Trace metal content of a herring oil at various stages of pilot-plant refining and partial hydrogenation

Samples of a typical Atlantic herring oil at various stages of pilot-plant processing were analyzed for cadmium, selenium, arsenic, mercury, copper, lead, and zinc. The FAO/WHO Codex Alimentarius requirements for low levels of specific metals in edible oils were always difficult to meet completely in either a washed and bleached oil or in two lots of oil processed from one crude oil by the additional steps of partial hydrogenation and deodorization. The mercury content of the crude oil was relatively low and was not greatly affected by processing. The selenium level of 47 ppb in the crude oil was significantly lowered by hydrogenation and deodorization. Arsenic was removed by alkali refining. The lead content was reduced by only 40% upon refining, probably because lead was present as an organometallic material. The concentration of the other heavy elements was generally lowered during processing.