Pyrolysis temperature influences the capacity of biochar to immobilize copper and arsenic in mining soil remediation.

Biochar is a promising material used for multiple remediation approaches, mainly in polluted soils. Its properties can differ depending on feedstock and pyrolysis temperature. In this context, we tested the capacity of three biochar products made from corncob, pyrolyzed at different temperatures (350, 500, and 650 °C), to remediate a mining soil affected by high levels of Cu and As. We performed an exhaustive characterization of the biochar. We found that biochar showed a higher surface area with increasing pyrolysis temperature, whereas high molecular weight PAHs were detected in biochar produced at the maximum temperature, thus indicating potential ecotoxicological risks. After the application of biochar to the soil, Cu was partially immobilized, especially when using that obtained at 500 °C. This effect is attributed to the structure of this material and an increase in soil pH and organic matter content. Conversely, As was increased in the soluble fraction for all three types of biochar but in a proportion that lacks relevance. On the whole, given its lower PAH content, higher Cu immobilization ratio, and an almost negligible increase in As availability, biochar obtained at 500 °C outperformed the other two products with respect to soil recovery. Of note, data on Cu and As availability were doubled-checked using two extraction methodologies. We propose that this operational approach for determining the most suitable pyrolysis temperature will find application in other soil remediation actions.

Ability of Cytisus scoparius for phytoremediation of soils from a Pb/Zn mine: Assessment of metal bioavailability and bioaccumulation.

Abandoned mining areas are an environmental concern for aquatic and terrestrial ecosystems due to their unfavourable soil properties and high levels of potentially toxic elements. Despite this, some plant species may grow spontaneously and colonise these areas; being suitable in many cases for restoration practices, since they may accumulate metals in their tissues. This study aims to assess the effectiveness of 14 chemical soil extractants to predict the bioavailability of toxic elements (Cd, Pb and Zn) in soils from the abandoned Pb/Zn mine of Rubiais (NW Spain), based on root and shoot metal contents in Cytisus scoparius (L.) Link, which grows spontaneously in this area. Afterwards, its potential for phytoremediation activities was assessed. Mine soils showed high contents Cd (1.77-14.38 mg kg-1), Pb (850-2137 mg kg-1) and Zn (1754-12090 mg kg-1). Cytisus scoparius grows in spite of these high metal contents; accumulating Zn and Pb in its roots, Zn in the aerial part and excluding mostly Cd from its tissues. None of the extractants used to determine the bioavailable content of Pb allow predicting its availability for C. scoparius. However, LMWOA was the most effective extractant to determine the bioavailability of Cd and Zn for this species. Besides, NH4NO3 and Ca(NO3)2 are also good indicators for Zn bioavailability. The analysis of bioconcentration and translocation factors suggest that C. scoparius behaves like a Zn accumulator plant, whereas alternatively, it behaves like a Pb phytostabiliser and as a Cd excluder species. Thus, C. scoparius can be used as a species for mine soil restoration, decreasing the mobility of metals and preventing their dispersion to another ecosystem compartments.

Pb pollution in soils from a trap shooting range and the phytoremediation ability of Agrostis capillaris L.

Pb pollution caused by shooting sport activities is a serious environmental problem that has increased considerably in recent decades. The aims of this study were firstly to analyze Pb pollution in soils from a trap shooting range abandoned in 1999, secondly to study the effectiveness of different extractants [CaCl2, DTPA, NH4OAc, low molecular weight organic acids (LMWOA), and bidistilled water (BDW)] in order to determine Pb bioavailability in these soils, and finally to evaluate the phytoremediation ability of spontaneous vegetation (Agrostis capillaris L.). To this end, 13 soils from an old trap shooting range (Galicia, NW Spain) were studied. It was found that Pb levels in the soils were higher than 100 mg kg(-1), exceeding the generic reference levels, and three of these samples even exceeded the USEPA threshold level (400 mg kg(-1)). In general, the reagent that best represents Pb bioavailability and has the greatest extraction efficiency was CaCl2, followed by DTPA, NH4OAc, LMWOA, and BDW. A. capillaris Pb contents ranged between 9.82 and 1107.42 mg kg(-1) (root) and between 6.43 and 135.23 mg kg(-1) (shoot). Pb accumulation in roots, as well as the presence of secondary mineral phases of metallic Pb in the adjacent soil, showed the phytostabilization properties of A. capillaris.