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Environ Monit Assess (2008) 136:227238 DOI 10.1007/s10661-007-9678-2
Assessment of heavy metal enrichment factorsand the degree of contamination in marine sediments from Tamaki Estuary, Auckland, New Zealand
G. M. S. Abrahim & R. J. Parker
Received: 22 October 2006 /Accepted: 23 February 2007 / Published online: 17 March 2007 # Springer Science + Business Media B.V. 2007
Abstract Eight sediment cores recovered from Tamaki Estuary were analysed for Cu, Pb, Zn, and Cd using downward cored sub-samples. The results indicate a significant upward enrichment in heavy metals with the highest concentrations found in the uppermost 010 cm layer. Assessment of heavy metal pollution in marine sediments requires knowledge of pre-anthropogenic metal concentrations to act as a reference against which measured values can be compared. Pristine values for the cored sediments were determined from flat baseline metal trends evident in lower core samples. Various methods for calculating metal enrichment and contamination factors are reviewed in detail and a modified and more robust version of the procedure for calculating the degree of contamination is proposed. The revised procedure allows the incorporation of a flexible range of pollutants, including various organic species, and the degree of contamination is expressed as an average ratio rather than an absolute summation number. Comparative data for normalized enrichment factors and the modified degree of contamination show that Tamaki Estuary sediments have suffered significant systematic heavy metal contamination following catch-
ment urbanization. Compared to baseline values the uppermost sediment layers show four-fold enrichment averaged across eight cores and four analysed metals.
Keywords Heavy metals . Enrichment factor . Degree of contamination . Sediments pollution . Tamaki Estuary. Auckland . New Zealand
Introduction
In the study of contaminated samples, the determination of the extent or degree of pollution by a given heavy metal requires that the pollutant metal concentration be compared with an unpolluted reference material. Such reference material should be an unpolluted or pristine substance that is comparable with the studied samples. The reference material then would represent a benchmark to which the metal concentrations in the polluted samples are compared and measured. Pollution, in this case, will be measured as the amount (or ratio) of the sample metal enrichment above the concentrations present in the reference material.
In assessing the impact of heavy...