(Beyond Pesticides, March 19, 2009) Researchers investigating the long-term immune effects of dioxin have found that exposure to dioxin during development or while nursing diminishes the capacity to fight infection later in life. The study, published in Toxicological Sciences, reported that mouse pups born to pregnant mice that were exposed to a small amount of dioxins had fewer white blood cells that normally kill the flu virus and more of a different kind that increases lung inflammation.
The study entitled, “The aryl hydrocarbon receptor affects distinct tissue compartments during ontogeny of the immune system,” aimed to identify the critical windows of exposure where fetuses are most sensitive to dioxin’s harmful effects. Pregnant mice were given a dose of 1,000 ppt dioxin either during pregnancy, lactation, or throughout pregnancy and lactation. After dosing, mothers and pups were kept dioxin-free. Researchers then infected mothers and pups with a non-lethal dose of the influenza virus.
Researchers found that the number of specialized white blood cells – referred to as CD8+ T-cells that specifically recognize and kill the flu virus, were significantly reduced in the pups but not their mothers. The most severe reduction in these white blood cells was seen when dioxin was administered only while the pups were nursing. Conversely, a different type of white blood cell, known as neutrophil, significantly increased in the dioxin-exposed pups. Neutrophils, important mediators of inflammation, were most severely increased when dioxin was given late in gestation and during lactation. The mothers of the pups mounted a normal immune response to the influenza infection with no decrease in CD8+ T-cells or increase in neutrophils.
These results illustrate how dioxin exposure in the womb, and/or during nursing, can permanently impact the development of the immune system. They also reaffirm the significance of the impacts of early exposures to harmful chemicals which can result in long-term changes that affect normal biological responses later in life. One notable aspect of this study was that changes in immune response were observed even though the pups were exposed a few times to a low-level dose of dioxin. This means that short-term exposures (as opposed to long-term, continuous exposures) can have significant long-term impact, especially if these exposures occur during important early developmental stages.
Dioxin refers to a family of chemicals linked to cancer, weakened immune systems and reproductive problems. They are persistent organic pollutants that bioaccumulate in humans and other animals, especially in fatty tissue. The main route of human exposure is through diet, especially through foods contaminated with pesticides and other hazardous chemicals that degrade or transform into dioxin. As seen in this study, dioxins are also transmitted from mother to child through breastfeeding. Previous reports have stated that infants exposed to high levels of dioxin in utero suffered poor psychomotor skills, altered thyroid hormone levels, and reduced neurological optimality.
The most infamous dioxin, 2,3,7,8-tetrachlorodibenzo-p-Dioxin (TCDD), is the most dangerous form of dioxin and part ingredient of Agent Orange, once used during the Vietnam War. War veterans exposed to Agent Orange have developed chronic lymphocytic leukemia, Hodgkin’s disease and non-Hodgkins lymphoma and diabetes. Many children of veterans exposed have been affected by their parents’ exposure to the chemical and show a wide range of symptoms.
Dioxin has been found in milk, cheese, beef, pork, fish, chicken, and other animals, as well as soil and sewage sludge. High levels of dioxin still exist in the Tittabawassee and Saginaw rivers and floodplains in Michigan, after being dumped there decades ago by Dow Chemical Co. Clean-up and restoration for these systems are still being debated. Even though dioxin levels in the environment have dropped considerably in recent years from their peak in the late 1970’s, it is important to be vigilant in the foods consumed in order to avoid increasing risk of exposure, since dioxins are persistent and bioaccumulative. A diet rich in organic foods can help minimize risk of dioxin exposure.
Source: Environmental Health News