Bis(1-ethylpentyl) Phthalate-d4, is the labeled analogue of Bis(1-ethylpentyl) Phthalate (B433990), one of the phthalate esters, which are ubiquitous environmental contaminants that interact with peroxisome proliferator-activated receptors (PPARs), a family of nuclear receptors. It is used as a plasticizer to impart softness and flexibility to PVC products.