Mercury distribution in continental shelf sediments from two offshore oil fields in southeastern Brazil

摘要

Most anthropogenic environmental impacts on marine areas are limited to protected coastal sites such as bays and estuaries, or semi-enclosed seas (Irion and Muller 1990). It is believed that open continental shelves are hardly affected by land-based pollutants sources. Exceptionally, offshore oil exploration is considered a potential source of pollutants to continental shelf environments both when drilling for prospecting (Rezende et al. 2002) and during oil production and transport (Kennicutt 1995). Whereas hydrocarbons may be released by offshore oil exploration and affect water masses for a varying time depending on their degradability, heavy metals and particularly Hg, that are ubiquitous components of oil industry effluents, are non-degradable and may accumulate in abiotic and biotic compartments reaching potentially toxic concentrations particularly in nearby bottom sediments (Rezende et al. 2002). The large Hg accumulating capacity of fine bottom sediments of continental shelves (Muller et al. 1999) and the low mobility of the benthic communities, maximize exposure and make possible deleterious effects upon the biota potentially affecting economically important open ocean fisheries through food chain transfer and biomagnification (Chapman et al. 1991). Although effects upon shelf biota are difficult to detect and monitor, the importance of shelf resources and the possibility of fisheries contamination by long-lasting contaminants such as Hg call for detailed studies in areas affected by oil exploration (Lacerda et al. 2000; Kennicutt 1995).