PBO is one of the chemicals selected by EPA to be part of the initial effort under the EDSP. The EPA issued its first list of chemicals for EDSP testing in 2009, consisting of over 60 pesticide chemicals, including the insecticide synergist PBO. The first list of chemicals for EDSP screening is not based on a potential for endocrine activity or a potential for adverse effects. Rather, the list is based on an EPA prioritization regarding exposure potential. PBO was added to this list because of its wide use pattern (1500 products registered with US EPA), and people may be exposed to low levels of PBO in their diets, from treated surfaces in their homes (e.g., carpet), and in certain occupations (e.g., pest control operators).