Metals, arsenic and hydrocarbons monitoring in marine sediment during drilling activities using NAFs

The impact of drilling oil activities using non-aqueous fluids (NAFs) was investigated with respect to Al, Fe, Mn, Ba, Co, Pb, Cu, As, Hg, Cr, Ni, Zn, Cd, V, aliphatic and polynuclear aromatic hydrocarbons concentrations in the sediment. As expected, Ba concentrations were remarkably increased relative to background levels, even 1 year after the drilling activities. High Ba concentrations were due to its massive content in the mud used for drilling. Minor increases of Mn and Fe levels were verified in reference sites (2500 m from the oil well), which were not accounted for by the drilling activities. Cd, Cr, Ni, As, Co, Cu, Pb, V and Zn concentrations were at the background levels. The Al, Ba, Cd, Cr, Cu, Ni and Zn mean concentrations were significantly different (P<0.05) among three sampling operations, while those of As, Cd, Fe and Pb were different according to the distance of the oil well, but independent of the sampling operation. In all samples the Hg concentration was below the detection limit (0.07 μg g–1). With regard to aliphatic hydrocarbons, the results revealed that hydrocarbons C14–C20 (typical hydrocarbons of NAF analyzed) increased slightly in some samples within the 500 m radius; the increase was very low, however, and was considered irrelevant in relation to environmental aspects, although concentrations were even higher for the third sampling operation. Polynuclear aromatic hydrocarbons (16-PAHs) concentration levels in sediments found were very low and not likely to cause effects on the local biota.