Coastal Pollution and Potential Biomonitors of Metals in Mauritius

Abstract

Contaminant metals are potentially toxic, accumulate in the sediment, are bioconcentrated by organisms and may cause health problems to humans via the food chain. Discharge of industrial wastewaters and untreated sewage pose a particularly serious threat to the coastal environment of Mauritius, but very little information exists on contaminant metals. This study aimed principally to assess such contamination by (i) reviewing available data, (ii) examining the results of metal (Cd, Cu, Cr, Pb and Zn) analysis in (a) seawater, sediment and biota from an island-wide survey of 20 sites in 1999-2000, (b) seawater from a water quality survey (high tide and low tide) in 2003 of a 10 km stretch of sewage-impacted coast.UNEP reference methods were used for sample collection and processing, and metal analysis was perfomed by flame atomic absorption spectrophotometry (AAS). Results were compared with established guidelines and data reported from elsewhere, and examined for suitable plant and animal species as biomonitors.The pioneering study by SOGETI (1995) provided indications of high marine sediment contamination in Mauritius compared to data reported from elsewhere. The 1999-2000 islandwide survey indicated even higher sediment contamination, namely at hotspots, requiring the use of sediment quality guidelines (SQG) for monitoring and assessment. Maximum metal concentrations from these two studies were as follows: 736 μgg −1 Zn, 329 μgg −1 Mn, 98.1 μgg −1 Pb, 93.38 μgg −1 Cu, 91.39 μgg −1 Cr, 65.53 μgg −1 Sn and 55.01 μgg −1 Cd. Seawater contamination corresponded closely to the pattern of sediment contamination, both showing a downstream and away-from-the-outfall gradient. Applicable guidelines for seawater were exceeded at more than 50% of the sites around Mauritius with maximum concentrations of Cr, Cu, Zn, Pb and Cd as follows: 0.41, 0.352, 0.312, 0.247 and 0.232 mgl −1 , respectively. Maximum concentrations of Cu, Cd, Zn, Pb and Cr along the sewageimpacted shoreline occurred during low tide as follows: 0.454, 0.329, 0.259, 0.138 and 0.123 mgl −1 , respectively. The recommended limits for Cu, Cd and Zn were exceeded in all the samples. High tissue accumulation by marine biota corresponded to high levels of seawater and sediment contamination at hotspots. Species showing the highest potential as biomonitors (namely Ulva lactuca, Enteromorpha ramulosa,Crassostrea cuculatta, Isognomon isognomon and Echinometra mathaei) were identified based on their common occurrence, high bioconcentration potential and successful utilization in studies elsewhere.Enhanced levels of contaminant metals were recorded and suitable biomonitors were identified. It is advocated that a rigorous use of the suite of biomonitors proposed in this study and others later will allow identification of the different metal sources as well as provide an improved assessment of the magnitude of metal contamination in the coastal marine environment of Mauritius.

Long-Term Water Quality Monitoring at an Industrial Site on the Northern Gulf of Aqaba, Red Sea

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Algae of economic importance that accumulate cadmium and lead: a review

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Bioremediation of heavy metals from aquatic environment through microbial processes: A potential role for probiotics?

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