Quantifying and Characterizing Metal Concentrations in Derwent Estuary Sediments using Portable X-Ray Fluorescence Spectrometry

The Derwent Estuary is highly enriched in potentially toxic elements such as Zn, Pb, Cu, As, Hg and Cd. This occurred due to inputs from historical industrial activity adjacent to the river, predominantly prior to strict environmental protection procedures introduced in the 1970s. Contaminants are now buried at shallow depths within the sediment profile, in one or two highly concentrated layers decreasing in concentration away from an electrolytic zinc refinery, regarded as the main source of the contaminants. Enriched metals (Zn, Pb, Cu, Cd and As) in the estuary were estimated from data collected from 37 sediment cores using a portable X-ray fluorescence spectrometer, validated against mass spectrometer analyses. The thickness of the metal and metalloid enriched layers ranges from 32.5 cm to 107.5 cm, with an average thickness of 63 cm. Sedimentation rates based on this layer and the time since the start of zinc processing are approximately 0.46 cm/year. Recent trends in sedimentation based on the thickness of sediments since maximum metal and metalloid concentrations produced rates between 0.17 – 1.64 cm/year. Based on these sedimentation rates, the average time it will take for surface sediments to return to background metal and metalloid concentrations is approximately 123 years.