Most people probably recognize arsenic as an old-time poison, but many do not know how potent it actually is. One-tenth of a teaspoon of arsenic can cause death in hours or days. It poses a direct danger to a large portion of the world’s population, as millions of people unknowingly ingest it every day in their food and water.
Mankind has used arsenic compounds since 3000 BC. Arsenic was known as the “king of poisons” because it is abundant, tasteless and easily dissolved in liquid.
Elemental arsenic is a steel-gray, metal-like material distributed throughout the Earth’s crust, especially in minerals and ores that contain copper or lead. It has been used in a multitude of applications, including batteries, ammunition, pesticides and animal feeds.
Arsenic in the Environment
Arsenic in groundwater is largely the result of dissolved minerals from weathered rocks and soils. Arsenic in soil or rock is bound to iron, calcium or magnesium. When those elements are stripped out of the soil, the bound arsenic is released. It is absorbed by all plants, but is more concentrated in leafy vegetables, rice, seafood, kelp, and apple and grape juice. The level of arsenic in natural water generally ranges between 1 and 2 ppb. Manufacturing and agricultural activities also distribute arsenic into the environment.
Most of the arsenic found in groundwater is either inorganic As(III) or inorganic As(V). In situations where the pH is high, arsenic may be released from surface binding sites that lose their positive charge. Of the inorganic species, As(III) is more toxic than As(V) .
Bacteria that reduce iron and transform it from solid phase Fe(III) iron into water-soluble Fe(II) iron facilitate the release of arsenic into the water. Additional bacteria in the water can reduce arsenic from As(V) to the more toxic As(III). Arsenic trapped in sulfide minerals can be released when the minerals are exposed to oxygen. This can happen when the water level drops and the minerals are exposed to air.
Emerging Danger Awareness
When exposure to arsenic occurs over a short period of time, symptoms may include vomiting, abdominal pain, diarrhea, confusion, coma and death. Long-term exposure can result in thickening of the skin, abdominal pain, chronic diarrhea, cardiovascular disease, diabetes, lung disease and cancer. Arsenic has been found to cause skin, bladder and lung cancer.
Arsenic is a more potent carcinogen than previously believed. Emerging evidence shows that low-level chronic arsenic exposures accelerate existing human cancer growth and decrease survival. Studies have shown that arsenic in drinking water at a level regarded as safe increases the incidence of aggressive subtypes of prostate cancer, stroke deaths in women, death from heart disease, lung infections, decreased IQ in schoolchildren, early death in children exposed at a young age and miscarriages.
Apple juice and rice are two foods known to accumulate arsenic. Apple trees and rice naturally extract more arsenic from the soil than other plants. Lead arsenate was used as a pesticide in orchards for decades, and inorganic arsenic-contaminated groundwater has been found near old apple orchards.
Organoarsenic compounds were used in poultry and swine feed to improve weight gain and reduce disease. These compounds were found as the more toxic inorganic form of arsenic in the animals, as well as in those who ate them.
Testing & Treatment
A maximum contaminant level (MCL) is an enforceable standard, but arsenic concentrations at the U.S. Environmental Protection Agency’s MCL of 10 ppb are not completely safe. It is determined to be a cost-effective enforceable level above which there is a significant risk of harm. New Jersey set its enforceable MCL at 5 ppb in the interest of improving safety. This likely will be a trend in the future as more data on the risks of long-term exposure accumulate.
Few domestic well users routinely test their water and those who do rarely test at the recommended yearly interval. Arsenic was detected in more than 50% of domestic wells tested nationwide, with more than 10% exceeding the 10-ppb MCL, yet there is still no federal regulation requiring testing or monitoring of private wells.
Well users in high-risk areas should test their water for arsenic. Methods should test for inorganic arsenic, which poses the health risk. Speciation of which form of inorganic arsenic is present is not important for well users, as any level of inorganic acid is concerning.
Home test kits specific for arsenic are available starting at $10 and give results in minutes. They typically involve conversion of arsenic in the water to arsine gas via a strong reducing agent. The gas is released from the water and concentration is measured with a colorimetric test strip, indicating the arsenic level in the original water sample. Tests typically take 10 to 40 minutes to complete and report a range from 0 to 500 ppb. Attributes of some commercially available kits are listed in Table 1.
There also are certified labs that will test a water sample. State health departments are a good resource for finding these labs. Test costs typically start at $30, require the user to collect and send the sample, and can take up to two weeks for a result.
Heating or boiling water will not remove arsenic. Because some water evaporates during the boiling process, the arsenic concentrations actually can increase slightly as the water is boiled. Chlorine disinfection also will not remove arsenic.
Treatment methods such as reverse osmosis, ultrafiltration, distillation and ion exchange are effective, but these methods typically are used to treat water at only one faucet. Follow-up testing should be performed after intervention.
Arsenic is more dangerous and widespread than many well users recognize. Because the goal is 0 ppb of arsenic in drinking water regardless of the enforceable MCL, well owners can mitigate the risk by testing well water at yearly intervals, and taking action and performing follow-up testing if arsenic is detected.