Recently studies in Maine demonstrated the presence of per- and poly-fluoroalkyl compounds (PFAS) that are resistant to degradation in eggs from backyard hens where the chemical was identified in drinking water. This suggests that hens could serve as valuable monitors of environmental contamination.  Approximately 30 communities in Maine are affected including Westbrook, Gorham, Auburn and Fairfield.  The contamination with "forever chemicals" follows spreading of industrial sludge and waste on fields resulting in contamination of soil with percolation to shallow water tables.  

Previously hens in suburban areas of New York City metro showed high levels of lead contamination in their eggs as a result of accumulation in soil and vegetation. Vehicle exhaust, prior to the banning of lead additives to gasoline was the source of lead contamination.