Variability in 24 hour excretion of cyanuric acid: implications for water exposure assessment.

Cyanuric acid (CYA) excretion in urine has been used to estimate the volume of water ingested during swimming and other recreational activities in outdoor pools containing this chemical. These estimates of water ingestion are based on the assumption of 100% excretion within 24 hours, but the supporting evidence for this is scant. While adapting this methodology to investigate other water ingestion scenarios, we observed a high degree of variability in cyanuric acid excretion among experimental subjects, with over 25% of individuals excreting less than 80% of an ingested dose. Use of cyanuric acid to measure inadvertent water ingestion may be a valuable tool to generate data for health risk assessment of non-potable water sources, but our observations indicate that this technique carries an inherent degree of underestimation that should be taken into account when calculating water exposure.