in drinking water
Perchlorate salt is a man-made compound used primarily in road flares, fireworks, rocket fuel and similar type products, and its one of the key ingredients in numerous national defense weapons systems. It is even thought to exist naturally in some nitrate-based fertilizer products. Perchlorate in the ground water originates principally from manufacturing sites of rocket fuel. The Environmental Protection Agency (EPA) of California has established a health limit of 6 µg/L. The French Ministry of Health recommends less than 4 µg/L for infants and 15 µg/L for pregnant women.
According to health experts, perchlorate interferes with iodide uptake into the thyroid gland. Because iodide is an essential component of thyroid hormones, perchlorate disrupts how the thyroid functions. In adults, the thyroid helps to regulate metabolism. In children, the thyroid plays a major role in proper development in addition to metabolism. Impairment of thyroid function in expectant mothers may impact the foetus and newborn and result in effects including changes in behavior, delayed development and decreased learning capability. Changes in thyroid hormone levels may also result in thyroid gland tumors. EPA’s draft analysis of perchlorate toxicity is that perchlorate’s disruption of iodide uptake is the key event leading to changes in development or tumor formation.
All strongly basic resins have a very strong affinity for the perchlorate anion ClO4–. As the measured concentrations of perchlorate in ground water are in the µg/L (ppb) range, resins can be used to remove perchlorate with a very long operating cycle, with practically zero leakage.
However, the hich selectivity of these resins for ClO4– also makes them difficult to regenerate. Besides, ion exchange is not a common process for routine treatment of drinking water, so a dedicated ion exchange installation must be built. In practice, there are two choices:
- use a non-regenerable resin filter loaded with a resin specially developed for perchlorate removal, such as AmberliteTM PWA2; with 25 µg/L in the feed water, the running time should be more than six months;
- in the case where nitrate is also a problem, use a nitrate-specific resin in a regenerable filter; as the cycle will be much shorter (about a day), there is a good chance that the little perchlorate loaded onto the resin will be eluted during regeneration.
Note that the BritaTM filter in your kitchen will not remove perchlorate, as this filter is filled with cation exchange resin and ClO4– requires an anion exchange resin to be removed.