Determination of cadmium, zinc, copper, chromium and arsenic in crude oil cargoes

One of the sources of trace heavy metal elements in air is emission by the oil industry, either directly through stack emissions from refineries or indirectly from emissions of combustion of hydrocarbons. Emission estimates are based mainly on the trace metal content of the crude oil processed. From a literature study carried out at the beginning of the 1990s it became clear that data on the trace metal content of crudes were scarce and showed a very large scatter. For this reason a measurement programme to assess the occurrence and concentrations of a number of trace metals, i.e. Cadmium (Cd), Zinc (Zn), Copper (Cu), Chromium (Cr), and arsenic (As), in crudes which are regularly processed in the Netherlands, was set up. By drafting strict sampling protocols and by constructing a special sampling device, as many as possible of the additional contamination sources were avoided. The study suggests that sample contamination may explain a significant amount of the scatter and some of the high concentrations reported in the literature for certain metals. The measured variation in the concentrations of Cd, Zn, and Cu is thought to be due to associated water and/or sediment particles from the producing wells or that picked up during transport. The greater consistency in our measurements for Cr and As suggests that these metals are predominantly associated with the hydrocarbon matrix. Based on the results of this work, it can be concluded that emissions of Cd, Zn, Cu, Cr, and As by the oil industry in the Netherlands are most probably significantly lower than hitherto assumed.