Cancer incidence and mortality in a New Zealand community potentially exposed to 2, 3, 7, 8‐tetrachlorodibenzo‐ p ‐dioxin from 2, 4, 5‐trichlorophenoxyacetic acid manufacture

Objective:To investigate whether the rates of all cancers and four cancers (soft tissue sarcoma, non‐Hodgkin's lymphoma, Hodgkin's disease and chronic lymphocytic leukaemia) associated with dioxin exposure are higher in New Plymouth, the site of a former 2, 4, 5‐T manufacturing plant, than for the rest of New Zealand.Methods:Analysis of 1970–2001 cancer data from the New Zealand Cancer Registry was undertaken for New Plymouth and the rest of New Zealand.Results:There is no evidence of an increased cancer risk apart from one period (1970‐74), which falls partly outside the 1962–1987 manufacturing period if 10‐year latency is assumed. For 1970‐74, there was an elevated risk for all cancer incidence (SIR=111, 95% CI 104–119), and for two of the four specific cancers that are associated with dioxin exposure (non‐Hodgkin's lymphoma SIR=175, 95% CI 121–246 and chronic lymphocytic leukaemia SIR=251, 95% CI 144–408).Conclusions and Implications:The results do not suggest an increased cancer risk among the New Plymouth population related to the period of 2, 4, 5‐T manufacture, although the study's limitations mean the possibility of an undetectable small elevation in cancer risk cannot be excluded. Although TCDD exposure in the first few years of 2, 4, 5‐T manufacture may have contributed to cancer incidence in 1970‐74, unknown exposure(s) before the start of 2, 4, 5‐T manufacture and chance are also possible explanations.