An apparatus and method for the addition of alcohol dehydrogenase (ADH) enzyme inhibitors to existing engine cooling systems to reduce or eliminate the coolant toxicity without the need to completely drain and replace the entire engine coolant. In addition, the present invention provides an apparatus and method for treatment of otherwise toxic coolants removed from engine cooling systems that are targeted for disposal and release into the environment and thereby reduce or eliminate the condition of creating relatively large amounts of toxic waste during routine maintenance and repairs.