An assessment of the impacts of chronic exposure of copper and zinc on the polychaete Nereis (Alitta) virens using an integrated ecotoxicological approach
Student thesis: Doctoral Thesis
Although copper and zinc are essential metals to aquatic organisms, they can become contaminants and potentially toxic to marine invertebrates due to anthropogenic activities. The king ragworm, Nereis virens is an ecologically and commercially important polychaete species of soft sediment inter-tidal communities found throughout Europe and the northern hemisphere and is exposed to elevated levels of contaminants including metals. However, the impact of longterm exposure of copper and zinc alone and combined has not yet been investigated. In this context, this study aimed to undertake a nine months experiment, sampling every three months, based on environmentally relevant concentrations obtained from a field sampling effort, in combination to a multi-biomarker approach. Using the polychaete N. virens as test species, this multi-biomarker approach revealed the effects of copper and zinc not only at an individual level but also and more importantly at a population level. It is valid to investigate chronic effects of these pollutants as this species readily acclimatises to captive conditions and the endocrine control of growth, maturation and reproduction is already well documented. N. virens were incubated for nine months in environmentally relevant concentrations of copper-spiked sediment, zinc-spiked sediment and copper & zinc combined-spiked sediment. These concentrations were obtained thanks to preliminary field samples of sediment, pore-water and N. virens collected from seven sites along the English Channel coast namely Mylor (Fal Estuary), Saltash, Tamar Estuary), Holes Bay (Poole Harbour), Tipner (Portsmouth Harbour), Broadmarsh (Langstone Harbour) and the Conservancy & Dell quay (Chichester Harbour). Results from these seven sites showed that site-specific metal levels and sediment characteristics were important in determining the bioavailability of metals to worms. Strong correlations were found between copper in the sediment and in the pore water and between zinc in the pore water and in N. virens. Zinc from the pore water was thus more readily available to N. virens than copper. Data also showed that metal concentrations in the worms were lower than those found in other closely related polychaetes, indicating that N. virens may regulate the uptake of metals. Based on data obtained from Holes Bay, Saltash and Mylor, the copper-spiked sediment values ranged from 70 mg kg⁻¹ to 575 mg kg⁻¹, the zinc-spiked sediment values from 200 mg kg⁻¹ to 1160 mg kg⁻¹ and the combination of both were used for the combined treatments. A range of endpoints were then used allowing the study of behavioural, biochemical, cellular and genetic changes over time. As high variability in responses were observed over time, this study revealed the complexity of interpreting metal toxicity. Overall, high copper and high copper & zinc combined treatments showed the most damages with hypoactivity, increase of metallothionein concentrations, inhibition of acetylcholinesterase activity, decrease in cell viability and increase of DNA damage. However, no significant correlations were obtained for acetylcholinesterase activity suggesting that this biomarker is not adequate when considering metal toxicity to N. virens. In addition, the effects of metals on energy reserves were difficult to evaluate as no clear trends were observed. Moreover, seasonal fluctuations and reproduction that occurred during the long-term experiment have proven to be important factors while investigating long-term effects of metals on N. virens. However, the results obtained in this study suggested that N. virens is tolerant to copper and zinc pollution through the activation of detoxification processes as defence mechanisms leading to the possibility of metal adaptation at a population level. For the first time, this study revealed that not only high levels of copper were toxic to N. virens but also that the combination of high copper & zinc treatment was highly and even more toxic to these worms. BioAccumulation Ratios showed that the competition for the uptake between copper and zinc varied over time and was dependent on metal concentrations. In addition, the evaluation of the Biomarker Response Index revealed 1. that the combined, high copper & zinc treatment, was the most toxic to the worms and 2. that DNA damage, metallothioneins and weight were the most sensitive and reliable endpoints used to evaluate copper and zinc toxicity.
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