This page is rather large, to say the least, but there's quite a bit of information on chlorine. The "table of contents" below, should make navigating it a bit easier.

Page Table of Contents:


Produced simply by electrolysis of salt water, chlorine was first discovered in 1774 by Swedish chemist Carl Wilhelm Scheele. Today it is one of the most produced chemicals in the US. It has been said that without chlorine, 80% to 90% of the worlds population would not have safe clean water to drink.

When chlorine is added to water, a reaction occurs splitting it into hypochlorous acid and hypochlorite ions. The hypochlorite ion does not actively contribute to the sanitizing ability of chlorine (only 1%), but is an extremely strong oxidizer The hypochlorous acid is the active, killing form of chlorine and what does the actual sanitizing. This chlorine molecule easily enters micro organisms through their cell walls and kills the organisms by destroying the sulfur groups on the cell's enzymes, causing the cell's metabolism to stop, resulting in the cell's death. Not only does chlorine kill bacteria, it does it very quickly. The Association of Analytical Chemists uses a kill time of 30 seconds to completely destroy a given concentration of bacteria as a standard for a hot tub, spa and swimming pool disinfectant.

The amount of hypochlorous acid and hypochlorite ion that is produced when chlorine is added to the water is directly related to the pH of the water. At a pH of 6.0, 96% of the chlorine will become the desired "killing" form of chlorine,  hypochlorous acid. At a pH of 7.0, 75% of the chlorine will become hypochlorous acid and at 8.0 the hypochlorous acid concentration is only 25%. At a pH of 7.5 (the average spa) the amount of hypochlorous acid produced is about 50%.

The hypochlorous molecule will continue to "kill" until it combines with a nitrogen or ammonia compound to become a chloramine, or is broken down into its component atoms and becomes "neutralized". Chloramines do not poses any substantial sanitizing ability and are usually the cause of many unpleasant problems, including eye and mucous membrane irritation and the source of chlorine odors. "Freeavailable chlorine" at levels up to 10-20 ppm has no detectable taste or odor and causes no irritation.

Before you get concerned about soaking in "acid", know that in chemistry there are strong acids and weak acids. While some strong acids can in fact damage human tissue, weak acids are relatively harmless. Citric acid (found in lemons and oranges) and acetic acid in vinegar are examples of weak acids. Hypochlorous acid falls into the weak acid category as well.

When testing for chlorine levels, there are two types of tests available. One tests for "free available chlorine" and the other for "total chlorine". "Free chlorine" is both the hypochlorous acid that has the sanitizing (killing) ability, and hypochlorite ion. "Total chlorine" is a measurement of both "free available chlorine" and the chloramines (combined chlorines) that have no sanitizing ability.

Chloramines should be removed from the water when they reach a level of 0.3ppm. The level of chloramines can be determined by subtracting the "free available chlorine" from the "total chlorine". The accepted method for removal of chloramines is to raise the level of "free available chlorine" to ten times the level of chloramines. The general recommendation is to raise the "free available chlorine" level to 10 ppm. This large concentration of free chlorine will eliminate the combined chlorine and leave behind a residual that is in the form of free active chlorine.

Chlorine Comparison Chart

Types of Sanitizers Form % of Available Sanitizer pH of the Product Soda Ash per gallon/ pound to neutralize pH Muriatic Acid per gallon/ pound to neutralize pH
Sodium Dichlor Granular 56 or 62 6.9 n/a n/a
Tri Chlor Tablets/Granular 90 2.9 4.5 oz. n/a
Sodium Hypochlorite* Liquid 12 - 15% 13 n/a 16 oz.
Household  Bleach Liquid 6% 13 n/a 16 oz.
Gas Chlorine Gas 100 below 1 2 lbs. n/a
Calcium Hypochlorite Tablets/Granular 65% - 70% 11.8 n/a 4 oz.
Lithium Hypochlorite 35 10.7 n/a 3-4 oz.

For comparative purposes, below are most other common sanitizing products.

1 Part Bromine Tablets 62%(Br)+30%(Cl) 3.6 3.5 oz. n/a
2 Part Bromine Liquid/Granular 94 6.5-8 n/a n/a
Non-Chlorine Shock Granular 0 2.3-3 4.5 oz. n/a
Ozone Gas Gas n/a 7 n/a n/a
*Liquid chlorine specifically for swimming pools, NOT regular household bleach

Types of Chlorine

Chlorine is available in a number of different forms. Granular, liquid or tablet, and can also be stabilised or unstabilised (stabilising refers to the combining of isocyanuric acid with chlorine to protect it from UV rays, which drastically reduces it's effectiveness). Chlorine can also be generated by a Salt Chlorinator.

Gas Chlorine

In its elemental state, chlorine exists as a gas. Gas is the purest form with an available chlorine content of 100%. While "available" as a sanitizer, it is extremely dangerous and restricted in its use. Due to stringent regulations, restrictions and licensing requirements only specialized professionals use it. Chlorine gas is extremely acidic and will drastically lower a waters pH.

Sodium dichloro-s-triazinetrione (Sodium Dichlor or Dichlor from short)

Sodium Dichlor is the only type of chlorine that should be used in spas. It's fast dissolving, will not cloud the water, is relatively pH neutral and has a long shelf life. Because of it's granular makeup, there's no way to automatically dispense it and it must be added by hand.

Sodium Dichlor is chemically produced by adding soda ash and cyanuric acid to a solution of trichlor. When dried the result is a granule that provides 56% - 62% available chlorine, depending on the method of manufacture.

Trichloro-s-triazinetrione (trichlor tablets)

Trichlor is designed for the cooler water of swimming pools and contains the highest percentage (90%) of available chlorine of all the different chlorine compounds. Trichlor should never be used in a spa as the high temperatures will cause it to dissolve very quickly. Available as a l-inch tablet, 3-inch tablet, a stick or a cartridge, it has a long shelf life, and it is very slow dissolving in cool water. This allows it to work extremely well in swimming pool floaters and erosion-type feeders.

Trichlor has a very low pH of 2.9 and requires frequent monitoring and adjustment of pH to prevent damage to equipment and other metal parts. Neutralizing the pH requires approximately 1 part soda ash per 4 parts trichlor.

Trichlor is produced by drying and cooling the sodium salt of cyanuric acid in the presence of chlorine gas. The resulting compound provides 90% available chlorine.

Sodium Hypochlorite ( Liquid Chlorine)

Liquid chlorine is manufactured by bubbling chlorine gas through a solution of caustic soda. The resulting yellow liquid yields 15% available chlorine, but the concentration is very unstable and within two weeks, the available-chlorine level will drop to approximately 12.5 percent and after 30 days it can drop to as low as 9%. Sunlight and high temperatures can increase the rate of degradation.

Besides the low concentration of available chlorine, sodium hypochlorite also greatly increases total dissolved solids and has an extremely high pH of 13. Neutralizing the pH requires approximately 1 part muriatic acid per 8 parts liquid chlorine.

Calcium Hypochlorite

Commonly called "Cal-hypo", calcium hypochlorite was patented in 1799 and called "bleaching powder." It comes in a large granular form or as 1-inch or 3-inch tablets and is produced by passing chlorine gas over slaked lime. The resulting powder or granules provide 65 to 70 percent available chlorine. Cal-hypo will support combustion and one needs to avoid mixing it with acids, ammonia, soda pop, oil, trichlor or just about anything but water. Mixing with organics will cause a fire.

Because it is slow to dissolve, it should be used either in a feeder, or pre-dissolved in water and then added as a liquid. Cal-hypo can temporarily cloud the water, because the calcium takes a long time to dissolve completely. It can also cause calcium scaling and deposits on surfaces and in circulating equipment. Cal-hypo tends to increase the water hardness level quickly and has a high pH of 11.8. Neutralizing the pH requires approximately 4 ounces of muriatic acid per pound of cal-hypo.

Lithium Hypochlorite

Lithium hypochlorite is one of the more recently developed forms of chlorine. It is produced by bubbling chlorine gas through a solution of lithium, sodium and potassium sulfates. When dried, the result is a free-flowing powder that provides only 35% available chlorine.

Lithium hypochlorite is calcium free, dust free and non-flammable. It has a long shelf life, and because it contains no calcium, it dissolves very rapidly without clouding or raising calcium levels. Because it dissolves so rapidly, it cannot be used in a dry-chlorine feeder and must be applied by hand. It has a high pH of 10.7, and neutralizing it requires  about 4 ounces of muriatic acid per pound of lithium hypochlorite.


When chlorine is added to water, it generally forms hypochlorous acid, the powerful killing form of chlorine, and a hypochlorite ion, a relatively weak form of chlorine. The percentage of hypochlorous acid and hypochlorite ions is determined by the pH of the water. As the pH goes up, less of the chlorine is in the killing form and more of the chlorine is in the weaker form . The total of hypochlorous acid and hypochlorite ions is the free available chlorine.

Chlorine can combine with ammonia and nitrogen compounds in the water to form chloramines, also called combined chlorine. By combining with ammonia and nitrogen, free chlorine in the water is disabled. Chloramines are 60 to 80 times less effective than free chlorine and are formed any time ammonia and nitrogen are in the water. Some of the ammonia and nitrogen compounds are introduced into the water by bathers in the form of perspiration, urine, saliva, etc. The average person sweats three pints per hour in a heated spa. Ammonia and nitrogen compounds are also introduced into the water by rain. Each drop of rain has some dissolved nitrogen from the atmosphere.

Not only do chloramines smell bad, but they are eye and skin irritants, and they can cloud the water.

Chloramines can be removed from the water by the following three methods:

  1. By adding a high dose of chlorine and raising the levels to 10 times the level of combined chlorines (5 to 10 ppm) for a minimum of 4 hours. This is called super chlorination. To remove chloramines, the ratio of chlorine to chloramines must be at least 7.6 to 1. If this ratio is not obtained more chloramines will be produced.
  2. By adding a non-chlorine shock to the water. The most common chemical used for this is potassium peroxymonosulfate (MPS). This "shocking" requires the addition of 1 oz. per 625 gallons of water.
  3. By adding ozone to the water. If an ozone generator is installed and wired so that it comes on each time the pump comes on, then oxidation of the ammonia and nitrogen compounds will take place on a continuous basis. This reduces, and can even eliminates the need for   shocking. Each time ammonia and nitrogen enter the ozonated water, they are oxidized by the ozone.

There may come a time when the sterilization, or decontamination of a spa may be necessary. One of these time may actually be when the spa is brand new. Most manufacturers water test their spas at the factory to check for leaks. The water they use can be recycled many times, and it may have sat in the spas plumbing for quite some time before arriving to you. Or simply water quality may have gone far out of control for a long period of time. Either of these situations (and others) can cause a dangerous build up of bacteria. The following is a procedure suggested by HotSpring Spas....

Procedure for Chemical Cleansing

1. Cartridge Filters: Remove the filter cartridge(s) and either clean or replace. To clean cartridge(s), first use a filter cleaner as per label directions. After rinsing the filter cartridge(s), completely submerge the cartridge(s) in a 1/10 solution of sodium hypochlorite (liquid bleach) and water for two hours. Inspect and clean the filter housing. Set the filters aside for installation after the spa decontamination is complete.

WARNING: Contains sodium hypochlorite.
Causes substantial, but temporary eye injury.
Harmful if swallowed.
May irritate skin. Do not get in eyes or on clothing.
For prolonged use, wear gloves.
Note: Baqua users (Biquanide) drain and refill spa before adding any chlorine.

2. Raise the water level in the spa 1/2 inch above the high water mark, and remove pillow if possible.

3. Turn on the jets - all of them - let them run for one hour.

Superchlorination and Neutralization:
4. Add at least 100 ppm chlorine to the spa being sure not to allow the Dichlor to come into direct contact with spa surface before is dissolves.

Sodium Dichloroisocyanurate - 56%
6.25 ounces per 250 gallons,
8.75 ounces per 350 gallons,
12.50 ounces per 500 gallons.

5. During Superchlorination, be sure to rotate any diverter valves or other systems to allow water flow through all jets and systems for at least 5-10 minutes in each position.

6. For the first 60 minutes, do not cover the spa with the spa cover.

7. Neutralize the chlorine in the water with 16 oz of Hydrogen Peroxide (3%). Test for chlorine: more Hydrogen Peroxide may be needed.

WARNING: Hydrogen Peroxide, 3% U.S.P.,
For external use, topically to the skin and mucous membranes.
Keep out of eyes.

8. Circulate the spa water for 10 minutes, during the Chlorine neutralizing process.

9. Stop circulation by turning off all jets.

10. Drain and flush the spa.

11. Clean the spa surface with a surface cleaner approved for you type of spa shell surface. Rinse the spa thoroughly!

Water Replacement and Treatment:
12. Refill the spa with water, reinstall the filter, which has been sanitized (or replaced).

13. Follow the startup procedure for your particular spa. Balance water chemistry before use.

14. Clean the underside of your cover.

Chlorine: The Everywhere Element

By Charlie Cray

Chlorine keeps our water safe, helps farmers bring an abundant and nutritious yield to market, helps doctors combat infectious diseases with modern pharmaceuticals, and creates many essential products of modern living, like plastics. Chlorine is such an essential element that it's hard to imagine 20th century life without it. Sound like a familiar argument? It should; it cost the chlorine industry $150 million dollars to spread it around. Meanwhile, the real story about chlorine is emerging in a variety of scientific journals which link chlorine to a range of modern illnesses, including a variety of cancers, birth defects, immune system suppression, endometriosis, declining sperm counts, and male reproductive failure.

A battle is escalating around the use of chlorine in industry, and public understanding about a public health crisis linked to the products of commercial chlorine chemistry is catching up with the propaganda campaign waged by the industry. A few years ago Dow (the world's largest maker of chlorine), Occidental (number two in the U.S.) and other companies formed a subgroup of the Chemical Manufacturers' Association called the Chlorine Chemistry Council (CCC). The CCC has since coordinated the lobbying efforts of the chlorine-producers and their major customers to deflect criticisms and delay action on phasing out the chlorine industry's arsenal of toxic products, including polyvinyl chloride (PVC), chlorinated solvents used in dry cleaning and other industries, pesticides, and chlorinated bleaching agents used in the manufacture of pulp and paper. According to Chemical and Engineering News, by the end of 1995 alone the CCC will have spent over $15 million on a public relations campaign aimed at consumers, the media, sympathetic scientists, and elected officials. Individual company expenditures are much higher: according to Occidental Chemical's CEO J. Roger Hirl, "these figures are just the 'tip of the iceberg;"' individual companies contribute people and resources equal to "at least ten times that amount."

This accounts for all the screaming in stories planted by the trade association about how plans to phase out chlorine would devastate our economy and how policy-makers should instead heed the call for "sound science" (i.e. let's study the issue some more before taking any action). Meanwhile, the CCC has worked tirelessly behind the scenes to take advantage of a zealous Congress to make sure such studies can't be funded (because Congress closed down its Office of Technology Assessment) and to ensure that specific regulations proposed to reduce emissions of dioxin and other chemicals cannot be proposed or enforced by the EPA, the FDA or other agencies.

I's Only Natural

The CCC, and its allies, has invested a lot in spreading confusion. One of their favorite canards is that chlorine is a "natural" compound. Proposals to phase out chlorine are thus irrational attempts to "wipe an element off the periodic table." (Lead is also an element on the periodic table, but we've phased it out of gasoline, paint, and other uses.) This argument blithely obscures the fact that most natural chlorine found in the environment is inertly bound up as salt. The chemical industry invests huge amounts of energy to split salt molecules to produce caustic soda and highly reactive chlorine gas, most of which is directed to form downstream products called organochlorines (carbon-bonded chlorine compounds). Nearly all organochlorines are toxic, persistent or liable to bioaccumulate in the food web once released into the environment.

The chlorine industry's products and byproducts have saturated the planet, from the Baltic to Antarctica, from the milk of Inuit women living above the Arctic circle to the Beluga Whales in the St. Lawrence (which are verging on extinction because they carry high levels of PCBs and other toxic chemicals in their bodies). Concerns about the global spread of these chemicals has grown to the point that at the end of October, the U.S. State Department will host a UN-sponsored meeting on the troublesome global spread of Persistent Organic Pollutants (POPs), most of which are chlorine-based, including toxaphene, DDT, dioxin, PCBs, dieldrin, heptachlor and chlordane.

The CCC and its allies are quick to point out that there are naturally-produced organochlorines found in abundance around the world. Recently, The American Council on Science and Health (an entrenched beltway corporate front group whose President, Elizabeth Whelan, once declared "there is no such thing as junk food") published a report which highlighted the prevalence of "natural" organochlorines in order to obscure industry's role in upsetting the balance of these chemicals in nature.

Simple organochlorines like methyl chloride, for instance, are produced in large quantities by ocean-living microorganisms. Some scientists surmise that methyl chloride has had a role in the natural regulation of the world's protective ozone layer. If that is true, there is no doubt that the homeostatic balance has been upset in the last few decades by the drift of ozone-depleting volatile organochlorines such as CFCs into the stratosphere. In 1991, EPA calculated that as a result of ozone-depletion over the next 50 years 12 million Americans will develop skin cancer, and that more than 200,000 of them will die.

Thus, in its zest to scour the planet for the thousand or so organochlorines with specific functions in natural processes, such as the particular organochlorine used by Ecuadoran tree frogs as a natural defense poison, the chlorine industry would have us forget how it has perilized entire ecosystems in just half a century.

Of course the industry really couldn't care less about the frogs in Ecuador, but they get nervous about the potentially huge alliance that could be organized by concerns of occupational health specialists, environmentalists, competing industries, and many of the chlorine industry's victims. These victims include the coalitions that form downwind of dioxin-spewing incinerators, Vietnam veterans exposed to Agent Orange (and a history of cover-up and corrupt science), the 10 to 15 percent of the population that Chemical and Engineering News says suffers from multiple chemical sensitivity (MCS), the many farmworkers and chemical plant workers who have been sterilized by DBCP and other pesticides; subsistence fishermen whose lifestyle has been destroyed by dioxin and other toxic chemicals that gush out of paper mills, and others such as firefighters, who must be especially careful because of the toxic gases created when polyvinyl chloride (PVC) burns in building fires.

Despite the industry's lobbying efforts, various regional intergovernmental conventions and agreements have highlighted the role of organochlorines in ecosystem-wide epidemics among wildlife and humans. In a bold report issued in 1992, The International Joint Commission (UC) on the Great Lakes recommended to the U.S. and Canadian governments that "if a chemical or group of chemicals is persistent, toxic or bioaccumulative, we should immediately begin a process to eliminate it. Since it seems impossible to eliminate discharges of these chemicals through other means, a policy of banning or sunsetting their manufacture, distribution, storage, use and disposal seems to be the only alternative."

"...In practice, the mix and exact nature of [organochlorine] compounds cannot be precisely predicted or controlled in production processes. Thus it is prudent, sensible and indeed necessary to treat these substances as a class rather than as a series of isolated, individual chemicals... We know that when chlorine is used as a feedstock in a manufacturing process, one cannot necessarily predict or control which chlorinated organics will result, and in what quantity. Accordingly the Commission concludes that the use of chlorine and its compounds should be avoided in the manufacturing process."

This statement brought the IJC out of obscurity into the center of a policy debate that EPA officials believe could become a "wicked battle" in the next few years, as the Agency gets whipsawed between the demands of industry (and its shills in Congress) and an increasingly sophisticated movement that attributes a variety of environmental and public health epidemics to the products of the chlorine industry.

On the heels of the UC's recommendation, the Clinton administration proposed in its 1993 Clean Water Act reauthorization package to study ways to reduce and eliminate the use of chlorine and chlorinated products. The CCC, led by Dow and others, responded hysterically to this proposal, which seemed to match their call for "sound science." A huge industry "grassroots" (more like astroturf) lobbying campaign generated over a million letters to Congress, most repeatedly denouncing EPA's silly attempt to "ban an element from the periodic chart."

The industry's "outrage" over the potential economic impacts of phasing out chlorine was outlined in a report the Chlorine Institute commissioned from Charles River Associates (CRA), an American consulting company. CRA claimed the UC's recommendation would cost the U.S. and Canadian economies $102 billion (U.S.) per year, would impact 1.4 million jobs, and would severely disrupt local and regional economies. The CRA's estimates of the costs of phasing out chlorine drastically overestimated the actual costs of a chlorine phase-out, largely because CRA assumed the transition would occur instantaneously by bureaucratic fiat, without any intelligent thought or planning. (Which is why the Clinton administration actually proposed a study of the uses of chlorine, rather than an outright ban). Though CRA admitted that alternatives are available for virtually all uses of chlorine, often they picked expensive alternatives when cheaper options were available for comparison. CRA also forgot to balance the costs with potential benefits, including reduced Superfund cleanup costs (which the industry is currently working with Congress to pass along to the taxpaying public), reduced health costs, and potential job creation in the alternatives.

Dioxin: The Watergate of Molecules

Nowhere has the battle over chlorinated compounds been more heated in the U.S. than in the evolution of EPA's ongoing examination of dioxin, the most extensive study of a chemical ever conducted.

Industry has invested much in influencing and interpreting this important scientific study since it has huge implications for regulatory policy. In 1994, Greenpeace was leaked a copy of a focus group study conducted for the CCC which concluded that the public doesn't understand the problems with chlorine (which they associate more with water than PVC, paper production, and the other products which dominate industrial chlorine chemistry) as much as they react strongly to the word "dioxin." The task for the CCC, the pollsters concluded, was to ensure the connection is not made in the public's mind. Preventing EPA from making the connection in its Dioxin Reassessment was therefore crucial, as it would open the door to new regulations that would potentially prioritize the phase-out of certain chlorine sectors.

Ironically, EPA undertook the dioxin reassessment because of pressure from industry. In 1991, various members of the paper industry, under attack for high emissions of dioxin and related chlorine-based chemicals, began pressuring the EPA (then headed by William Reilly, a Bush-appointed official who later left to join the board of DuPont) to reexamine the toxicity of dioxin, which they believed the EPA would find was overrated. After considerable study, EPA issued its long-awaited draft conclusions in September 1994. Despite industry's expectations, after consulting with over 100 (mostly external) scientists the Agency issued a nine-volume report which concluded that dioxin is even more toxic than previously supposed. One lead scientist on the EPA reassessment team, Dr. Linda Birnbaum, said she and her colleagues now consider dioxin an "environmental hormone" capable of disrupting a large number of bodily processes in fish, birds, and mammals, including humans. Dioxin, EPA said, is especially powerful in its effects on the unborn and the newly-born. Startling new evidence has revealed dioxin may have a role in a society-wide epidemic of cancer, endometriosis, impaired child development, suppression of the immune system and a variety of male reproductive problems, including falling sperm counts, rising rates of testicular and prostate cancer, and deformed genitalia in the offspring of exposed adults.

Industry spin doctors went on the offensive as the EPA's Science Advisory Board reviewed the draft document. Examination of giant industrial dioxin sources (such as PVC manufacture) became a secondary question as EPA staff spent much time defending the report's conclusions about the toxicity of different dioxin-like molecules, subcellular toxicological mechanisms, and assumptions about how much dioxin we carry in our cells and are exposed to through our daily diet.

While industry's hired scientists poked holes in all the minutiae in EPA's draft document, the CCC's spin doctors promoted bogus scientific theories to confuse the media and elected officials, resurrecting the widely discredited theory (first proposed by Dow in 1979) that dioxin occurs principally from natural events such as forest fires. No credible scientist would back the industry up on this issue: EPA and its advisors concluded that dioxin is largely a 20th-century industrial product. Extremely low levels of dioxin in ancient mummies and the precipitous rise of dioxin levels in lake sediments after 1930 make this clear.

The EPA's Science Advisory Board issued its review of the Draft Reassessment this fall, finding that:

  • The agency was correct in finding that dioxin is properly classified as a probable human carcinogen, according to data from both animal and human studies. This designation is more serious than the current EPA classification for dioxin.
  • As EPA concluded last September, dioxin can cause serious harmful effects on the immune, nervous, and reproductive systems of humans. In fact, these non-cancer effects may be more serious than dioxin's ability to cause cancer.
  • Dioxin, as EPA outlined, does have adverse effects on animals at levels of exposure far below those previously believed to be safe.

If there is any weakness in EPA's Dioxin Reassessment it is its lack of a clear prescription for action. This is because EPA's inventory of dioxin sources failed to reveal the simple truth that dioxin is formed as an accidental by-product in scores of industrial processes involving chlorine. If this were made clear EPA might have availed itself of a range of opportunities to get beyond the balkanized old end-of-pipe regulatory approaches to dioxin established in such statutes as the Clean Water Act and the Clean Air Act, whose administration has illustrated exactly what the IJC had to say about the futility of managing toxic pollution.

Had EPA made the role of chlorine in dioxin formation central to its discussion of dioxin sources, it might not have missed potentially major dioxin sources such as accidental building fires involving PVC. More importantly, the Agency would rave availed itself of the opportunity to solve the dioxin crisis by promoting an orderly phase-out of chlorine as an industrial feedstock, an approach to toxic pollution that has the potential to be cheaper than all the expensive regulations that Congress is raving about.

Congressional attacks on EPA have skillfully pointed out the symptomatic failures of the current regulatory approach without promoting the new vision proposed by the IJC and other groups such as the American Public Health Association, which has also called for a chlorine phase-out.

Unfortunately, most of the beltway environmental groups have responded in a short-sighted way to the wholesale attack on the EPA. Liberal environmentalists have sent out numerous alerts about measures such as the House Appropriations bill (which would gut EPA's ability to issue new dioxin-reducing measures to control dioxin from incinerators and paper mills or enforce existing statutes like Superfund) without making use of the fact that the Republicans (who designed many of the rules to begin with, during the Nixon era) fail to offer a coherent program which might replace the major environmental statutes (and all their expensive pollution control requirements). Simply put, if EPA were to promote chlorine-free alternatives, the costs of implementing complex regulations to control chlorine-based processess would be avoided. (EPA's office of Pollution Prevention has actually done this, in one exceptional case: EPA funded a "Design for the Environment" project to demonstrate the viability of water-based "wet cleaning" as an alternative to perchloroethylene-based dry cleaning)

One Republican understands this. Gordon Durnil, ex-chair of the Indiana Republican Party, was appointed by George Bush to be the lead commissioner of the IJC before it recommended the chlorine phase-out. Durnil describes the economic and public health benefits of the chlorine phase-out in his new book, The Making of a Conservative Environmentalist. Durnil's approach contrasts sharply with that of his old Republican colleagues who now dominate the Congress.

At one point in his book Durnil describes what amounts to a zero tolerance philosophy on life-threatening toxic chemicals: "When a child molester molests again, we ask, 'Why was he out on the streets? Why didn't people keep him away from our kids?' But when the executive of some large conglomerate violates the laws by discharging some noxious substance into the water, or air, or onto the ground, we pay little attention. We don't ask why he wasn't kept away from chemicals. We don't ask why he wasn't required to keep those unmanageable substances away from our kids."

Of course he knows why: We don't do this because our elected officials, who make these decisions, are instead carrying out the agenda of their paymasters, who they view as their real constituents. According to the Center for Responsible Politics, Dow corporate PACs alone gave $322,800 to members of Congress in 1993-1994. Some of the biggest recipients of this largesse include Tom DeLay (R-Tx; $5,050), a former exterminator who has openly advocated reversing the ban on DDT, Newt Gingrich ($4,000); and Greg Laughlin (D-Tx; $12,050), whose district includes Dow's massive chlorine-production plant in Freeport.

Greenpeace recently issued a report, "Dow Brand Dioxin ... Makes You Poison Great Things," which outlines how Dow has manipulated the Congressional assault on EPA to its own ends. Dow has gone so far as to "loan" Dale Humbert, a regional lobbyist, to the staff of the U.S. House of Representatives Commerce Committee. It's hard to whisper in someone's ear from across the room.

A direct attack on the EPA came from the House Subcommittee on Energy and the Environment of the Committee on Science when the committee decided to hold a public hearing to investigate "whether sound science is being distorted for preconceived policy ends, and the potential economic impact of future mandates based on" EPA's Dioxin Reassessment. The witch hunt was canceled before its scheduled mid-September date, most likely because it appeared improper to attack EPA before the Science Advisory Board had a chance to conclude its review of the reassessment.

The attack on EPA is a dangerous game, not only because industry science doesn't hold up to scrutiny, but also because as one consultant warned the industry in April at a conference sponsored by Chemical Week, "the pendulum of public opinion can swing wildly," and politicians should not underestimate the public's understanding of who the real "special interest groups" are that have been manipulating politics at the expense of public health and the environment.

A growing network of environmental justice and public health activists is coming to understand all this and is bent on organizing a long-range campaign to phase-out chlorine, especially in its most harmful and unnecessary uses. The Citizens Clearinghouse for Hazardous Wastes, whose Executive Director Lois Gibbs was once a Love Canal homeowner, just issued a new book called Dying from Dioxin (South End Press) which outlines grassroots strategies to eliminate dioxin. Numerous other groups, including Greenpeace (the leading promoter of a chlorine phase-out), Great Lakes United, the Institute for Agriculture and Trade Policy, the Public Interest Research Groups and various environmental justice and health activists are all making the chlorine phase-out a priority for environmental activism.

With or without EPA and the Congress, the transition to a chlorine-free society has begun:

  • In 1989, the National Academy of Science published Alternative Agriculture, which outlined a series of measures which would save taxpayers and farmers alike money by replacing pesticide-dependent practices with alternatives, including mechanical and crop-rotational methods. NAS describes the barriers to alternative agriculture, which are more bureaucratic than technical. Nevertheless, the organic produce market and farming movement continues to grow each year, demonstrating the practicality of NAS's vision.
  • In the past few years neighborhood multiprocess wet cleaners ("green cleaners") have set up shop in places like New York and Chicago to demonstrate that alternatives to perchloroethylenebased dry cleaning are practical, effective and profitable. Demonstrations of this alternative process, which saves neighborhood dry cleaners the cost of increased chemical-control equipment and avoids potential groundwater cleanup liability (a major industry concern) has proven to a once chemically-dependent industry that there are safer, cheaper alternatives.
  • Over 25 mills in Europe and a few in North America have been producing high-quality totally chlorine-free paper. With the help of major chlorine-free paper procurement policies (especially at corporations like Time, which has yet to uphold a pledge to go chlorine-free) the market could swing further in that direction as mills overcome short-term cost considerations to take advantage of this emerging market.
  • In Europe bans and restrictions on the use of PVC in packaging and public building construction are spreading. Auto companies, appliance manufacturers, flooring makers and others have also begun phasing out PVC. In the U.S., concerns about high levels of dioxin from medical waste incinerators has quietly shaken the hospital industry. Supply manufacturers are beginning to market products like IV bags made of alternative resins while hospitals are looking at alternative waste treatment methods and ways to substitute durables for disposable items.

The transition to a chlorine-free economy will eventually cause the major chlorine manufacturers like Dow to reorient their product lines. Dow has already quietly hedged its bet by offering alternatives to many chlorinated products, including a chelating agent that can be used in totally chlorine-free paper production, solvent-free cleaning products, polyolefin resins which company officials have suggested are in part able to replace PVC for many applications, and biological "crop-protection" products which, though warranting their own scrutiny, can substitute for chlorinated pesticides. For the most part, however, Dow's policy seems to be to publicly deny any problems with chlorine, a stance that makes its critics wonder if chlorine won't evolve into the next major corporate public relations crisis after silicone breast implants.

Finding a way to openly discuss the transition process is important because the ultimate phase-out of chlorine will impact on customer businesses, workers, and the communities where chlorine manufacturing facilities are located. The industry's campaign of denial only makes the consequences of an abrupt transition more likely and more dangerous. While industry buries its head in the sand, organizations like Greenpeace and the Oil, Chemical and Atomic Workers (OCAW) have promoted an orderly and just transition process, and begun to explore economic instruments and market mechanisms that will facilitate the transition. For instance, OCAW has proposed a tax on chlorine and related chemicals; the revenue would be used to encourage reinvestment in affected communities and provide income protection, continued health care, and meaningful opportunies for higher education and re-employment for workers and their families. Such a measure can only be effective if it is part of a larger transition plan, however, a possibility only in a society that takes the need for a chlorine phase-out seriously.

For more information: Greenpeace: 1436 U St., NW, Washington, DC (202) 462-1177; Citizens Clearing House on Hazardous Wastes: (703) 237-2249.



Hazard Summary

  • Acute (short-term) exposure to high levels (>30 ppm) of chlorine in humans results in chest pain, vomiting, toxic pneumonitis, pulmonary edema, and death. At lower level, (<3 ppm), chlorine is a potent irritant to the eyes, the upper respiratory tract, and lungs.
  • Limited information is available on the chronic effects of chlorine in humans. Reports from the older literature stated that chronic exposure to concentrations of chlorine of around 5 ppm caused respiratory complaints, corrosion of the teeth, inflammation of the mucous membranes of the nose, and increased susceptibility to tuburculosis.
  • The Reference Concentration (RfC) and the Reference Dose (RfD) for chlorine are under review by the U.S. Environmental Protection Agency (EPA).
  • No information is available on the developmental or reproductive effects of chlorine in humans or animals via inhalation exposure. A study reported no adverse effects on growth, lifespan, or fertility in rats exposed to 100 ppm chlorine in their drinking water for their entire lifespan, over seven generations.
  • No information is available on the carcinogenic effects of chlorine in humans from inhalation exposure, and chlorine has not been found to be carcinogenic in oral animal studies. EPA has not classified chlorine for carcinogenicity.

Please Note: The main source of information for this fact sheet is EPA's Drinking Water Criteria Document for Chlorine, Hypochlorous Acid and Hypochlorite Ion. Other secondary sources include the Hazardous Substances Data Bank (HSDB), a database of summaries of peer-reviewed literature, and the Registry of Toxic Effects of Chemical Substances (RTECS), a database of toxic effects that are not peer reviewed.

Environmental/Occupational Exposure

  • Workers may be exposed to chlorine in industries where it is produced or used, particularly in the food and paper industries. In addition, persons breathing air around these industries may be exposed to chlorine. (1)
  • Exposure to chlorine may also occur through drinking water and swimming pool water, where it is used as a disinfectant. (2)
  • Accidental releases are another potential source of chlorine exposure. (3)

Assessing Personal Exposure

  • No data were located regarding detection of personal exposure to chlorine.

Health Hazard Information

Acute Effects:

  • Chlorine is a potent irritant in humans to the eyes, the upper respiratory tract, and the lungs. Several studies have reported the following effects: 0.014 to 0.054 ppm: tickling of the nose; 0.04 to 0.097 ppm: tickling of the throat; 0.06 to 0.3 ppm; itching of the nose and cough, stinging, or dryness of the nose and throat; 0.35 to 0.72 ppm: burning of the conjunctiva and pain after 15 minutes; above 1.0 ppm: discomfort ranging from ocular and respiratory irritation to coughing, shortness of breath, and headaches. (4)
  • Higher levels of chlorine have resulted in the following effects in humans: 1 to 3 ppm: mild mucous membrane irritation; 30 ppm: chest pain, vomiting, dypsnea, cough; 46 to 60 ppm: toxic pneumonitis and pulmonary edema; 430 ppm: lethal after 30 minutes; 1,000 ppm: fatal within a few minutes. (3)
  • Chlorine is extremely irritating to the skin and can cause severe burns. (3)
  • Acute animal tests, such as the LC50 test in rats and mice, have shown chlorine to have high acute toxicity. (5)
  • EPA'sOffice of Air Quality Planning and Standards, for a hazard ranking under Section 112(g) of the Clean Air Act Amendments, considers chlorine to be a "high concern" pollutant based on severe acute toxicity. (6)

Chronic Effects (Noncancer):

  • Several studies in the older literature reported that chronic exposure to chlorine concentrations of around 5 ppm caused respiratory complaints, corrosion of the teeth, inflammation of the mucous membranes of the nose, and increased susceptibility to tuberculosis in workers. (7)
  • Animal studies have reported decreased body weight gain, eye and nose irritation, and effects on the respiratory tract, liver, and kidney from chronic inhalation exposure to chlorine. (4)
  • Other studies have indicated that exposure to chlorine, via inhalation, may alter disease resistance in animals, with higher incidences of emphysema, pneumonia, and tuberculosis reported. (4)
  • The RfC and the RfD for chlorine are under review by EPA. (8)

Reproductive/Developmental Effects:

  • No information is available on the developmental or reproductive effects of chlorine in humans or animals via inhalation exposure.
  • No adverse effects on growth, lifespan, or fertility were reported in rats exposed to 100 ppm chlorine in their drinking water for their entire lifespan, over seven generations. (4)
  • Since chlorine is highly reactive, uptake at sites such as the ovaries and testes which are remote from the respiratory tract, is anticipated to be minimal. (2)

Cancer Risk:

  • No information is available on the carcinogenic effects of chlorine in humans from inhalation exposure.
  • Several human studies have investigated the relationship between exposure to chlorinated drinking water and cancer. These studies were not designed to assess whether chlorine itself causes cancer, but whether trihalomethanes or other organic compounds occurring in drinking water as a result of chlorination are associated with an increased risk of cancer. These studies show an association between bladder and rectal cancer and chlorination byproducts in drinking water. (5)
  • Chlorine has not been found to be carcinogenic in animals; no tumors were noted in a study where rats were exposed to 100 ppm chlorine in their drinking water over their lifespan, for 7 generations (see Reproductive/Developmental Effects section). (4)
  • Another study evaluated the potential carcinogenicity of chlorinated drinking water in rats and mice and found no statistically significant increase in tumors that could be related to the chlorinated water. (2)
  • EPA has not classified chlorine for carcinogenicity. (8)

Physical Properties

  • Chlorine is a greenish-yellow gas that is slightly soluble in water. (7)
  • Chlorine has a suffocating odor; the odor threshold is 0.31 ppm. (9)
  • The chemical formula for chlorine is Cl2, and its molecular weight is 70.90 g/mol. (4)


  • Chlorine is used for water disinfection and for treatment of sewage effluent. It is also used to disinfect equipment and utensils in beverage and food processing plants, and as an intermediate in the manufacture of a number of organic products such as antifreeze, rubber, cleaning agents, and pharmaceuticals. (2,4)

Inhalation Exposure

ACGIH TLV--American Conference of Governmental and Industrial Hygienists' threshold limit value expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effects.
LC50 (Lethal Concentration50)--A calculated concentration of a chemical in air to which exposure for a specific length of time is expected to cause death in 50% of a defined experimental animal population.
NIOSH REL--National Institute of Occupational Safety and Health's recommended exposure limit; NIOSH-recommended exposure limit for an 8- or 10-h time-weighted-average exposure and/or ceiling.
OSHA PEL--Occupational Safety and Health Administration's permissible exposure limit expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effects averaged over a normal 8-h workday or a 40-h workweek.

a Health numbers are toxicological numbers from animal testing or risk assessment values developed by EPA.
b Regulatory numbers are values that have been incorporated in Government regulations, while advisory numbers are nonregulatory values provided by the Government or other groups as advice.


  1. U.S. Environmental Protection Agency. Drinking Water Criteria Document for Chlorine, Hypochlorous Acid and Hypochlorite Ion. (External Review Draft.) Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Cincinnati, OH. 1992.
  2. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Chlorine. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1993.
  3. U.S. Department of Health and Human Services. Hazardous Substances Data Bank (HSDB, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.
  4. E.J. Calabrese and E.M. Kenyon. Air Toxics and Risk Assessment. Lewis Publishers, Chelsea, MI. 1991.
  5. R.D. Morris, A. Audet, I.F. Angelillo, T. C. Chalmers, and F. Mosteller. Chlorination, Chlorination by-products, and cancer: A meta-analysis. American Journal of Public Health, 82(7):955-977. 1992.
  6. U.S. Environmental Protection Agency. Ambient Water Quality Criteria for Chlorine. EPA 440/5-84-030. Office of Water Regulations and Standards, Washington, DC. 1985.
  7. American Council of Government of Industrial Hygienists (ACGIH). Documentation of the Threshold Limit Values. Fourth Edition. Cincinnati, OH. 1986.
  8. U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances (RTECS, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.
  9. J.E. Amoore and E. Hautala. Odor as an aid to chemical safety: Odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. Journal of Applied Toxicology, 3(6):272-290. 1983.

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