Speciation of mercury and tin in marine sediments and biological matrix

Full text: The aim of this study was to investigate for the first time, the distribution of mercury and tin compounds in marine sediments and mussel tissues collected in Bizerte lagoon, Tunisia during two seasons (summer and winter). Butyl-, Phenyl- and octyltin compounds were determined using a rapid speciation method. This analytical procedure is based on one-step simultaneous ethylation/extraction with sodium tetraethylborate in aqueous phase. Gas chromatography interfaced to Pulsed Flame Photometric Detection (GC-PFPD) was used to perform quantitative determination. Analysis of methylmercury MMHg and inorganic mercury Hg2+ was performed by hyphenated system combining ethylation and/or hydride generation on-line with Cryogenic trapping, gas chromatography and atomic fluorescence spectrometry. Validation of methods was performed using a certified sediment and biological reference material. Results of organotin species cannot allow to establish any significant difference between the seasonal levels of contamination. The high values found in the South East of the lagoon and specially in the region of Menzel Bouguiba can be related to the intense industrial activities in this area. The predominance of butyl- and phenyltins comes probably from antifouling paints on boats and piers. Indeed tributyl- and triphenyltins contained in these paints are directly released into the environment. Results show the predominance of butyltin compounds for all stations, and of monosubstituted compounds during summer. Among all the organotins, the trisubstituted ones and specially TBT have quite high concentrations, which are widely due to releasing from antifouling paints, since an important maritime traffic exists in the lagoon. The increasing of mono- and disubstituted compounds is attributed to the biodegradation phenomenon, which conducts to the successive desalkylation or desarylation of all the organotins since the concentrations of monoorganotins are slowly increasing. Organotin contamination of biomass probably limited because concentrations observed in mussel tissues are rather low compared to those found in other coastal living organisms. Results for speciation of mercury suggest that a fraction of the inorganic mercury load in the sediments of the lagoon undergoes methylation pathways. The MMHg produced is assimilated in the mussels more readily than the Hg2+. However, anthropogenic sources of inorganic mercury Hg2+, most probably from metallurgy or tire production industries have been evidenced. One part of Hg2+ is methylated in the sediments and is assimilated by the mussels from the lagoon of Bizerte more readily than do Hg2+. Finally, MMHg contamination of biological organisms is probably limited because concentrations observed in mussels tissues are rather low when compared to other coastal environments. Consequently, for filter-feeding organisms, such as mussels, the concentrations of mercury and tin species determined in the Bizerte Lagoon do not present significant toxicological risk for human consumption. (author)