RESUMO
The mean and range of concentrations of mercury in crude oil processed by U.S. refineries in 2004 were determined using two analytical methods. One hundred seventy separate crude oil streams were sampled repetitively to obtain 328 individual samples. Samples were retrieved immediately upstream of refinery tank farms. Losses of mercury during production, separation, and transportation were not examined. The arithmetic mean and median of 170 oil streams were 7.3 and 1.5 microg/kg in total mercury, respectively. The total mercury concentration of oil processed in the United States in year 2004, including all species and both dissolved and suspended forms, expressed as a volume-weighted mean was calculated to be 3.5 +/- 0.6 microg/kg. The range of measured concentrations extended from below the analytical detection limit (0.5 microg/kg) to approximately 600 microg/kg. Good agreement was found with other recent and independent studies of mercury in crude oil refined in North America. The total amount of mercury in crude oil processed in the U.S annually is less than five percent of the amount contained in U.S. coal produced annually.