November/December 1997
|
|
November/December 1997 |
by Michael Gilbertson
A group of senior policy makers from the United States and Canada concluded that new information provides a reliable scientific basis for undertaking costly actions to stop the injury to human health that is occurring in the Great Lakes basin. The actions include cleaning up harbor sediments, leaking disposal sites and other sources of persistent toxic substances, particularly PCBs (polychlorinated biphenyls).
The senior regulatory officials from health and environmental agencies, along with representatives from industry, environmental groups and academia, were called together by the International Joint Commission's Great Lakes Science Advisory Board on September 5-7, 1997 to assess the policy implications of scientific findings reported earlier this year (see Focus, July/August 1997, pages 3-5).
The policy makers considered the evidence from extensive studies in both the United States and Canada that has brought forth more definitive statements from health officials. In place of previous statements about "potential effects" to human health, the new statements say that effects have been occurring and will continue if nothing further is done to reduce exposure to persistent toxic substances and to decrease the overall presence of these chemicals in the environment.
For example, a recent report by staff of the U.S. Agency for Toxic Substances and Disease Registry states "the weight of evidence based on the findings of wildlife biologists, toxicologists and epidemiologists clearly indicates that populations continue to be exposed to PCBs and other contaminants, and that significant health consequences are associated with these exposures."
The studies found higher levels of PCBs in people who ate Great Lakes fish and developmental deficits and neurological problems in children whose mothers ate PCB-contaminated fish. While these children were not mentally retarded, there were measurable differences depending on the level of PCBs they were exposed to in the womb. As infants, for example, their short term memory was deficient and they were less able to adjust to mildly negative conditions, such as lights or noise. The more highly exposed children did not outgrow such differences and did not perform as well later in school.
The policy makers reached consensus that the new information confirms evidence that has been accumulating for more than 10 years that chemicals in the Great Lakes are causing effects on the development of infants. They also agreed that these findings can be used by regulatory officials as a reliable basis for further actions to clean up the sources and sinks of persistent toxic substances, and particularly PCBs, in the Great Lakes.
Levels of persistent toxic substances reached a peak in the 1970s and declined significantly from 1975 to the early 1980s following bans on production and use of several substances. Since then there has been almost no improvement and many substances continue to enter the water from contaminated sediments in harbor bottoms, leaking landfills and uses outside the basin. A large amount of PCBs also remains in use within the basin.
In the short term, one way to reduce exposure to persistent toxic substances would be to reduce the amount of Great Lakes fish people eat. But the workshop participants were reminded that many people are heavily dependent on Great Lakes fish for their subsistence and would suffer if they stopped eating this source of nutritious food. The new research has shown the extent of Great Lakes fish consumption by members of native groups, the urban poor, sport anglers and commercial fishermen.
In the longer term, the policy makers concluded that the sources and sinks of persistent toxic substances must be cleaned up. A start has been made to prepare plans to restore the most degraded areas, called Areas of Concern, but coming to grips with the large quantities of contaminated sediments in tributaries, harbors and bays is going to be extremely costly. In those Areas of Concern where the investment to clean up the sediments has been made, however, communities are starting to reap returns. For example, businesses are growing and the real estate market has improved along the harbor in Waukegan, Illinois, which has become a more desirable spot for fishing and recreation. Three years after the PCB-contaminated sediments were dredged and treated, the county health department determined that the local fish consumption advisory is no longer needed (See FOCUS, July/August 1997, pages 17-18). Policy makers suggest that restoration plans in several Areas of Concern should be re-evaluated to determine whether human health concerns need to be reconsidered and addressed.
Chemical landfill sites that are leaking persistent toxic substances into rivers, harbors and the lakes pose another challenge. A few of the worst sites, such as the notorious Love Canal situated next to the Niagara River, have been cleaned up. But the sheer scale of these sources and time needed to address them means that a new political commitment to efforts, such as the U.S. Superfund program, will be needed to complete the job. Workshop participants believe the new conclusions by the health authorities might form the basis for this new political commitment.
Draft Lakewide Management Plans currently are being prepared for four of the five Great Lakes to address critical contaminants at the regional level. The International Joint Commission held another workshop on September 18-19, 1997 on the need to incorporate the human health evidence into the Lakewide Management Plans. While little can be done to clean up contaminated fish habitat in deep waters, they will slowly be covered over with cleaner layers of sediments if the cleanup of nearshore contaminated sediments and chemical landfill sites is successful.
Significant amounts of persistent toxic substances also enter the Great Lakes through the atmosphere. In Lake Superior, for example, over 80 percent of PCBs and dioxins may arrive through the air. Since much of this contamination likely comes from sources outside the Great Lakes basin, policy makers see the need to work at the national and international levels to control atmospheric emissions. For example, there is a need for international cooperation to ensure that new PCBs are not manufactured, imported and used, and to verify that existing PCBs are properly taken out of service, and stored and destroyed safely.
If all this work is undertaken, the levels of persistent toxic substances and the associated effects will probably start to decline again, and there will be a need for reliable monitoring programs. Humans are not the best subjects for monitoring trends because human studies are expensive and people are mobile and eat foods from all over the world. Surprisingly, Great Lakes wildlife have become reliable monitors of the levels of persistent toxic substances to which humans are exposed. The health authorities are beginning to appreciate that monitoring the levels and effects of persistent toxic substances in wildlife may be the most reliable sentinel for determining the safety of Great Lakes fish as food for humans.
The cost of the clean-up over the next two decades will probably amount to several billion dollars. Policy makers will continue to face the question of whether the injury to human health is serious enough to warrant this kind of expenditure. In the early 1980s, there was a conscious decision by the governments to curtail further cleanup expenditures in most Great Lakes localities. Because of the large costs, policy makers believe that it may be necessary to estimate the socio-economic benefits that would result from the cleanup efforts.
Sommaire
Un groupe de décideurs de haut niveau des États-Unis et du Canada est arrivé à la conclusion qu'il n'y a plus aucun doute quant à la nécessité de prendre des mesures coûteuses pour mettre fin aux activités nuisibles à la santé humaine dans le bassin des Grands Lacs. Ces mesures d'assainissement visent les sédiments des ports, les fuites dans les sites d'enfouissement et les autres sources de substances toxiques persistantes, surtout de biphényles polychlorés (BPC).
Du 5 au 7 septembre 1997, les cadres supérieurs responsables de la réglementation dans certains organismes de santé et d'environnement ainsi que les représentants des groupes industriels et environnementaux se sont réunis à la demande du Conseil consultatif scientifique des Grands Lacs de la Commission mixte internationale pour évaluer l'incidence, sur les politiques, de certains résultats scientifiques présentés en début d'année (voir Focus, juillet/août 1997, pages 3-5).
Les décideurs ont étudié les résultats d'études approfondies, effectuées tant au Canada qu'aux États-Unis, qui ont amené des énoncés plus fermes de la part des autorités sanitaires. Au lieu d'aborder les « effets possibles » sur la santé humaine comme dans les énoncés antérieurs, on indique que les effets se sont déjà manifestés et qu'ils continueront de le faire si aucune mesure n'est prise pour réduire les substances toxiques persistantes.
Par exemple, un rapport récent de la U.S. Agency for Toxic Substances and Disease Registry indique que « l'ensemble des constatations des biologistes de la faune, des toxicologues et des épidémiologistes montrent clairement que les populations sont toujours exposées à des concentrations de BPC et à d'autres contaminants, et que cela entraîne de sérieuses répercussions pour la santé humaine.
Les études font état de concentrations plus élevées de BPC dans les poissons des Grands Lacs et par conséquent chez les humains qui en consomment. On a signalé également des faiblesses constitutives et des problèmes neurologiques chez les enfants dont les mères avaient consommé du poisson contaminé par les BPC. À court terme, on peut diminuer les effets nuisibles des substances toxiques persistantes en limitant la consommation de poissons des Grands Lacs. À long terme, les décideurs estiment qu'il faut éliminer les sources et les puits de substances toxiques persistantes.
Michael Gilbertson is a biologist with the International Joint Commission. For more information, or a copy of the background document for the September 5-7, 1997 Workshop on the Policy Implications of Evidence Regarding Toxic Substances and Human Health, contact the author at International Joint Commission, 100 Ouellette Avenue, Windsor, ON N9A 6T3, or International Joint Commission, P.O. Box 32869, Detroit, MI 48232-2869. Fax (519)257-6740; email gilbertsonm@ijc.wincom.net(.)
Revised: 24 December 1997
Maintained by Kevin McGunagle,
mcgunaglek@ijc.wincom.net