Is Chlorine Dioxide the Answer to the 'EtO Problem'?

The controversies surrounding ethylene oxide (EtO) use for sterilization of medical devices seemed to hit a crisis point last year when the Environmental Protection Agency (EPA) proposed new guidelines for its use to help dissipate the risks of environmental contamination and negative human health impacts like various cancers.

Since the proposal hit a shocked, and reasonably concerned, medical technology industry, multiple updates to alternative options have since been presented as a potential answer to the “EtO problem”.

ClorDiSys Solutions, a company providing decontamination and sterilization equipment and services to multiple industries, recently highlighted the potential uses of chlorine dioxide (CIO2) sterilization as a replacement for EtO in certain circumstances at MD&M West in Anaheim, CA. During the session, Emily Lorcheim, project manager of ClorDiSys, discussed the properties of CIO2, its benefits, and how it compares to EtO sterilization.

Chlorine dioxide

CIO2 sterilization is a chemical-based sterilization method which uses the gas phase of CIO2 as the active sterilant, according to FDA. The gas phase of the chemical can penetrate medical device packaging and sterilize it through an “oxidative mechanism at low sterilant concentration at room temperature and at atmospheric pressure,” Lorcheim said. “This sterilization process is validated using the overkill method to achieve a sterility assurance level of 10-6.”

During the sterilization process, chlorides, chlorites, and chlorates are left as residue. These residues, according to reported literature, have low toxicity concerns. Additionally, while compatibility information is limited, CIO2 is not incompatible with the most commonly used materials in medical devices including stainless steel, anodized aluminum, painted steel, plastics, gasket materials, and electronics. Lithium ion and other batteries are also compatible with CIO2.

CIO2 is a yellow green gas. The color provides the ability to monitor the distribution of the gas in real-time with a photometric device and can be controlled for parametric release. It is water soluble and considered to be as “true gas” at room temperature at use concentration with a boiling point of -40°C.

Chlorine vs chlorine dioxide

While they may have similar names, chlorine and chlorine dioxide are very different chemicals, Lorcheim said in her presentation.

“Just like carbon is very different from carbon dioxide, chlorine is not the same as chlorine dioxide,” the session slides wrote.

Firstly, chlorine kills from chlorination, while CIO2 kills through oxidation. “As [chlorine dioxide] does not chlorinate organic material, it eliminates the formation of trihalomethanes (THMs), haloacetic acids (HAAS), and other chlorinated organic compounds that chlorine produces when used for water treatment,” she said.

Additionally, chlorine reacts with water to form hydrochloric acid, and CIO2 does not. Chlorine is also far more aggressive on all materials than CIO2.

CIO2 vs EtO

In relation to its sterilization abilities for medical devices, which currently rely heavily on EtO, ClorDiSys pointed to multiple sterilization process validation steps that are identical between the chemicals. The validation is the same during these steps:

The only differences in the validation process are its lab testing and process characterization. As CIO2 gas breaks down into benign ions, residual testing is done through ion chromatography. CIO2 gas has also been seen to lower endotoxins, according to the company.

Some of the biggest differences between CIO2 and EtO are its toxicity and explosive nature. CIO2 is non-carcinogenic, non-flammable, and non-explosive at use concentrations. EtO on the other hand is seen as a carcinogenic, flammable, and highly explosive.

The two sterilization cycles are also different. For CIO2, the process is broken down into five steps:

The entire process happens within the sterilization chamber and lasts on average 4-8 hours from the beginning of pre-conditioning through aeration.

EtO sterilization requires 12-72 hours to go through the entire cycle and product and packaging must be able to withstand 47°C (118°F) with 65% relative humidity. It is considered a vacuum cycle with necessary cycle parameters including heat, moisture, gas concentration, and time.

Aeration also requires a separate room for EtO sterilization and is a highly heated environment of 50°C to 60°C for eight to 12 hours. Aeration in environments of 20°C last seven days. While CIO2 finishes the cycle with no or negligible residuals detected, higher concentrations of EtO increase the risk of residuals.

A safe alternative

Lorcheim highlighted that while many in the industry may be hearing of CIO2 for the first time, the sterilization method has been around for a long time and was originally developed by Johnson & Johnson. The method has been utilized for true sterilization of products and components since 2001 in various industries and provides a strong alternative for companies wanting to move away from EtO sterilization as the EPA continues to tighten environmental parameters.