The use of lead stabilizer in Chinese imported trees has been an issue of concern among politicians and scientists over recent years. A 2004 study found that while in general artificial trees pose little health risk from lead contamination, there do exist "worst-case scenarios" where major health risks to young children exist. A 2008 United States Environmental Protection Agency report found that as the PVC in artificial Christmas trees aged it began to degrade. The report determined that of the fifty million artificial trees in the United States approximately twenty million were nine or more years old, the point where dangerous lead contamination levels are reached. A professional study on the life-cycle assessment of both real and artificial Christmas trees revealed that one must use an artificial Christmas tree at least twenty years to leave an environmental footprint as small as the natural Christmas tree.