Health Effects of Long-Term Exposure to 2,3,7,8- Tetrachlorodibenzo-p-dioxin

In 1971, sludge wastes contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were mixed with waste oil and sprayed on a dirt road in a residential mobile home park in Missouri, USA. In 1984, we performed a comprehensive examination of 154 persons exposed at that site and 155 unexposed persons to determine whether these environmental TCDD contaminations had induced any acute/subacute health effects. There were no consistent differences between the two groups on medical history, physical examination, serum and urinary chemistries, and neurologic tests. Results of liver function tests suggested possible subclinical effects: i.e., higher mean urinary uroporphyrin levels and lower mean serum bilirubin levels in the exposed group and statistically significant direct dose-response relationships of serum levels of five enzymes that may originate in the liver (i.e., SGOT, SGPT, GGTP, alanine aminopeptidase, and beta-glucuronidase) by years of residence at the contaminated site (i.e., a surrogate for cumulative TCDD dose). Although these findings may indicate the presence of subclinical hepatotoxic effects, their significance must be interpreted cautiously. Immunologic tests showed that the exposed group had an increased frequency of anergy (11.8% vs. 1.1%) and relative anergy (35.3% vs. 11.8%); the exposed group also had non-statistically significant increased frequencies of abnormal T-cell subset tests (10.4% vs. 6.8%), a T4T8 ratio <1.0 (8.1% vs. 6.4%). and an abnormality in the invitro functional T-cell tests (12.6% vs. 8.5%). These findings suggest that long-term exposure to TCDD is associated with depressed cell mediated immunity, although the effects have not resulted in an excess of clinical illness in the exposed group. Further studies are indicated to elucidate the pathophysiology and clinical significance of all of these findings. Studies are in progress to follow affected individuals to see if normal cellular immune function and/or hepatic function is recovered or clinical disease develops; other studies are planned to correlate adipose tissue levels of TCDD with measured health effects.