Naturally occurring biochemicals can be degraded and assembled rapidly in living systems by the action of enzymes, which have evolved over millions of years. When organic chemicals persist in the environment and bioaccumulate in animal tissues, it is an indication that the enzymes required to denature them either don’t exist or are extremely inefficient. Examples of this are provided by a number of organo-chlorine compounds.
Until the beginning of this century, the chlorine on our planet existed as inorganic salts, mainly common salt. Since then, a steadily increasing quantity of chlorine gas has been made by the electrolysis of brine. For over a decade, the global production has been around 40,000,000 tonnes per annum (Howard et al, 2000). The original primary motive for this is to use the sodium produced to make caustic soda, a feedstock for many chemical production processes, e.g. soap. However, the chlorine gas is too toxic to be released into the environment, so it has to be ‘tied up’ in a less toxic form.The chlor-alkali industry that has evolved has dealt with this by combining chlorine with carbon, which is available from oil and coal.
There are over 11,000 commercially available organochlorine compounds, including plastics, solvents, paints, floor coverings, pesticides and medicines (Howard et al, 2000). After release into the environment in combustion, biodegradation and other processes, an unknown number of additional carbon-chlorine compounds are formed. When organochlorines become involved in combustion processes, for example incineration of waste or house fires, a large number of products of incomplete combustion are formed. Amongst the most widely known and studied are the dioxins. There are no naturally occurring organochlorine compounds found in the mainstream of the biochemistry of life, for example in any vertebrate animal.
Many organochlorine compounds are persistent and bioaccumulative, because they are fat-soluble and not easily biodegraded. In addition, many are highly toxic, some by design e.g. pesticides such as Lindane and some by misfortune e.g. chemicals such as PCBs. This class of compounds undergoes long-range transport and the process of ‘global distillation’, preferentially condensing in the colder regions.They bio-magnify up the food chain - bio-magnification factors in excess of 20,000,000-fold have been measured between the water of the Great Lakes and top predators (Colborn T et al, 1996). Inuit Indians currently have much higher body burdens of certain organochlorines than most other populations (Kuhnlein et al, 1995). For example, their levels of the pesticide toxaphene are over 3 times higher than the levels in the inhabitants of the regions where it is used.
The body burden of many organo-chlorine compounds increases with age. When women become pregnant, they pass part of their body burden to the baby, initially across the placenta and then subsequently in the breast milk (at about 15% of the body burden per month).
The known adverse effects of dioxin and dioxin-like substances include carcinogenesis and the non-cancer effects include hormone disruption, immuno-suppression and neurobehavioural deficits. Recent research in The Netherlands has shown that at current background body burdens the most highly exposed mothers are producing adverse effects on the development of their children (Koppe et al, 2000). An average 4-point loss of IQ and a 6-fold increase in the incidence of middle ear infections have been described.
Once chlorine is not bound to sodium or some other cation any more it will remain so for centuries. This means that we are steadily increasing the amount of potentially reactive chlorine in the environment. Toxic products like pesticides can be regulated through a ban combined with sound measures of elimination of the stocks. Byproducts like dioxins will always be produced as long as we continue to increase the load of non-permanently fixed chlorine in the environment.
Thus far, legislation for the control of POPs has always been retrospective, after the recognition that a problem has emerged. In general, the introduction of a Tolerable Daily Intake (TDI) has been adopted as a standard for the protection of human health. The actual level adopted has often appeared to be what is politically achievable without much regulatory activity, rather than on genuine health grounds. Thus, when the WHO adopted a TDI for dioxins of 10 pgTEQ/kg body wt/day (10 picogramme Toxic Equivalent per kilogramme body weight per day), it was regarded by many as a perverse decision but it was clearly one which did not require any immediate action by governments. Since then, there has been a degree of backtracking. Based on the recent Dutch breast milk studies, the Dutch Health Council(Sixma, 1996) recommended to the Dutch Government that a TDI of 1 pgTEQ/kg body wt/day be adopted. This would have had immediate political implications, because the average adult daily intake of dioxins in The Netherlands is currently between 2 and 3 pgTEQ/kg body wt/day, over twice the proposed TDI. The WHO then reconsidered its position (Van Leeuven & Younes, 1998) and recommended a TDI of between 1 to 4 pgTEQ/kg body wt/day, with a strong recommendation that it should be 1 pgTEQ/kg body wt/day. This juggling act thus acknowledged the standard proposed by the Dutch Health Council but by allowing the range to extend up to 4 pgTEQ/kg body wt/day, no political action to reduce sources was required.
Is the TDI actually a useful metric to use for the protection of human health with respect to POPs? The answer must be "No". Index levels such as TDIs were developed for non-persistent pollutants, where a reduction in the environmental level is mirrored by an immediate fall in body levels. That is not true of a persistent bioaccumulative pollutant. Additionally, they are based on average age, weight, health and consumption over a lifetime etc and therefore don’t take account of special subsets of the population, such as children.
With POPs which bioaccumulate, the total body burden is the metric of choice, as proposed for dioxins by Dr Linda Birnbaum (1998) of the USEPA. When total body burdens are examined, we find that the average US citizen has about 10 ngTEQ/kg body wt, while about 1% of the population has between 30 to 40 ngTEQ/kg body wt. It is at this latter level that deleterious effects have been observed in experimental situations. The Dutch breast milk study (Koppe et al, 2000), by concentrating on the most vulnerable members of society, infants, supports the notion that there is a proportion of the population which are exposed to dioxins in excess of the no-effect levels and are therefore not protected by the current TDI regulatory system. This carries a completely different political message. Sensible action to protect human health now requires positive action to restrict the release of dioxin and dioxin-like substances and their precursors into the environment. That means the manufacture of less organochlorine compounds. As the chlorine industry constitutes an appreciable proportion of the chemical industry, this poses a big political problem.
The next policy problem is mixtures of chemicals. The polychlorinated dioxins and furans themselves are made up of over 100 different congeners (=slightly different molecules). This is true of many other families of organochlorine compounds such as the PCBs, PCNs, toxaphenes, etc, each of which consist of several hundred congeners. Added to this now is the widespread introduction of polybrominated (Howard and Staats de Yanes, 2001) and polyfluorinated compounds.
It is conservatively estimated that we have in our bodies measurable residues of several hundreds of environmental pollutants. One hundred years ago, few if any of these anthropogenic compounds could have existed and in the past 50 years their levels have been rising inexorably. We simply do not have the toxicological tools to analyse the effects of such a mixture (Howard, 1997). However, the current regulations nearly all require the toxicology to be addressed one chemical at a time. Current regulations demand conclusive proof of harm before a particular chemical has to be removed from the market. Effects have to be massive and/or cause very unusual conditions for them to be identified. More usually, alterations to the pattern of existing diseases, such as cancer, occur. These are very difficult or impossible to elucidate. While it may be possible in time to develop assays for testing the toxicology of complex mixtures, in toto, that will still not indicate which compounds in the mixture are the real problem.
Specifically this means:
Based on these considerations ISDE takes the following position on persistent organic chemicals. ISDE future work one chemicals will be based on this position:
The fundamental principles, which should underpin a sustainable chemicals policy, are:
The international regulatory framework has already started a move from an end of pipe approach in controlling the waste management to an approach banning the production of the most toxic chemicals. This shift should be continued towards a reduction in the production of the precursors of POPs such as Dioxin.
The long term aim has to be a move out of the bulk unsustainable chemical production, as the long term aim in climate policy has to be a move out of the bulk use of fossil fuels. In the short and medium term priorities have to be set considering a balance of factors, with health outcome as the guiding measurement. Health outcome has to be seen in a broad and integrative manner including short and long term environmental health burdens, health benefits of the chemicals application (e.g. water pipes are essential for safe water and sanitation), availability of alternatives, health aspects and risks of these alternatives and to some extent economic consideration. That is a long term approach which can only work with a global agreement avoiding a simple shift of production from one country to another. Therefore a global cap on chemical production should be set and reduced stepwise. This would allow the creation of a production rights trading system which would lead to an internationalisation at least part of the external costs. A global Framework convention would also be the right place to bring current non-binding work on principles on sound management of chemicals as it is done by the Intergovernmental Forum on Chemical Safety, OECD and others into a binding form.
Birnbaum L S (1998). Sensitive non-carcinogenic effects of TCCD in animals. Organohalogen Compounds 38; 291-294, ISBN 91-89192-07-9.
Colborn T, Dumanowski D & Myers J P (1996). Our stolen future. New York: Dutton.
Howard C.V. (1997). 'Synergistic Effects of Chemical Mixtures - Can we rely on Traditional Toxicology?' The Ecologist, 27, 5, September/October 1997, 192-195
Howard C.V., Staats de Yanés G. and Nicolopolou-Stamati P (2000). 'Persistent Organic Chemical Pollution: An Introduction.' In Health Impacts of Waste Management Policies, auth/eds. P Nicolopolou-Stamati, L Hens and C V Howard (Kluwer Academic Publishers, Dordrecht, The Netherlands, 2000, ISBN 0-7923-6362-0) 29-40.
Howard C.V. and Staats de Yanes G. (2001). ‘Endocrine Disrupting Chemicals: A Conceptual Framework’ In Environmental Health Aspects Of Endocrine Disruptors, auth/eds P Nicolopolou-Stamati, L Hens and C V Howard (Kluwer Academic Publishers, Dordrecht, The Netherlands, 2001) 219-250. Accepted for publication in July 2001
Koppe, J.G., ten Tusscher, G., and de Boer, P. (2000) Background exposure to dioxins and PCBs in Europe and the resulting health effects, in P. Nicolopoulou-Stamati, L. Hens, and C.V. Howard (eds) Health Impacts of Waste Management Policies, Kluwer Academic Publishers, Dordrecht, the Netherlands, pp. 135-154.
Kuhnlein H V, Receveur O, Muir D C G, Chan HM & Souieda R. (1995). Arctic Indigenous women consume greater than acceptable levels of organochlorines. Journal of Nutrition 125: 2501-2510.
Sixma JJ (1996). Letter of August 6, 1996 to the Dutch Minister of Health, presenting the report of the Health Council of the Netherlands dioxin assessment, entitled "Dioxins. Polychlorinated dibenzo-p-dioxins, dibenzofurans and dioxin-like polychlorinated biphenyls."
Van Leeuwen F X R & Younes M (1998). WHO revises the Tolerable Daily Intake (TDI) for dioxins. Organohalogen Compounds 38; 295-296, ISBN 91-89192-07-9.
<![if !supportFootnotes]><![endif]> This paper deals with Organochlorides and other halides. Other classes of chemicals such as heavy metals (mercury, lead, arsenic, manganese) are also very health relevant but will be dealt with in the separate forthcoming paper.