Mutagenic effects can come from many sources, not just direct modification of DNA. Anything that interrupts or interferes with the replication process can easily influence the quality of the output. Tumor Treating Fields [1], for example, use ~150-200kHz alternating electrical fields to mechanically disturb microtubule formation to corrupt mitosis and destroy cells in the process of reproducing. There's nothing remotely ionizing about this process but on the fringes of effect it could result in damaged but not destroyed cells.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5035531/