Extraction of heavy metals in Sydney Harbour sediments using 1M HCl and 0.05M EDTA and implications for sediment‐quality guidelines

Abstract

Sixty sediment samples with a wide range of heavy‐metal concentrations and sediment textures were collected from Sydney Harbour. The samples were extracted with 1M HCl, 0.05M EDTA and HClO4/HNO3 and analysed by flame atomic absorption spectrometry for Zn, Pb, Cu and Cd. 1M HCl extracted a large proportion of heavy metals in oxic sediments (60–100%), whereas the extractability of metals with 0.05M EDTA was generally lower (by ∼20%). Extractability was unrelated to the level of contamination or to sediment texture. The extractability of Cu in anoxic sediments was substantially lower with 1M HCl (∼20%) and 0.05M EDTA (∼10%) than with HClO4/HNO3. The extractability of Pb with 0.05M EDTA was also reduced in anoxic sediments (to ∼70%). The use of weak extractants, in particular 1M HCl, is recommended by the recently introduced ANZECC and ARMCANZ interim sediment‐quality guidelines. These extractants are believed to provide a better measure of the bioavailable metal content than strong acid extractants. In this study, anoxic, sulfidic environments had a major influence on metal extractability with weak extractants. The implication of this is that the number of samples requiring further testing, as stipulated by the guidelines, would be significantly reduced in anoxic sediments.