Arsenic is a naturally occurring metalloid widely distributed in the earth’s crust. Its presence in groundwater is a persistent public health concern, as this highly toxic inorganic form often leaches into private well water from natural bedrock deposits. Arsenic contamination is undetectable by human senses, possessing no taste, odor, or color, meaning only specialized testing can confirm its presence.
Long-term consumption of arsenic-contaminated water, even at low concentrations, is linked to serious chronic health issues. Exposure over many years can lead to an increased risk of developing various cancers, including those of the bladder, lung, and skin. Chronic exposure also contributes to cardiovascular disease, diabetes, and negative developmental effects in children, making routine testing necessary for those who rely on private wells.
Deciding on a Testing Method
The choice of testing method depends on the desired accuracy and the intended use of the results. Certified laboratory testing is the gold standard, providing the most definitive results for arsenic concentration. This process involves sending a water sample to a state-certified facility that uses highly sensitive instruments, typically requiring a turnaround time of seven to ten business days.
Certified labs test for “Total Arsenic” and perform speciation to distinguish between the two inorganic forms. This detail is crucial for making informed decisions about water treatment systems. While laboratory analysis is the most accurate option, it is also the most expensive and time-consuming method.
Home screening kits offer a rapid and more affordable preliminary check of water quality, providing immediate, on-site results. However, simple field-based tests feature significantly lower precision and sensitivity compared to laboratory instruments. The accuracy of many screening kits is unreliable, often resulting in false negative or false positive readings.
These kits should only be used for initial screening. Results must always be confirmed with certified laboratory analysis before any permanent treatment decisions are made.
The Sample Collection Process
Proper sample collection is paramount to ensure the accuracy of laboratory results. Most certified labs provide a sterile collection kit, often containing bottles pre-dosed with a chemical preservative like nitric acid. This preservative stabilizes the arsenic forms until analysis, so you must never rinse these bottles, as doing so compromises the sample’s integrity.
To collect a representative sample, first remove any aerators or screens from the faucet and turn on the cold water tap. Allow the water to run vigorously for four to five minutes, or until the temperature stabilizes, to ensure you are sampling fresh well water, not stagnant water from the plumbing system. After flushing, reduce the flow to a thin stream to minimize splashing and contamination.
Fill the provided sample bottle only to the fill line, taking care not to touch the inside of the bottle or the underside of the cap. The sample should be taken from a cold water tap used for drinking. If a treatment system is in place, both treated and raw (untreated) water samples may be necessary. Once capped, the sample must be immediately chilled to \(4^\circ\)C and shipped quickly, ideally within 48 hours, to meet holding time requirements.
Understanding and Interpreting Test Results
Arsenic concentration is reported in micrograms per liter (\(\mu g/L\)) or parts per billion (ppb), which are equivalent measurements. The regulatory benchmark for public drinking water is the EPA’s Maximum Contaminant Level (MCL) of 10 ppb. Although this standard is not legally enforceable for private wells, it is the accepted threshold homeowners use to evaluate water safety.
Laboratory reports typically show “Total Arsenic,” representing the sum of all arsenic forms present. If the total concentration exceeds the 10 ppb benchmark, a secondary speciation test is recommended. Speciation analysis determines the ratio of Arsenic III (arsenite) to Arsenic V (arsenate) in the water.
This distinction is important because the toxicity and treatability of arsenic species differ significantly. Arsenic III is the more toxic form and is uncharged at typical groundwater pH levels, making it difficult to remove with many common treatment technologies. Arsenic V is a charged ion that is less toxic and much easier to remove, meaning speciation results dictate the most effective removal strategy.
Water Treatment Options for Arsenic Removal
Effective treatment for arsenic contamination falls into two categories: Point-of-Use (POU) and Point-of-Entry (POE) systems. POU systems, such as Reverse Osmosis (RO) and Anion Exchange, treat water only at a single tap, typically the kitchen sink. RO systems are highly effective, using a semi-permeable membrane that filters out arsenic ions, often achieving over 99% removal efficiency for Arsenic V.
Anion exchange systems utilize a strong base resin that chemically swaps the charged Arsenic V ion for a harmless chloride ion. This method is selective but can be affected by high concentrations of competing ions like sulfate, which exhaust the resin’s capacity. When treating the difficult Arsenic III, it must first be converted into Arsenic V using an oxidant like chlorine, regardless of the POU technology chosen.
POE systems treat all water entering the home and include Adsorptive Media and Oxidation/Filtration units. Adsorptive media uses granular materials, such as iron oxide or activated alumina, to which arsenic chemically bonds as water passes through. This process is effective and simple, but the media must be replaced once its capacity is exhausted.
Oxidation/Filtration is a comprehensive POE approach involving two steps. First, an oxidant is injected to convert Arsenic III to Arsenic V. This converted arsenic is then removed either by co-precipitation with native iron or by filtration using media that captures the newly formed charged particles.