ICP-MS analysis of trace metals in pacific oysters (Crassostrea gigas) within the port of Saldanha, South Africa

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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: The aim of the study was to monitor the accumulation of the trace metals, Manganese(Mn), Cadnium (Cd), Zinc (Zn), Copper (Cu) and Mercury (Hg) in oysters that were cultivated in Saldanha Bay over the period 2018 until 2020. Eight strategic positions were selected in Saldanha Bay for biomonitoring; three at the oyster growers lease areas in Small Bay, one at the oyster growers lease areas in Big Bay and four close to the Multi-purpose Terminal. At each monitoring station a cohort tower was deployed which contained the oysters used for biomonitoring. At most, ten of these oyster spat were selected and assessed for trace metal content to establish a baseline condition to measure trace metal accumulation. The oysters were analysed for trace metal content over long- and short-term intervals. Long-term monitoring entailed deploying the long-term oyster cohort for a total period of 24 months. After every three months of deployment, the oyster towers were retrieved and a sample of five oysters was selected from the long-term cohort, placed in a labelled plastic bag, and sent for analysis. The short-term monitoring, on the other hand, entailed deploying a fresh oyster cohort every three months over a period of 24 months. After three months of deployment, the oyster tower was retrieved and a fresh batch of oyster tower was replaced in the same sampling point for both long-term and short-term intervals. The samples of both long-term and short-term monitoring were sent to the ICP-MS laboratory, University of Stellenbosch, where tissue was extracted from the oysters, frozen and submitted for trace metal analysis using an Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). It was found that the average concentration of Mn ranges between 1.14 mg/kg and 1.80 mg/kg and Zn ranges between 55.45 mg/kg and 97.90 mg/kg. It was assumed that the anti-fouling products used in the Small Bay influenced the concentration of Cu, which gave high values ranging from 2.18 mg/kg up to 4.49 mg/kg. Concentration of Cd range from 0.75 mg/kg to 1.20 mg/kg and Hg was between 0.00 mg/kg and 0.01 mg/kg. When looking at short-term trends, generally after deployment, oysters recorded an increase in concentrations for the following metals, Mn, and Zn, while Hg, Cu, and Cd recorded a general decrease in concentrations over the same short-term deployments. Not all general trends were omnipresent as spatial and temporal specific variations were observed during the study. This suggested that in some cases trace metal supply intake coupled with seasonal variation could influence the amount of trace metal present in the oyster at any time. The average trace metal concentrations in oysters presented were in a decreasing trend of Zn > Cu > Mn> Cd > Hg. The oyster proved to be good biomonitors due to its ability to accumulate trace metals over time. There were however, oyster mortalities over the period of the study, but these mortalities were related to parasitic infections.
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Thesis (MMil)--Stellenbosch University, 2022.
Trace elements, Pacific oyster (Crassostrea gigas), Biological monitoring, Saldanha Bay (South Africa), Biomonitoring (Toxicology), Inductively Coupled Plasma Mass Spectroscopy ((ICP-MS), UCTD