Recycled toilet paper: A novel source of sensitizer contamination in rivers

Abstract Sensitizers contain an aromatic ring, accumulate in aquatic biota, exhibit the aryl hydrocarbon receptor-mediated activity. Effluent from paper recycling plants has been identified as a source of contamination. The presence of sensitizers in toilet paper may be a novel source in the aquatic environment. To examine possible sources of contamination by sensitizers, this study investigated the levels of sensitizers in recycled toilet paper. We also studied the prevalence of sensitizers in rivers receiving effluents from sewage treatment plants in Japan, between 2020–2022. We detected 8 sensitizers and related compounds in both toilet paper and river water samples; their total concentrations ranged between 0.78–34 µg/g (mean: 12 µg/g) for toilet paper and 58–1167 µg/L (median: 77 µg/L) for water. In the water samples, sensitizers and related compounds were partitioned between liquid and suspended solid phases, and in suspended solids, sensitizers and related compounds accounted for an average of 42% of the total. Correlation analysis showed a high correlation between sensitizer and related compound composition in the water from a river receiving sewage treatment plant effluents and toilet paper (0.82 < r < 0.87 on average, during the survey period). This study was the first to detect 4,4'-dimethyldiphenylmethane, 1,1-di(4methylphenyl)ethane, m-terphenyl, and benzyl 2-naphthyl ether in paper products. Since these compounds were also detected in the water samples analyzed in this study, toilet paper should be considered a novel source of sensitizer and related compound contamination in sewage treatment systems.