By Rick Andrew
Arsenic is a naturally occurring mineral that is present in many residential water sources. Many consumers have no worries about arsenic—surveys of US drinking water
indicate that about 80 percent of water supplies have less than two ug/L of arsenic. There are some consumers, however, who have significant concerns, as two percent of water supplies exceed 20 ug/L of arsenic. These concerns arise from documented potential adverse effects of arsenic on human health. In fact, inorganic arsenic has been utilized as an effective poison since ancient times. Remember the old movie, Arsenic and Old Lace? High oral doses over 60,000 ug/L can cause death due to acute health effects. Lower doses of inorganic arsenic (about 300 to 30,000 ug/L) can be a problem, too, as they can cause stomach and intestinal irritation, including stomach ache, nausea, vomiting and diarrhea. Other effects of oral consumption of arsenic may include decreased production of red and white blood cells. This condition can lead to abnormal heart rhythm, blood-vessel damage, fatigue and impaired nerve function.
Aside from these effects of arsenic consumption, probably the most characteristic effect of long-term oral exposure to inorganic arsenic is skin damage. The skin may develop dark spots and discoloration, and corn or wart-like areas may appear on hands, feet and other areas. These corn or wart-like areas have the potential to develop into skin cancer. Additionally, oral ingestion may also increase the risk of lung, liver, bladder,
prostate or kidney cancer. Because of these links to cancer, the Department of Health and Human Services (DHHS) has determined that inorganic arsenic is a known carcinogen, while the International Agency for Research on Cancer (IARC) has determined that inorganic arsenic is a human carcinogen. US EPA and the National Toxicology Program (NTP) have both classified inorganic arsenic as a known human carcinogen.
Because of the numerous potential health effects of oral consumption of inorganic arsenic, on January 22, 2001 US EPA adopted a new standard of 10 ug/L as a maximum contaminant level (MCL) for arsenic. The previous MCL was 50 ug/L. Public water systems were required to comply with the 10 ug/L standard by January 23, 2006. When this regulation went into effect, many communities were forced to improve their water treatment capabilities for arsenic reduction. Many individual well owners were suddenly faced with the fact that their well water did not meet the new MCL. Not only were these consumers faced with a health concern over the levels of arsenic in their well water, but they also have experienced difficulties in selling their homes because of the arsenic.
Small communities and individual well owners alike are searching for proven POU technologies and products to help them treat unacceptable levels of arsenic. This need for proven arsenic reduction performance in POU water treatment devices is supported by a number of NSF/ANSI Drinking Water Treatment Unit (DWTU) Standards that address arsenic reduction methods, claims and requirements, including NSF/ANSI 58 for POU RO systems.
Figure 1. Example of Consumer Arsenic Facts Sheet from NSF/ANSI 58
Arsenic (abbreviated As) is found naturally in some well water. Arsenic in water has no color, taste, or odor. It must be measured by a laboratory test. Public water utilities must have their water tested for arsenic. You can get the results from your water utility. If you have your own well, you can have the water tested. The local health department or the state environmental health agency can provide a list of certified labs. The cost is typically $15 to $30. Information about arsenic in water can be found on the Internet at the US Environmental Protection Agency website: www.epa.gov/safewater/arsenic.html.
There are two forms of arsenic: pentavalent arsenic (also called As(V), As(+5), and arsenate) and trivalent arsenic (also called As(III), As(+3), and arsenite). In well water, arsenic may be pentavalent, trivalent, or a combination of both. Special sampling procedures are needed for a lab to determine what type and how much of each type of arsenic is in the water. Check with the labs in your area to see if they can provide this type of service.
Reverse osmosis (RO) water treatment systems do not remove trivalent arsenic from water very well. RO systems are very effective at removing pentavalent arsenic. A free chlorine residual will rapidly convert trivalent arsenic to pentavalent arsenic. Other water treatment chemicals such as ozone and potassium permanganate will also change trivalent arsenic to pentavalent arsenic. A combined chlorine residual (also called chloramine) may not convert all the trivalent arsenic. If you get your water from a public water utility, contact the utility to find out if free chlorine or combined chlorine is used in the water system.
The [model number] system is designed to remove pentavalent arsenic. It will not convert trivalent arsenic to pentavalent arsenic. The system was tested in a lab. Under testing conditions, the system reduced [0.30 mg/L (ppm) or 0.050 mg/L (ppm)] pentavalent arsenic to 0.010 mg/L (ppm) (the US EPA standard for drinking water) or less. The performance of the system may be different at your installation. Have the treated water tested for arsenic to check whether the system is working properly.
The RO component of the [model number] system must be replaced [frequency] to ensure that the system will continue to remove pentavalent arsenic. The component identification and locations where you can purchase the component are listed in the installation/ operation manual.
Test requirements
POU RO systems are not very effective at reducing concentrations of trivalent arsenic in water. POU RO systems, however, can be highly effective at reducing concentrations of pentavalent arsenic. This does not mean that RO cannot be used to treat trivalent arsenic. In fact, a free chlorine residual will oxidize trivalent arsenic to pentavalent arsenic with minimal contact time. Ozone and potassium permanganate can also be effective oxidizing agents for trivalent arsenic. The oxidized pentavalent arsenic can then be effectively treated by the RO system. For these reasons, NSF/ANSI 58 does not have a test method or a claim for trivalent arsenic reduction. The standard instead requires that literature be challenge level is that consumers of water from supplies that were previously in compliance with the 50 ug/L arsenic MCL would be able to choose systems that have been demonstrated to treat water at that level or below, to the new requirement of 10 ug/L.
Figure 2. POU RO test stand
POU/POE Industry meets consumer needs
In 2006, the US federal government promulgated a new maximum contaminant level for arsenic. This meant that many consumers were now faced with issues of non-compliance. These issues are certainly a health concern, but also a financial concern for those seeking to sell their homes. Mortgage lenders in certain parts of Michigan are requiring arsenic analyses on the drinking water for those homes using wells in areas with known arsenic concentrations in the groundwater. The POU/POE industry foresaw this need and was ready to address provided to consumers advising them of the differences between trivalent and pentavalent arsenic, and the need for effective oxidation of any trivalent arsenic that may be present in their water source prior to RO treatment (See Figure 1 for an example of the consumer arsenic facts sheet required by NSF/ANSI 58).
For testing, sodium chloride is added to chlorine-free deionized water to achieve a concentration of 750 mg/L. Pentavalent arsenic, in the form of sodium arsenate, heptahydrate, is added to make up a challenge water of 300 ug/L. Two test systems are operated for seven days, and multiple samples of influent and effluent are collected throughout the seven days to evaluate system performance (see Figure 2 for an example of a POU RO test stand). The test systems must reduce the arsenic so that the arithmetic mean of all product water sample results, and 90 percent of the individual product water samples, are less than or equal to the MCL for arsenic, which is 10 ug/L.
Alternatively, a 50-ug/L challenge of pentavalent arsenic may be used instead of 300 ug/L. The philosophy for the higher it. By developing products to treat arsenic, by understanding the complexities of these processes, and by contributing to NSF standards development process to provide a basis for performance validation, the industry was once again proactive and successful in serving consumers, helping them to improve their health, and helping enhance the value of their homes.
About the author
Rick Andrew is the Operations Manager of the NSF Drinking Water Treatment Units Program for certification of POU/POE systems and components. Prior to joining NSF, his previous experience was in the area of analytical and environmental chemistry consulting. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email [email protected].