Ecological risk from potentially toxic element legacy contamination in sediment from the Forth and Clyde Canal, Scotland, UK

Industrial activities on the banks of waterways can degrade both the waterbody and the surrounding area and continue to exert pressure on the environment even after the closure of the industries involved. An assessment was undertaken to determine concentration, distribution, mobility and ecological risk of potentially toxic elements (PTE) from legacy contamination in sediments of the Forth and Clyde Canal, UK. Concentrations of PTE, determined by ICP-MS following aqua regia digestion, were 5.54–219 mg kg ⁻¹ for As, < 0.025–11.0 mg kg ⁻¹ for Cd, 44.8–883 mg kg ⁻¹ for Cr, 39.3–618 mg kg ⁻¹ for Cu, 35.8–72.1 g kg ⁻¹ for Fe, 720–4460 mg kg ⁻¹ for Mn, 42.0–154 mg kg ⁻¹ for Ni, 93.9–2740 mg kg ⁻¹ for Pb, 5.36–122 mg kg ⁻¹ for Sn and 288–3640 mg kg ⁻¹ for Zn. With the exception of Fe and Mn, higher levels were observed at urban locations than at rural. Enhanced Cr, Pb and Sn content at suburban locations could be attributed to historical industrial activities on the canal bank, while widespread distribution of As and Pb was consistent with atmospheric deposition. In the inner-city area, sediment quality was severely deteriorated, and the potential ecological risk was very high. Fractionation patterns, determined using the modified BCR sequential extraction, indicated a particularly high risk of mobilization for Cd, Mn and Zn, and the highest exchangeable fraction risk from Zn. The research highlights the need to assess and, where necessary, manage legacy contaminated sites in line with the UN 2030 Agenda for Sustainable Development.