The use of plants for soil remediation at Milford Haven refinery in South Wales

The objectives of this thesis was to investigate if the plant Brassica juncea (Indian mustard) was able to extract more bioavailable toxic metals (principally nickel) from the metal and oil contaminated soil compared to Trifolium repens (Clover) and Lolium perenne (Ryegrass) and to evaluate the effects of agronomic practices (e.g. fertilizer and soil pH) on the metal uptake by the plants. The study was carried out in a pot experiment at the University of Wales, Aberystwyth. The soil used was from Elf Oil Refinery in Milford Haven. There was no significant difference in metal (Zn and Ni) uptake between the three plants species. The average Zn concentration was between 35-67 mg/kg (dry weight) and 10-18 mg/kg (dry weight) of Ni according to Figure 4. The average reduction with nutrients was over 30% in both Zn and Ni concentrations in the plants. Ryegrass indicated a higher response to nutrient treatment and a more uniform uptake of Zn and Ni compared to Indian mustard and Clover. Results show that the concentrations of both Zn and Ni, with high significance (Plandfarm soil. Even if calculations are made with optimal Ni concentration and optimal biomass of Indian mustard the time span of 20 years (the time Elf Oil wanted the soil to be remediated) was too short. Nothing indicated either, if the bioavailable pool of Ni will be replaced of Ni from the unavailable pool after plant uptake or not. Other clean up options which has been described in the literature review have to be considered. Even if this work was not able to give a clear answer about metal uptake of the plants, phytoremediation may still be the viable decontamination method of the refinery soil. The ability of plants to accumulate heavy metals seems to have a great future potential and further research is necessary to validate the possibility to clean the site with phytoremediation.