Determination and speciation of heavy metals in sediments from the Cumbrian coast, NW England, UK

Abstract

Chromium, manganese, nickel, vanadium and uranium have been determined in inter-tidal sediments collected from locations along the Cumbrian coast. Total concentrations of chromium, nickel and vanadium were determined by electrothermal atomic absorption spectrometry (ETAAS). Manganese was determined by flame AAS and uranium was quantified by alpha particle spectrometry with a surface barrier detector. Two alternative approaches to calibration were investigated in an attempt to obviate the need for routine use of the full standard additions procedure. It was found that the response following a single addition of standard solution, at a concentration 50% of the initial estimate, could be used to correct for the minor interference effects observed. Elevated levels of chromium (39.5 ± 0.9 µg g^–1), vanadium (33.0 ± 0.6 µg g^–1) and uranium (39.0 ± 1.2 Bq kg^–1) were observed at Whitehaven, whilst concentrations of manganese were highest in samples from more northerly locations. The uranium enhancement is due to the extraction of phosphates from ore naturally rich in radionuclides at the nearby Albright and Wilson ‘Marchon’ chemical manufacturing plant. The chromium contamination may also arise from chemical manufacturing, whilst the vanadium is thought to originate from oil spillage. Interferences associated with use of the European Communities Bureau of Reference (BCR) sequential extraction protocol were investigated, and the operationally-defined speciation of chromium, manganese, nickel and vanadium was then determined. Chromium, nickel and vanadium were found mainly in association with the residual sediment phase, except at Whitehaven and Maryport where increases in the oxidizable fractions were apparent. A large proportion of the manganese at all sites was present as exchangeable species, i.e., soluble in 0.11 mol l^–1 acetic acid, and this was not affected by sample drying (at 60 °C) nor by storage (for 6 months) prior to extraction.