to answer these questions we had different. at the could so institute in strasbourg scientists spend more than 18 months on a study investigating life estate residues and hair samples from hundreds of people in use at all 6 we take strands less than 3 centimeters long. hair is considered a reliable bio monitoring tool to measure long term exposure to harmful substances . because of what. we found life is a residues in the hair of half the subjects which means that these people have been chronically contaminated with this substance exposed to. the study draws no conclusion as to whether this poses a health hazard but it does show how prevalent the substances in the environment.