Chlorodifluoromethane

Endpoint summary

Additional information

Chlorodifluoromethane (R-22) in the commercial available grade was found to reproducably respond positive in the Salmonella typhimuriumreverse mutation assay (Ames' test) modifid for gaseous substances. This positive response was shown to be dependent neither on the presence of rat post-mitochondrial supernatant in the incubation medium nor in the presence of known mutagenic gases contaminating the commercial grade substance.

Chlorodifluoromethane was retested in Salmonella typhimurium strains TA 1535, TA 1537, TA 98 and TA 100 in atmospheres containing up to 40%. A 48 hour exposure period was used. The compound is mutagenic in strain 1535 in both the activated and non-activated assay. In the activated assay this activity corresponds to an 11 -fold increase in the spontaneuos mutation frequency.

In a test equivalent or similar to OECD Guideline 473 methane, chlorodifluoro— was tested for mutagenic activity in the Chinese hamster Ovary Cell Assay with and without an activation system. The test sample did not exhibit mutagenic activity.

In an in-vivo test for

clastogenicity the frequency of micronucleated polychromatic erythrocytes did not increase in any of the treatment groups.So it was considered that Arcton 22 was not clastogenic in mice under test conditions.

Short description of key information:
In Salmonella typhimurium reverse mutation assays (Ames' test) chlorodifluoromethane was tested with concentrations of 0%, 15% (150,000 ppm) , 25% (250,000 ppm), 40% (400,000 ppm) for 24 h in glass gas chambers.
In the Chinese hamster Ovary Cell Assay the substance was tested at 0%, 33% (330,000 ppm), 67% (670,000 ppm), 100% (1,000,000 ppm) in plastic chambers for 18-19 h (without activation) and for 5 h (with activation).
In an in-vivo test for
clastogenicity mice were exposed to vapor concentrations of 0 (5 mice/sex), 50,000 (5 mice/sex) or 150,000 ppm (15 mice/sex) for 6 hours in a dynamic air-flow chamber.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

In assays performed under carefully controlled gaseous exposures Chlorodifluoromethane is mutagenic to Salmonella typhimurium strains TA1535 and TA100 in the presence and in the absence of an exogenous metabolic system. In tests with non-bacterial cells such as mutation induction at the HGPRT locus of Chinese hamster cells mutagenicity has not been demonstrated.

Using the mouse bone marrow micronucleus protocol together with concurrent positive (vinyl chloride) and negative (nitrogen) inhalation controls no evidence of clastogenicity was found.

Salmonella typhimurium strains TA 1538 and TA 98

did not show any activity. Taking

all of this data into account, there is strong support for the conclusion that this activity appears to be the result of a bacterial specific metabolism. The in vivo cytogenetic and dominant lethal studies in the rat and mouse provide no evidence

of consistent or dose-related genotoxic activity. Taken with the negative result of the

inhalation micronucleus test, the findings indicate that chlorodifluoromethane does not

possess genotoxic activity in vivo.

The available experimental results on chlorodifluoromethane are conclusive but are not sufficient for a classification as genotoxic.