Pollutants in students' blood unrelated to recent food/dust exposure.

Roosens, L, A-E Mohamed, S Harrad, H Neels and A Covaci. 2009. Current exposure to persistent polychlorinated biphenyls (PCBs) and dichlorodiphenyldichloroethylene (p,p'-DDE) of Belgian students from food and dust. Environmental Science and Technology doi:10.1021/es9021427.

Levels of persistent organic pollutants in the blood of university students in Belgium may be more related to their historic, not current, exposures.

The authors of the study– which was published online in the journal Environmental Science and Technology – report the levels of PCBs and a DDT marker in the students' blood samples were not associated to the food or dust they recently ate.

This study found that the amounts of the chemicals in the food the students ate were 100 to 200 times higher than in the dust they breathed in their rooms. Prior studies also have reported that food is a bigger source of the persistent pollutants than dust.

Yet, the authors found no associations between the chemicals in the food and the levels in the blood of the participants. Because of that, the researchers speculate that blood levels in the students are due more to past than current exposure since the pollutants remain in the body for months or even years. Another explanation is that the recent high exposures were not captured in this study.

While different in structure and use, PCBs and DDT are types of long-lived pollutants that can persist in the environment, concentrate through food chains, and accumulate in fatty tissue of wildlife and people. They are slow to leave the body and are linked to some endocrine effects and cancers.  They can be toxic to wildlife.

Massive quantities of PCBs were produced and used in electrical transformers, paints, lubricants and other products during the 1950s and 1960s. Their insulating properties and resistance to heat and breakdown also made them persistent in the environment. They remain widespread despite a ban on their production in the 1970s.

DDT - also banned in North America in the same decade – is still used as an insecticide in some tropical countries to control mosquitoes and malaria outbreaks. DDE – DDT's main breakdown product – commonly contaminates fish and fatty foods.

Exposure to both chemical types have leveled off after rapid decreases during the 1980s and 1990s following their bans.

It is not known how much of the current, low PCB and DDE exposure in people is due to food, dust or other sources. To find out, researchers followed 19 students at the University of Antwerp. The study's authors collected the same meals the students ate for one week, dust from the students' rooms, and blood samples. The food, dust and blood samples were measured for five types of PCBs and DDE.

The results reaffirm that food – and not dust – is the main source of exposure for the chemicals measured. Daily exposures to PCBs and DDE from food were up to 200 times higher than dust. Researchers found that the students were exposed to up to 204 nanograms per day of PCBs and 214 nanograms per day of DDE in food and a maximum of 1.7 nanograms per day of PCBs and 1.1 nanograms per day of DDE from dust.

Blood levels of PCBs and DDE in these students were lower than what has been measured in people in other European countries. No relationship was found between blood levels of these contaminants and recent diet or dust exposure for these people. Therefore, the researchers believe the body levels are from historical exposures.