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Abstract Chromated copper arsenates (CCA) have been extensively used as wood impregnation agents in Europe and North America. Today, CCA contaminated sites remain abundant and pose environmental risks that need to be properly managed. Using a TRIAD approach that combined chemical, ecotoxicological and ecological assessment of soil quality, we investigated the abilities of biochar and zero-valent iron (ZVI) to remediate CCA contaminated soil in a microcosm experiment. Soil samples from a highly contaminated CCA site (1364, 1662 and 540 μg g−1 of As, Cu and Cr, respectively) were treated with two different biochars (fine and coarse particle size; 1% w w−1) and ZVI (5% w w−1), both as sole and as combined treatments, and incubated for 56 days at 15 °C. In general, bioavailable As (As bio) and Cu (Cu bio) determined by whole-cell bacterial bioreporters corresponded well to water-extractable As and Cu (As water and Cu water). However, in biochar treatments, only Cu bio and not Cu water was significantly reduced. In contrast, under ZVI treatments only Cu water and not Cu bio was reduced, demonstrating the value of complementing analytical with bacterial bioreporter measurements to infer bioavailability of elements to soil microorganisms. The combined fine particle size biochar and ZVI treatment effectively reduced water extractable concentrations of Cr, Cu, and As on site by 45%, 45% and 43% respectively, and led to the highest ecological recovery of the soil bacterial community, as measured using the [3H]leucine incorporation technique. We conclude that the combined application of biochar and ZVI as soil amendments holds promise for in-situ stabilization of CCA contaminated sites. Graphical abstract Unlabelled Image Highlights • Chromate copper arsenate (CCA) contaminated soils pose risks to the environment. • In-situ stabilization of CCA contaminated soil was tested with biochar and ZVI. • Soil remediation was evaluated based on chemical and microbiological techniques. • Biochar reduced bioavailable (Cu bio), but not water-extractable Cu (Cu water). • Combination of biochar and ZVI most effectively reduced toxic effects of CCA. [ABSTRACT FROM AUTHOR]

Abstract The physico-chemical factors affecting the distribution, behavior and speciation of chromium (Cr), copper (Cu) and arsenic (As) was investigated at a former wood impregnation site (Fredensborg, Denmark). Forty soil samples were collected and extracted using a sequential extraction technique known as the Chemometric Identification of Substrates and Element Distributions (CISED) and a multivariate statistical tool (redundancy analysis) was applied. CISED data was linked to water-extractable Cr, Cu and As and bioavailable Cu as determined by a whole-cell bacterial bioreporter assay. Results showed that soil pH significantly affected the solid phase distribution of all three elements on site. Additionally, elements competing for binding sites, Ca, Mg and Mn in the case of Cu, and P, in the case of As, played a major role in the distribution of these elements in soil. Element-specific distributions were observed amongst the six identified soil phases including residual pore salts, exchangeable, carbonates (tentative designation), Mn-Al oxide, amorphous Fe oxide, and crystalline Fe oxide. While Cr was strongly bound to non-extractable crystalline Fe oxide in the oxic top soil, Cu and notably, As were associated with readily extractable phases, suggesting that Cu and As, and not Cr, constitute the highest risk to environmental and human health. However, bioavailable Cu did not significantly correlate with CISED identified soil phases, suggesting that sequential extraction schemes such as CISED may not be ideally suited for inferring bioavailability to microorganisms in soil and supports the integration of receptor-specific bioavailability tests into risk assessments as a complement to chemical methods. Graphical abstract Unlabelled Image Highlights • CISED and redundancy analysis was used to assess factors affecting the solid phase distribution of Cr, Cu and As. • pH is the key parameter affecting all three elements. • P with As and Ca, Mg and Mn with Cu could compete for binding sites. • As and Cu were associated with readily extractable phases while Cr was not. • Cu bioavailability to microbes cannot be inferred solely using CISED. [ABSTRACT FROM AUTHOR]