A preliminary assessment of source, distribution and fate of potentially toxic elements in the upper River Derwent, UK

Sediment is a major repository, and medium for dynamic adsorption and desorption, of potentially toxic elements (PTEs). Hence studies are required to gain insight into factors affecting the transport and fate of PTE in freshwater systems. In the current work, inductively coupled plasma mass spectrometry was used to determine As, Cd, Cr, Cu, Fe, Ni, Mn, Pb, and Zn in five sediment samples collected from the upper River Derwent, following pseudototal digestion with aqua regia and sequential extraction with the revised BCR procedure [1]. Pseudototal element concentrations were: As 22.8-4.34 mg kg-1; Cd 6.92-0.183 mg kg-1; Cr 20.6-7.61 mg kg-1; Cu 41.6-3.36 mg kg-1; Fe 29100-15200 mg kg-1; Mn 2420-656 mg kg-1; Ni 25.1-11.8 mg kg-1; Pb 5840-68.0 mg kg-1; and Zn 1670-91.1 mg kg-1. The high levels of some analytes reflected the influence of historical mining and smelting on the catchment. The fractionation patterns obtained from the BCR sequential extraction indicated that more than 50 % of Cd, Cu, Ni, Pb, and Zn were distributed in the exchangeable, reducible, and oxidisable fractions, signifying anthropogenic sources and relatively high potential mobility for these analytes. Risk assessment values were calculated based on the concentration of each PTE in the exchangeable fraction of the BCR sequential extraction divided by the sum of the fractions (including the residual) [2]. Based on this the risk was estimated as Cd, Mn (very high risk) ˃ Zn (high risk) ˃ Ni, Pb (medium risk) ˃ Cu, As (low risk) ˃ Fe, Cr (no risk). [1] Rauret G, Lopez-Sanchez JF, Sahuquillo A, Rubio R, Davidson C, and Ure A. J. Environ. Monit. 1999) 1: 57 – 61. [2] Oyeyiola OO, Davidson CM, Olayinka KO, and Alo BI. Environ. Monit. Assess (2014) 186: 7321 – 7333.