Dioxin's 'fingerprint' lingers for decades.

Dioxin's 'Fingerprint' Lingers for Decades

Over time, the human body rids itself of some of its dioxin contamination. Only a few years ago, scientists thought that telltale residues even of high exposures would fade beneath the level of detection, erasing evidence of exposure, long before any manifestation of disease. But several new studies recently presented at an international meeting in Fukuoka, Japan, show that a characteristic, latent "fingerprint" of dioxin contamination remains in body fat more than 20 to 30 years after exposure. Two of the studies were even able to find that indelible fingerprint in the blood.

These studies, reported at the Sixth International Symposium on Chlorinated Dioxins and Related Compounds, hold open the prospect of at last identifying individuals who had heavy dioxin exposure in the past. It is by comparing their health against that of individuals with almost no exposure that dioxin's elusive toxicology is likely to be resolved.

Recently, several research teams have reported using sophisticated analytical techniques to identify an apparent low-level background human contamination with dioxins in industrialized societies (SN:7/13/85,p.26). But the exposures they identified were not necessarily old, nor did most show high elevations of dioxins in those individuals who had -- according to questionnaires -- received potentially heavy exposure. At the Japan meeting, several research groups reported finding fingerprints that appeared not only to be decades old but also to earmark signs of heavy exposure.

For example, traces of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were identified in the fat of six workers contaminated during a 1953 chlorophenol explosion in West Germany. Arnold Schecter of the State University of New York in Binghamton and John J. Ryan of Health and Welfare Canada in Ottawa report that one of these workers still carries TCDD levels of 141 parts per trillion (ppt) in his fat -- 10 to 20 times the general population's background level. "If we calculate back, using a five-and-a-half-year half-life, he must have had 12,000 ppt TCDD contamination at the time of the initial exposure," Schecter says. Ironically, he adds, this man was denied workmen's compensation for health problems because he's been unable to prove heavy contamination.

Inability to demonstrate contamination has also plagued U.S. Vietnam veterans with health problems that they believe may be the result of exposure to Agent Orange (SN:5/19/86,p.314), a defoliant contaminated with trace levels of TCDD. But at the meeting, a researcher with the New Jersey Agent Orange Commission in Trenton reported finding an average 10-fold excess of TCDD -- roughly 45 ppt in fat -- among 9 of 10 veterans who had been Agent Orange sprayers in Vietnam roughly 20 years ago. They compared this group with two sets of matched controls: veterans who never served in Southeast Asia and Vietnam veterans whose jobs should not have exposed them to Agent Orange. Until now, says Peter Kahn, a biochemist from Rutgers University in New Brunswick, N.J., and one of the study's authors, "nobody had established that heavily exposed Vietnam veterans had more [TCDD in them] than unexposed veterans."

Because the body stores dioxin in fat, human dioxin analysis has been done on fat-rich breast milk or on surgically extracted fat. Most researchers would prefer a simple blood test. At the Japan meeting, both Kahn's group and chemists from the Centers for Disease Control (CDC) in Atlanta independently reported for the first time being able not only to detect dioxin in the fat of blood from people who had fasted, but also to demonstrate that the concentration of dioxins in the blood's fat matches their concentration in the body's fat deposits. (Fasting draws stored fat into the blood.)

Both Kahn and Larry Needham at CDC say their technique needs some refinement before dioxin analysis can be reliably conducted using blood. Even then, Needham says, this type of analysis -- because it's complicated, expensive and requires a lot of blood -- is not likely to become "routine."