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Diss Factsheets

Administrative data

Key value for chemical safety assessment

Additional information

THPC is classified as structurally alerting by virtue of its natural electrophilicity. However, THPC is negative in the bacterial reverse mutation assay. THPC was tested and found to be clearly positive in threein-vitrotests for genotoxicity: a test for chromosomal aberrations in CHO cells, a test for mutations at the thymidine kinase (TK) locus in mouse lymphoma L5178Y cells, and a test for sister-chromatid exchanges (SCE) in CHO cells.

No indications for genotoxicity were found with a close related substance (THPS) in the followingin-vivotests: two tests for micronuclei (MN-PCE) and for chromosomal aberrations (CA) in bone marrow cells of oral treated mice and two tests for micronuclei (MN-PCE) and for chromosomal aberrations (CA) in bone marrow of dermal treated mice. Further, no indications for genotoxicity was found with a commercial preparation of THPC (Proban CC) in the mouse micronucleustest according current protocol.

Short description of key information:
In vitro: positive (CA, MLA, SCE)
In vivo: negative (MN, CA)
Carinogenicity: negative (2 oral, dermal)

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

THPC was found to be a genotoxic compound when tested for this endpoint in vitro. However, no genotoxic effects were found in relevant in-vivo studies. This marked difference may be attributed to the electrophilic reactivity / complete biotransformation of the THP ion and the rapid irreversible binding to proteins. Apparently no parent compound reaches the bone marrow in which the formation of micronuclei is studied. The positive in-vitro effects can then be explained by the fact that under in-vitro conditions degradation and/or binding are not occurring to an extent large enough to prevent the parent compounds to reach the DNA. The lack of in-vivo genotoxicity complies with the absence of treatment-related carcinogenicity in the 2-year gavage studies with rats and mice (NTP 1987). Moreover, the open literature provides a dermal carcinogenicity study in which no local or other carcinogenic effects were observed (Van Duuren 1978).