In what way can chemicals cause leukemia?

Yes, sometimes: There are some chemicals that are known to cause bone marrow damage leading to acute leukemia. Most of these are chemotherapy drugs of the alkylating agents-class. Some petrochemicals like benzene are also implicated in some cases. Radiation from excessive exposure like from atomic bombs, or nuclear accidents are also known to cause it.

See below...: Exposure to certain chemicals like benzene or formaldehyde may increase the risk for cancer including leukemia. This is probably due to the mutagenic effect of these agents, meaning they can induce mutations in otherwise normal cells resulting in abnormal cells that can become cancerous; however, the process is usually multifactorial and other conditions need to be met to develop cancer.