As focus on lead contamination grows, arsenic concerns continue
After moving, new home buyers settle in and take stock of their surroundings. For those switching from a municipal water source to a private well, questions about water quality may arise.
“The ongoing concern is that private well owners test their water for bacteria, nitrate and anything of local concern, which for many Americans would include arsenic,” said Cliff Treyens, director of general public outreach for the National Ground Water Assn. (NGWA). “Unfortunately, it’s widely understood that many well owners don’t test their water quality.”
That is troubling, considering the harmful health effects related to arsenic. A recent study conducted by the National Cancer Institute tracked an increase in bladder cancer in Maine, New Hampshire and Vermont. It found that drinking water from private wells contributed to the increase, particularly when it pertained to wells dug in the first half of the 20th century. Arsenic leeching from underground rock or commonly used arsenic-based pesticides from the 1920s to 1950s are considered to be the culprits.
“Arsenic is an established cause of bladder cancer, largely based on observations from earlier studies in highly exposed populations,” said Debra Silverman, Sc.D., senior author of the study. “However, emerging evidence suggests that low to moderate levels of exposure may also increase risk.”
Not a Localized Issue
Arsenic should be given serious attention. Ingestion of as little as 100 mg can result in severe poisoning. Amounts in water are normally much lower, but even low concentrations can lead to chronic symptoms.
When ingested in small amounts, the effects of arsenic appear over time. It may take several years for the poisoning to become apparent. Chronic arsenosis can ultimately lead to death. Inorganic arsenic is absorbed from the gastrointestinal track and distributed throughout body tissues and fluids, leading to the health effects seen in Table 1.
Arsenic can be found in drinking water sources due to natural or human activities. It occurs naturally in rocks, soil, water, air, plants and animals. It also can be released in the environment from volcanic activity, erosion of rocks and minerals, and forest fires. Ninety percent of the arsenic use in the U.S. stems from wood preservatives. However, it is also used in paints, pesticides, petroleum production, drugs, dyes, soaps, metals and semiconductors. It also can be found in agricultural applications, mining and smelting.
Higher levels of arsenic more often are found in groundwater than in surface water sources. In groundwater, arsenic can combine with other elements to form inorganic as well as organic compounds; the inorganic derivatives are considered more toxic. Inorganic forms usually exist in potable water in two chemical valence states: arsenite or arsenate. Aerated surface water contains arsenate, while well water contains arsenite. Tests to determine the concentration of each form, also known as speciation, must be performed to choose the proper removal technique.
Current technology suggests several techniques may be used to remove arsenate, arsenite and organic forms of arsenic from drinking water. However, the effectiveness of treatment technologies is reduced by interfering reductants and competitive adsorbates. Therefore, it is suggested to conduct a complete water analysis prior to any treatment.
The application—residential point of entry, residential point of use or municipal—determines the course of treatment. Common treatments for each category per the Water Quality Assn. (WQA) technical fact sheet for arsenic are shown in Table 2.
Inorganic arsenic can be present as arsenite or arsenate. Arsenite is considered more detrimental to human health and is more difficult to remove. For example, anion exchange treatment is not effective at removing arsenite. If arsenite is present, an initial pretreatment stage must be employed upstream of the anion exchange system to oxidize the arsenite and convert it to arsenate.
The treatments in Table 2 should reduce arsenic in drinking water to the maximum contaminant level of 10 ppb, an enforcement level set by the U.S. Environmental Protection Agency under the authority of the Safe Drinking Water Act. Although the enforcement level is 10 ppb, no amount of arsenic in drinking water is considered safe.
“We’ve been working hard at NGWA to develop well owner tools with the goal of informing and motivating well owners to test, including for arsenic where that is a problem locally,” Treyens said.
Certified water treatment professionals are a good source for information on arsenic, water testing and water treatment. The WQA Modular Education Program can teach water treatment professionals how to select the proper treatment strategy for the type of arsenic. Certified products for arsenic reduction offer a clear option when it comes to treating water.
Legislation pending in Maine seeks to increase the number of wells being tested each year. Other bills aim to beef up education efforts about the risk of arsenic throughout the state, provide state funds to help public agencies identify the households most at risk for drinking water contamination, and help income-eligible homeowners buy water treatment systems.
With much of the public’s focus on lead, arsenic is getting less attention. That is a problem. The water treatment industry needs to be ready to help anyone who can be, or has already been, affected by it.