Another Natural Chlorinated Compound Discovered

Published November 1, 2000

Researchers with Canada’s Wildlife Service have discovered a brominated and chlorinated chemical, C10H6N2Br4Cl2 (1,1-dimethyltetrabromodichloro-2,2-bipyrrole), in marine aquatics.

Sheryl Tittlemier and colleagues note in the January 1999 issue of Environmental Science & Technology that the chemical, first discovered in 1988, behaves like PCBs–some of the world’s most-criticized industrial wastes– yet it originates from something natural in the oceans.

Environment Canada (EC) researchers have christened the new chemical HDBPs, for Halogenated Dimethyl BiPyrroles. According to Ross Norstrom, EC project leader, the chemical appears to originate naturally, as a product of biosynthesis (production of a chemical compound by a living organism). If true, the new chemical’s discovery calls into question the anti-chlorine activists’ most fundamental premise: that chlorinated compounds are “unnatural,” and therefore dangerous.

HDBPs have been found in Pacific Ocean and Atlantic Ocean samples, but not in samples from the Great Lakes. Since the Great Lakes is an industrial center inhabited by nearly 40 million persons, if a chemical doesn’t exist here, it probably isn’t industrial. The apparent absence of HDBPs from the five freshwater Great Lakes also suggests they are not airborne, according to science reporter Tom Spears, writing in Priorities for Health.

No one knows where HDBPs originate. Wildlife researchers suspect that marine bacteria secrete them as a defense against predators; or, as Spears notes, they may be a slow macroscopic organism incapable of fighting, such as a sponge or a marine worm. This would make HDBPs similar to the natural toxic chemicals that appear to be present in all plants, which serve to protect them against fungi, insects, and animal predators. Bruce Ames and his colleagues have suggested we are ingesting in our diet at least 10,000 times more by weight of these toxins–natural pesticides–than of manmade pesticide residues.

Although nearly 2,400 naturally produced organohalogens have been identified, these natural sources are often overlooked by regulators and environmental activists. A report from the Science Advisory Board to the International Joint Commission on the Great Lakes concluded, for example, “There is something non-biological about the halogenated organics.” And articles in Science and elsewhere have noted that “some types of synthetic compounds, including halogenated hydrocarbons such as PCB, are not found in nature.”

There is no conclusive evidence that the background levels of PCBs to which some occupational groups are exposed have resulted in acute effects, increased cancer risk, endocrine disruption, or any harm to children exposed to the chemical in utero. According to a position paper issued by the American Council on Science and Health in 1997, the only health effects that have been attributed to PCBs are skin and eye irritation. Nevertheless, as William Baarschers pointed out in his 1996 book, Eco-Facts & Eco-Fiction, the general perception is that PCBs are “linked to cancer” or are “cancer-causing chemicals.” Such unfounded fears have resulted in complex legislation that makes transport–and cleanup–of PCBs difficult and expensive.

Dr. Renate Kimbrough, the scientist who conducted the original PCB research in 1975, published in 1999 the results of a long-term study of occupational exposure to PCBs. Kimbrough’s original work showed that force-feeding rats their body weight in PCBs once a day will eventually give some of them liver cancer. For her more recent work, Kimbrough studied humans–more than 7,000 former GE employees who worked with PCBs between 1946 and 1977. Hers was the fifth such study to conclude PCBs pose no cancer risk to humans.

Chemicals like PCBs and DDT have been banned because they “bioaccumulate”–that is, their concentrations in the environment (water sediment, soil, etc.) build up in living organisms because the chemical is metabolized or eliminated very slowly. In her book The Dose Makes the Poison, M. Alice Ottoboni explains that some scientists have suggested unnatural (man-made) bioaccumulants cause reproductive problems in mammals, birds, and fish; other scientists have questioned this research.

On the basis that chemicals which combine chlorine and organic molecules are bioaccumulants, politicians in the U.S., Canada, and Mexico have moved steadily toward “zero-discharge” rules concerning them. Implicit in these rules is the notion that only unnatural chemicals are bioaccumulants.

HDBPs upset that apple cart, since they are a PCB-like bioaccumulant in marine aquatics. It can no longer be assumed that just because a chemical is building up, it must be man-made.

Jack Dini is a scientist and environmental writer in Livermore, California. He can be contacted by email at [email protected].

For more information

see Tom Spears’ article in Priorities for Health, “The Mystery of SNOB–Nature’s PCB?” at

William H. Baarschers book, Eco-Facts & Eco-Fiction: Understanding the Environmental Debate (Routledge, July 1996, 264 pages), is available for $24.99 (paper) and $75 (cloth) from

M. Alice Ottoboni’s book, The Dose Makes the Poison: A Plain-Language Guide to Toxicology (John Wiley & Sons, 256 pages) is available for $39.95 (paperback, May 1997) from