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This study examines the concentration of metal contaminants in different parts of the Dee Estuary, an estuary located in North Wales and once a site for major industrial activity which likely had considerable environmental impact (Hutchinson, 1994). Similar work has been done in many other estuaries; for example, one study, by Grand and Middleton (1990), which looked at metal contamination of sediments in the Humber Estuary, used “sediments deposited in the Humber approximately 5000 years B.P.” to establish a baseline for metal concentrations. Anthropogenic enrichment was indicated by findings of P, As, Pb, Cu and Zn concentrations “between 3.5 and 6-fold” the baseline. In this study, concentrations are examined for arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). Of critical importance to this study is the test for metal concentration in macroalgae (seaweed) samples, surface sediment samples, and sediment core samples taken from salt marshes.
The use of sediment cores, particularly in the documenting of a timeline of anthropogenic metal contamination, is well established; Fox et al. (1999) obtained sediment cores from marshes in the Mersey Estuary and found, for example, that 137Cs, Hg, and DDT presence in the cores matched historical progress in the regional chemical industry, including “recent regulatory and technological efforts to minimise estuarine contamination and the discontinuation of specific manufacturing and refining processes.” However, the use of biological indicator organisms to examine metal contamination has advantages over the examination of sediments; for example, according to Phillips (1977), sediment testing is complicated by different regions having different sedimentation rates and by the varying amounts of organic matter present in the areas and in the samples. Advantages of sampling organisms include the fact that they allow simple and inexpensive analysis by accumulating and concentrating metals; they also “represent a moving time-averaged value for the relative biological availability of metals at each site studied.” A critical complication in the use of organisms is that they are complex in a way that water and sediments are not – for example, different parts of the organism may have different metal concentrations, or the age of the organism may be a determining factor as well. Phillips concludes that, with these potential confounding factors in mind, macroalgae, such as Fucus vesiculosus, and bivalve molluscs yield the best results...
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