Health Canada
www.hc-sc.gc.ca
Common menu bar links
Polychlorinated Dibenzodioxins and Polychlorinated Dibenzofurans - PSL1
Effects on the Ecosystem
Several incidents have focused the public's attention on the dioxin and furan issue. Deaths occurred in exposed animals at Seveso, Italy and in Missouri, USA. Adverse effects on reproduction and malformations in offspring of fish-eating birds have been noted in the Great Lakes and on the West Coast of Canada. It is difficult to determine the full extent to which dioxin and furan contamination affects the environment because of the parallel presence of a large number of other chlorinated organic compounds.
Over the years a number of incidents involving dioxins have focused public attention on these chemicals and on the subject of environmental contamination in general. One of the earliest incidents involved the death of chicken flocks in the United States during the mid-1950s. The causative agent (identified only twelve years later) was hexachloro-dioxin from pentachlorophenol. It had been accidentally added to feed stock from a tallow by-product of (he leather industry. Since that event, there have been many additional incidents, but few have successfully documented specific effects of dioxins and furans alone as their effects are difficult to separate from those of other chemicals in the environment.
Two well-documented incidents took place in Seveso, Italy and Missouri, USA.
Seveso, a small Italian town near Milan, was contaminated by several chemicals, including 2,3,7,8-tetrachlorodibenzodioxin, when a chlorophenol reactor exploded in 1976. While this was only one among many such explosions in the United States and Europe, it differed from the others because the resultant widespread environmental contamination was well documented. Many wildlife deaths, particularly of rabbits, were noted.
The Missouri incident, which occurred in the early 1970s, involved the death of a number of horses at an arena after it had been sprayed with waste oils for dust control. Birds also died and some children became ill. The cause was eventually attributed to 2,3,7,8-tetrachlorodibenzodioxin. The source was waste from the manufacture of 2,4,5-trichlorophenol that had been mixed with PCBs and waste oils. The arena was only one of many areas that was sprayed for dust control. After 10 years, the true dimensions of the Missouri dust spraying incident became clear with the discovery of widespread contamination in the town of Times Beach.50
Great Lakes
During the 1970s, reports of chick edema disease in herring gulls, together with egg failure and birth deformities, were ascribed to dioxin contamination. The incidence of birth anomalies was 100- to 200-fold above the background level for the period 1971 to 1975.51 At that time, levels of 2,3,7,8-tetrachlorodibenzodioxin ranged from 489 to 1996 nanograms per kilogram in Lake Ontario herring gull eggs.
Reproduction rates and the incidence of anomalies returned to normal after 1976.52 By this time levels of 2,3,7,8-tetrachlorodibenzodioxin dropped below 500 nanograms per kilogram in eggs. A cause-effect relationship between 2,3,7,8-tetrachlorodibenzodioxin and reproductive failure could not be established because many other contaminants were also present at very high levels in the eggs and adults.53
West Coast
In 1982, unexpectedly high concentrations of dioxins and furans were found in the eggs of great blue herons in the Eraser River estuary.54 Dioxin levels were also significantly elevated at a colony near a pulp mill at Crofton, British Columbia, that used chlorine in the bleaching process.53 In 1987, heron productivity was normal at three other colonies, while the colony near Crofton failed to produce any young. Mean levels of 2,3,7,8-tetrachlorodibenzodioxin in eggs from the Crofton colony increased threefold from 66 nanograms per kilogram in 1986 to 210 nanograms per kilogram in 1987.
As a result of these studies, as well as recent discoveries of dioxins and furans in pulp mill effluents from plants using chlorine in the bleaching process, a national sampling program was undertaken by the federal government.
Following the first set of results, issued in November 1988, the prawn, shrimp and crab fisheries were closed in the immediate vicinity of the Woodfibre and Port Mellon pulp mills. The crab fishery near the Prince Rupert pulp mill in British Columbia was also closed. Additional commercial shellfish closures took place at seven coastal areas in B.C. in 1989. Furthermore, health advisories were issued by Health and Welfare Canada for some recreational and native shellfish fisheries at nine British Columbia coastal sites as well as for fish species at four British Columbia inland locations and at one Quebec inland location.
