Abstract
Contaminated land is increasingly becoming an important issue worldwide. Many metal contaminants are persistent in the soil for a large number of years. Immobilisation of metals/metalloids has proven to be a challenging task and a cost-effective, non-invasive and socially acceptable technology is required for its remediation. The present study involves the in-situ immobilisation of metals/metalloids in Tamar Valley soil using compost enriched with iron oxide and/or zeolite (up to 20% w/w). The results illustrated that 15% compost 5% iron oxide (15C5IO) and 15% compost 1% iron oxide (15C1IO) were effective in reducing the leaching of Cu to < 1% compared to the control sample. For Cd, all the amended samples decreased the leaching effectively to < 1% compared to the control. However, for reducing the leaching of As, 10% compost 2% iron oxide (10C2IO) and 15% zeolite 5% compost (15Z5C) were effective. The sequential extractions results show that control sample showed the order of association of As in the soil: residual fraction (69%) > reducible fraction (11%) > organic fraction (10%) > exchangeable fraction (9%); For Cu: organic fraction (55%) > residual fraction (26%) > reducible fraction (13%) > exchangeable fraction (6%) and for Cd: organic fraction (56%) > reducible fraction (25%) > residual fraction (14%) > exchangeable fraction (6%). The results of bioavailability tests demonstrated that 15% compost 5% iron oxide (15C5IO) and 15% compost 1% iron oxide (15C1IO) were effective in reducing the take up of Cu by ryegrass to 24 mg kg-1 and 35 mg kg-1 respectively. For Cd, 5% compost 5% zeolite (5C5Z) and 5% compost 5% iron oxide (5C5IO) yielded the best result for reducing the take up to 3 mg kg-1. For As, 15% compost 5% zeolite (15C5Z) and 15% compost 5% iron oxide (15C5IO) reduced the take up to 2 mg kg-1. SEM-EDX and XRD analyses were performed on the control and amended samples. However, no new phases were detected by both the methods. It was concluded that zeolite and/or iron oxide enriched compost can be used effectively for immobilising Cu, Cd and As in the contaminated soils.