The joint assessment is part of a larger process to review 200 chemicals to determine the safety for people and the environment. This regulatory step allows government to regulate chemicals and eliminate the use of dangerous substances under the Canadian Environmental Protection Act.

D5 is used in pharmaceuticals, cleaners and cosmetics. It is considered bioaccumulative and can harm aquatic organisms at low concentrations. D4 is used in lotions, plastics and soaps, and is shown to be persistent in the environment.

Ottawa issues assessments on batches of priority chemicals but in November and December the government missed its own deadlines. Environmentalists say federal reviews stopped due to pressure from industry and are concerned delays will affect the timeline for assessing other substances.