Study looking at cancer in New Plymouth
12 December 2005
Ministry releases study looking at cancer in New Plymouth during time of 2,4,5-T manufacture.
A Ministry of Health funded study comparing cancer rates in New Plymouth with the rest of New Zealand for the last three decades provides a level of reassurance about cancers associated with dioxin.
The study found that there was a slight downward trend for the number of people diagnosed with cancer and the number of people who had died as a result of cancer in New Plymouth compared to the rest of New Zealand for the period 1970 to 2001.
It found there was no evidence of an increased cancer risk related to the entire period of 2,4,5-T manufacture from 1962 to 1987, but the possibility of an undetected small elevation in cancer risk could not be excluded.
The study was commissioned in response to community concerns about cancer because there is some evidence that exposure to dioxin can increase cancer risk. The evidence for an increased risk of all cancers combined is stronger than that for any specific cancer but there is an association between exposure to dioxin and four rare cancers, non-Hodgkin?s lymphoma, Hodgkin?s disease, soft tissue sarcoma and chronic lymphocytic leukaemia.
In a study released by the Health Ministry earlier this year, it was found that New Plymouth?s Paritutu residents who had lived very close to the former Ivon Watkins Dow (IWD) agrichemical plant for more than 15 years from 1962 to 1987 were more likely to have higher levels of dioxin than other New Zealanders. IWD manufactured the gorse controlling pesticide 2,4,5-T from 1962 to 1987. The dioxin, 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) is a by-product of that process.
The study looked at the incidence (number of people diagnosed) and death from (mortality) all cancers, as well as the incidence of and mortality from the four rare cancers in New Plymouth compared to the rest of New Zealand from 1970 ? 2001, which includes the period that 2,4,5-T was manufactured in the region (1962-87).
The study found there was a slight downward trend for cancer incidence and mortality as a result of cancer in New Plymouth compared to the rest of New Zealand and there was no evidence of an increased cancer risk related to the entire period of 2,4,5-T manufacture (1962-1987).
Director of Public Health, Mark Jacobs said there was a period from 1970-1974 in which there was a higher rate for all cancers and two of the rare cancers that have been associated with dioxin exposure in New Plymouth compared to the rest of New Zealand.
>From 1970-1974 there was an elevated incidence for all cancers (total number of cases 876, expected number of cases 789; an 11% increase) non-Hodgkin?s lymphoma (total number of cases 33, expected number of cases 19; a 75% increase) and chronic lymphocytic leukaemia (total number of cases 16, expected number of cases 6; a 2.5 fold increase). This was followed in 1975-1979 by an increased death rate for non-Hodgkin?s lymphoma (24 deaths, expected number 15; a 58% increase). There was one time period, 1995-99, when the incidence in New Plymouth was significantly less than expected (total number of cases 1529; expected number of cases 1680; a 9% decrease).
However Dr Jacobs said it was not possible to make any link between the higher rates during that limited period and dioxin exposure.
?Cancer usually takes more than 20 years to develop after an exposure. However there is some evidence that cancer may begin to develop as early as 10 years after dioxin exposure but even then it would put the critical period of exposure partially outside the manufacturing period for 2,4,5-T (1962-1987).?
The authors of the study suggest that chance, unknown exposures or higher levels of fugitive emissions in the early manufacturing period are possible explanations.
Dr Jacobs said the results were reassuring. ?This study suggests that overall New Plymouth residents are not more likely to develop cancer than other New Zealanders.?
The Ministry is working to ensure that the small group of long term exposed Paritutu residents have access to adequate healthcare. The Ministry has allocated some additional funding for this though the services to be provided are still being finalised.
The study is one of two the Ministry has commissioned in response to community concerns. The second, due next year, is reviewing birth defects for New Plymouth compared to the rest of New Zealand.
Two occupational health studies looking at effects and exposure of workers at the plant are also underway, one by Otago University and the other by Massey University?s Centre for Public Health Research.