Perchlorate and Human Health

Perchlorate is chemical used in military and industrial products such as solid rocket fuels, munitions, explosives and fireworks, road flares and air bag inflation systems. It can also occur naturally at low levels in the environment, for example in certain arid regions of the world. Recent sampling has detected the presence of very low levels of perchlorate in some Canadian drinking water sources.

In Canada, preliminary analysis of ground water and surface water samples show very low levels of perchlorate, indicating that perchlorate levels in drinking water would be extremely low or non-existent. To date, perchlorate has only been found in one Canadian public drinking water supply, at a concentration below 1 part per billion (ppb); a ppb is equivalent to the content of half a teaspoon in an olympic-sized swimming pool. American data show that perchlorate may also be found in foods such as lettuce, milk and bottled water.

The risk to human health from exposure to current levels of perchlorate in drinking water is extremely low. Exposure to significantly higher levels of perchlorate has the potential to cause some health effects, primarily related to thyroid function. Perchlorate inhibits the transfer of iodide from the blood to the thyroid gland, which is required for the gland to produce hormones essential for metabolism and growth. Although short-term fluctuations in thyroid hormones are not a concern to healthy adults, long-term disruptions may result in hypothyroidism and related changes in metabolism, decreased mental performance, and altered development. This is of particular concern for people who are already experiencing hypothyroidism, as well as for pregnant women and children.

Scientific studies and guideline development related to perchlorate are on-going. In 2005, the American National Academy of Science produced a report on the health implications of perchlorate ingestion, which has been used by the U.S. Environmental Protection Agency to establish a preliminary clean-up goal of 24.5 ppb for perchlorate in water. There is currently no enforceable national drinking water standard for perchlorate either in Canada or in the United States, although various states have implemented guidelines or goals ranging from 1 ppb to 18 ppb for perchlorate in drinking water.

Where a contamination of drinking water supplies in Canada has occurred, Health Canada recommends a drinking water guidance value of 6 ppb, based on a review of existing health risk assessments from other agencies.

There is no documented case of perchlorate contamination of Canadian drinking water supplies at levels near or above 6 ppb. If a contamination situation is suspected, communities that rely on drinking water from sources that could be contaminated by perchlorate may choose to assess the presence and levels of perchlorate in their drinking water supply. If levels of perchlorate greater than 6 ppb were to be found, the community, in consultation with health and municipal authorities, should consider actions to reduce exposure. Options include: finding an alternative source of drinking water; enhancing treatment to reduce the level of perchlorate in the drinking water to below the guidance value; and using certified drinking water treatment devices where individual households obtain drinking water from private wells.

Technologies for reducing perchlorate in the water supply are available. There are municipal-scale treatment systems and several certified reverse osmosis residential systems that reduce perchlorate to 6 ppb or less. Should consumers wish to purchase treatment systems, Health Canada strongly recommends that consumers look for a mark or label indicating that the device has been certified by an accredited certification body as meeting the appropriate NSF/ANSI drinking water materials standard. These standards have been designed to safeguard drinking water by helping to ensure the material safety and performance of products that come into contact with drinking water.

More research is required to examine levels of perchlorate in water supplies (ground and surface waters) and foodstuffs, as well as the possible linkages between exposure to perchlorate and potential health effects. Sampling programs are planned or underway to determine the extent of perchlorate contamination in Canadian water and food supplies. Health Canada will continue to work with its partners, including the provinces and territories and international agencies, to assess the situation and ensure the safety of Canada’s drinking water and food supplies.

We will update this information sheet as new data become available.

For more information on drinking water quality issues visit Health Canada’s Water Quality Website at: