Chlorine and organochlorines in the environment: a perspective.
Chlorine and chlorine-containing compounds continue to be the subject of the type of simpleminded judgement illustrated by George Orwell in his modern parable Animal Farm. In the spirit of that story the argument is: "Chlorine bad, no chlorine good."
If the situation were this simple then chemists, toxicologists, and other scientists would be unnecessary in this debate. The truth of the matter is much less certain, much less simple, and much less comprehensive. The strident demand for the elimination of chlorine and the wholesale banning of all organochlorines from modern society is based on both poor science and poor judgement. In this examination of the question of the ecotoxicological significance of chlorine, and especially chlorine-containing organic chemicals, three main areas will be examined:
* pertinent chemical and toxicological information;
* the general process of making judgements;
* the consequences of judgements made.
This examination could be viewed as a court case; the pro and con arguments can be viewed as the defence and the prosecution. The general nature of the processes employed to make scientific and related judgements is consistent and similar with fundamentals of legalistic judgements. Both decision-making processes are plagued with problems including: determination of a de minimus level, errors in judgement, and risk cost-benefit analysis. In legal terms, the de minimus concept means that the law does not concern itself with trifles, i.e., some transgressions are inconsequential. In toxicology, it has a similar meaning: there is an exposure level below which a risk of an adverse effect is negligible.
It could be said that chlorine and chlorine-containing organic compounds have been accused of being the toxicological equivalent of a gang of mass murderers based on having one or more chlorine molecules in their chemical structure. Although the focus is disinfection of water and waste waters via chlorination, information on various modern general applications of chlorine will be discussed as it has been argued that all, or more recently the vast majority of, uses of chlorine and chlorine-containing compounds should be stopped: "... phase-out the use, export, and import of all organochlorines, elemental chlorine, and chlorinated oxidizing agents (e.g. chlorine dioxide and sodium hypochlorite)." |1~
The seminal statement on toxicology by Paracelsus, considered by many as the founder of toxicology, is often rendered colloquially as "The dose makes the poison." However, the translation from the Latin is most correctly placed in the negative: "Everything is a poison, what is there that is not a poison? Only the dose makes a thing not a poison."
Clearly, toxicologists have a view of toxicity that is inverse (some might say perverse) to that of the public. Lay people consider that chemicals are only toxic at or above a certain dose level and must be "safe" below that level. Toxicologists do not consider anything "safe" in absolute terms, only not producing toxic effects in the circumstances in question.
Thus, every chemical, substance, organism, and process is potentially a toxic agent. Unfortunately, in common usage, chemicals are often classified as those that are toxic and, by implication, those that are nontoxic, irrespective of the circumstances. Rather than using this rigid and misleading dichotomous classification, it would be more useful to employ the risk analysis approach and recognize that "safe" represents a practical, operational human judgement, subject to all the limitations of that process, and as such is clearly not a scientific fact.
The discipline of risk assessment or risk analysis is evolving as the scientific policy framework to guide the scientific judgement process for environmental and human health problems. This process explicitly recognizes that every solution to any problem carries some risk and the solution itself represents another risk. The only sensible objective is to achieve an acceptable balance of risk, benefit, and economic cost. |2~ Carrying out this process is termed risk cost-benefit analysis (RCBA).
Risks to the environment and human health are based on a basic toxicological principle. That principle is that the possibility of occurrence and magnitude of adverse effects increases proportionally to the degree and duration of exposure to the toxic agent and the relative hazard of that toxic agent. This can be presented in the relationship:
exposure X hazard = risk.
Thus, as risk is a product of exposure and hazard, an equivalent degree of risk or toxicity can be the result of either high hazard and low exposure or low hazard and high exposure. Risk management, the technical term for what people do every day in a variety of circumstances, comes down to a few basic approaches to reducing risk. If the exposure can not be altered then substituting a different toxicant with a lower relative hazard will produce a lower risk. Alternatively, if the hazard can not be changed then reducing the exposure will also lower the risk. Where possible, reducing the hazard and decreasing the exposure is a third option.
Finally, risk transference must be considered. For example, decreasing one risk, such as death from cancer, may increase another risk, such as death from heart attack. Pharmacology can be viewed as an exercise in applied risk management. It is well understood that no drug is risk free. In practical terms, there is no such thing as zero hazard: only risk reduction is possible; risk elimination is impossible.
A familiar example may help to illustrate this point. The occasional use of aspirin (ASA, acetylsalicylic acid) at a dose of one to four tablets (|approximately equal to~ 0.3-1 g of ASA) brings relief from headaches and minor pains; consumption of a large number (10-150 g of ASA) of these same tablets may cause death. The difference between beneficial effects and death is related to the size of the exposure dose.
Although ASA does not contain chlorine, many other drugs and pharmaceuticals do. The list of chlorine-containing drugs includes: chloroquine, an important anti-malarial drug; halogenated tetracycline-based antibiotics such as chlortetracycline; and the family of halogenated antipsychotics such as chlorpromazine. A ban on chlorine-containing organics would remove many drugs from the medical arsenal.
Another popular position must be examined in the light of risk assessment and toxicology; zero discharge of chlorine in any form is the prudent decision. Such a concept, although theoretically conceivable, is meaningless in practical terms. Chemical analysis technology cannot reliably detect single molecules in environmental samples, making detection of some violations impossible. If such detection was possible, it is almost certain that any substantial environmental sample would contain at least one molecule of the chemical in question. Thus, moving almost anything in the world from one place to another, effectively "discharging" it, would violate the zero discharge rule.
A more reasonable approach is the current practice of determining a level or dose that is devoid of adverse responses. A guideline level, which is lower than this initial level, is then generated by some means, often by applying a safety factor, to account for sensitive individuals and/or species, uncertainty in the toxicity estimates, presence of other toxic agents, etc. This process is not perfect but many consider it to be reasonable, logical, and flexible.
Chlorine versus the environment
Chlorine and organochlorines have been accused of many sins. Brief versions of some of the major charges made and responses to them follow. A specific discussion of water disinfection via chlorination is the final argument.
1. Chlorine is "artificial."
Chlorine is an element, one of the basic building blocks of the universe. It exists in several states and in various combinations with other elements, like most other elements. For example, iron in its pure metallic state is rare in nature, while iron oxide is common, due to the proclivity of that reactive relative of chlorine, oxygen. Iron is not considered to be "artificial" because it is usually present as iron oxide rather than the pure metal.
2. Organochlorines are "unnatural" and are not found naturally in animals.
Over 1500 halogenated (chlorine, bromine, iodine) organics are found naturally in living organisms, ranging from bacteria to mammals. |3~ Many of these compounds are relatively low molecular weight compounds, but complex, relatively high molecular weight chlorinated organics also occur naturally in the environment. They are often measured as the general parameter of adsorbable organically-bound halogens (AOX). This simply represents a measure of organic matter that is associated with chlorine or other halogens.
The exact composition of AOX varies depending on the source. Anthropogenic sources include chlorinated sewage effluents and pulp and paper mill effluents, while natural sources, which have been reported to have AOX levels as high as some effluents, include bogs and rivers that are supplied by natural microbial breakdown of plant material.
3. Chloromethane, from marine bacteria and fungi, is the only significant naturally occurring organochlorine.
Millions of tons of organochlorines are produced yearly by natural biological and chemical processes. It has been reported |3~ that the global production from natural sources of the chlorinated organic chemical chloroform (trichloromethane) is of the order of millions of tons per year. The bulk of the 2,4,6-trichlorophenol found throughout the world is thought to be from ocean and soil production, not from anthropogenic sources. There are additional examples that can be seen by an examination of his publication.
4. All organochlorines are "persistent" and "bioaccumulative".
Although there can be many definitions of these terms, the following are generally accepted for regulatory purposes. Persistent is often defined as having a half-life of presence in the environment of greater than eight weeks and bioaccumulative is often defined as accumulating to body residues of greater than 1,000 times the environmental level in water or having a log octanol-water partition coefficient (log Kow) of greater than 4.0.
Presence in chlorinated water or sewage effluent is not firm evidence for creation by chlorination; many chlorinated organic chemicals are used in various industrial and domestic uses. The major byproducts of water and wastewater chlorination include:
* Monochloramines and organic chloramines;
* Trihalomethanes (chloroform, bromoform);
* Chlorinated aliphatics (chloroethanes, chloropropanes, chloropropanones);
* Chlorinated aromatics (chlorophenols, chlorobenzenes);
* Chlorinated acetic acids.
The types and amounts of chemicals produced vary depending on whether chlorine, chlorine dioxide, or chloroamines are used in the treatment, whether drinking water or sewage effluent is being treated, and whether the water is fresh or salt. However, in all cases, the concentrations produced are very low. Furthermore, as these chemicals are relatively volatile, of low molecular weight, and readily degraded by natural physical, chemical, and biological processes, they do not meet the criteria to be considered persistent or bioaccumulative.
5. All organochlorines are equally "bad" in a toxicological sense and all should be banned.
There are many beneficial uses of chlorine and organochlorines. Probably the most significant direct use of chlorine is in drinking water disinfection. This use alone has saved many millions of human lives and is considered one of the greatest advances ever made in human health and hygiene. |4~
Disinfection of raw sewage and treated sewage effluent is a vital component of human and environmental health protection by reducing potential effects from this natural disease pathway. It is rare that sewage is not dumped into water courses used for various consumption purposes or where humans and other animals can be exposed, and disinfection by chlorination serves an important role in health protection.
Despite considerable research effort there is no evidence that alternative processes such as ozonation or UV light treatment are risk-free and are substantially more effective and/or more economical than chlorination, the most effective and cost-efficient disinfection method known. This specific use of chlorine and chlorinated organics represents the most direct and pressing RCBA problem extant. 6. Organochlorines are more toxic than non-chlorinated organics.
Toxicity is a very broad term that covers a multitude of modes and mechanisms of toxic action, which may act alone or in concert, as well as a variety of endpoints, ranging from systemic toxicity to cancer, not all of which are initially lethal. Although there are often trends in many chemical and physical parameters within chemical groups, the biological and toxicological trends are much less certain in groups that are defined by chemical properties. The presence of chlorine in a molecular structure neither can be uniquely linked to various types of systemic toxicity nor, as will be seen later, carcinogenicity. Some examples illustrate that the presence or absence of chlorine guarantees neither mechanism of action nor potency.
* Botulinus toxin, non-chlorinated bacterial proteins, is very toxic.
LD50 - 0.00001 mg/kg IV in rat
* 2,3,7,8-TCDD (dioxin), a chlorinated organic, is very toxic.
LD50 - 0.001 mg/kg IV in guinea pig
* Ethanol, a nonchlorinated organic, is relatively non-toxic.
impaired at about 0.1% in blood (|approximately equal to~ 70 mg for 70 kg human)
* Chlorobutanol, a chlorinated organic, is relatively nontoxic.
Human drug, oral hypnotic dose of 300-1000 mg
7. Organochlorines are particularly dangerous especially with regard to carcinogenicity.
It has been suggested that human exposure to pesticides is about 1.5 g per day exposure. More than 99% of human exposure is to organic pesticides naturally present in food of plant origin, not modern manufactured pesticides. This is not to diminish the importance of proper care and control of synthetic pesticides, rather it simply serves to provide perspective.
Due to the concern about the possible carcinogenicity of synthetic pesticides, some of which contain chlorine and a few of which may be carcinogenic, it should be instructive to examine the carcinogenic potential of the natural, organic pesticides that form the bulk of human exposure. For example, it has been observed that there is about 10 mg of known rodent carcinogens in every cup of coffee. One of the 16 carcinogens in coffee, hydroquinone, is a known byproduct of water ozonation. Of the pesticides naturally produced by various plants, 27 are known to be carcinogenic to rodents. These natural pesticides are present at concentrations of 10 ppm or greater in: apples, celery, cabbage, dill, grapefruit juice, grapes, honey, potatoes, and many other food items. |5~
No one is suggesting that fruit and vegetables should be banned for human consumption; in fact, just to the contrary, eating these items is a vital part of good nutrition. In risk management terms the benefits far outweigh the drawbacks.
A detailed structure-activity evaluation of rodent and human carcinogens has indicated that the presence of chlorine or another halogen in the molecular structure is not a guarantee of carcinogenic activity. |6~
There are examples where adding chlorine to a structure makes a compound noncarcinogenic and removing it makes it carcinogenic. Benzene is an interesting example as it is a nonchlorinated carcinogen, while many compounds formed by chlorine substitution -- mono-chlorobenzene, pentachlorobenzene, cresol -- are chlorinated noncarcinogens.
As is the case for other chemical groups, a few organochlorines are carcinogenic while many are not. The presence of chlorine in the molecular structure has little predictive power for estimating carcinogenic activity.
8. Disinfection of drinking water and sewage treatment plant effluent by chlorination is an undesirable process due to the organochlorines produced and the resultant human and environmental risks.
Chlorination of wastewater from industrial and sewage treatment facilities has generally proven to be safe, highly effective, and economical. |7~ It has also been demonstrated to be necessary by cases where untreated sewage effluent has caused human diseases, both from recreational use and via consumption of contaminated shellfish. |8~
In contrast to the clearly established benefits noted, there is not a large body of evidence indicating that chlorinated effluents have produced substantial adverse ecological effects solely attributable to chlorination. |9~ The amounts of chlorinated chemicals produced in chlorine disinfection are typically insufficient to produce chlorine-related adverse effects in organisms exposed via most receiving waters.
Furthermore, a recent comprehensive review of chlorination of drinking water and its byproducts by the International Association for Research on Cancer (IARC) concluded that there was inadequate evidence for the carcinogenicity of chlorinated drinking water to either experimental animals or humans: "Chlorinated drinking water is not classifiable as to its carcinogenicity to humans (Group 3)."
Although this does not appear to be a strong statement denying carcinogenicity it should be noted that IARC does not classify chemicals or processes as not carcinogenic, as one can not make an unequivocal judgement on a question framed in the negative.
In fact there are only 3 categories: Group 1, carcinogenic to humans; Group 2, probably carcinogenic to humans; and, Group 3, can not be classified. Although not all chlorine and chlorine-containing organics have not been individually examined for carcinogenic activity, available data indicate that most are not carcinogenic.
In recent public hearings about the proposed Halifax-Dartmouth Metropolitan Wastewater Management System it was argued that chlorination of sewage treatment plant effluent to remove pathogens represented an unnecessary risk due to the formation of certain organochlorines. Although the organochlorines produced are somewhat different depending on whether sewage or raw drinking water is treated and whether fresh or salt water is chlorinated, the main general argument is that persistent and bioaccumulative organochlorines are created by chlorine disinfection.
As noted, NONE of the major byproducts of chlorine disinfection meet the criteria for being either persistent or bioaccumulative, let alone persistent and bioaccumulative. This is because the major byproducts of chlorination of water and wastewater are relatively volatile, low molecular weight chemicals that are readily degraded by natural physical, chemical and biological processes. It also ignores the fact the levels of most of these chemicals produced by chlorination are very low.
In any decision-making process there are four possible outcomes. Of these four outcomes, two -- ban when the facts are true and do not ban when the facts are false -- are clearly supportable. The other two possible outcomes are clearly less desirable: ban when the facts are false and do not ban when the facts are true. Serious consideration is usually given to the consequences that might occur if one of the latter two outcomes occurs.
In legal judgements, society has accepted that it is more important to prevent the innocent from being falsely convicted that it is to eliminate the guilty from being acquitted. Even the guilty are considered to have some redeeming characteristics. In general, risk cost-benefit analysis terms, the question is: Do the general health and economic benefits of chlorine and each chlorine-containing organic chemical exceed the risks associated with their uses, and are the risks associated with the use of alternatives, including no action at all, lower than the risks of continuing the use in question?
The call for a broadly-based ban implies that we are willing to sacrifice situations of known benefit for those of potential harm without weighing the consequences of such sacrifices. Furthermore, banning chlorine and virtually all organochlorines in a single broad decision suggests that society would accept deserting the centuries-old legalistic judgement framework of examination on a case-by-case approach.
There is a price to pay for an ultra-conservative approach such as banning. Already we are beginning to see the unfortunate consequences of misinformation and misguided interim judgements in the case of chlorine and chlorine-containing compounds, specifically, using chlorine in water disinfection. Much concern has been raised about the potential toxicity via the possible carcinogenic activity of both chlorine and chlorine-containing compounds used and/or produced in the purification of drinking water and disinfection of domestic sewage effluent.
Even if we were to conclude, for the sake of discussion, that chlorination of drinking water created a small, but definite, increase in the cancer rate of humans, another factor must be considered. The statistical possibility of an increase of few additional deaths per million people exposed over an expected lifetime of about 70 years must be balanced against the risk of not chlorinating drinking water. Although other methods of water purification exist, none are as effective and as cost-effective as the various forms of chlorination.
Unfortunately this is not a hypothetical situation. There is a real example showing the human consequences of banning chlorine without due consideration of the alternatives. Many cities in Latin America have stopped chlorinating water due to concerns over possible cancer risk.
Water that was previously disinfected is no longer treated with chlorine as there is no economically viable alternative. A cholera epidemic that has caused over 590,000 cases and some 5,000 deaths in an 18-month period is the result. This is in addition to the 300,000 deaths due to diarrhea-related diseases caused by unsanitary water reported in 1990. |10~ In this situation it is dear that any risks associated with the use of chlorine for water disinfection are much, much less than the risks of not using it.
There are many other situations where the benefits of chlorine or organochlorines dramatically outweigh any negative aspects. This is not to say that changes in the nature and amounts of chlorine or organochlorines used may not be appropriate, or even overdue in some cases; rather, it is important that the arguments be specific to the situation and chlorinated compounds in question. Furthermore, it must be remembered that in each case the risk associated with alternative solutions to a problem are not guaranteed to be less risky than the existing situation.
I think the case for treating chlorine and all chlorine-containing organic chemicals as a common gang of murderous chemicals can not be sustained. The call for treating all chemicals containing chlorine as toxicologically "evil" or "bad" represents a specious argument at best. To agree with the charge represents the chemical and toxicological equivalent of racism. |10~
There are criminals in every group of humans, no matter how you formulate the group, but they are identifiable only by their criminal actions, not by their membership in the group. Such is also the case for chemicals, they must be identified by their specific toxicological characteristics, not by their membership in a generally-defined group. A ban on chlorine and organochlorines represents an exercise in both poor science and poor judgement and neglects to consider the very substantial benefits obtained in many situations by appropriately controlled uses.
Thus, judgements about chlorine and organochlorines must be made on a chemical-by-chemical and case-by-case basis if scientific logic and judgement are to prevail. The due process of societal judgment has flaws and may be considered unsuitable or unreasonable by some, but, as Churchill observed about a more general process of making decisions "Indeed it has been said that democracy is the worst form of government exit for all those other forms that have been tried from time to time." So too is the practical and formal legal framework of making decisions the worst form of societal decision-making, except for all the others we have tried.
Thanks to M. Power for discussions and suggestions that have helped to clarify some of the arguments and their presentation.
1. Thornton, J., 1991. The Product is the Poison: The Case for a Chlorine Phase-out. A Greenpeace Report. Greenpeace U.S.A., Washington DC. 59 p.
2. CSA, 1991. Risk Analysis Requirements and Guidelines. Canadian Standards Association, Toronto ON. 42 p.
3. Gribble, G.W., 1992. Naturally occurring organohalogen compounds: a survey. J. Natural Products (Lloydia) 55:1353-1395.
4. IARC, 1991. Chlorinated Drinking Water. In: IARC, Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 52. Chlorinated Drinking Water; Chlorination Byproducts; Some other Halogenated Compounds; Cobalt and Cobalt Compounds. International Agency for Research on Cancer, Lyon, France. pp. 45-141.
5. Ames, B.N. and L.S. Gold, 1991. Cancer prevention strategies greatly exaggerate risks. Chem. Eng. News 69:28-32.
6. Ashby, J. and D. Paton, 1993. The influence of chemical structure on the extent and sites of carcinogenesis for 522 rodent carcinogens and 55 different human carcinogen exposures. Mutat. Res. 261:3-74.
7. Ellis, K.V., 1991. Water disinfection a review with some consideration of the requirements of the Third World. Crit. Rev. Environ. Control 20:341-407.
8. WPCF Disinfection Committee, 1987. Assessing the need for wastewater disinfection. J. Water. Pollut. Control. Fed. 59:856-864.
9. Jolley, R.L., 1985. Basic Issues in Water Chlorination In: R.L. Jolley, R.J. Bull, W.P. Davis, R.H. Morris, (Jr.), and V.A. Jocobs (eds.), Water Chlorination: Environmental Impact and Health Effects. Volume 5. Lewis Publishers Inc., Chelsea MI. pp. 19-38.
10. Carpenter, G,D., 1993. The fragile relationship of business and environmental science. Environ. Toxicol. Chem. 12:1335-1337.
11. Mackay, D., 1992. Is chlorine really the evil element? Environ. Sci. Eng. 1992:50-55.
L.S. McCarty, ecotoxicology and risk assessment, Scientific Research and Consulting, Oakville, ON.
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|Publication:||Canadian Chemical News|
|Date:||Mar 1, 1994|
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