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Journal of Cell Science, Vol 10, 15-25, Copyright © 1972 by Company of Biologists
Submitted on June 2, 1971
1 Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, U.S.A.
The conclusion of earlier studies that the pronounced cytological effects of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) formulations are actually due to 2,4,5-T is unwarranted. Inhibition of mitosis and the development of cytological abnormalities are caused by a contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin. The appearance and behaviour of dividing endosperm cells of the African blood lily (Haemanthus katherinae Baker) subjected to a 10-4 M solution of highly purified 2,4,5-T, observed in vitro by phase-contrast microscopy for a 2-h treatment period, did not differ significantly from controls. Subjecting these cells to 0.2 or 1.0 µg/l. dioxin, to 0.2 µg/l. dioxin plus 10-4 M 2,4,5-T (highly purified sample), or to 10-4 M 2,4,5-T containing dioxin as a contaminant caused a dramatic inhibition of mitosis. These preparations also induced formation of dicentric bridges, chromatin fusion with formation of multinuclei or a single large nucleus. Impairment of the functioning of the mitotic apparatus was evident; chromosomes ‘floated free’ in the cytoplasm. Both quantitative and qualitative data substantiate these conclusions.
In view of the extreme toxicity of dioxins to man, of their demonstrated teratogenic effects in some animals under experimental conditions, of their effectiveness in producing cytological effects in dividing cells formerly ascribed to 2,4,5-T of their presence as contaminants in 2,4,5-T, pentachlorophenol, and other polychlorophenols, and of the potential for widespread contamination of the environment with dioxins, investigation of all facets of this class of compounds should be given high priority. It is quite possible that contamination of the environment with dioxins from sources of polychlorophenols is far greater than that contributed by 2,4,5-T. Amplification of dioxin levels in food chains is, of course, of particular concern.
Submitted on June 2, 1971
