Conformity of commercial bleachers and stability of 1g/l dilutions using different drinking water sources

Abstract

Bleach, known as Sodium Hypochlorite (HS) solution, is a broad-spectrum, fast-acting, widely available germicidal agent that is key in infection control. In the context of COVID-19, the WHO recommends the use of HS 1 g/L, since it inactivates SARS-CoV-2 and most environmental pathogens. However, few studies evaluate the stability of diluted solutions and none consider the influence of the hardness of the water used for their preparation. The objective of the work was to verify the concentration of active chlorine (ACC) in commercial brands of HS and to study the stability to propose a beyond use date (BDU) for solutions of HS 1 g/L, with drinking water from different sources.

The CCA was determined as a function of time (by iodometric titration) in 5 different commercial preparations (nominal concentration between 25-60 g/L) and in dilutions of 1 g/L (in triplicate), using water from different water treatment plants in Córdoba, Argentina. The samples were stored at room temperature, exposed and protected from light. The BUD was reached when the CCA fell below 90% of the initial. Assays were performed in triplicate and are reported as the mean (±SD).

The CCA in the commercial solutions was within the acceptable values, as established in the current regulations. Light-protected dilutions showed less than a 10% decrease in CCA during the first 10 days of testing, and one sample exceeded the acceptance limit after 14 days. In contrast, in the light-exposed sample, the CCA fell to 96.4% at 24 hours and 79.3% after 48 hours. No differences related to drinking water sources were observed.

The nominal CCA was confirmed in all commercial brands tested. Regardless of the drinking water source used for dilution, 1 g/L HS solutions were stable for 10 days when stored at room temperature and protected from light. In contrast, light-exposed solutions maintain CCA for only 24 hours.