Agriculture Reference
In-Depth Information
Chlorine Dioxide
Chlorine dioxide is a small, volatile, and highly energetic molecule. In contrast to the
hydrolysis of chlorine gas in water, chlorine dioxide in water does not hydrolyze to
any appreciable extent but remains in solution as a dissolved gas (Aieta and Berg
1986). Chlorine dioxide cannot be stored commercially or shipped as a gas because
it is highly explosive under pressure; therefore, it must be generated at the point of
use. There are multiple ways to generate chlorine dioxide. Most conventional genera-
tors react sodium chlorite (NaClO
2
) with gaseous chlorine (Cl
2
), hypochlorous acid
(HClO), or hydrochloric acid (HCl) to generate chlorine dioxide gas (ClO
2
). The reac-
tions are as follows (Anonymous 1999):
Gaseous chlorine - chlorite solution:
2
+= +
Aqueous chlorine - chlorite solution:
NaClO
Cl
2
ClO
2
NaCl
2
2
2
2
NaClO
+
HClO
=
2
ClO
+
NaCl
+
NaOH
2
2
Acid - chlorite solution:
5
NaClO
+
4
HCl
=
4
ClO
+
5
NaCl
+
2
H O
2
2
2
Electrochemical generators cycle sodium chlorite solutions through an electrolyte cell
to generate chlorine dioxide.
Compared to the amount of information available on chlorine as an antimicrobial
for fresh produce, much less is available about aqueous chlorine dioxide on the effec-
tiveness as an antimicrobial for fresh and fresh-cut produce. One benefi t of using
chlorine dioxide instead of chlorine is that chlorine dioxide produces fewer potentially
carcinogenic chlorinated by-products such as trihalomethanes in the presence of
organic material (Richardson and others 1998). Chlorine dioxide is also less affected
by pH and is typically used between pH 6-10 (Dychdala 1991). However, like chlo-
rine, the antimicrobial activity of chlorine dioxide is diminished in the presence of
organic matter that reacts and reduces chlorine dioxide's effectiveness (Dychdala
1991; Beuchat and others 2004b). As a dissolved gas in water, chlorine dioxide will
off-gas if the concentration in solution or the water temperature is too high or if agita-
tion is added to the wash system (Kelley 2004). From a safety perspective, levels as
low as 3 ppm chlorine dioxide used in recirculated wash water led to off-gassing and
caused respiratory discomfort for workers (Reina and others 1995; Roberts and
Reymond 1994). Thus, in indoor situations ventilation equipment would be necessary
to prevent worker exposure to excessive chlorine dioxide vapors.
Chlorine dioxide is approved for use as an antimicrobial agent in water used to
wash fruits and vegetables that are not raw agricultural commodities in the amount
not to exceed 3 ppm residual chlorine dioxide (Anonymous 2007a). In addition, the
treatment of produce with chlorine dioxide must be followed by a potable water rinse
or blanching, cooking, or canning. Although the inactivation mechanism of chlorine
dioxide is not well understood, it is thought that chlorine dioxide disrupts the outer
