Former workers at a New Plymouth chemical plant have offered a mixed reception to a study that found no evidence of increased cancer or disease related to dioxin exposure.
Neil Herdson, 60, who worked at the herbicide factory from 1977 to 1986 and allowed his blood to be sampled for the study, was not reassured.
Neither he nor Andrew Gibbs accepted that no one who worked at the plant was at risk from dioxins, as the amount in their blood was below the US Centres for Disease Control minimum health risk level – 495 parts-per-trillion (ppt).
Mr Gibbs told The New Zealand Herald blood dioxin levels declined over time, so some workers could have exceeded 495 ppt when they were working at the plant.
But another former worker – Bob Moffat – told the Taranaki Daily News he was pleased with the results. His level was 11 ppt.
“It pretty much confirmed what I’d felt all along,” he said.
Ivon Watkins-Dow chemical plant, now called Dow Agrosciences, made the herbicide 245-T from 1962 to 1987.
The impact of the chemical on workers and the residents of Paritutu has been disputed and the subject of several studies.
The release of a Dow company funded Otago University study of the blood of 346 former workers yesterday continued that trend.
Researchers said the report showed the health of workers involved in the study had not been endangered by working at the plant.
Those who were potentially exposed to the dioxin TCDD had levels in their blood of 10ppt on average, the study found.
Death from all causes and all cancers was within the normal range expected in New Zealand, it said.
Life expectancy of those who worked at the plant between 1962 and 1987 was the same as the rest of New Zealand.
Those whose work history at the plant did not indicate potential exposure had on average 5ppt of dioxins in their blood.
In 1997, an update from a global study by the International Association for Research on Cancer (IARC) said exposure to dioxin may be associated with a small increase in overall cancer risk and in the risk of soft tissue sarcomas and non-Hodgkins lymphoma.
In 2005, an IARC study of just New Zealand workers found no increase in these two cancers, but suggested a small increase in another condition, multiple myeloma.
A total of 1754 employees were followed in the study period and 247 died during the period.
The study observed more than expected deaths among short-term workers, but concluded the increase was not related to exposures at the site.
The study used blood analysis to determine whether workers had blood dioxin levels above most New Zealanders.
Of the 1599 people who worked at the site in the relevant period, 508 still live in Taranaki, 346 volunteered to have their blood taken and completed a questionnaire.
The Otago study took the data from the New Plymouth volunteers and used it to estimate the dioxin exposure of the entire worker group of 1599.
The estimated dioxin levels of the New Plymouth workers were relatively low compared to estimates for other workers as reported in overseas studies.
The study then analysed all the data to determine whether there was a relationship between level of dioxin exposure and an increased risk of cancer or other diseases and found that among potentially exposed workers total deaths were at expected levels.
There were non-statistically significant increases in all cancers combined, non-Hodgkins lymphoma, soft tissue sarcoma, multiple myeloma, and ischemic heart disease, while lung cancer, prostate cancer, and diabetes were less than expected.
The full report will be released by Allen and Clarke Policy and Regulatory Specialists at a public meeting to be held in Taranaki on April 29.
Ministry and Taranaki District Health Board officials will attend the meeting and describe the implementation of the health service and the eligibility assessment process.