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% Cl 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% Cl 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.