Legacy Trends In Heavy Metal Pollution In a Saltmarsh Sediment Profile In The Clyde Estuary, Scotland, United Kingdom.

The Clyde estuary, in west central Scotland, received large inputs of heavy metal pollutants from the start of the industrial revolution (~ 1800) until the mid 20th century. A saltmarsh sediment core from a position on the lower estuary was analysed in an attempt to establish historical trends of heavy metal pollution. A core, (length 1 m), was sectioned into 5cm intervals, and analysed for organic carbon and heavy metals, ²¹⁰Pb and ¹³⁷Cs were also analysed in an attempt to establish a chronology for the core. Unsupported ²¹⁰Pb was detected only in the top (0-5 cm) sample while ¹³⁷Cs exhibited a peak in the 5 – 10 cm section. The specific activity of ¹³⁷Cs decreased rapidly below 15 cm but low levels persisted to a depth of 95 cm indicative of downward diffusive migration. It was not possible to derive a chronology from the radionuclide data but the results indicated that recently deposited (< 60 y old) sediment was confined to the top ~ 15 cm. High levels of pollutant metals (Pb, Cr, Zn and Cu) were observed throughout the core suggesting that the sediment was deposited ~ post 1800 but with clear evidence of much lower concentrations in the sediment deposited within the last ~ 60 years except for Pb. Organic carbon content ranged from 9.4 – 14.0%, peaking in the 5-15 cm surface layer, with Pb being positively correlated with this trend.  The metal profiles do not correspond to any obvious trends of industrial activity or sludge dumping and are similar for all contaminant metals except for the 5-10cm peak in Pb. This Pb peak may represent the input of petrol Pb or organically-bound Pb.  The positive impact of legislation to protect the environment from heavy metal pollution is clearly observed in this core alongside the historical industrial burden.

Keywords: industrial contamination, saltmarsh sediment, heavy metals, Pb, radionuclide chronologies