Bioavailability of heavy metals in soils that are in close proximity to mine tailings in Copperbelt, Zambia.
| dc.contributor.author | Kaninga, Belinda.K. | |
| dc.date.accessioned | 2022-10-14T06:46:33Z | |
| dc.date.available | 2022-10-14T06:46:33Z | |
| dc.date.issued | 2022 | |
| dc.description | Thesis | en |
| dc.description.abstract | Mine tailings are a significant source of heavy metal contamination for soils in their proximity. In Zambia’s Copperbelt Province, historical and current mining operations have resulted in large outputs of tailings. Food crops grown on contaminated soils may be a conduit for transfer of heavy metals to the food chain. Current soil assessments of risk are based on total soil concentrations and yet only the bioavailable fractions are potentially taken up by plants. This study aimed to evaluate the effect of lime and manure amendments on the bioavailability of heavy metals in contaminated soils near mine tailings, and their uptake by maize and pumpkin. A field experiment was conducted in an agricultural settlement area around a large mine tailings dam in Kitwe Zambia and a complementary pot experiment with soil from the study area was conducted in the glass house at Zambia Agriculture Research Institute. Plots located within 200 m and others between 300-400 m away from the tailings dam were arranged in a Randomised Complete Block Design. The treatments of i) lime, ii) manure, iii) lime and manure, iv) control with no amendment and replicated four times were assigned to the plots. Lime was applied at 2 ton ha-1 and manure at 5 ton ha-1 at the onset of the study, and data on bioavailable fractions of Cadmium, Copper, Nickel, Lead and Zinc were collected over two cropping seasons (2016-17 and 2017-18). Bioavailable Cd, Cu, Ni, Pb and Zn in the soil were determined by extraction with DTPA and 0.01 M Ca(NO3)2 before, and after soil was amended, and all elemental determinations were done by ICP-MS. Total elemental concentrations in crops were determined by ICP-MS following microwave-assisted acid digestion.. Data were analysed with a linear mixed model to account for non-homogeneity as a result of differences in plots within a field, differences between fields and the hierarchical nature of the study where repeated measurements were taken in the same plots over 2 seasons. For the pot experiment, chinese cabbage was planted as a test crop and data were used for validation of the Windermere Humic Aqueous Model seven (WHAM VII). The soils were highly contaminated with Cu but not Cd, Ni, Pb and Zn. When compared to unamended plots, lime application with/ or without manure reduced bioavailable Cd, Cu, Ni, Pb and Zn. The response to lime was greater in soils with an initially acidic pH than in those with approximately neutral pH values. Manure reduced DTPA extracted Cd but increased Pb. In alkaline conditions manure increased soluble Cu and Pb. On amended soils only the concentration of Cu and Pb in pumpkin v leaves were above the FAO /WHO safe limit. In maize grain all the five heavy metals were below this limit. The accumulation of heavy metals in crops corresponded with the bioavailable fraction of the heavy metals in soil. The soils and subsequently the crops were more highly contaminated with Cu than other elements, therefore only the results of cu were used to validate the model. The best prediction of Cu concentration in the soil solution was with DTPA extracted Cu concentration as an input to WHAM VII. Free ion Cu was the most predominant species at pH below 5. Above pH 5.5, Cu speciation in solution was dominated by colloidal fulvic acid. Fulvic and Humic acids were the dominant solid sorption phases, with humic acids dominating more at pH<6. Iron oxides were dominant at around neutral pH. The model’s prediction of soil solution Cu was overestimated at higher pH and particulate Fe and Al oxides concentrations, and lower particulate humic acid content. The concentration of Cu in the Chinese Cabbage did not corelate with either the measured or the predicted soil solution concentrations. The study adds new understanding of the soil factors driving bioavailability of Cu in tropical soils. These findings can be applied to devising modelling approaches for predicting crop uptake from soils. | en |
| dc.identifier.uri | http://dspace.unza.zm/handle/123456789/7875 | |
| dc.language.iso | en | en |
| dc.publisher | The University of Zambia | en |
| dc.subject | Bioavailability of heavy metals--Contaminated soils. | en |
| dc.subject | Soil contamination--Heavy metal. | en |
| dc.title | Bioavailability of heavy metals in soils that are in close proximity to mine tailings in Copperbelt, Zambia. | en |
| dc.type | Thesis | en |