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The people of New Plymouth and former workers at its Dow weedkiller factory can be reassured that their health has not been endangered by dioxin chemicals at the processing plant, say researchers who have studied more than 1700 employees.
But an ex-employee and residents are sceptical of the findings, released in part yesterday.
Ivon Watkins-Dow, now called Dow AgroSciences, produced the herbicide 2,4,5-T in the suburb of Paritutu from 1962 to 1988. It also produced one of the raw materials, trichlorophenol, from 1969 to 1987.
Many in the local community have expressed serious concerns about the health risks of the dioxins within the plant and which were emitted over the surrounding area. The production of both products is associated with the dioxin TCDD.
Otago University yesterday released some results from a study of Dow employees, funded by the United States-based parent company of the plant.
The study, from blood tests on 346 people, found that workers potentially exposed to TCDD had higher levels of it in their blood. On average they had 10 parts per trillion (ppt) and the maximum was 100 ppt.
It also found that the workers' life expectancy was the same as the general population's and that while potentially exposed workers' death rates from cancer and heart disease appeared higher, the rise was not great enough to be statistically significant.
The study leader, Dr David McBride, of the university's department of preventive and social medicine, said the findings were "good news" for Dow workers and for the people of New Plymouth.
Professor Emeritus Sir John Scott, of Auckland University, who was on the scientific panel which advised the study group, said the large size and high local participation rate helped make the study a "definitive assessment" of dioxin exposure in the city.
"The fact that the unexposed group have dioxin levels in line with the rest of New Zealand should be very [reassuring] for the people concerned."
A summary of the study says the US Centres for Disease Control had reported that an increased incidence of cancer in workers exposed to dioxin might be linked with blood levels of between 495 and 31,800 ppt.
The study appears to be at least partly at odds with one by Massey University's Professor Neil Pearce and colleagues, which found that while working in herbicide production was associated with a "non-significant excess cancer mortality", it was also linked with an increased rate that was statistically significant of one type of cancer, multiple myeloma.
Dow Chemical chief epidemiologist Dr Jim Collins, of Michigan, said the independent Otago study involved more people.
WHAT THE STUDY FOUND
* Dow Chemical funded the study by Otago University, but neither will state the cost.
* 1754 people were followed up who had worked at Dow's factory in Paritutu, New Plymouth.
* 346 had their blood tested for levels of the dioxin TCDD.
* Those who were potentially exposed to dioxin at work had TCDD levels in their blood of 10 parts-per-trillion (ppt) on average, and the maximum was 100 ppt.
* Those whose work history did not indicate potential exposure had on average 5 ppt (and up to 31), but when those exposed elsewhere, such as on a hobby farm, were excluded, the average was 4.
* The New Zealand average in a 1997 Government study was 4 ppt for the same age group, 50-plus.
* A separate study, for the Health Ministry, of residents near the plant found an average of 6.5 ppt, but long-term residents between 1962 and 1987 had an average of 14.6.
* The Otago University study found the Dow workers' life expectancy was no different from the general New Zealand population.
* Potentially exposed workers' death rates from cancers overall and heart disease appeared higher, but not enough to be statistically significant, and their death rates from lung cancer, prostate cancer and diabetes were lower than expected.
Finding fails to convince former staff member
Neil Herdson, a former worker at the Dow herbicide factory, is unconvinced by the findings of the dioxin study for which he allowed his blood to be sampled.
He would not reveal his own blood dioxin level because he wants to focus attention on the wider issues and what he says are the inadequacies of the information releasedyesterday by Otago University.
He said an assertion in the study summary - that in New Zealand there was "no evidence of increased cancer or disease related to dioxin exposure" - was unreliable because the researchers had not asked him about his medical history. All the study could report on was death rates in relation to dioxin exposure, and levels of dioxin inthe blood.
Study leader Dr David McBride later agreed. The summary had incorrectly suggested that health effects had been studied.
Mr Herdson, 60, worked at the plant in Paritutu from 1977 to 1986. He was one of the first workers to have a claim accepted by the Accident Compensation Corporation. ACC said yesterday that seven claims had been accepted and six declined.
"The study is not reassuring," Mr Herdson said.
He and another local campaigner, Andrew Gibbs, said they could not accept the study's assertion that no one who worked at the plant was at risk from dioxins because the maximum blood level found - 100 parts per trillion (ppt) - was below the minimum health-risk level, 495 ppt, stated by the US Centres for Disease Control.
Mr Gibbs said that since blood dioxin levels declined over time, some workers might have had levels higher than 495 ppt when they were working at the plant. The study went back to the 1960s, and this was before the dioxin reduction measures implemented from 1971 to 1973.
He said it was also significant that the average levels reported among workers potentially exposed to dioxins were around one-third lower than those of long-term residents tested for a Ministry of Health study.
Another former worker and former Paritutu resident, Auckland Methodist minister the Rev Brian Peterson, 59, was excluded from the study because he no longer lives in Taranaki. He said his skin rash, prostate cancer, for which he had just finished treatment, and his wife's maternity troubles could all be connected to dioxin exposure.
