A 1991 study,[14] fourteen years after the accident, sought to assess the effects on the thousands of persons that had been exposed to dioxin. The most evident adverse health effect ascertained was chloracne (193 cases). Other early effects noted were peripheral neuropathy and liver enzyme induction. The ascertainment of other, possibly severe sequelae of dioxin exposure (e.g., birth defects) was hampered by inadequate information; however, generally, no increased risks were evident.
A study published in 1998 concluded that chloracne (nearly 200 cases with a definite exposure dependence) was the only effect established with certainty. Early health investigations including liver function, immune function, neurologic impairment, and reproductive effects yielded inconclusive results.
An excess mortality rate from cardiovascular and respiratory diseases was uncovered, and an excess of diabetes cases was also found. Results of cancer incidence and mortality follow-up showed an increased occurrence of cancer of the gastrointestinal sites and of the lymphatic and hematopoietic tissue. Results cannot be viewed as final or comprehensive, however, because of various limitations: the lack of individual exposure data, short latency period, and small population size for certain cancer types.
A 2001 study confirmed in victims of the disaster, that dioxin is carcinogenic to humans and corroborate its association with cardiovascular- and endocrine-related effects. In 2009, an update including 5 more years (up to 1996) found an increase in "lymphatic and hematopoietic tissue neoplasms" and increased breast cancer.[15]
A 2008 study[16] evaluated whether maternal exposure is associated with modified neonatal thyroid function in the highly exposed population in Seveso and concluded that environmental contaminants such as dioxins have a long-lasting capability to modify neonatal thyroid function after the initial exposure.
The male children of mothers who were, during pregnancy of those children, exposed to high levels of toxic dioxins due to the Seveso disaster, have been found to have lower-than-average sperm counts. This result of the underlying Seveso study has been noted to provide the most pronounced evidence for prenatal exposure to an environmental chemical causing low sperm counts.[17]
