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The term "dioxin" (or "dioxins") is a very loose one, referring to a family of complex but related chlorinated compounds with similar structures and biological activity. They are often denoted with a quick molecular sketch that looks like a series of numbers hovering around a piece of chicken wire. The family includes 210 different polychlorinated dibenzo-para-dioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs). The famously destructive PCBs, or polychlorinated biphenyls, are also related. Out of the three groups, there is a subset of 29 compounds that have been identified as having varying levels of "dioxin-like" toxicity. The dioxin TCDD tops the charts and is the most lethal human made poison next to radioactive waste. Tiny, tiny amounts can wreak havoc in biological systems.

The health effects associated with dioxins are similar to those for PCBs. They act on the chemical messengers of the body, are passed on through the generations, and include reproductive effects from low sperm count to endometriosis. Other health effects include hyperactivity; allergies, immune and endocrine system malfunctions; diabetes; low birth weight, poor motor co-ordination, and lower IQ for children.

The International Agency for Research on Cancer classifies dioxin as a human carcinogen. It is recognized as a tumour promoter along with other roles in modifying and disrupting growth functions.

Dioxins are products of combustion and other industrial processes. They are released at ground level from burning wood for residential heat, from backyard burning, and from land clearing burning. Extremely high levels are released right where people live and breath during the unnecessary and illegal practice of residential backyard garbage burning.

Coastal BC pulp mills are some of the largest producers of dioxins in the country. This is due to the practice of feeding boilers wood waste that has been transported by salt water. Chloride from the salt-laden wood forms toxic organo-chlorine pollution at certain temperatures, including dioxin formation.

Most of the dioxins formed in this way at the Catalyst Port Alberni mill are captured in the electrostatic precipitators. Ash from the precipitators is deposited in Catalyst Landfill, just off Franklin River Road, on the slopes of Mount Hankin.

Some dioxins escape the mill stack into the air, especially during start-up, shut-down and other boiler combustion upset conditions. Tests for how much dioxin escapes into the air are done once a year. Figures from that testing are used to estimate annual dioxin emissions.

According to the pulp and paper research arm, known as PAPRICAN (Pulp and Paper Research Institute of Canada), results from this kind of testing have been widely variable from test to test, year to year, and mill to mill. Here is a quotation from the 2003 Executive Summary of their research entitled, "Investigations into the Variability and Control of Dioxins Formation and Emissions from Coastal Power Boilers":
"The results from single tests on any of the coastal power boilers vary by a factor between 4 and 45 and four of the 8 mills have measured emissions in the last three years that exceed the Canada Wide Standards for existing facilities (0.5 ng TEQ/m3 @11% O2)."

Catalyst has engaged a number of initiatives to improve combustion efficiencies and decrease dioxin emissions. In 2011, under the Green Transfer Program, the company was awarded $18 million credits for the burning of black sludge. Port Alberni Catalyst applied to use $4.5 million of that for improvements to boiler efficiencies including upgrades to secondary combustion air. It is expected that the changes will lead to a reduction in dioxin formation and emissions.