Butter could help monitor airborne pollution. Scientists at the University of Lancaster, UK, have used butter to track persistent organic pollutants (POPs) and other chemicals. When these pollutants get deposited on the ground cows consume them and the compounds accumulate in dairy fat. The researchers' analysis of commercial butter samples from 23 countries found the level of POPs high enough to make butter a meaningful medium for comparing levels of organic pollutants in different regions, says a report dated March 26, 2001 in the New York Times .