Complex sentence: Arsenic, chromium, iron, and nickel may be associated with the production of reactive oxygen species, nickel may also be linked to DNA hypermethylation and histone deacetylation, while cadmium may inhibit DNA mismatch repair.
Split into simpler sentences: Arsenic, chromium, iron, and nickel may be associated with the production of reactive oxygen species, and some of these may also alter the fidelity of DNA replication. Nickel may also be linked to DNA hypermethylation and histone deacetylation, while cadmium may inhibit DNA mismatch repair.