Abstract

Purpose: The Plym Estuary (SW England) has a history of contamination from industrial discharges in its catchment and estuary. The total and labile concentrations of metals Al, Fe and Mn and trace metals Cd, Cu, Ni, Pb and Zn were determined in sediment cores taken from the estuary. The aim was to address the impact of the discharge of metal contaminants on sedimentary contamination and on the tissues of the burrowing organism Hediste diversicolor (O.F. Müller 1776). Methods: Collection of sediments and organisms from the Plym Estuary involved cores of 20 cm depth from four strategic sites, together with samples of H. diversicolor. Cores were sectioned, digested and analysed for total metals. Available metals were recovered using a 1 M HCl and a digest for acid volatile sulphide (AVS) and simultaneously extracted metals (SEM). Total acid digests of H. diversicolor tissues were carried out along with the sedimentary concentrations of metals associated with the enzyme proteinase-K were obtained by protein extraction. Metal contents of digests were analysed by ICP-MS/OES and the total and organic contents of C and N of the sediments were determined combustiometrically. Results: Sediment trace metal concentrations were ordered in the sequence Zn > Cu > Ni > Pb > > Cd and, in some cores, there was a systematic decline of metal concentrations from the sediment surface to the bottom. Metal concentrations at all sites exceeded sediment quality Threshold Effect Levels (TEL) whereas some sites had Cu and Ni concentrations that exceeded their Probable Effect Levels (PEL). Trace metals bound to Proteinase-K had low concentrations. Principal Component Analysis (PCA) involving total metal concentrations, AVS and organic C and N contents of the sediments showed that 78.8% of the variation was explained by the first and second components, whereas the first and third components accounted for 13.8% of the variance. Conclusions: Sediments were contaminated with Cd, Cu, Ni, Pb and Zn all being above their respective TELs and Cu and Ni were above their PELs at some sites. The land-based contaminant sources included intermittent discharges of wastewater from sewage treatment plants and a persistent metal-rich discharge from a waste disposal site. The results identified metal uptake by H. diversicolor which argued for improved management of discharges to the Plym estuary and other estuaries impacted by discharges from sewage treatment plants and/or managed waste disposal sites.