Methoxychlor in the bedroom

At a glance

Regulatory & certification status

Where methoxychlor stands across the major regulatory systems. Each row names the governing instrument; where a jurisdiction has no measure covering this compound, that absence is stated rather than left blank, because the absence is itself the finding in one case.

What it is

Methoxychlor is a synthetic organochlorine insecticide, CAS 72-43-5, chemical name 1,1,1-trichloro-2,2-bis(4-methoxyphenyl)ethane. US registration covered houseflies, mosquitoes and cockroaches, and the compound was used on field crops, stored grain, livestock, ornamentals and domestic pets. It was marketed and widely regarded as the lower-toxicity substitute for its structural cousin DDT, which put it into ordinary homes and gardens through decades when DDT itself was being withdrawn.

The cancer evidence never carried the case against it. IARC placed methoxychlor in Group 3, not classifiable as to its carcinogenicity to humans, in a 1987 evaluation. EPA's IRIS classification is Group D, also not classifiable, and the NCI/NTP bioassay TR-035 returned negative evidence of carcinogenicity in male and female rats and mice. What ended it was persistence, bioaccumulation and long-range transport, the criteria the Stockholm Convention applies. Those are properties of the molecule in the environment rather than findings about tumours.

One detail matters for reading any regulation on this compound. The EU and UK POPs entries are group entries. They cover "any possible isomer of dimethoxydiphenyltrichloroethane", list seven CAS numbers followed by "and others", and sit under a single EC number. CAS 72-43-5 is the primary p,p'- member of that group, not the whole of it.

Where it shows up

Not in the bed. Methoxychlor was never a mattress, foam or textile chemical, and nothing in a bed frame, cover or foam layer emits it. It reaches a bedroom the way chlordane and DDT do: as residue in settled house dust, left by indoor and garden applications made decades ago and topped up by treated soil walked in on shoes.

What earns it a page rather than a footnote is that it is still being found. Dodson and colleagues sampled dust in 49 California homes in the late 2000s and reported that several historic-use pesticides including DDT, DDE, DDD, chlordane and methoxychlor were detected in the majority of homes. Peer-reviewed — Dodson et al. 2015

Deziel and colleagues found methoxychlor in 48% of 68 California homes in a repeated-sampling study, and recorded no agricultural applications of methoxychlor near the study residences at all. Peer-reviewed — Deziel et al. 2013 That combination is the useful part: with no nearby drift to blame, the residue came from inside the house or the ground immediately around it.

What the research says

• It concentrates in the finest dust. ATSDR records size-fractionated North Carolina house dust at 1,000 ng/g of methoxychlor in the fraction below 4 microns against 120 ng/g in the coarse 250–500 micron fraction. The trend runs with particle size but not step by step: the 25–53 micron fraction reads 740 ng/g and the finer 4–25 micron fraction below it reads 680 ng/g. Fine dust is what lifts when someone crosses a carpet or shakes out bedding, and what transfers most readily to skin. Regulatory — ATSDR 2002
• Cancellation stopped the market, not the residue. EPA cancelled all registered technical sources in 2003 and revoked every tolerance, so any methoxychlor found indoors now is a residue of past application rather than a current product. Regulatory — EPA RED 2004
• The one study that measured it in carpet dust and looked for a childhood cancer signal found none. In a population-based case-control study of childhood acute lymphocytic leukemia, methoxychlor was measured directly in the sieved fine fraction of California carpet dust. The authors observed no significant positive associations for chlordane, DDT, DDE, methoxychlor or pentachlorophenol; the signal in that study was PCBs. Peer-reviewed — Ward et al. 2009
• Presence is not dose. No measured sleeping-zone air concentration or mattress-dust concentration for methoxychlor was found anywhere in the research behind this page. Floor-dust detection frequencies say the compound is in the room. They do not say what a sleeping person inhales, and no page on this site will pretend otherwise. Inferred — absence of evidence, stated as such

What helps

Take shoes off at the door. Tracked-in soil is the main route by which legacy organochlorines re-enter a house that stopped using them decades ago. It is also the cheapest intervention on this list.

Vacuum with a sealed HEPA machine and empty it outdoors. Focus on the bedroom carpet and the floor under and around the bed. The residue lives in settled dust, so removing dust is the control that matches the exposure.

Damp-wipe instead of dry dusting or sweeping. Hard floors, baseboards and the tops of bed frames. Dry methods lift the fine fraction, which is the fraction carrying the highest concentration.

Wash bedding and anything that touches the floor on a regular schedule, and keep bedding off the floor while changing it.

In housing built or treated before the mid-2000s, replacing old wall-to-wall carpet removes the reservoir rather than managing it. Carpet is where this class of residue accumulates and stays.

For young children, hand-washing before meals and before bed. ATSDR identifies ingestion, dermal contact and inhalation of house dust as potentially a substantial portion of a child's pesticide exposure, and a small child on the carpet beside the bed is the person this page is really about. Regulatory — ATSDR 2002

What does not help

• Buying a new mattress. Methoxychlor was never a mattress chemical. A swap addresses nothing here, and the money does more on the floor.
• Leaning on an air purifier as the primary control. This is a settled-dust exposure. ATSDR notes methoxychlor was not reported as detected in the collected air samples of the residential monitoring study it summarises. A purifier that catches resuspended dust is a marginal help, not the answer.
• Certifications on bedding. Organic, GOTS, GREENGUARD and CertiPUR govern what a manufacturer puts into a new product. They say nothing about what has accumulated in the floor of an older house.
• Airing out the room, or waiting for off-gassing to finish. There is no ongoing emission source to wait out. The residue is already deposited and is not volatilising from a product.
• Assuming the 2023 Stockholm listing or the EU and UK prohibitions changed anything indoors. Those instruments stop new production and new placing on the market. They do not remove residue that has been in a carpet since the 1990s.
• Buying a home test kit on the strength of a dust detection. There is no sleeping-environment inhalation benchmark to compare a result against, so a number would not tell you what to do next.

Open research questions

• Does EPA's Regional Screening Level table carry an inhalation reference concentration for methoxychlor, or only an oral RfD? If the answer is oral-only, this compound belongs in The Dose Gap: measured in homes, regulated by mouth, unbenchmarked for the air a person sleeps in. Speculation
• Has methoxychlor ever been measured in mattress dust or bedding specifically, rather than floor and carpet dust? No such measurement was found. Until one exists, the carpet numbers should not be read as bed numbers. Speculation
• Will Canada implement the Stockholm Annex A elimination obligation for methoxychlor? It is absent from Schedule 1 of SOR/2025-270 as made, and whether another CEPA instrument covers it was not verified. Speculation
• Which IARC monograph volume produced the Group 3 evaluation? ATSDR attributes it to 1987; the volume number is not printed here because it could not be confirmed against the IARC classification list. Speculation
• Because the EU and UK entries cover every isomer of dimethoxydiphenyltrichloroethane, does enforcement apply the 0.01 mg/kg threshold to the isomers jointly, given that analytical methods often report them separately? Speculation

Citations

1. Agency for Toxic Substances and Disease Registry (2002). Toxicological Profile for Methoxychlor. U.S. Department of Health and Human Services, Public Health Service. atsdr.cdc.gov Regulatory
2. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances (2004). Reregistration Eligibility Decision (RED) for Methoxychlor. archive.epa.gov Regulatory
3. European Parliament and Council of the European Union (2019). Regulation (EU) 2019/1021 on persistent organic pollutants (recast), Annex I Part A — Methoxychlor. Official Journal of the European Union, consolidated text 02019R1021-20260101. eur-lex.europa.eu Regulatory
4. Department for Environment, Food and Rural Affairs (2025). The Persistent Organic Pollutants (Amendment) Regulations 2025 (SI 2025/296). legislation.gov.uk. legislation.gov.uk Regulatory
5. Secretariat of the Stockholm Convention, United Nations Environment Programme (2023). The New POPs under the Stockholm Convention — Methoxychlor, decision SC-11/9. pops.int Regulatory
6. Dodson RE, Camann DE, Morello-Frosch R, Brody JG, Rudel RA (2015). Semivolatile Organic Compounds in Homes: Strategies for Efficient and Systematic Exposure Measurement Based on Empirical and Theoretical Factors. Environmental Science & Technology 49(1). doi:10.1021/es502988r Peer-reviewed
7. Deziel NC, Ward MH, Bell EM, Whitehead TP, Gunier RB, Friesen MC, Nuckols JR (2013). Temporal Variability of Pesticide Concentrations in Homes and Implications for Attenuation Bias in Epidemiologic Studies. Environmental Health Perspectives 121(5). doi:10.1289/ehp.1205811 Peer-reviewed
8. Ward MH, Colt JS, Metayer C, Gunier RB, Lubin J, Crouse V, Nishioka MG, Reynolds P, Buffler PA (2009). Residential Exposure to Polychlorinated Biphenyls and Organochlorine Pesticides and Risk of Childhood Leukemia. Environmental Health Perspectives 117(6). doi:10.1289/ehp.0900583 Peer-reviewed

Frequently asked questions

• Is methoxychlor in mattresses?

  No. Methoxychlor is an insecticide, not a mattress, foam or textile chemical, and nothing in a bed emits it. It reaches a bedroom as residue in settled house dust from past indoor, garden and pet applications, and from treated soil tracked in on shoes. No measurement of methoxychlor in mattress dust or bedding specifically was found in the research behind this page, so the carpet numbers should not be assumed to transfer to the bed.

• Methoxychlor was cancelled in 2003. Why is it still being found?

  Cancellation stops sales, not residues. EPA cancelled all registered technical sources in 2003 and revoked all 79 residue tolerances, but organochlorines deposited in carpet and floor dust stay put. Dodson and colleagues detected methoxychlor in the majority of 49 California homes sampled for dust, alongside DDT, DDE, DDD and chlordane. Deziel and colleagues found it in 48% of 68 California homes in a study that recorded no nearby agricultural applications of it at all, meaning the source was in or immediately around the house.

• Is methoxychlor a carcinogen?

  The cancer evidence is weak. IARC placed methoxychlor in Group 3, not classifiable as to its carcinogenicity to humans, in a 1987 evaluation. EPA's IRIS classification is Group D, also not classifiable. The NCI/NTP bioassay TR-035 returned negative evidence of carcinogenicity in male and female rats and mice, and methoxychlor is not listed in the NTP Report on Carcinogens. Regulators eliminated it for persistence, bioaccumulation and long-range transport, not for a demonstrated cancer risk at household levels.

• Is methoxychlor banned?

  In the EU and the UK, yes. It is listed in Annex I Part A of the EU POPs Regulation (EU) 2019/1021, so manufacture, placing on the market and use are prohibited, with relief only for unintentional trace contamination at or below 0.01 mg/kg. The UK made the same listing through SI 2025/296, in force 1 April 2025. The Stockholm Convention listed methoxychlor in Annex A at COP-11 in May 2023 by decision SC-11/9, without specific exemptions. In the United States there has been no legal pesticide market for it since 2003, though that was a cancellation rather than a POPs prohibition. Canada has no entry for methoxychlor in Schedule 1 of SOR/2025-270.

Related compounds

• DDT — the compound methoxychlor was sold to replace, and the one it is most often found beside in dust
• Chlordane — organochlorine termiticide detected in the same California house-dust surveys
• Lindane — organochlorine insecticide, also a Stockholm Annex A POP
• Pentachlorophenol — chlorinated biocide measured alongside methoxychlor in the childhood-leukemia carpet-dust study
• PCBs — the class that did show an association in that same study
• Toxaphene — organochlorine insecticide, once the most heavily used in the United States
• Heptachlor — persistent organochlorine that reaches homes through treated soil
• Dieldrin — persistent organochlorine found in soil and settled dust
• Hexachlorobenzene — organochlorine POP with a harmonised EU classification, unlike this one
• Propoxur — a later household insecticide, tracked in the same repeated-sampling home study

Embr is a sleep environment company researching and addressing the chemistry of the bedroom. Research and product development in progress.

Last reviewed 2026-07-25. If you find a factual error, contact us.