The Future of Chlorine

Published May 1, 1996

Numerous reports in the media have ascribed possible detrimental health effects to chlorine, dioxin and other chlorinated chemicals, often subjecting the public to exaggerated and misleading information.

Greenpeace, a worldwide environmental activist group, has led the attack, pushing for a total ban on chlorine and chlorinated chemicals. Greenpeace charges that the use of chlorine in manufacturing processes and drinking water purification is causing higher rates of cancer than would otherwise occur. More recently, Greenpeace has claimed that the exposure of pregnant mothers to even tiny traces of chlorinated chemicals has negative effects on the development of their unborn children.

Is Greenpeace right? Should chlorine be banned?

What scientists say

Greenpeace’s claims face formidable opposition from the scientific community. In public reports responding to Greenpeace’s campaign against chlorine, several prominent groups of scientists and doctors have emphasized that current regulations dealing with chlorinated chemicals are sufficient and that there is no need to ban the entire group.

The Society of Toxicology declared in October 1994 that toxicologic principles do not support the banning of chlorine. In only the third position statement in its 35-year history, this 3,500-member professional organization stated that the Clinton Administration’s proposal to “develop a national strategy for substituting, reducing or prohibiting the use of chlorine and chlorinated compounds” is simplistic and ignores the basic principles of toxicology that govern risk assessment.

All chlorine-containing compounds are not equally hazardous, continued the position statement, and a broad-based ban of this class “would be irresponsible and unscientific.” Moreover, the society added that the most scientifically sound approach is “to assess the toxicity of agents on a chemical-by-chemical basis.”

In April 1994, the American Chemical Society wrote to Congress saying that it “sees no reason for singling out such an extensive group of chemicals for study,” and it urged the EPA to focus on chlorinated chemicals of primary concern.

In June 1994, the American Medical Association urged the EPA to evaluate environmental risks on the basis of reliable data specific to each chlorinated compound.

The Michigan Environmental Science Board, convened by the state’s governor to review the chlorine issue, concluded in July 1994 that there is “insufficient scientific evidence” to suggest that short-lived chlorinated compounds produce environmental and health threats. The panel opposed “sunsetting” all uses of chlorine and organochlorines and stated that not all chlorine-containing compounds are harmful.

Dr. Lawrence Fischer, Director of the Institute for Environmental Toxicology at Michigan State University and Chairman of the panel, said that “the focus on chlorine is misplaced.” The panel also found that current regulations are “reasonably adequate,” but that “periodic review, aggressive enforcement, and better monitoring” are needed.

An extensive study published in Regulatory Toxicology and Pharmacology evaluated the use of chlorine in several industries, including the PVC, pulp and paper, drinking water, incineration, and pesticide industries. The 1,100-page study, published in September 1994, concluded that “although much remains to be learned about chlorinated organic chemicals, enough is known to ensure that now and in the future, they can be used and discharged with assurance that adverse effects will be absent.”

Part of the natural environment

One reason to suspect that Greenpeace might be wrong is that many of the chlorinated chemicals it attacks are produced naturally and in huge quantities. They therefore cannot be “banned” any more than air, gravity or sunlight.

Chlorine is one of more than 100 elements that make up our universe and is one of the 20 or so elements that make up all living things. Chlorine occurs in nature in several forms, such as inorganic chloride salts (i.e., sodium chloride, common table salt) and the numerous chlorinated organic (i.e., containing carbon) compounds found in plants, the soil, the atmosphere and ocean life.

The natural world contains more than 1,500 chlorine-containing chemicals. Many organochlorines–the very same class of chemicals that are on environmental hit lists–are produced naturally. For example, 2,4-dichlorophenol, used to manufacture several pesticides and herbicides (including Agent Orange), is produced naturally by a species of Penicillium, the genus of mold that produces penicillin.

The roster of living organisms known to produce natural chlorinated organic compounds is a long one: seaweeds, algae, assorted plants, some vegetables and fruits, fungi and mushrooms, lichen, microorganisms, marine creatures, frogs, insects and even some mammals. In the human body, white blood cells generate hypochlorite to fight infection. Hydrochloric acid in the stomach is essential for proper digestion; chloride ions are necessary for muscle and nerve function.

Chlorine compounds are synthesized by many species of plants and animals for very specific metabolic purposes. They are essential for the normal growth and reproduction of those organisms. The ability of organisms to synthesize these compounds has evolved over time under the stress of natural selection. Chlorine, in other words, is part of our natural ecosystem.

Hydrogen chloride is produced in massive amounts in volcanoes, and many chloride salts are present in the earth’s crust. Combustion is also a major source of organochlorines. Natural combustion sources include lightning-induced forest and brush fires as well as volcanoes. Whenever organic material is burned in the presence of chloride, organochlorines are produced. These include dioxins, chloromethane and other chlorine-containing compounds.

The benefits of chlorine

Why should we come to the defense of chlorine? For starters, almost everything we encounter in our daily life–from wood-veneer furniture, to luggage and shoes, to medical devices such as pacemakers–has had a chlorinated compound included at some point in its production. Nearly 1.3 million American jobs are linked to chlorine chemistry.

Chlorine is used to purify drinking water and to disinfect swimming pools, both of which might otherwise be contaminated with fecal microorganisms that could cause diseases such as cholera, typhoid fever and dysentery. Some 98 percent of our public water systems are purified by chlorine or chlorine-based products.

Chlorination is the water treatment of choice in North America, preventing inestimable deaths every year. In the words of the director of the International Life Sciences Institute’s Risk Science Institute, “chlorination and disinfection of the water supplies are the public health success story of the century.”

The World Health Organization estimates that worldwide 25,000 children die every day from waterborne diseases resulting from a lack of water disinfection. In Peru, the suspension of water chlorination as an experiment in 1991 resulted in a massive and unnecessary epidemic–causing more than one million cases of cholera and 19,000 deaths to date–that has spread to fourteen other South and Central American countries.

Ozone has been suggested as a substitute for chlorine in water disinfection, but ozone is less effective than chlorine. Ozone breaks down very rapidly and thus does not guard against recontamination, while chlorine provides residual disinfection from the treatment plant to the tap. Additionally, there is no assurance that ozone’s by-products, including bromate (an animal carcinogen), will be any less toxic than by-products produced during chlorination.

One of the most important uses of chlorine is in the production of polyvinyl chloride (PVC, or vinyl). PVC is a versatile and nontoxic material that has a distinct advantage in many product applications and in the marketplace. The presence of chlorine in PVC makes this material inherently flame retardant, which is why PVC is used in many construction and furnishing applications.

PVC is the world’s leading electrical-insulating material, with more than 500 million pounds used annually for wire, cable and other electrical applications. In fact, PVC is used in a vast array of everyday products. On a typical day the average person will use more than a dozen PVC products, including luggage, shoes, raincoats and umbrellas, fabric and paper coatings, computers and keyboards, magnetic recording tape, recreational equipment, inflatable boats and water floats, baby strollers, furnishings, food packaging, garden hoses and lawn furniture, floor and wall coverings, and more.

Chlorine is also an essential component in the production of many life-saving pharmaceuticals. Among the chlorine-containing pharmaceuticals is vancomycin–an antibiotic used to fight hospital staphylococcal infections. Other pharmaceuticals that contain chlorine include drugs used to treat depression, arthritis, fungal diseases, glaucoma, psoriasis, yeast infections, allergies, osteoporosis, ulcers, malaria, coronary disease and cancer. The millions of American children who develop middle-ear infections are now best treated with the chlorine-containing antibiotics Ceclor and Lorabid.

The dioxin scare

One way Greenpeace has gained attention to its campaign against chlorine is by linking it to dioxin, a widely feared chlorine-containing chemical. Upon closer inspection, however, both the link and the basis for the fear appear suspect.

The name “dioxin” technically refers to a family of about 75 chemicals, but in public discourse it generally refers to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), thought to be the most toxic of the group. Dioxins are produced during any combustion process–waste incineration, running motor-vehicle engines, steel-making and smelting, residential wood burning and even forest fires. They are also produced when chlorine is used to bleach paper pulp, a fact often cited by Greenpeace as one reason to ban or restrict the use of chlorine.

The amount of dioxin produced by the paper pulp industry in the U.S. is extraordinarily small–less than one pound annually from the whole industry. Even this small amount is being steadily reduced as paper manufacturers switch from chlorine to chlorine dioxide, a less reactive form of chlorine that produces fewer toxic emissions.

Greenpeace claims that incineration of chlorine-containing products also produces dioxin. Once again, however, Greenpeace tells only a partial truth. Since combustion of virtually any compound produces dioxins, singling out chlorinated compounds is disingenuous. And indeed, the amount of dioxin produced by incinerating chlorine-containing products is vanishingly small.

A properly operating incinerator will have dioxin emissions below detection levels. The dioxin emitted by the 22 million wood-burning fireplaces in homes in the U.S. dwarfs the amount released by the incineration of chlorine-containing products. And the dioxin produced “naturally” by forest fires exceeds by thousands of times the amount produced by waste incinerators each year.

How deadly is dioxin?

Despite assorted claims over the past twenty years, the dioxin known as TCDD is not the “doomsday chemical of the 20th century,” nor is it the “deadliest substance ever created by chemists.” Physicians and epidemiologists have been carefully observing the health of people who have been exposed to high levels of TCDD–industrial workers, civilians, Vietnam veterans–and have been unable to attribute unequivocally any human cancers or deaths to TCDD exposure.

The only documented adverse health effect of exposure to dioxin is the skin disease chloracne. Although it is often persistent and disfiguring, chloracne is not life-threatening and is often reversible when exposure ceases.

Studies following certain groups of Vietnam veterans who were exposed to high levels of dioxin, a contaminant of the defoliant Agent Orange, show no association between dioxin tissue levels and cancer or other health effects. A two-part, twenty-year mortality and health-effects evaluation of 995 Air Force Ranch Hands, the personnel who handled and sprayed Agent Orange, found no chloracne, no increase in nine immune-system tests and no increase in either melanoma or systemic cancer (cancers of the lung, colon, testicle, bladder, kidney, prostate; Hodgkin’s disease; soft tissue sarcoma or non-Hodgkin’s lymphoma).

The authors of this 1990 study concluded that “there is insufficient scientific evidence to implicate a causal relationship between herbicide exposure and adverse health in the Ranch Hand Group.”

Studies of more than 800 dioxin-exposed workers in nine industrial-plant accidents in the United States, England, Germany, France, Czechoslovakia and the Netherlands fail to indicate serious long-term health effects in these men, some of whom have dioxin concentrations in their bodies exceeding 1,000 ppt (parts per trillion) thirty years after their initial exposure. Some 465 cases of chloracne were observed in these workers.

A study of 2,200 Dow Chemical workers who were potentially exposed to dioxin revealed that they had a slightly lower mortality than a control group and that they have had no total cancer increase. A study of 370 wives of dioxin-exposed men showed no excess miscarriages and no excess fetal deaths or birth defects in their children.

Life-threatening health effects in humans, in short, have not been linked definitively to dioxin, despite our fears to the contrary. Over 40,000 scientific papers have provided enormous information about this greatly misunderstood chemical, and the scientific and medical communities will continue to monitor the health of those people who have been exposed to large amounts of dioxins. The evidence now in hand does not support claims that dioxin is a major health threat.

Estrogenic effects on fertility Greenpeace alleges that dioxin and other organochlorines may do more than cause cancer. It alleges that dioxin and other chlorinated chemicals mimic estrogen, adversely affecting the immune system and possibly causing birth defects.

Although dioxin causes birth defects in laboratory animals, none of the many studies undertaken shows that dioxin causes birth defects in humans. The women most heavily exposed to dioxin during an accident in Seveso, Italy, showed no increased incidence of birth abnormalities in their newborn children. Moreover, the examination of medically aborted fetuses during the period following the Seveso accident failed to indicate birth defects. (Tragically, many women in Seveso needlessly elected to have abortions out of fear that their children would be born with defects.)

Various reports linking decreased human sperm counts worldwide to chlorinated chemical exposure are based on questionable data and grand exaggeration. Much of the furor over sperm counts came from a 1992 report in a British medical journal citing a 50 percent decline in sperm counts from 1938 to 1990 among men from industrialized countries. After promoting, in a 1993 Lancet article, the hypothesis that this decline was associated with estrogenic compounds, the authors later admitted that the apparent decrease in sperm counts was due to computational error and was not supported by a reanalysis of the data.

A ten-year study of the semen quality of Wisconsin men showed no change over time in sperm concentration or motility. (It must be noted, however, that virtually all studies of sperm health suffer from methodological problems, including how subjects are selected and the number of samples taken.)

While sperm concentration and motility are not the only determinants of male fertility, the 1965 Princeton National Fertility Study and the large, broad-based surveys conducted by the National Center for Health Statistics in 1976, 1982 and 1988 indicate that rates of infertility have remained constant over the past three decades at 8 to 11 percent, with male infertility accounting for approximately one third of the cases.

Furthermore, reproductive problems have not been detected in the groups of people who were most heavily exposed to dioxin: Vietnam Air Force Ranch Hands, occupationally exposed workers and the populations of Times Beach, Missouri, and Seveso, Italy.


Chlorine is an inextricable part of our lives and is necessary for the maintenance of the present high standards in our food, water and housing. Chlorine contributes in the fields of medicine, transportation and communications.

Chlorine is a building block for nearly all chemical processes. It plays a vital role in the health of the population and in maintaining a clean and safe environment. From chlorine-containing pharmaceuticals to fire-resistant and recyclable PVC construction materials, and from water purification to the raising of safe, insect-free food crops, chlorine makes a crucial contribution to the health and well-being of our society.

If chlorine and its chemical derivatives are banned, the expense to the American people in finding replacements will cost billions of dollars and result in the loss of hundreds of thousands of jobs. The loss of useful products–plastics, pharmaceuticals, even safe drinking water–will be a needless tragedy. We will have taken a giant step backward in our standard of living.

The scientific community in industry, academia and government must continue to ensure that the future use of chlorine, PVC and other chlorinated chemicals is based on sound science, thoughtful risk assessment and cost/benefit analysis, along with full consideration of health and environmental factors.

Gordon W. Gribble, Ph.D., is a professor of chemistry at Dartmouth College. This essay is excerpted with permission from Chlorine and Health, published in August 1995 by the American Council on Science and Health (ACSH).