DNA, microorganisms and chemicals should not be stored in refrigerators with food or beverages. DNA should not be allowed to defrost between uses, as this will break long molecules. New cultures of bacteria should be propagated at least monthly to have live cells. If bacteria or DNA are spilled, wear gloves and absorb the spill with paper towels or bench protector paper. It is recommended that DNA isolation procedures be chosen that avoid the use of chloroform or phenol.
Chloroform is toxic and phenol burns the skin on contact.
Because of the possible carcinogenic and mutagenic effects of ethidium bromide, National Association of Biology Teachers recommends that pre-college level teachers use methylene blue to stain gels. Students should not use either ethidium bromide or handle gels stained with ethidium bromide. Since methylene blue is mildly toxic, gloves should be worn at all times when staining gels. Methylene blue can be used up to four times before disposal. Check with local waste management authorities before disposing of the used methylene blue.