The effect of sample pre-treatment and speciation of potentially toxic elements in freshwater sediments impacted by historical metal mining

Student thesis: Doctoral Thesis

Abstract

This work involved evaluation of the impact of historical mining operations on potentially toxic elements (PTE) distribution in freshwater sediments from the catchment, of the River Derwent, UK. In parallel, the influence of sample pretreatment on the operational speciation (fractionation) of PTE in sediment with different matrix characteristics was investigated. Freeze, air, and oven drying separately caused less than 9 % changes in PTE fractionation relative to sediment extracted as received, while freeze storage for 12 months was worse (37.5 % changes). Iron was the analyte most prone to changes in fractionation. Sediments rich in iron (hydr)oxides appeared least stable. Harmonisation of sample pre-treatment procedures is recommended to increase results comparability.The study confirmed that the River Derwent remains the main source of PTE contamination in the Derwent Reservoir and that the sediments are significantly enriched in Cd, Pb and Zn. Arsenic, Cd and Pb concentrations in sediments decreased along the length of the reservoir, possibly due to settlement of discrete sand-sized particles, whereas Mn concentration increased probably due to the accumulation of clay-and silt-size particles downstream. Hierarchical cluster analysis revealed three grouping: As, Cd, Cu and Pb (cluster one); Fe, Ni and Zn (cluster two); and Mn (cluster three). The potential mobility and bioavailability of As, Fe, Ni and Zn increased in sediment near the dam compared with the reservoir upstream probably due to weathering. The PTE pollution index was in the heavily- and severely- polluted range and the mean risk assessment code of PTE in the Derwent Reservoir sediments was Cd, Mn (˃ 50 %: very high risk) ˃ Zn (31- 50 %: high risk) ˃ Ni (11- 30 %: medium risk) ˃ As, Cu, Fe and Pb (1- 10 %: low risk). The study shows that historical mining sites are persistent source of PTE in water resources.
Date of Award14 Oct 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorChristine Davidson (Supervisor) & Richard Lord (Supervisor)

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