1-Hydroxypyrene, a biomarker of exposure to polycyclic aromatic hydrocarbons (PAHs), is analyzed in urine samples. 1-Hydroxypyrene is the major biomarker of exposure to pyrenes. 1-Hydroxypyrene is the orally active agonist for aryl hydrocarbon receptor (AhR) and can lead to renal fibrosis[1][2].