much higher than normal values, with an annual average concentration reaching 5405 ng/g. Soils 1, 2 and 4 km away from the plant were also analyzed, showing that the concentration of HBCD in soil decreased accordingly with the distance from the pollution sources. In order to investigate the effect of the season on HBCD content, the soil samples were collected in all four seasons of the year 2017-2018. According to variations in the wind direction, the concentration of HBCD in soil was also changed. The distribution trend showed that the concentration of HBCD in soil in the downwind direction of the prevailing wind was higher than that in the upwind direction. In addition, this work analyzed the distribution of HBCD in vertical soil sections. It was found that the concentration of HBCD decreased with depth in the soil vertical profile. Finally, the various diastereoisomer patterns in the soil compartments were examined, finding that α-HBCD and γ-HBCD were the predominant diastereoisomers in the soil of the study area.

Evaluating a Bayesian modelling approach (INLA-SPDE) for environmental mapping

Understanding the uncertainty in spatial modelling of environmental variables is important because it provides the end-users with the reliability of the maps. Over the past decades, Bayesian statistics has been successfully used. However, the conventional simulation-based Markov Chain Monte Carlo (MCMC) approaches are often computationally intensive. In this study, the performance of a novel Bayesian inference approach called Integrated Nested Laplace Approximation with Stochastic Partial Differential Equation (INLA-SPDE) was evaluated using independent calibration and validation datasets of various skewed and non-skewed soil properties and was compared with a linear mixed model estimated by residual maximum likelihood (REML-LMM). It was found that INLA-SPDE was equivalent to REML-LMM in terms of the model performance and was similarly robust with sparse datasets (i.e. 40-60 samples). In comparison, INLA-SPDE was able to estimate the posterior marginal distributions of the model parameters without extensive simulations. It was concluded that INLA-SPDE had the potential to map the spatial distribution of environmental variables along with their posterior marginal distributions for environmental management. Some drawbacks were identified with INLA-SPDE, including artefacts of model response due to the use of triangle meshes and a longer computational time when dealing with non-Gaussian likelihood families.