Linking the technology of contaminant phytoextraction with the use of biochar to immobilize residual soil contaminants

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There are numerous Brownfield sites in Canada today that are contaminated with persistent organic pollutants (e.g. PCBs and DDT) and/or with metals such as arsenic, cadmium, and lead. Phytotechnologies are defined as, 'the use of vegetation to contain, sequester, remove, or degrade inorganic and organic contaminants in soils, sediments, surface waters, and groundwater.' As a group, these technologies have gained acceptance in the past two decades as cost-effective, non-invasive alternatives or complementary technologies for engineering-based remediation methods. An identified research gap is that of multi-year field studies at actual contaminated sites. In addition, despite recognized successes, concerns remain as residual contaminants, continue to enter the food chain and pose environmental and human health risks. To address current research concerns, we propose to field test a novel application of biochar, whereby residual contamination is stabilized in place by biochar once the maximum amount of phytoextraction has been achieved within a realistic time period. Traditionally, biochar (a charred, thermally-treated biomass material), has been added to agricultural soil to improve soil quality and increase crop yields. Adding biochar to soils can also be a means of sequestering atmospheric carbon dioxide. Here, we propose another application of biochar; - to reduce the bioavailability of contaminants in soil, specifically through exploiting binding of soil contaminant residues to biochar. We propose to link the process of i) phytoextraction with ii) immobilization of residual contamination using biochar, and test their joint efficacy at three different contaminated sites in Ontario. In addition to carrying out multi-year field scale studies to address an identified research gap, we will undertake complementary greenhouse and laboratory investigations using soils from each of the three sites. Ultimately, we aim to develop a two-step 'green' remediation package. The first step involves extracting the maximal amount of contaminant feasible via phytoextraction. The second step will involve immobilizing any residual contaminants in the soil using biochar.