2,4,6-Trichlorophenol (TCP) induces chromosome breakage and aneuploidy in vitro

2,4,6-Trichlorophenol (2,4,6-TCP), a non-mutagen to Salmonella, was reportedly negative in tests for chromosome breakage in vitro, but did produce numerical chromosome changes and micronuclei in V79 cells (Jansson and Jansson, 1992). This apparent specific ability to induce aneuploidy is of interest since aneuploidy testing is not part of routine genotoxicity test procedures. Here we show 2,4,6-TCP clearly induces structural chromosome aberrations in CHO cells and in V79 cells using a 3-h treatment and 20-h sampling time (17-h recovery). The isomers 2,4,5- and 2,3,6-TCP were also clastogenic in this protocol. There was no increase in aberrations when we used the protocol of Jansson and Jansson (1992), i.e., a 24-h treatment with sampling either immediately, or with a 24-h recovery period. However, positive results were obtained when a recovery time of 4-12 h was allowed after the 24-h treatment with 2,4,6-TCP. Previous negative aberration tests of 2,4,6-TCP (Galloway et al., 1987; Ishidate, 1988) are also likely due to inappropriate protocols. All these results were obtained without S9 metabolic activation. We also found positive results in CHO cells when 2,4,6-TCP was tested with S9. The present study demonstrates that 2,4,6-TCP induces both structural and numerical aberrations, and underscores the importance of protocol design, in particular the appropriate recovery time after treatment, for detecting clastogenic activity in vitro.