Temporal stability of the conjugated species of bisphenol A, parabens, and other environmental phenols in human urine

Human exposure to environmental phenols can be assessed by measuring the urinary concentrations of these compounds or their metabolites. Total concentrations, which include both free and conjugated (i. e., glucuronide and sulfated) species, are usually reported. Because conjugation may reduce the potential bioactivity of the compounds, measuring separately both the concentrations of free and conjugated species can be of interest. Data on the stability of these conjugated species in urine is critical if the concentrations of free and conjugated species are to be compared. Over a period of 6 months, we investigated the stability of the urinary conjugates of eight environmental phenols ( bisphenol A, 2-hydroxy-4-metoxybenzophenone or benzophenone-3, triclosan, 2,5-dichlorophenol, methyl paraben, ethyl paraben, propyl paraben, and butyl paraben) at three storage conditions ( room temperature, 4 degrees C, and -70 degrees C). After collection, conjugated species appeared to be stable for at least 7 days when the urine was stored at 4 degrees C, and for at least 180 days at -70 degrees C. By contrast, some of the environmental phenol conjugates commenced to degrade within 24 h after collection when the urine was stored at room temperature although the total concentrations remained relatively constant for at least 30 days. These results suggest that if the concentrations of free and conjugated species will be used for exposure assessment purposes, urine specimens collected for analysis of environmental phenols should be kept at room temperature for the shortest possible time after collection.