Human made chemical compounds called organohalogens get loads of attention as they are best known for their often harmful effect on the environment - substances like the CFCs (the ozone-damaging chemicals), dioxin (found in the herbicide Agent Orange), PCBs (industrial fluids) and several pesticides.
Their naturally occurring cousins, however, don't get the recognition they deserve, according to Dartmouth Chemistry Professor Gordon Gribble. Gribble has taken it upon himself to help scientists and the public understand that there are more than 4,000 naturally occurring organohalogens, and many are similar or even identical to their synthetic counterparts.
"Humans have been manufacturing organohalogen compounds like bleach, pesticides, pharmaceuticals, and other industrial chemicals for decades," says Gribble, who wrote about these compounds in the July-August issue of American Scientist, the magazine of the scientific research society Sigma Xi. "I think researchers forget to look to nature for remarkable examples of similar and often identical halogenated organic chemicals. These amazing compounds are a vital part of life, and they serve natural purposes as hormones, pheromones, repellents and natural pesticides."
Organohalogen compounds all contain one of the halogen elements chlorine, bromine, iodine or fluorine. Gribble keeps a record of newly discovered natural organohalogens. Because of improved underwater exploration and research capabilities, most new ones, he says, are being found in the ocean's marine life. The cone snail, for instance, which lives in tropical marine environments, produces a bromine-based venom that is extremely toxic to people, but allows the snail to effectively immobilize and kill its prey. Gribble explains that the cone snail's particular organobromine peptide is in human clinical trials for the treatment of pain.
"Sponges and tunicates are great examples of using chemicals for survival," says Gribble. "Being anchored to the reef, they can't swim and they don't have protective shells or teeth, so they biosynthesize chemicals for defense, many of which contain halogen due to the ocean's high salt content." Sponges and other marine organisms produce a variety of bromine-based organohalogens, which repel predatory fish and prevent bacterial overgrowth, he says. These compounds are being studied to someday prevent barnacle growth on the underside of ships. Several other marine organohalogens have promising medicinal value, including treatment for cancer, bacterial infection and HIV.