A new test for plant bioaccessibility in sulphidic wastes and soils: A case study from the Wheal Maid historic tailings repository in Cornwall, UK
van Veen, E.M.
Science of the Total Environment
Reason for embargo
Currently, bioaccessibility testing at contaminated sites is dominated by techniques designed to assess oral bioaccessibility to humans. Determining the plant bioaccessibility of toxic trace elements is also important. In mining landscapes, sulphides are an important source of potentially toxic elements. Simple tests to evaluate readily leachable metals and metalloids exist but do not extract elements temporarily constrained within the sulphide fraction. Sequential extractions describe the association of trace elements with different geochemical fractions but are time consuming, costly and provide excessive detail. This paper proposes a new test for plant bioaccessibility in sulphidic mine wastes and soils that uses hydrogen peroxide to simulate environmental oxidation. The bioaccessible fraction determined is operationally defined and does not predict actual plant uptake. The test targets a) the portion of an element that is currently available in the pore water for uptake by plant roots and also b) the fraction that is temporarily constrained in sulphide minerals but may become available upon oxidation of the substrate. A case study was conducted at a historic mine waste repository site in Cornwall, U.K. where near total As concentrations were extremely elevated and Cd, Cu, Pb, Sb and Zn were also high. Our test determined that bioaccessible concentrations of As, Cd, Cu and Zn and to a lesser extent Sb and Pb were highest in samples of pyritic grey tailings. This is attributed to sulphide mineral oxidation and, particularly for Cd and Zn, the dissolution of soluble secondary minerals. High As concentrations in the marbled tailings were not bioaccessible.
The authors would like to acknowledge the support of CRC ORE through the Environmental Indicators project 1B. The Australian Government CRC programme supports industry led end-user driven research collaborations to address the major challenges facing Australia. CRC ORE is focused on Optimising Resource Extraction. The analytical facilities at the Central Science Laboratory, University of Tasmania, were used for SEM-MLA and NAG/paste pH measurements in this project. Analytical facilities at CODES (ARC Centre of Excellence in Ore Deposits) were used for some XRD measurements. Analytical facilities at the ESI (Environment and Sustainability Institute) and CSM (Camborne School of Mines), University of Exeter were used for sample processing and preparation.
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.
Available online 5 February 2016