Evaluation of pH as an Indicator for Assessing Rinsing Efficiency in Automated Washing in the Central Sterile Supply Department

Automated washing in the Central Sterile Supply Department (CSSD) is crucial for effective disinfection and sterilization, and rinsing performance must be evaluated. However, no clinically feasible method for evaluating rinsing efficiency has been established. In rinse performance testing, process chemical manufacturers typically assess pH, conductivity, and detergent residues. Therefore, we examined whether pH could serve as an indicator of rinsing efficiency by relating the pH of diluted detergents to cell viability. Five Japanese detergents for automated washing (two alkaline, one mildly alkaline, and two neutral enzymatic) were serially diluted and their pH measured. L929, SIRC, and Chang conjunctiva cells were tested, and viability was determined by the MTT assay using ultrapure water as the control. According to ISO 10993-5:2009, viability of 70% or higher was judged non-cytotoxic. For alkaline and mildly alkaline detergents, pH decreased with dilution, and at non-cytotoxic concentrations pH was consistently lower than at cytotoxic concentrations, suggesting that pH may indicate cytotoxicity in rinse wastewater. In contrast, neutral enzymatic detergents showed little pH change, so pH could not distinguish cytotoxic from non-cytotoxic concentrations; thus, our results indicate that pH may serve as one indicator for rinse performance testing for alkaline and mildly alkaline detergents.