Arsenic

Arsenic occurs naturally in some groundwaters in our region in concentrations that exceed the drinking water standard. Arsenic is associated with a number of adverse health effects and is known to cause several types of cancers. The U.S. EPA a few years ago, after years of investigation, revised the drinking water standard (MCL) to a more stringent value of 10 micrograms per liter (µg/L). Regulatory agencies consider that arsenic poses a risk of cancer at any level greater than zero; the lower the level of arsenic, the lower the risk of cancer.

Arsenic levels vary considerably in our area so it is difficult to predict where it will be a problem. Some areas in Paulden and southern Chino Valley have very high arsenic levels in groundwater. Some wells in the Dewey-Humboldt area exceed the arsenic MCL, and soil arsenic is very high near the Iron King Superfund site. There are certainly additional areas with arsenic problems. We recommend that every domestic well be tested for arsenic using testing methods approved by the State of Arizona. Arsenic removal systems for domestic use are available at reasonable cost.

Arsenic is associated with a large number of health effects including cancer, hyper pigmentation, callus-like growths, hypertension, diabetes and more. Importantly, EPA determined that either the data were not adequate to develop an MCL for the non-carcinogenic effects or that any potential MCL would be greater (less stringent) than the MCL for cancer. Therefore, cancer was considered to be the end point of concern and formed the numerical basis of the MCL. 

Arsenic is classified as a known carcinogen causing cancer at multiple sites including lung, bladder and skin. Data for lung and bladder cancers were used to quantify the MCL. Regulatory agencies  most often assume that there is no safe threshold or risk-free level for carcinogens.  A national cost/benefit balance of the number of cancers avoided and the cost to achieve a corresponding MCL was used to select the MCL.

The forms of arsenic in water of most concern are inorganic arsenite (+3) and arsenate (+5). The MCL however, is expressed as total arsenic.

<p>All water providers serving more than 25 people are required to test for arsenic and report the results to their customers. The City of Prescott, for example, issues an annual report for all the parameters it is required to test and presents the results next to the regulatory MCL. These annual reports can be obtained at the city’s web site. Furthermore, suppliers are required to publish notifications when requirements are not met.</p> <p>Arsenic levels in private well in the Prescott region can vary considerably with no certain way of predicting levels other than by testing. Because levels of arsenic considerably above the MCL have been reported in this region’s groundwater, we highly recommend that private wells be tested at least once and perhaps more depending on the levels found. We also recommend the use of state certified laboratories using EPA approved analytical methods to ensure reliable results. Contact the AZ Department of Health Services for certified labs (likely in Phoenix) who will provide information and bottles for sampling. Local businesses have been be available to collect and ship arsenic samples for an additional cost.</p> <p>Test results from private well should be compared to the MCL for assessment of health risks. Where results exceed the MCL, the consumers should discuss the results with local public health and medical officials to assess the potential risks. Where the levels greatly exceed the MCL, it may be appropriate to not use the supply until corrective actions are taken.</p>

Well owners should have their well water tested periodically. Although Federal and Arizona drinking water standards (known as MCLs or Maximum Contaminant Levels) and testing regulations do not apply to wells for individual homes, the test results can be compared to the standards to determine safety.&nbsp;<a href="http://bradshawmtnenv.com/"><br /></a> <div><br />See our recommendations in the "Water Quality" FAQ.</div>

Arsenic is the 20th most common element in the earth’s crust, constituting 0.0005% of the rock and soil. That is only 5 parts per million, on average, but it is not distributed uniformly. 

Arsenic is often found combined with copper and iron sulfides. When these minerals are mined, the arsenic is exposed in tailings piles or can become airborne from refining. Arsenic can be emitted into the air from large fossil fuel burning power plants, so it can be inhaled into our lungs or washed out of the air into our water supplies by rain. Most commercial uses for arsenic have been eliminated because of the toxicity for humans.

Water in contact with arsenic mineral deposits in the ground will dissolve some of the arsenic. This naturally occurring arsenic is likely the primary source of arsenic for the Prescott region’s water supplies.

It is difficult to speak of “safe” when talking about carcinogens. As noted above, regulatory agencies consider that there is some risk of cancer at any level above zero. Indeed, the unenforceable EPA goal or MCLG for arsenic and virtually all carcinogens is zero. EPA reviewed other lower levels, but selected 10 in consideration of its nation-wide evaluation of cost to achieve the MCL.  Presumably, if the costs for arsenic removal were less, it would have adopted a “safer” more protective MCL. The above implies that public water suppliers and even individuals can evaluate their specific cost to achieve lower arsenic levels.

In its Arsenic in Drinking Water 2001 Update, NAS estimated the excess cancer risk at 3, 5,10 and 20 ppb. At 10 ppb the individual’s risk of bladder or lung cancer from a life time consumption of one liter per day is about one in 300¹. The risk at the other levels were directly proportional. For example, a one in 600 cancer risk at an arsenic level of 5 ppb. The risk level for the EPA MCL may be considered low compared to, for example, the voluntary cancer risk of smoking. However, the involuntary risk level for the 10 ppb MCL is much higher than any other carcinogenic MCL adopted by EPA at the time and likely still is. 

The City of Prescott’s reported arsenic levels have remained under, but close to, the MCL of 10 ppb at the time of this publication (2024). It has been achieved primarily by blending multiple supply wells with higher and lower levels. CWAG believes the City or other suppliers should evaluate the increased costs of treatment to achieve lower arsenic levels including near the analytical detection level of 2 or 3 ppb. Suppliers could then discuss with local, state or national public health officials the health benefits and decide if additional treatment is worthwhile in their specific situation.

Reference 1: Arsenic in Drinking Water, 2001 Update, National Research Council of the National Academy of Sciences, Table S-1. Average of males and females and combined bladder and lung cancers. 

Private well owners with high levels of arsenic or residential customers of public water supplies who wish to further reduce their consumption of arsenic can install an treatment system. For most situations a Point of Use system under a kitchen sink will be satisfactory. Where levels of arsenic are very high, a Point of Entry system may be warranted.

Commonly used household filters for removal of taste, odor and some organic compounds will not remove arsenic. Arsenic removal is typically achieved with multi-cartridge systems using either reverse osmosis or an oxidation/adsorption filtration process. Commercial suppliers can be found locally. The costs for a point of use system, including purchase, installation and maintenance, will be expensive; point of entry systems more so.

For more information, see the "Water Contam

Water filters are not monitored by the U.S. Food and Drug Administration.  CWAG recommends that you thoroughly evaluate and compare filtration options using multiple sources of information and especially for larger systems, obtain more than one reference.  There are three different certifications to look for on a label for a filter or filtration system; these organizations can also assist you in selecting a filter or system that meets your needs.  The three organizations, also accredited by the American National Standards Institute (ANSI), are:

• NSF International (National Sanitation Foundation International), an independent global organization that certifies many water treatment devices, 
• The Water Quality Association, another leading authority on water filter standards that provides third-party product certification, and
• Underwriters Laboratories (UL), also has water filter testing and certification programs.

Consumer Reports also evaluates and recommends water filters and publishes a Water Filter Buying Guide.

For more information on water filters and treatment, see the following publications: 

• United States Environmental Protection Agency (USEPA) Fact Sheet on Filtration Facts,
• USEPA Overview of Drinking Water Treatment Technologies, and
• Centers for Disease Control and Prevention Choosing Home Water Filters & Other Water Treatment Systems.