Determination of cadmium, zinc, copper chromium and arsenic in crude oils

One of the sources of trace heavy metal elements in air are emissions 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 in the beginning of the nineties 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. Cd, Zn, Cu, Cr, and 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, all avoidable contamination sources were excluded as much as possible. From the study it can be concluded that sample contamination explains to a large extent the large scatter and high concentrations reported in literature. Furthermore the results demonstrated that cadmium, zinc, and copper are not indigenous to the crude oil hydrocarbon matrix, but are the result of contamination with associated water and/or sediment particles from the producing wells or picked up during transport. Chromium and probably also arsenic on the other hand are shown to be for the major part 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 then hitherto assumed