Timber workers exposed to dioxins – study


Massey University researchers say some former timber workers exposed to the wood preservative pentachlorophenol (PCP) have twice as much dioxin in their blood as people who lived next door to New Plymouth’s 245-T pesticide plant.

“As cumulative exposure (to PCP) increased, there was also increased prevalence of neuro-psychological symptoms, including memory loss, depression and tiredness,” said lead investigator Dave McLean today.

PCP was often contaminated by some types of dioxin during manufacture and was banned in 1998 for its toxic effects on people.

Dioxins – known to increase the risk of cancer – spread into the environment from the Ivon Watkins-Dow chemical plant, now called Dow Agrosciences, when it was making the herbicide 245-T from 1962 to 1987.

Associate Health Minister Damien O’Connor said this week that the Government acknowledged that people who lived around the plant in the suburb of Paritutu “may potentially have been exposed to harm” from dioxins, and offered them lifetime health checks.

The Health Ministry is reported to be considering whether similar health checks should be offered to timber workers who worked with PCP.

When the researchers compared mortality in sawmill workers exposed to PCP with sawmill workers who weren’t exposed, they found a 40 per cent increase in the risk of death from cancer for PCP-exposed workers.

The researchers also found a 200 to 300 per cent increase in deaths from chronic non-cancerous respiratory disease in PCP-exposed workers – a new discovery which may have been caused by workplace contaminants other than PCP.

About 10 per cent of workers who had relatively high levels of dioxin in their blood worked in the industry for 10 years or more, or did high risk jobs such as cleaning out PCP containers.

Some former dip bath operators or table-hands on the “green chain” at sawmill, or workers who mixed PCP solutions, cleaned sludge from dip tanks and handling timber wet with the fungicide had significantly higher levels of exposure and of serum dioxin levels.

The highest dioxin level recorded in the 2007 study was in a former worker who had the equivalent of 90.2 parts per trillion (PPT)- suggesting it would have been as high as 360 ppt – 720 ppt 20 years ago.

Dr McLean tracked and analysed health information and the work practices of almost 4000 randomly-selected timber workers who worked in the industry before the late 1980s.

The research included interviews and clinical examinations of 293 surviving workers.

“We established that about 10 per cent of the former timber workers had heavy exposure to PCP,” he said today.

These people were three times more likely to have respiratory disease.

People with more PCP exposure also had increased prevalence of a number of other health conditions, including eczema, thyroid disorders, unexplained persistent fevers, recurrent nausea and diarrhoea, heart palpitations and low libido.

Not all of the increased risks were statistically significant because the number of workers with heavy exposure studied was quite small.

He warned that the increased prevalence of memory loss, depression and tiredness was an indicator that there may have been damage to the central nervous system, at a level similar to that of people heavily exposed to solvents.

This was a worry because older people had less ability to compensate for such damage: “We’re measuring sub-clinical changes – but that in people of this age there may be repercussions because they will have reduced capacity to compensate for the effects of ageing”.

A third phase of the study – blood tests for dioxin levels in 71 of the exposed workers and 23 non-exposed workers – were combined with the results of blood tests on 23 members of the Sawmill Workers Against Poisons (SWAP) group.

The exposed workers had much higher dioxin levels than those not exposed, and there was a clear dose-rate relationship: people who mixed the solutions, handled the timber and cleaned the sludge in the dip tank had the highest levels.

The exposed workers had dioxin levels averaging 14 ppt, about the same as those observed in former long-term Paritutu residents, while SWAP members had levels about twice that.

Although PCP was deregistered 1991, it was mistakenly approved again by the Environment Risk Management Authority in 2006 when hazardous substances were transferred to a new regulatory regime, but no formulations of PCP are approved for use in New Zealand.

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