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Seasonal Variation in Bivalve Antioxidant Enzymes: Can they be used as indicators of heavy metal contamination?

Seasonal variations in the activity of several enzymes (glutathione reductase (GR), glutathione S-transferase (GST), and glutathione peroxidase (GPx)) involved in the glutathione cellular defence system were measured in whole tissues of the common New Zealand cockle (Austrovenus stutchburyi) as biomarkers of oxidative stress. Three sites (Glendowie, Panmure, and Tiraumea) were sampled in Tamaki Estuary, Auckland, New Zealand, that represented a heavy metal contamination gradient. These sites were selected as metal contaminants can affect the activity of antioxidant enzymes by increasing the formation of reactive oxygen species, therefore these enzymes have been proposed as biomarkers of diminished health. Cockles from the three sites were expected to show differences in enzyme activities due to the gradient in metal levels. Sites were sampled monthly over a thirteen month period, from April 2007 - April 2008. Environmental co-variables (sediment silt-clay fraction, organic matter content, chlorophyll a, median grain size, cockle condition index, water temperature and salinity) were also measured in order to relate biomarker activities to them. From these measures it was established that a gradient existed in sediment properties, water parameters, and condition index, among the three study sites. Condition index significantly correlated with both GPx (r = 0.761) and GST (r = 0.721) activity, therefore condition index provides a good measure of overall health. The silt-clay fraction of the sediment also showed a significant negative correlation with both GPx (r = -0.558) and GST (r = -0.498). GPx was the only enzyme to have significant correlations with metal concentrations including, Pb sediment concentration (r = -0.561), Cu sediment concentration (r = -0.539) and Cu tissue concentration (r = -0.530). Therefore this enzyme showed the most promise as a biomarker of contamination. The highest GPx and GST activities were measured in cockles from Glendowie, this site was characterised by lower concentrations of metals. There was seasonality observed in the activity of GPx and GST. The activity of these enzymes greatly increased from January onwards, and remained elevated for the remainder of the sampling period (until April 2008) this increase however, was more pronounced at Glendowie. The increase in enzyme activity in January could have been the result of a number of reasons including 1) changes in the cockles metabolic status due to gonadal development and spawning 2) a combination of environmental co-variables not measured in this study, or 3) a recovery from a stress event that occurred prior to sampling. Both GST and GPx showed promise as biomarkers of contamination; however GR did not as there were little differences in enzyme activities among sites. Further annual sampling at these sites should be carried out to determine if the increased GST and GPx activities in summer were the result of an abnormal event or a typical seasonal variation that occurs annually.
Type of thesis
Gibson, A. C. (2009). Seasonal Variation in Bivalve Antioxidant Enzymes: Can they be used as indicators of heavy metal contamination? (Thesis, Master of Science (MSc)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/3261
The University of Waikato
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