New health study eases dioxin concerns

One of the world's largest dioxin exposure studies has found that workers at the former 2,4,5-T manufacturing plant in New Plymouth have blood dioxin levels well below the accepted level of health concern.

The University of Otago study of employees at the Dow AgroSciences (formerly Ivon Watkins-Dow) plant showed that people who worked there between 1969 and 1988 have the same life expectancy as the general population of New Zealand. The study also showed no dioxin-related increase in cancer or other diseases.

Department of Preventive and Social Medicine researcher Dr David McBride says blood samples were taken from 346 former and current workers now living in Taranaki who agreed to participate.

"As expected, many workers directly involved with 2,4,5-T manufacturing had increased dioxin levels*, ranging from 1-100 ppt (parts per trillion) with an average of 10 ppt," Dr McBride says. "But even these levels are well below comparable 2,4,5-T workers in a recent overseas study, where levels ranged up to 176 ppt."

The levels are well below the level of concern recently published by the US Centers for Disease Control (CDC), which reported that increased incidence of cancer in occupationally exposed workers may be associated with dioxin levels of 495 to 31,800 ppt.

Dr McBride says that levels found among people in unexposed jobs, such as those who worked in offices on the site, were generally low by New Zealand and international standards.

"Among the 105 volunteers whose work history indicated no potential for job exposure, the dioxin level found ranged up to 31 ppt and averaged 5 ppt. There were a few people in this group who reported potential dioxin exposure outside the New Plymouth site, such as spraying on a hobby farm.

"Apart from three such individuals, the average in the unexposed group is 4 ppt. This is very consistent with background dioxin levels for the comparable age groups in the New Zealand population," Dr McBride says.

Professor Emeritus at the University of Auckland School of Medicine Sir John Scott – representing the independent expert science panel which advised the study team – says the results were positive, especially for the residents of New Plymouth.

"The scale of this study and the very high participation rate by local people mean that we now have a definitive assessment of dioxin exposure in New Plymouth. The fact that the unexposed group have dioxin levels in line with the rest of New Zealand should be very assuring for the people concerned and the general population of the city."

Dow Chemical Company Chief Epidemiologist Dr Jim Collins was a member of the study team. He says the research showed exposure levels among the local workers were low compared with studies done elsewhere in the world (see table).

Dr Collins says Dow intends updating the study on a regular basis to ensure ongoing monitoring of the health of workers.

* There are many different dioxins. In this context dioxin is commonly used to refer to 2,3,7,8-TCDD, the particular dioxin contaminant found in 2,4,5-T, and its main ingredient, Trichlorophenol.

 

Range of 2,3,7,8-TCDD reported in other studies and estimated time from last exposure to blood draw:

Population and study description	Number of bloods analyzed	Estimated time between last exposure and blood draw in years	Range of 2,3,7,8- TCDD blood serum levels in ppt**
Community release in Seveso, Italy	424	1	2-56,000
Trichlorophenol workers in Hamburg, Germany (Boehringer-Ingelheim Company)	48	5-37	15-300
Trichlorophenol workers in the NIOSH Dioxin Registry, United States	280	15-37	2-3,400
Ranch Hand veterans spraying Agent Orange in Vietnam	147	16-25	<5-313
Trichlorophenol workers in Austria	9	17	98-659
Trichlorophenol workers in The Netherlands	47	18-43	1.9-194
Trichlorophenol workers in Ufa, Russia (Khimprom Company)	34	26-27	35-1,680
Trichlorophenol workers in Ludwigshafen, Germany (BASF Company)	138	20-36	<1-553
Trichlorophenol workers in Midland, US (The Dow Chemical Company)	280	24-63	2-176
Trichlorophenol workers in New Plymouth, New Zealand (Current Study)	239	17-30	1-100

Summary of Findings

Introduction
The Dow Chemical Company commissioned the University of Otago to lead a multi-stage study into mortality and dioxin exposure among workers at the Dow AgroSciences New Plymouth site during the time 2,4,5-T was manufactured there. The study has now been completed and this summary draws from the conclusions of separate papers which will shortly be submitted for publication in a peer-reviewed journal.

The overall conclusion of the research is that, among the workers involved in the study, death from all causes and all cancers is within the normal range expected in New Zealand, and there is no evidence of increased cancer or disease related to dioxin exposure.

The Health Study
The New Plymouth facility (formerly Ivon Watkins-Dow) manufactured the herbicide 2,4,5-T from 1962 to 1988, and the raw material Trichlorophenol (TCP) from 1969 to 1987. The contaminant 2,3,7,8-TCDD (referred to here as dioxin) is associated with the manufacture of these products.

In 1991, the International Association for Research on Cancer (IARC) studied almost 19,000 phenoxy herbicides sprayers and production workers in 10 countries, including New Zealand. A 1997 update concluded that exposure to dioxin may be associated with a small increase in overall cancer risk and in the risk of two specific cancers, soft tissue sarcomas and non-Hodgkins Lymphoma. A study published in 2005 of just the New Zealand workers in the IARC study found no increase in these two cancers, but suggested a small increase in another condition, multiple myeloma.

Given these contradictory findings, and ongoing debate about whether dioxin exposure increases cancer risk, the Otago study was commissioned. The overall purpose of the study was to determine verifiably whether there is any direct association between occupational dioxin exposure and long-term health.

The first phase was a General Mortality Study (GMS) to identify and include all employees who worked at the site between 1969, the first date of complete work records, and 2003, and to follow this group up to 2004 to determine whether they have mortality levels different from the NZ population as a whole.

A total of 1754 employees were followed during the study period and 247 deaths were observed. Life expectancy of this group was similar to the New Zealand population. There was no increase in mortality from cancers overall, and no statistically significant increase in any of the cancers identified as a concern in previous studies. The study did observe more than expected deaths among short-term workers, but this increase was concluded not to be related to exposures at the site.

This phase of the study found no increased risk of deaths among people who had worked at the New Plymouth site.

The second phase of the study was designed to use analysis of blood samples to determine whether workers at the site have blood dioxin above New Zealand background levels and whether these dioxin levels were related to cancer or other disease risk.

A total of 1,599 people were identified who worked at the site between 1969 and 1988, when 2,4,5-T manufacture ceased. Of these, 508 still live in Taranaki and were invited to participate in the blood study. A total of 346 (68%) volunteered to have their blood taken and completed a questionnaire.

Blood was drawn at a clinic in New Plymouth and was analyzed by AsureQuality (formerly AgriQuality) in Wellington. To assure the highest quality control, some samples were also analyzed by an independent laboratory in the United States. The analytical procedures used in the study and the evaluation of dioxin levels were audited by Dr Don Patterson, a recognized world authority in the field.

As expected, many of those most directly involved with handling 2,4,5 -T or TCP had serum dioxin levels greater than New Zealand background. Most of the workers with unexposed jobs had levels consistent with NZ background.

Of the 346 people sampled, 241 were classified as having potential occupational exposure during the time they worked on the New Plymouth site. The serum dioxin levels in this group ranged up to 100 ppt (parts per trillion) and averaged 10 ppt.

Among the 105 volunteers whose work history indicated no potential for job exposure, the dioxin level found ranged up to 31 ppt and averaged 5 ppt. There were three people in this group who appear to have dioxin exposure outside their normal work on the New Plymouth site, such as spraying on a hobby farm. With the exception of these people, the average in the unexposed group is 4 ppt.

While serum dioxin in individuals reduces over time, these levels can be compared with the NZ national serum dioxin evaluation done in 1997 by the Ministry of the Environment. In that study, background dioxin levels for the comparable age groups in the NZ population (50-64 and 65 +) ranged up to 7 ppt with an average of 4 ppt.

For the workers with occupational exposure, there is no published equivalent industrial group in NZ. However, for comparative purposes, a recent overseas study of trichlorophenol workers showed dioxin levels up to 176 ppt. Other reported groups occupationally exposed to 2,4,5-T include BASF workers in Germany (up to 553 ppt), US Ranch Hand Veterans in Vietnam (up to 313 ppt), and the US NIOSH Dioxin Registry (up to 3,300 ppt).

The US Centres for Disease Control (CDC) recently reported that an increased incidence of cancer in occupationally exposed workers may be associated with dioxin levels of 495 to 31,800 ppt.

The third phase of this Otago study took the serum analysis data from the New Plymouth volunteers and used it to estimate the dioxin exposure of the entire worker group of 1,599, including those who did not participate in the blood study and those who were already deceased.

Using blood dioxin sampling, work history records and biological modeling employed in previous research, the study team reconstructed a dioxin profile for each individual in the study. The estimated dioxin levels of the New Plymouth workers were relatively low compared to estimates for other 2,4,5-T workers as reported in overseas studies. This fourth and final phase of this study analyzed all this data to determine whether there is any relationship between level of dioxin exposure and an increased risk of cancer or other diseases.

Of the total of 1,599 workers studied, 1,134 had potential workplace exposure to 2,3,7,8- TCDD dioxin. Among these potentially exposed workers, total deaths were at expected levels compared to the NZ population. 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. There was no increasing trend of cancer or disease with increasing dioxin exposure.

Among the 465 non-exposed workers, life expectancy and death rates fro both cancers and other causes were at expected levels.

In summary, the complete study found that there is no evidence of increased cancer or disease related to dioxin exposure.

Study Personnel
The study team is led by Dr David McBride of the Department of Preventive and Social Medicine at the University of Otago, supported by biostatistician Peter Herbison of Otago.

The study team also includes Dr Jim Collins and Dr Carol Burns from the Department of Epidemiology at the Dow Chemical Company in Midland, Michigan, and Dr Noel Humphry, Dow Medical Director for Asia-Pacific.

The Science Advisory Panel of local and international experts appointed to oversee all major steps of the research comprises Dr. Elizabeth Delzell, Professor of Epidemiology, University of Alabama, USA; Professor Des Gorman, Head of the School of Medicine, Auckland University; Dr. Rhonda Rosengren, Senior Lecturer in Pharmacology and Toxicology, Otago University; Professor Sir John Scott, Emeritus Professor of Medicine at Auckland University and former President of Royal Society of New Zealand; and Dr. Thomas Sorahan, Professor in Occupational Epidemiology, University of Birmingham, UK.

Serum analysis was done by AsureQuality (previously AgriQuality) of Wellington. Expert peer review of the laboratory analysis was provided by Dr Don Patterson of Trium Environmental Solutions, a recognized world expert in the field who recently retired from the US Centres for Disease Control and Prevention (CDC) at Atlanta, Georgia.