Contaminant levels and the use of molecular organic markers to characterise the coastal environment of the Chagos Archipelago

To investigate the extent of contamination and to characterise organic inputs into coastal sediments of the Chagos Archipelago, selected pollutants and molecular organic markers were quantified using capillary gas chromatography (cGC) and cGC-mass spectrometry (cGC-MS). Hydrocarbons present in the sediments were predominantly biogenic from an autochthonous source such as planktonic plants. There was negligible evidence of oil contamination. Ultra-sensitive selective ion monitoring -MS did, however, reveal the presence of some petrogenic and pyrogenic polycyclic aromatic hydrocarbons (PAH) at very low (sub to low ng.g-1 dry sediment) levels. Sterol results confirm that the primary sources of organic materials are planktonic and/or benthic algae but also indicate a small terrigenous input. Coprostanol (5_-cholestan-3_-ol; a sewage pollution indicator) was not detected. Organochlorine analyses (using cGC-electron capture detection) revealed that only some PCB congeners and lindane were above the limits of detection (2-18 pg.g-1 dry sediment). The comparatively volatile nature of the compounds identified probably indicates that atmospheric transport is the major route for introduction of organochlorines to the region. In summary, results from our screening analyses reveal extremely low levels of the selected anthropogenic contaminants and, in comparison with other marine areas, Chagos can be considered as pristine.
Readman J , Tolosa I , Bartocci J , Cattini C , Price Andrew , Jolliffe A .
Hydrocarbons, oil, organochlorines, PCBs, lindane, sterols, pollution, sediments, Indian Ocean