HUMAN EXPOSURE TO NATURALLY-OCCURRING HYDROQUINONE

Hydroquinone (HQ) is a nonvolatile chemical used in the photographic, rubber, chemical, and cosmetic industries. HQ is also known to occur i n nature as the beta-D-glucopyranoside conjugate (arbutin), and free H Q is a known component of cigarette smoke. Low concentrations of HQ ha ve been detected in the urine and plasma of humans with no occupationa l or other known exposure to HQ. The studies reported here investigate dietary and other potential sources of HQ and their contribution to H Q concentrations in the plasma and urine of human volunteers. Analysis of possible food sources of HQ by CC indicated significant amounts of arbutin in wheat products (1-10 ppm), pears (4-15 ppm), and coffee an d tea (0.1 ppm). Free HQ was found in coffee (0.2 ppm), red wine (0.5 ppm), wheat cereals (0.2-0.4 ppm), and broccoli (0.1 ppm). After consu ming a meal including arbutin- and HQ-containing foods, volunteers sho wed significant increases in plasma and urinary levels of HQ and its c onjugated metabolites (total HQ). Mean plasma concentrations of total HQ peaked at 5 times background levels at 2 h after the completion of the meal, and mean urinary excretion rates of total HQ peaked at 12 ti mes background at 2-3 h after the meal. Immediately after smoking four cigarettes in approximately 30 min, mean plasma concentrations of tot al HQ were maximally 1.5 times background levels; mean urinary excreti on rates of total HQ peaked at 2.5 times background at 1-3 h after smo king. These data indicate that considerable human exposure to HQ can r esult from plant-derived dietary sources and, to a lesser extent, from cigarette smoke.