Arsenic Toxicity: Why and How to Remove It from Drinking Water
By Gary Battenberg
What is arsenic toxicity?
Arsenic toxicity, also referred to as chronic arsenicosis in humans, is well known and occurs when one is exposed to high levels of arsenic more than 0.05 mg/L. Arsenic is generally found in one of two chemical valence states: as arsenite AS+3 (ASIII) and arsenate AS+5 (ASV). Effects of arsenic ingestion in small amounts appear slowly and may take several years before poisoning becomes apparent. When ingested in large amounts, chronic arsenicosis manifests itself in many ways in different parts of the world.
Arsenic can be inhaled and may be taken up dermally through the skin. For example, those working in the smelting industry may be exposed to airborne inorganic arsenic which may be present in coke emissions. Therefore, it is prudent to wear appropriate breathing apparatus to prevent inhalation. Most plants now have air-emission scrubbers to eliminate toxic gasses and chemicals. Dermal exposure from wood products treated with chemicals containing arsenic can cause arsenic poisoning as well.
Where is arsenic prevalent?
Countries where high levels of arsenic have been confirmed in groundwater include the United States, Mexico, China, India and Taiwan. Western US states typically have arsenic levels that exceed 10 micrograms per liter (µg/L, ppb) compared to the rest of the US. Groundwater from artesian wells in villages along the southwest coast of Taiwan containing extremely high levels of arsenic are known to cause Blackfoot Disease. Patients afflicted with this disease suffer severe systemic arteriosclerosis with black, mummified dry-foot gangrene, which often requires amputation in lower extremities. Fortunately, implementation of treated tap water to these villages has resulted in a dramatic decrease in the severity of arsenic poisoning over the past 30 years.
What are symptoms of arsenic poisoning?
Health effects range from mild to very severe symptoms. What makes arsenic so dangerous is that it has no taste or odor, which means one can be exposed to it without knowing it. Some of the symptoms include:
- Tingling of fingers and toes, red or swollen skin and changes such as lesions or warts
- Muscle cramps and abdominal pain
- Diarrhea, nausea, vomiting and persistent digestive problems
- Persistent sore throat
- Damage to cardiovascular and nervous systems
- Endocrine disruptor
Arsenic has been shown to cause cancer of the skin, bladder, prostate, kidney, liver, lungs and nasal passages. The most common cause of arsenic poisoning is contaminated groundwater, where it is abundant in the earth and leaches from natural deposits. Additionally, arsenic seeps into groundwater from industrial plant runoff as well as from other sources, such as:
- Living near industrialized areas, exposed landfills or waste sites
- Breathing contaminated air containing arsenic from plants or mines that use arsenic
- Breathing in smoke or dust from treated wood or waste products
- Smoking tobacco products
Arsenic regulations and guidelines
US EPA, under authority of the Safe Drinking Water Act (SDWA), has set the maximum contaminant level goal (MCGL) for arsenic at zero mg/L as a health-based goal. The maximum contaminant level (MCL) establishes the highest level of contaminant that is allowed in drinking water. MCLs are enforceable standards that are set as close to MCLGs as feasible, using the best available technologies while taking costs into consideration. Current standards for arsenic are:
The first rule in water treatment is to obtain an accurate and complete water analysis where health-related contaminants are known or suspected to be present in a water supply. A complete analysis will reveal background issues that may affect the performance of the treatment methods available for remediation. Effective, reliable and consistent arsenic removal can be achieved when accurate interpretation of a water analysis is rendered, which eliminates those treatment methods that don’t provide optimal results. This allows water treatment specialists to present viable options to prospective customers.
There are several treatment methods available that are generally recognized as being effective in reducing arsenic to meet or exceed the maximum contaminant level. A look at some of the available methods may be helpful when sourcing effective arsenic remediation.
Where arsenic is present in municipally treated water with measurable free available chlorine (FAC), it will be in the oxidized state of arsenate. In this state, arsenic is easy to remove from water. Where the water is only treated with monochloramine (NH2CL), however, it has been found that all the arsenite may not be converted to arsenate. For municipally treated water with monochloramine, it is wise to obtain an arsenic speciation test to determine the concentration of each form. RO and distillation are the most prevalent technologies currently being used to remove/reduce arsenic from municipal and groundwater supplies. Other options include activated alumina, which exhibits a high affinity for arsenic, lead and fluoride. This media works in pH range between 4.0–10.0 with optimal pH at 5.0 for best results. Performance is flow-dependent so care must be used when specifying this treatment option.
Pre-coated or impregnated iron-based media will reduce both species from water when properly applied within application guidelines. These types of media have a specific service life based on the calculated capacity within a specific volume of media, relative to the total arsenic levels in the water. Strong base anion resins chosen for their selectivity have proven very effective at removing arsenic from water. Some anion resins are functionalized with hydrous iron oxide nanoparticles, which provide a very high affinity for arsenite and arsenate. Care in handling spent media for disposal is critical and it should comply with federal guidelines. Newer media can be processed to remove arsenic before the resin is taken to a land fill.
Manganese Greensand (which dates to the 1950s and is still used today in many water treatment plants) is the grandfather of treatment methods to remove iron, manganese, arsenic and radium. Many dealers today still use manganese greensand for pretreatment of problem water containing iron, manganese and hydrogen sulfide. In fact, many water wells across the US contain arsenic where pump depths approach and/or exceed 200 feet (60 meters). Arsenite is converted to arsenate, bound with the oxidized iron and held in the bed until regeneration removes the oxides and capacity is restored after regeneration. Use care when handling potassium permanganate (KMnO4) and follow the package instructions. The newer Manganese GreensandPlus provides the same capability as the original, with the added benefit that water temperature is no longer limited to 85°F (29.4°C) because the media substrate is silica-based.
There are some very exciting technologies in R&D as well as field testing which will soon be available. Advancements in treatment media such a proprietary filter paper are on the horizon. Organoclays and granular activate carbon (GAC) with arsenic selective sorbents have been in use now for over 10 years with very good success. Choices today for treatment methods are many. Be sure and clearly understand, however, the capabilities and limitations of the chosen treatment method with accurate interpretation of the complete water analysis. Identify those contaminants or conditions that reduce the effectiveness of the chosen technology, which may mean rejecting it because the method will not yield the desired results.
Arsenic is a very dangerous and damaging health-related contaminant, so it is very important to apply due diligence when sourcing, selling and servicing treatment products for arsenic remediation. Products should be certified to WQAS-200, NSF 53, NSF 58 and NSF 62 for arsenic reduction. These certifications give the dealer and consumer the assurance of effective remediation when properly installed and maintained with timely media or cartridge replacement according to manufacturer recommendations.
About the author
Gary Battenberg is a Business Development Manager-Senior for Argonide Corporation. Previously, he was Technical Manager, Water Treatment Department of Dan Wood Company. Prior to that, Battenberg was Technical Support and Systems Design Specialist with Parker Hannifin Corporation. His nearly four decades of experience in the water industry include a proven, successful track record in areas of sales, service, design and manufacturing of water treatment systems. Battenberg’s technology base covers mechanical and adsorptive filtration, ion exchange, UV sterilization, RO and ozone technologies. He has worked in the domestic, commercial, industrial, high-purity and sterile water treatment arenas. A contributing author to WC&P International magazine and a member of its Technical Review Committee since 2008, Battenberg was voted one of the magazine’s Top 50 most influential people in the water treatment industry in 2009. He can be reached by email at email@example.com or by phone (407) 488-7203.