At a glance
| Chemical family | Metalloid (As, atomic number 33); multiple oxidation states; biologically distinct categories — inorganic arsenic (toxic and carcinogenic), organic arsenic compounds in seafood (arsenobetaine and arsenosugars, generally non-toxic at typical dietary intake) |
| CAS number | 7440-38-2 (elemental); 1327-53-3 (arsenic trioxide); 7778-44-1 (calcium arsenate); other CAS for specific compounds |
| Classification | IARC Group 1 (arsenic and inorganic arsenic compounds, carcinogenic to humans, Monograph Vol 100C, 2012); IARC Group 2B (dimethylarsinic acid, a methylated metabolite); EPA drinking water Maximum Contaminant Level (MCL) 10 ppb; WHO drinking water guideline 10 µg/L; FDA action level 10 ppb in apple juice and 100 ppb inorganic arsenic in infant rice cereal |
| Where you encounter it | Drinking water — especially private wells in geologically-arsenic regions (NE, parts of SW, upper Midwest, Mississippi Delta); rice and rice products (brown higher than white due to bran retention); seafood (mostly organic, less toxic); apple juice and some fruit juices (FDA action level 10 ppb); CCA pressure-treated wood from pre-2004 outdoor structures (banned 2003 residentially); historical pesticide residues in older agricultural soils; coal combustion as ambient source |
| Sleep micro environment relevance | Indirect — the dominant exposures (water, rice, treated wood deck dust tracked indoors) happen outside the bedroom but contribute to total body burden. Households with pre-2004 outdoor treated-wood structures where children play barefoot or eat outside have a more direct pathway via dermal and hand-to-mouth contact |
| Activated carbon capture | Not applicable for VOC capture. For drinking water above 10 ppb, certified reverse osmosis (NSF/ANSI 58) and specifically-certified NSF/ANSI 53 arsenic-reduction filters and activated alumina filters are the validated technologies. Inferred from established residential arsenic water remediation engineering; generic activated carbon for VOC capture is not the relevant technology |
What it is
Arsenic — chemical symbol As, CAS 7440-38-2, atomic number 33 — is a metalloid with multiple oxidation states (+5, +3, 0, -3) and a corresponding diversity of biological behaviors. The two categories that matter most for human exposure assessment are inorganic arsenic (primarily arsenate As(V) and arsenite As(III) — the forms in water and soil and the carcinogenic forms) and organic arsenic compounds (primarily arsenobetaine and arsenosugars in seafood — generally non-toxic at typical dietary intake). The IARC Group 1 carcinogen classification applies to "arsenic and inorganic arsenic compounds"; the methylated metabolites dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) have been separately evaluated, with DMA classified as Group 2B in Monograph Vol 100C (2012).
Arsenic occurs naturally in the Earth's crust at varying concentrations depending on local geology. Groundwater in certain US regions (parts of New England, the Southwest, upper Midwest, and the Mississippi Delta) carries naturally elevated arsenic from interaction with arsenic-bearing rock and sediment. Globally, the largest known arsenic public-health crisis is in Bangladesh and West Bengal, where shallow tube wells installed to provide bacteriologically-safe drinking water inadvertently exposed tens of millions of people to chronic arsenic via well water contaminated by arsenic-bearing alluvial sediments. The historical industrial uses (lead-arsenate pesticides, arsenic-trioxide wood preservatives, copper-acetoarsenite pigments) have largely been phased out in the US, but legacy contamination persists in older agricultural soils and pre-2004 CCA pressure-treated wood.
The biological behavior that drives arsenic's exposure assessment is its relatively short biological half-life — most absorbed inorganic arsenic is methylated by the liver (to MMA and DMA) and excreted in urine within 1-4 days, with smaller amounts persisting in keratin-rich tissues (hair, nails) reflecting integrated exposure over weeks. The short half-life means current blood and urine arsenic measurements reflect recent exposure rather than lifetime cumulative dose. Hair and nail measurements provide a longer-window biomarker. Unlike lead and cadmium, arsenic does not accumulate substantially in body tissues over decades — stopping the exposure source produces relatively rapid reduction in body arsenic.
Where you encounter it
From drinking water
The largest global inorganic arsenic exposure source. US municipal water systems are regulated under the Safe Drinking Water Act with the EPA MCL of 10 ppb (lowered from 50 ppb in 2001). Private wells are not subject to mandatory testing or treatment, and naturally-elevated groundwater arsenic affects an estimated 1.5 to 2.0 million US private-well households. The geological-arsenic regions known for elevated well water include parts of New Hampshire, Maine, Massachusetts (the Merrimack Valley specifically), upstate New York, Michigan's Upper Peninsula, Minnesota, Wisconsin, parts of the Southwest including New Mexico and Nevada, and the Mississippi Delta. One-time well testing is the highest-leverage household action in any of these regions.
From rice and rice products
Rice plants accumulate arsenic from soil and water more efficiently than other major grains because of the anaerobic flooded paddy growing conditions that mobilize arsenic into a plant-available form. Inorganic arsenic concentrates in the bran layer, which is why brown rice typically carries 50-80% more inorganic arsenic than corresponding white rice of the same variety. The FDA set an action level of 100 ppb for inorganic arsenic in infant rice cereal in 2020 following years of consumer reporting and analytical work. Regulatory Cooking rice in excess water (5:1 water-to-rice) and draining the excess reduces inorganic arsenic by approximately 40-60%.
From CCA pressure-treated wood
Chromated copper arsenate (CCA) was the dominant US residential pressure-treatment chemistry from the 1970s through 2003, used in decks, picnic tables, play structures, raised garden beds, and fencing. The EPA voluntary cancellation took effect December 31, 2003, after which residential applications shifted to ACQ (alkaline copper quaternary) and copper-azole formulations that do not contain arsenic. Pre-2004 CCA-treated wood still in use continues to release surface-dislodgeable arsenic at slowly-decaying rates. Children's playground structures, backyard decks where children play barefoot, and raised vegetable garden beds with CCA-era timbers are the most consequential bedroom-adjacent exposure scenarios.
From seafood, juices, and other dietary sources
Seafood carries the highest total arsenic concentrations of any common food category, but the form is overwhelmingly organic arsenic (arsenobetaine, arsenosugars) that is rapidly excreted without metabolism or toxicity. Total arsenic measurements on seafood are not directly comparable to total arsenic in water without speciation analysis. The FDA set an action level of 10 ppb for inorganic arsenic in apple juice in 2023. Coal combustion is a meaningful ambient atmospheric arsenic source contributing to background environmental loading.
What the research says
Carcinogenicity — the IARC Group 1 classification
The IARC Monograph Volume 100C (2012) reaffirmed arsenic and inorganic arsenic compounds as Group 1 carcinogenic to humans, with sufficient evidence for lung, urinary bladder, and skin cancers and limited evidence for kidney, liver, and prostate cancers. Regulatory The classification is built on decades of epidemiological evidence from Bangladesh, West Bengal, Taiwan, Chile, Argentina, and northern China — populations exposed to high inorganic arsenic via drinking water with documented dose-response for the IARC-recognized cancer sites.
Chile and the long-latency cancer signal
Marshall, Ferreccio, Steinmaus, Smith and colleagues 2007 in JNCI reported the 50-year follow-up of populations in northern Chile exposed to a documented high-arsenic drinking water period (Antofagasta, 1958-1971, when the municipal water source briefly drew from a high-arsenic mountain river before remediation). The study documented continued elevated lung and bladder cancer mortality decades after the high-exposure period ended — illustrating the long latency between arsenic exposure and cancer manifestation. Peer-reviewed
Beyond cancer — the broader chronic-effect picture
Naujokas, Anderson, Ahsan, Aposhian, Graziano, Thompson and Suk 2013 in Environmental Health Perspectives reviewed the broader scope of chronic arsenic health effects beyond cancer: cardiovascular disease, type 2 diabetes association, developmental and cognitive effects in childhood, immunological effects, and the characteristic dermatological lesions (hyperpigmentation, hyperkeratosis, palmoplantar keratosis) documented in Bangladesh and similar high-exposure populations. Peer-reviewed The non-cancer outcomes add to the picture that justifies the conservative regulatory drinking-water limits and the FDA's attention to dietary arsenic sources.
Regulatory reference values
The EPA drinking water Maximum Contaminant Level for total arsenic is 10 ppb (10 µg/L), lowered from 50 ppb in 2001 and effective for compliance in 2006. Regulatory The WHO drinking water guideline is 10 µg/L, matching the EPA MCL. Regulatory The ATSDR Toxicological Profile for Arsenic sets a chronic oral Minimal Risk Level for inorganic arsenic. Regulatory The US EPA IRIS oral cancer slope factor for inorganic arsenic is 1.5 per mg/kg/day. Regulatory
What helps reduce exposure
For private well households: test the well for arsenic. This is the single highest-leverage action for a private-well household. The one-time cost of testing (typically $25-50 through state laboratories) is small relative to the lifetime health implications of unknown chronic exposure. Re-test every 3-5 years; aquifer arsenic can change over time.
For water exceeding 10 ppb: install certified arsenic-reduction filtration. NSF/ANSI 58 (reverse osmosis) is the most thoroughly validated for arsenic. NSF/ANSI 53 filters specifically certified for arsenic reduction (verify the specific certification — not all NSF 53 covers arsenic) and activated alumina filters are also effective. Point-of-use at the kitchen sink is typically the cost-effective configuration for drinking and cooking water.
Rinse rice thoroughly; cook in excess water and drain. 5:1 water-to-rice ratio with draining reduces inorganic arsenic by 40-60% and reduces cadmium meaningfully as well. Vary grains across the week (oats, quinoa, barley, millet) rather than relying daily on rice.
For infants and toddlers: vary cereal grains rather than relying daily on rice cereal. Oat, barley, and multigrain cereals are reasonable rotations. The FDA action level of 100 ppb inorganic arsenic in infant rice cereal is met by most current products but reduces, not eliminates, the rice-cereal arsenic contribution.
For pre-2004 outdoor CCA-treated wood: seal, replace, or restrict use. Sealing with deck stain reduces surface arsenic transfer. Don't use CCA-era wood for raised vegetable garden beds (food contact pathway) or as cutting surfaces. Replace play structures and decks where feasible — current ACQ and copper-azole-treated wood is arsenic-free.
For pre-2004 backyard play structures: handle children's hand washing and shoe removal at entry. The take-in pathway from CCA play structures involves dermal contact with surface arsenic, hand-to-mouth ingestion, and tracked-in dust. Standard hand-washing-before-eating and shoes-off-at-door practices break the path.
What does NOT help
- Generic activated-carbon-only pitcher filters. Standard carbon filters not specifically NSF 53-certified for arsenic do not reliably reduce arsenic. Verify the certification language; "filters lead and other contaminants" claims without specific arsenic certification are not adequate.
- Boiling water. Concentrates rather than removes arsenic — as water evaporates, dissolved arsenic stays in the smaller volume.
- Generic "filtered water" claims. Without specific certification, the claim is unverified for arsenic.
- Avoiding all seafood. Seafood arsenic is mostly organic forms that are rapidly excreted. The dietary omega-3 benefits favor continued seafood consumption (with attention to mercury per the separate mercury page guidance, not arsenic).
- Avoiding all rice in adult diets. Moderation and grain variety are more effective for most adults than full elimination. The infant rice cereal case is different because of higher rice-per-body-weight in infant feeding patterns.
- Chelation therapy for routine arsenic exposure. Chelation is a medical treatment for acute poisoning, supervised by physicians. The short half-life of inorganic arsenic means source removal produces relatively rapid body burden reduction without chelation.
Open research questions
- Low-level chronic dietary inorganic arsenic exposure below current regulatory thresholds and long-term cancer risk — the dose-response above ~100 ppb in drinking water is well-characterized; the dose-response at typical US dietary intake (mostly below 10 ppb water equivalent) is less precisely characterized. Speculation re: shape below regulatory MCL; established above
- Developmental windows of vulnerability — in utero and early childhood arsenic exposure dose-response for cognitive outcomes is documented at higher exposures; the threshold and exposure-window sensitivity is an active area. Speculation
- Nutritional modifiers of arsenic toxicity — selenium, folate, and B vitamin status appear protective in some Bangladesh studies; the protective effect size and the question of whether nutritional supplementation could meaningfully reduce risk in chronically-exposed populations is being studied. Speculation
- Regional well-water remediation cost-effectiveness at scale — private-well household testing rates remain low in many high-arsenic regions; the policy and public-health infrastructure to drive testing-and-filtration uptake is an active area beyond pure toxicology. Inferred from general well-water public-health policy literature
Citations
- International Agency for Research on Cancer (2012). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100C: Arsenic, Metals, Fibres and Dusts — arsenic and inorganic arsenic compounds Group 1. Lyon: IARC. NCBI Bookshelf — Arsenic Monograph Regulatory
- Agency for Toxic Substances and Disease Registry. Toxicological Profile for Arsenic. atsdr.cdc.gov/ToxProfiles/tp2.pdf Regulatory
- US Environmental Protection Agency. Inorganic arsenic — Integrated Risk Information System chemical assessment. Oral cancer slope factor 1.5 per mg/kg/day. iris.epa.gov Regulatory
- World Health Organization. Drinking Water Quality Guidelines — arsenic 10 µg/L. who.int Regulatory
- US Food and Drug Administration. Arsenic in Food and Dietary Supplements — including the 100 ppb action level for inorganic arsenic in infant rice cereal and the 10 ppb action level in apple juice. fda.gov Regulatory
- Marshall G, Ferreccio C, Yuan Y, Bates MN, Steinmaus C, Selvin S, Liaw J, Smith AH (2007). Fifty-year study of lung and bladder cancer mortality in Chile related to arsenic in drinking water. JNCI: Journal of the National Cancer Institute, 99(12):920-928. DOI 10.1093/jnci/djm004 Peer-reviewed
- Naujokas MF, Anderson B, Ahsan H, Aposhian HV, Graziano JH, Thompson C, Suk WA (2013). The broad scope of health effects from chronic arsenic exposure: update on a worldwide public health problem. Environmental Health Perspectives, 121(3):295-302. DOI 10.1289/ehp.1205875 Peer-reviewed
- Steinmaus C, Moore L, Hopenhayn-Rich C, Biggs ML, Smith AH (2000). Arsenic in drinking water and bladder cancer. Cancer Investigation, 18(2):174-182. DOI 10.3109/07357900009038249 Peer-reviewed
- US Environmental Protection Agency. Chemicals Evaluated for Carcinogenic Potential by the Office of Pesticide Programs — Arsenic Rule (2001 final rule, 10 ppb MCL, compliance effective 2006). epa.gov/dwreginfo Regulatory
- US Environmental Protection Agency. Chromated Copper Arsenate (CCA) — Voluntary cancellation of residential CCA-treated wood, effective December 31, 2003. epa.gov Regulatory
Frequently asked questions
Is arsenic in rice dangerous for babies?
Inorganic arsenic in rice has been a documented concern for infant rice cereal — the FDA set an action level of 100 ppb for inorganic arsenic in infant rice cereal in 2020 following years of consumer reporting and analytical work. The practical recommendation for infants and toddlers is to vary cereal grains rather than rely on rice cereal daily — oat, barley, and multigrain cereals are reasonable rotations. For older children and adults, rice in moderation within a varied diet is generally not the dominant arsenic exposure pathway.
Should I test my well for arsenic?
Yes if you draw drinking water from a private well — this is the single highest-leverage action a private-well household can take. Arsenic occurs naturally in groundwater in many US regions (New England, parts of the Southwest, parts of the upper Midwest, the Mississippi Delta) and private wells are not subject to the EPA testing and treatment requirements that apply to municipal water systems. State health departments and EPA Region offices maintain lists of certified water-testing laboratories. The one-time cost of testing is small relative to the lifetime health implications of unknown chronic arsenic exposure.
Does brown rice have more arsenic than white rice?
Yes. Arsenic concentrates in the bran layer of rice grains, which is removed during white-rice processing but retained in brown rice. FDA testing data shows brown rice typically carries roughly 50-80% higher inorganic arsenic than corresponding white rice of the same variety. This is a real arsenic-versus-fiber-and-nutrient trade-off; the practical answer for most adults is moderation and grain variety rather than systematic avoidance of either form.
Is arsenic in seafood the same as arsenic in water?
No — and the distinction matters substantially. Most arsenic in seafood is organic arsenic, primarily arsenobetaine and arsenosugars, which are absorbed but rapidly excreted in urine without significant metabolism or toxicity. Arsenic in water and soil is primarily inorganic arsenic, which is the carcinogenic form (IARC Group 1). The same total arsenic measurement on a urine test means very different things depending on whether the person recently ate seafood or has chronic inorganic arsenic exposure from water — speciation analysis (separating inorganic from organic forms) is required to distinguish them.
How long does arsenic stay in the body?
Inorganic arsenic has a relatively short biological half-life — most absorbed arsenic is excreted in urine within 1-4 days, with smaller amounts persisting in keratin-rich tissues (hair, nails) reflecting integrated exposure over weeks. The short half-life means current blood and urine arsenic reflect recent exposure rather than lifetime cumulative dose. Hair and nail measurements provide a longer-window biomarker. The acute kinetics also mean that stopping the exposure source produces relatively rapid reduction in body arsenic burden — unlike lead and cadmium, which accumulate for decades.
Can you remove arsenic from water?
Yes, with appropriate certified filtration. The two NSF/ANSI standards specifically validated for arsenic reduction are NSF/ANSI 58 (reverse osmosis) and NSF/ANSI 53 (specifically certified for arsenic reduction — not all NSF 53 filters are; verify the specific arsenic claim). Activated alumina filters are also effective. Standard activated-carbon-only pitcher and faucet filters without specific arsenic certification do not reliably remove arsenic. Boiling concentrates rather than removes arsenic. For private wells with chronic arsenic exceedance, point-of-use reverse osmosis at the kitchen sink is typically the cost-effective intervention.
Is arsenic from old pressure-treated wood still a risk?
Some — but the decay is slow. CCA (chromated copper arsenate) pressure-treated wood was banned for residential use in the US in 2003. Decks, picnic tables, raised garden beds, and playground structures built before 2004 may still contain CCA-treated wood, and surface-dislodgeable arsenic decays slowly. For pre-2004 outdoor structures still in active use, sealing with a deck stain reduces surface arsenic transfer. Don't use CCA-era wood for raised vegetable garden beds (food contact) or as cutting surfaces. Replacement with current ACQ or copper-azole-treated wood removes the arsenic concern entirely.
Related compounds
Embr Sleep is a sleep environment company researching the chemistry of the bedroom. See the methodology page for how this Atlas tags claims by evidence strength. For broader context on well-water and rural exposure, see farm family sleep; for dietary and household contamination framing, see non-toxic bedroom.
Last reviewed 2026-05-25. If you find a factual error, contact us.