Chlor-Alkali Manufacturing
Since the late-1800s, chlor-alkali plants have used large vats containing several tons of elemental mercury as a catalyst to convert salt water into common chemicals such as caustic soda (sodium hydroxide), potash (potassium hydroxide), chlorine gas, chlorine bleach (sodium hypochlorite), hydrogen gas, and hydrochloric acid. It is well-established in the chemical industry that this process causes some level of mercury contamination in those chemicals. Further, chlor-alkali plants have been the source of extensive mercury contamination via emissions and waste-water effluent, such as the Minimata mercury poisoning incident in Japan. Mercury emissions are measured and accounted for at U.S. chlor-alkali plants. An additional 20 - 100 tons of mercury annually has been unaccounted for (“lost”, but not due to emissions), with some of this mercury contaminating consumer products. Advances in technology have successfully allowed these plants to cost-effectively convert to a mercury-free process. However, as this new technology’s use is not federally mandated, there are chlor-alkali plants in the U.S. that continue to use the mercury-based process. Plants using mercury as a catalyst are called “mercury-cell chlor-alkali plants”, and chemicals produced at those plants are known as “mercury-grade” (e.g., “mercury-grade caustic soda”) or alternatively as “rayon-grade”.
Chlor-alkali chemicals are widely utilized as an ingredient in consumer products as diverse as polyurethane flooring, polyvinyl chloride (PVC), and food additives such as MSG, sodium benzoate, and potassium benzoate. Chlor-alkali chemicals are also used to process the raw ingredients and to adjust pH levels in many chemical processes, including the corn wet-milling process that produces High-Fructose Corn Syrup (HFCS), dextrose, corn starch, and other corn sweeteners for human consumption. Corn wet-milling products are used to produce citric acid and aspartame (NutraSweet). Corn wet-milling products not destined for human consumption are used as livestock feed for cattle, turkeys, pigs, and chickens. Chlor-alkali chemicals are also used to produce products such as pharmaceuticals, bleach, and toothpaste, and are important for water purification.
A peer-reviewed study by Renee Dufault et al was published in January 2009 on mercury levels in HFCS. The HFCS samples, which were collected at the FDA in 2005, contained total mercury in the 0.000 – 0.570 mcg Hg per gram of HFCS (i.e. 0.000 – 0.570 ppm). As comparison, fish at 1 ppm methylmercury exceed the FDA action level and are not allowed to be sold. Per capita consumption of corn sweeteners grew rapidly from 9 to 40 grams (2 to 10 teaspoons) per day from 1978-1985, primarily due to introduction of HFCS into soft drinks and dextrose into foodstuffs, and is currently at about 50 grams (12 teaspoons) per day. Corn sweeteners are used as a primary ingredient in a wide range of food products, including many that are not readily obvious, such as the dextrose used in IV feeding solutions for premature infants and certain types of baby formula. Further, per the Dufault study, there seems to have been a preference by corn sweetener producers to utilize mercury-grade caustic soda (rather than other grades of caustic soda) due to its preservative qualities.
As for ending this mercury contamination, progress is being made towards banning the mercury-cell chlor-alkali process:
- In the USA, Oceana is an environmental organization that has been pressing for a ban on the use of mercury in chlor-alkali production. Oceana has produced informative reports on when certain USA chlor-alkali plants have converted to mercury-free manufacturing and which ones still utilize the mercury chlor-alkali process. In 2007, then-Senator Barack Obama sponsored an Oceana-inspired bill to eliminate the mercury-cell chlor-alkali manufacturing process. The bill has been re-introduced to the 2009 Congress.
- Internationally, governments are also taking action to encourage or mandate the conversion of chlor-alkali plants to mercury-free technology.
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