Chlorophenoxyacetic acid herbicides

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Chlorophenoxyacetic acid herbicides: a major class of weed-killers. They were once the most important class of herbicides, but their role has been decreasing. Some of them contained PCDD/Fs, 2,4,5-T in fact contained TCDD at relatively high concentrations during the 1970s. 2,4,5-T gained notorious reputation as an antifoliant agent (Agent Orange) in Vietnam War. It has later been claimed to have caused a number of side effects, including cancer and birth defects. Large epidemiological studies have not been able to substantiate these claims, but doubts have lingered ever since. Also Swedish studies suggested increased cancer rates (soft-tissue sarcomas and non-Hodgkin lymphomas) in forest workers and others using these herbicides. Studies from other countries have not substantiated the high risk levels published in Sweden, but the most recent studies suggest some occupational risk. It is not completely clear whether this would be due to the herbicide itself or to dioxin impurities (for details, see Kogevinas et al., Am. J. Epidemiol. 1997:145:1061-1075, [2]; Tuomisto et al. Int. J. Cancer, 2004:108:893–900, [3]).