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1. INTRODUCCIÓN
The recent emergence of severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2) causing COVID-19 is a major
burden for health care systems worldwide. Consistent and correct
disinfection procedures are of enormous importance.
Bleach, also known as sodium hypochlorite solution, is a
germicidal agent, commonly used for surface disinfection. It is fast-
acting and effective against bacteria, fungi and viruses, even when
used in very low concentrations. It is also widely available at a low
cost (1–4).
Sodium hypochlorite solution is a strong oxidizing agent,
in which the CI atom of the available chlorine species, i. e. hypoch-
lorous acid (HOCl) and hypochlorite ion (OCl-) behave as Cl+, a
strong electrophile that reacts with substances of high electronic den-
sities (5).
The germicidal activity of sodium hypochlorite solutions
mainly depends on the concentration of HOCI species, since it can
passively diffuse through the cell wall and plasmatic membrane of
microbes, affecting both the exterior and interior of the cell. On the
contrary, the ionized OCl- has a low germicidal activity due to its li-
mited ability to diffuse through the microbial cell wall, and mainly
acts oxidizing the cell surface (Figure 1).
The relative concentration of available chlorine species is
significantly affected by the solution pH, which is known to also affect
the chemical stability of the solution (5).
Figure 1. A model that represent the mechanisms of the germicidal actions of HOCl and OCl- based on their ability to penetrate the membrane into the microbial cell.
Adapted from reference (5).
Compliance of commercial bleaches and stability of 1 g/L-dilutions
232 using different sources of drinking water
María E. Gavelli, Laura C. Luciani , Carolina Bustos, María E. Olivera
An. Real Acad. Farm. Vol. 86. Nº4 (2020) · pp. 231 - 236
ANALES
RANF
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As shown in equation 1, Cl2 predominates at acid pH; ho-
wever, it easily escapes from the solution since it is a low water so-
luble gas. As the solution pH increases, the equilibrium shifts towards
the formation of the HOCl species (prevalent at pHs between 5.5-
9.5) and OCl- (pHs above 11).
Cl2 H3O+ HClO OH- CLO- equation 1
^a ^a
As can be seen in equations 2 to 5, the standard electrode potentials
for the reduction of HOCI is higher than that of OCl- (5), which means
that HOCl species is more reactive; the challenge for practical use
of bleach is that although chlorine solution shelf-life is greatest at
pH>11 (pH of concentrated solutions), it is more effective in disin-
fecting at pH <8 (pH of diluted solutions) (6,7).
2 HClO+2H++2e- ¨Cl2+2 H2O E0=1.63 v equation 2
HClO+H++2e- ¨Cl-+ H2O E0=1.48 v equation 3
OCl-+ H2O +2e- ¨Cl-+OH- E0=0.81 v equation 4
Concentrated trademark presentations of bleach with avai-
lable chlorine concentrations between 20 to 110 g/L are regulated
as household products.
In the context of COVID-19, the World Health Organization
(WHO) has recommended the use of extemporaneously prepared
bleach solutions of 1 g/L, as a conservative concentration able to in-
activate SARS-CoV-2 and the vast majority of other pathogens that