| With the rapid development of coastal industrial and agricultural economy, the estuaries, bays and coastal waters are often contaminated by heavy metals transported from rivers into the sea. Because of their environmental persistence, heavy metals could be harmful to eco-physiology of marine life and even cause death when accumulating to a certain concentration. Therefore, it is necessary to monitor heavy metal pollution in seawater and carry out ecological risk assessment.Metallothioneins (MTs) and oxidative stress indicators are two kinds of biomarkers which are commonly used in monitoring heavy metal toxicity. However, biomarkers of the same kind in different species respond differently to the same pollution are quite different. Therefore, selecting appropriate biomarkers according to species are necessary for heavy metals monitoring. Ruditapes philippinarum, an indicator organism of heavy metals in seawater, are widely distributed in marine benthic environment. However, the temperature, salinity, pH, and DO levels vary considerably in different seawater environments. It will be difficult to interpret and analyze the results of biomarker if these environmental factors fluctuations could cause direct or indirect interferences on the biomarker level.Using Ruditapes philippinarum and lead(Ⅱ),copper(Ⅱ) as a representative of bivalves and heavy metals respectively in seawater, the aim of this work was to study the response of metallothioneins (MTs) and oxidative stress indicators in Ruditapes Philippinarum including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase(GPx), reduced glutathione (GSH), oxidized glutathione (GSSG) and glutathione-S-transferase(GST), when exposed to trace lead(Ⅱ) and copper(Ⅱ) for 7 days under controlled laboratory conditions, and then select appropriate biomarkers according to sensitivity and correlation analysis to indicate the heavy metal levels in marine. On this basis, the influences of seawater temperature, salinity, pH and hypoxia conditions on sensitive biomarkers were further studied, in order to identify the main interference factors in marine biological monitoring of heavy metals and provide the technical basis for appling these biomarkers to monitoring heavy metals in seawater. The main conclusions are listed as follows: (1) The trends of 7 biomarkers in gills and viscera of Ruditapes philippinarum showed that all the other biomarkers had the greatest degree of induction after 5 days exposure to low concentration lead(Ⅱ) (0.1~100μg/L) in seawater except MTs, CAT . Due to the significant correlations between the induction levels of SOD, GSH, GST and GSSG in viscera and the lead concentrations in seawater, these indicators could be used as the best representative biomarkers in indicating trace lead pollution. The antioxidant defense system in calms played an important role in against the lead(Ⅱ) invasion .There were significant functional synergies between SOD and GST, GSSG in gills, as well as SOD and GPx in viscera.(2) The trends of 7 biomarkers in gills and viscera of Ruditapes philippinarum showed that all the other biomarkers had the greatest changing rates after 3 days exposure to low concentrationcopper(Ⅱ) (5~80μg/L) in seawater except MTs. A significant negative correlation was found between the induction level of GST in gills and the concentration of copper(Ⅱ). As a result, GST in gills could be used as the best representative biomarker in indicating trace copper pollution. The antioxidant defense system in calms played an important role in against the copper(Ⅱ) invasion and there were significant functional synergies between GST, GSH and GSSG were also observed..(3) The marine environment factors had some influences on biomarkers of clams in indicating heavy metal pollutions. Among the four environmental factors, temperature and hypoxia could cause more significant effects to sensitive biomarkers (P<0.05) , so it need to pay great attention when appling these biomarkers to monitoring heavy metals in seawater. In the temperature range of 8 ~ 23℃, the level of SOD, GSH and GST were all induced gradually along with the temperature increasing and reached the highest value when temperature was up to 23℃. Hypoxia (DO 1.5mg/L) increased the activity of SOD and decreased the content of GSH in viscera, and also enhanced the induction of GSSG when exposed to lead(Ⅱ). There were not significantly change of SOD and GST in viscera when the variation range of salinity was between 12 and 28. The content of GSH, GSSG maintained stability in the salinity range of 20~32 and 28~32 respectively. It had no significant change of SOD activity in the pH range of 7.0~9.0. When pH fluctuated from 7.5 to 9.0, all the levels of GSH, GSSG and GST did not significantly change. |
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