Statistical comparison between consecutive winter and summer concentrations in zinc and lead from sediments in a tropical urban estuary in Mauritius.

Zn and Pb were quantified using atomic absorption spectrometry from urban and rural estuarine sediments collected along the western coast of Mauritius over three consecutive dry winter and wet summer periods from August 2004 to February 2009. The mean concentrations of Zn (204.0 +/- 92.3 mg kg(-1)) and Pb (44.5 +/- 16.4 mg kg(-1)) in sediments at Sable Noir, an urban estuary, can be considered below those from contaminated estuarine sediments in industrialised countries. Pb significantly decreased from two consecutive winters 2004/2005 to summer 2005/2006 at Sable Noir at 5% significance level due to flash floods in summer and dilution with cleaner background sediments. Pb was however significantly higher at Sable Noir in winter 2004 compared to winter 2005 and significantly increased from summer 2005 to summer 2006 due to a minor diesel spill in the estuary. Both Pb and Zn were significantly higher at Sable Noir in winter 2004 compared to Flic en Flac in winter 2008. Pb and Zn were also significantly higher at Sable Noir in summer 2005 compared to Flic en Flac in summer 2009. The concentrations of Zn and Pb were also significantly positively correlated in the estuarine sediments. The potential common sources of Pb and Zn in the urban estuarine sediments at Sable Noir were considered to arise from road runoff and zinc galvanised road furniture causing significant quantities to be trapped. There is at present a need for long-term studies in the cycling of Pb and Zn in estuarine sediments to integrate coastal zone management strategies.