The thyroid gland.

SIR,-Epidemiological evidence implicates chromium as a possible carcinogen that is responsible for nasal and lung tumours encountered in industries dealing with the extractions of chromium from its ore, with chromium plating or with chromium pigments etc. (for references see International Agency Research Cancer Monographs, 1973; Langard and Norseth, 1975). Yet, when various chromium preparations were tested in experimental animals, the yields of tumours were minimal. When, however, calcium chromate suspended in arachis oil was used, it caused local swelling and irritation and 18 out of 24 rats developed sarcomata at the site of subcutaneous injections (Roe and Carter, 1969). My interpretation of the carcinogenic efficiency of calcium chromate in arachis oil, as compared with the very low activity of chromium preparations in gelatin, trioctanoin etc., is as follows: The triglycerides in arachis oil on hydrolysis, possibly by lipases released from lysosomes of the damaged cells, would yield glycerol and fatty acids, including the polyunsaturated linoleic acid. These substances could on oxidation by the hexavalent chromium (in calcium chromate) yield carcinogenic aldehydes and epoxyaldehydes. The epoxyaldehyde derived from glycerol via acroleine is glycidal (Fig. 1) which is known to be carcinogenic to mice and to rats when tested by the subcutaneous route or by skin application (Van Duuren, 1969). 3,4,5Trimethoxycinnamaldehyde, a derivative of acroleine, is also carcinogenic (Schoental and Gibbard, 1972). There appears to be an interesting