Arsenic water treatment technical tips

Feb. 3, 2014

A breakdown of this harmful contaminant and what customers must be mindful of.

Today, most consumers and prospects are at least mildly aware of the health risks involved with drinking water containing high levels of arsenic (As), or even low levels over a period of time. Water treatment dealers often face a different challenge when communicating that arsenic may be present in a consumer’s water.

Since arsenic is an odorless, tasteless metalloid, which can enter water naturally through the erosion of natural deposits in the Earth, most end consumers will not be able to conclude that this contaminant is present in their drinking waterwithout testing.

Explaining arsenic to consumers

At one time, arsenic was regulated in the U.S. at 50 µg/l. In 2001, the standard was lowered to 10 µg/l. Arsenic is element 33 in the periodic table with an atomic weight of 75. Natural arsenic is the stable isotope that contains 33 protons and 42 neutrons. Arsenic is found in oxidation states of -3 (arsenides), 0 (elemental arsenic), +3 (arsenite and arsenic trichloride) and +5 (arsenate) so it can exist in many inorganic and organic compounds (e.g., methylarsonic acid and its salts). 

As mentioned, arsenic is widely distributed in the Earth’s crust. It is found in groundwater as arsenite (AsO3-3) or arsenate (AsO4-3) salts. World water concentrations range from less than 1 µg/l to multiple mg/l amounts. There are pockets of high arsenic levels in groundwater in the northeast and western U.S. as well as other locations.

Arsenic is acutely toxic, but it also has chronic toxicity and it is a human carcinogen. Inorganic arsenic (arsenate and arsenite) is considered more of a risk than the organic forms that predominate in the diet. Skin, bladder and lung cancer have been identified from exposures to inorganic arsenic at high water and dietary exposure levels.

Recommending treatment options

Commonly available methods for analyzing arsenic in water include ICP-MS (detection limit ~0.1 µg/l) and the older hydride generation atomic absorption and flame atomic absorption (detection limits ~1-2 µg/l). Easy-to-use test kits that allow quick on-site colormetric measurements that can readily detect amounts below 5 µg/l are also available on the market.

In terms of treatment options, the following are recommended:

  • Conventional coagulation can achieve less than 10 µg/l in public water plants using either alum or ferric salts.
  • Coprecipitation during iron removal is also effective.
  • Reverse osmosis (arsenate > arsenite), and anion exchange processes using iron-based products and activated alumina are very effective.
  • Water softening is effective by sorption if magnesium or iron precipitation is occurring, but not with calcite alone.
  • Point-of-use technologies are particularly cost effective in home well or small community applications.
  • Anion exchange, RO and distillation are available for POU/POE applications. POU will be most cost effective because only a few liters of water will be needed each day for drinking and cooking.
  • Community-supplied bottled water is also a viable approach.

Helping customers understand the As species types

As mentioned, the contaminant can occur in two forms: Trivalent arsenic (AsIII, or arsenite) or pentavalent arsenic (AsV, or arsenate). Generally, As(III) is found in areas with wells that do not have enough oxygen. Compared to As(V), As(III) is more difficult to treat because of the charge it possesses. As an uncharged species in plus-3 form, As(III) cannot be effectively removed using an adsorption media.

Field and laboratory testing are available to identify total arsenic in water. Further speciation testing is available at an additional cost. Just as when dealing with most contaminants in water, the more you know about the water’s quality, the better off you’ll be when recommending treatment and implementing a system.

Knowing the species of arsenic present will also help the customer understand why costs might increase. As(III), being much more difficult to treat, requires oxidation or other treatment. Furthermore, for well water customers, they need to understand that well water chemistry changes throughout the year for various reasons.

Easing customers in

For many homeowners and business owners, finding out that arsenic is present in water in any form can be a concerning discovery. Although problem water and finding solutions is part of your everyday life as a water treatment dealer, customers may have a more dramatic reaction to positive tests of arsenic. As a result, dealers should help customers put their exposure to arsenic on a regular basis into perspective.

Arsenic is found in foods with fish and shellfish being by far the largest contributors to daily diet. About 99 percent of seafood with arsenic contains organic forms that are likely less toxic than the inorganic forms. It is common in cereals, poultry, grains and vegetables with only trace amounts in milk. Rice can contain on the order of 6.7 µg of inorganic arsenic per cup depending upon where it was grown. Rice is grown in water so it has a greater opportunity to accumulate arsenic from the environment.

And, specific to water, it is the dealer’s responsibility to let all consumers know about the health risks associated with consuming arsenic in water. According to, known health effects associated with drinking water containing arsenic include: Skin damage or problems with circulatory systems and potentially an increased risk of getting cancer.

Some of the information for this article was originally published in a recent edition of our magazine’s popular section “Contaminant of the Month,” written by Water Technology’sTechnical Editor Dr. Joseph Cotruvo.

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