First Detection of Fluorescent Brighteners in Breast Milk and Urine of Lactating Mothers from South China: Occurrence, Determinants, and Potential Infant Exposure

Fluorescent brighteners (FBs) are ubiquitous in the environment and may enter the human body via sources such as indoor dust, drinking water, and daily-use products. However, data on their occurrence, profiles, and determinants in humans remain limited. This study presents the first biomonitoring of 25 FBs in matched breast milk and urine samples from 99 lactating mothers in South China. Up to 12 nonionic and 12 ionic FBs were detected, with detection frequencies ranging from 5% to 96%, marking their first reported occurrence in these biological matrices. Median FB concentrations were 5.83 ng/mL in breast milk and 13.1 ng/mL in urine, with ionic FBs being more abundant than nonionic FBs. Comparative analysis indicated that ionic FBs were primarily excreted in urine, while nonionic FBs exhibited higher detection frequencies and concentrations in breast milk compared to urine. Multivariate analysis revealed that greater consumption of convenience foods and bottled water was associated with increased nonionic FB exposure, whereas higher use of personal care products predicted greater ionic FB exposure. Exposure assessment identified breastfeeding as a significant pathway for infant FB exposure. Although the high estimated daily intakes (2190 ng/kg bw/day) may not pose immediate risks, it exceeded levels of some well-known toxicants such as PFASs by several fold. This elevated exposure raises concerns about long-term health effects, highlighting the need for comprehensive toxicological assessments and ongoing exposure monitoring.