4. What are the effects of dioxins on human health?
- 4.1 Have dioxins caused cancer to humans?
- 4.2 What non-cancer effects have been observed in children?
- 4.3 What non-cancer effects have been observed in adults?
4.1 Have dioxins caused cancer to humans?
4.1.1 Most information on the carcinogenicity of the dioxin 2,3,7,8-TCDD in humans comes from epidemiological studies of both accidentally exposed workers in herbicide plants and people living near the Seveso chemical factory in Italy.
However, most studies concern mixtures of several kinds of dioxins. As such, the evaluation of risks for individual dioxins is difficult. The 2,3,7,8-TCDD levels of exposed herbicide workers were comparable to the ones that induced liver cancers in rats, but on average, the exposures around Seveso were lower. More...
4.1.2 Herbicide plant workers heavily exposed to dioxins had more cancers of all types combined than the general population. The number of cancers increased with exposure (dose-response relationship).
In Seveso, the number of deaths due to cancer has not increased since the accident, but it is still too early to reach definite conclusions. However, several studies showed excess risks for some specific cancers.
A 22 year study of people in Japan who ate rice oil highly contaminated with PCBs and other dioxin-like compounds, showed an increase in liver cancer. No cancer increase was found after 12 years for another group in Taiwan who ate rice oil that was less contaminated.
In summary, there is strong evidence that people accidentally exposed to the highest dioxin levels had an increased overall cancer risk (about 40% increase); there is less strong evidence of increased risks for specific cancers. In comparison, the average exposure of the general population is a hundred to a thousand times lower for TCDD and ten to hundred times lower for all dioxins combined. More...
4.2 What non-cancer effects have been observed in children?
Studies showed neurodevelopmental delays and neurobehavioral effects in children. The effects are attributed to exposure of the unborn child through the placenta rather than through breast feeding. These effects even occurred at background levels, but only affected the infants with the highest exposure. In at least one US study, mothers were, however, simultaneously exposed to chlorinated pesticides and heavy metals.
Following the rice oil contamination incidents in Japan and Taiwan, effects, at least partly related to dioxins, were observed in new born children due to pre-birth exposure. Effects included skin defects, general persistent development delays, low birth-weight, mild behavioral disorders, decrease in penis length at puberty, reduced height among girls at puberty and hearing loss.
A study in the Netherlands showed that breast fed infants had a better neurobehavioural development compared to formula fed infants. However, within the group of breast fed infants, those receiving milk with higher dioxin content had poorer neurobehavioural test results.
In Seveso, it was observed that fathers highly exposed to TCDD had a lower boy to girl birth ratio than normal. More...
4.3 What non-cancer effects have been observed in adults?
Information on effects in adults comes from several studies of populations exposed to high levels of dioxins: the US Air Force staff who were exposed to the Agent Orange defoliant in Vietnam, a second study in Vietnam, studies in the populations around the Seveso chemical factory, and of the contaminated rice oil incidents in Japan and Taiwan.
Exposed workers showed biochemical effects including elevated levels of gamma GT, triglyceride and glucose in blood and an increase in diabetes. In Seveso, data show an increased death rate in women from diabetes and from cardiovascular diseases in men. A higher rate of heart diseases was also observed in some occupationally exposed groups of men.
Adults affected by contaminated rice oil experienced various effects including a skin rash called chloracne, conjunctivitis, sebaceous cysts and inflammation, decreased nerve conduction velocity, fatigue and malaise, skin problems (hyperpigmentation and hyperkeratosis), as well as an increased death rate from non-cancer liver diseases. More...