Ministry of Health's 2005 dioxin serum study provided scientists with incorrect information.

Paritutu residents may have been misled about the amount of dioxin they were exposed to from the Ivon Watkins-Dow plant during the 1970s.

Evidence has been uncovered showing at least one participant from the Ministry of Health's 2005 dioxin serum study provided scientists with incorrect information.

Dioxin campaigners say this casts further doubts on the study and its conclusions.

Most importantly, they say, it could mean that those who lived in Paritutu in the 1970s were exposed to lower levels of the cancer-causing chemical than previously thought.

However, the ESR scientist who led the study is adamant the new findings do not change any of his original conclusions.

Jeff Fowles' team found evidence of exposure to dioxins for people who lived close to the agrochemical plant between 1962 and 1987.

On average, residents had four times more dioxin in their blood than other New Zealanders, and in some case up to seven times as much.

The latest information shows, however, it may only be those living in Paritutu during the 1960s who had such elevated levels.

The findings come from New Plymouth dioxin campaigner Andrew Gibbs, who was approached by a participant's family with concerns about the study.

They show one of the study's 52 participants had lived in Paritutu for three years during the early 1960s – not just in the 1970s and 80s as listed previously.

Although Mr Gibbs and another independent reviewer, John Leonard, raised concerns about this particular participant before, there has been no proof until now of their allegations.

Mr Gibbs says the new evidence – in the form of legal documents such as title certificates– shows the participant was placed in the wrong residency group and the findings for that post-1969 group of participants is skewed by that inclusion.

The error needed to be corrected, Mr Gibbs said, because that participant had the only significant levels of dioxin exposure of any of the post-1969 participants. "By including that participant in the post-1969 group, the average level of dioxin for those participants was elevated by 40 per cent," Mr Gibbs said. "This proves what we've always said – the main period of exposure was in the 1960s. By skewing this exposure data they have steered away from that critical time," he said. "No one ever checked out this error, even though we pointed it out at least three times before."

Ad Feedback But Dr Fowles says the participant in question had long been known as an anomaly in the results and that had been investigated. "This was taken into account in all analyses we have done since the 2005 report. In fact, we have done all our time-period calculations, and based conclusions with and without [that participant] included," he said.

"This assures that this participant did not critically influence the overall conclusions."

Dr Fowles said any revisions made by participants to their stated residency periods were beyond the research team's control, and were most unfortunate. "I cannot speak for ESR, but I have not seen conclusive evidence of this 1961-1963 residency period, but even if true, it would amount to at most, a minor adjustment to the findings."

He said the participant in question was not the only reason to consider 1970s exposure to be significant. Others living in Paritutu showed some evidence of exposure.

An ESR spokeswoman said the organisation stood by its report because it was accurate based on the content at the time.

The study has already been peer-reviewed twice and minor changes made.

Taranaki Daily News 27/05/2010