Polychlorinated naphthalenes in the bedroom

At a glance

Regulatory & certification status

What it is

A polychlorinated naphthalene is a naphthalene ring with one or more of its hydrogen atoms replaced by chlorine. That definition is the EU Regulation's own, and it describes a family rather than a substance: 75 congeners are possible, toxicity rises with chlorination, and each congener has its own CAS number. The class identifier 70776-03-3 covers the group, which is why the Regulation writes it as "70776-03-3 and others". Any single figure attached to PCNs, whether a hazard classification or an exposure limit, has to say which congener it applies to.

Technical PCN mixtures were sold from about 1910 to 1980, most familiarly under the Halowax trade name. They insulated cable, filled capacitors as dielectric fluid, went into lubricants and cutting fluids, and preserved wood, paper and fabric. Manufacture ceased voluntarily in Europe, North America and Japan during the 1980s. They also form unintentionally during combustion, which is why the Stockholm Convention listed them under Annex C as well as Annex A.

IARC has never evaluated PCNs. That absence is worth stating precisely, because it is easy to read as reassurance and it is not. The WHO/IPCS assessment gives the reason in one line: no long-term toxicity or carcinogenicity study of PCNs has been identified. EFSA reached the same conclusion in 2024, finding no chronic toxicity or carcinogenicity studies in its literature search. No classification exists because nobody ran the study.

What is established is dioxin-like behaviour. Hexachloronaphthalene congeners activate the aryl hydrocarbon receptor in the same potency range as dioxin-like PCBs. EFSA nonetheless could not derive toxic equivalency factors for PCNs, because the persistence and repeat-dose data needed to compare them with TCDD are missing. PCNs therefore sit outside the WHO-TEQ framework that dioxin regulation runs on, so routine dioxin monitoring does not capture them.

One more distinction matters more than any number here. Naphthalene, the mothball compound, is CAS 91-20-3 and carries an IARC Group 2B classification. PCNs are a different class of substance. Naphthalene's classification does not transfer to them, and the reverse reading, that PCNs must be worse because they are chlorinated, is equally unsupported.

Where it shows up in a bedroom

Not in the mattress. No foam, cover fabric, adhesive or flame-retardant treatment in a modern bed contains or generates PCNs. A product sold as PCN-free is advertising against a hazard its category does not have.

PCNs arrive by two indirect routes. The first is settled house dust, where they form one strand of the dioxin-like background alongside dioxins and furans, coplanar PCBs and brominated dibenzofurans. Suzuki and colleagues quantified 33 Japanese indoor dust extracts by GC-HRMS and calculated each class's contribution to the dioxin-like TEQ. PCNs came in at 0.10 percent, against 17 percent from brominated dibenzofurans, 14 percent from PCDDs and 8.8 percent from PCDFs. If dust in a bedroom is worth attention for dioxin-like activity, PCNs are not the reason.

The second route is tracked-in soil. Seo and colleagues measured surface soils and street dusts at 19 residential and industrial sites in Detroit and found a geometric mean of 61 ng/g total PCNs, range 11 to 1,933 ng/g. Their conclusion is the more interesting part: given the short half-lives of PCNs and the restrictions on production, the pattern implies ongoing or recent releases. Forty-five years after manufacture ended, this is not a closed chapter.

Older buildings hold the real domestic reservoir. Pre-1980 cable insulation, capacitors and treated timber still in place are exactly the material the EU and GB exemption for "articles already in use before or on 10 July 2012" describes. Left in place and undisturbed, they are legal. Cut, sanded or burned, they are a source.

What the research says

The most useful finding for anyone reading this page in a bedroom is a gap. EFSA's 2024 opinion opens its indoor-environment section with the sentence: "There is very little information reported in the literature about PCNs in indoor air and dust." No study has measured PCNs in the air of an ordinary bedroom. The only indoor dataset with congener-level detail comes from Waheed and colleagues' work in Pakistani e-waste recycling hubs, where sum-39 PCNs in indoor dust ranged from 0.25 to 697 ng/g and in indoor air from 7.0 to 9,583 pg/m³. That is an occupational-adjacent setting, not a normal home, and the congener profile pointed to combustion rather than to the old technical mixtures.

Nor is there a number to compare a measurement against. No inhalation reference value for PCNs has been published: no EPA IRIS value, no PPRTV, no ATSDR minimal risk level, no California REL. This compound is a clean example of the pattern the Dose Gap tracks. It is persistent enough to be prohibited in three jurisdictions, detectable in dust and in human serum, and there is no published benchmark for the air a person breathes for eight hours a night.

The route that does dominate is diet. Fernandes and colleagues put it directly: since the restriction of manufacture and controls on inadvertent production during combustion, the principal route of human and animal exposure is likely to be dietary intake. EFSA's own dietary assessment then concluded, with at least 99 percent certainty, that exposure to hexachloronaphthalenes through food does not raise a health concern for any population group it assessed, including breast-fed infants at the highest consumption. The dominant exposure route was assessed, and the margins of exposure came out far above the threshold of concern.

The documented human harm from PCNs came from industry, not homes. Chloracne and severe liver disease appeared among workers handling these waxes in the 1930s and 1940s, at exposures no household encounters. That history is why occupational air limits exist, and why those limits are the wrong benchmark to hold a bedroom against.

What helps

Everything on this list is a general dust-and-combustion measure. None of it is PCN-specific, and that is the point: the same habits address dioxins, PCBs and brominated dibenzofurans riding in the same dust.

• Take shoes off at the door, with a mat inside and out. Urban soil and street dust are a documented PCN reservoir, and shoes are the transport route into a bedroom.
• Vacuum with a sealed HEPA machine and wet-mop hard floors, including under the bed. PCNs are semivolatile and ride on settled dust. Removing dust is the only lever that works on this whole class of persistent compounds at once.
• Treat pre-1980 electrical material as contaminated during renovation. Old cable insulation, capacitors and sealed equipment should be handled and disposed of properly rather than cut, sanded or burned. This is precisely the material the EU and GB exemption for articles already in use describes, and it is the actual reservoir in an older building.
• Do not burn treated, painted or salvaged wood, cable or electronic waste indoors, in a wood stove or on a garden fire. PCNs form in combustion. EFSA lists waste incineration, cement kilns and the burning of firewood and coal in private dwellings among the sources, so burning the wrong fuel is one of the few ways a household creates them rather than inheriting them.
• Ventilate hard during and after any indoor combustion, and keep a stove or fireplace properly drafted. A general combustion-byproduct measure that covers PCNs alongside the PAHs and dioxin-like compounds in the same emissions.

What does not help

• Shopping for a "PCN-free" mattress or bedding. No mattress has a PCN source. A claim like that is marketing against a hazard the category does not have, which is a reason to distrust the rest of the label.
• Buying an air purifier for this. PCNs travel on dust and in food, and no measured bedroom-air concentration exists for a filter to reduce. A HEPA vacuum for dust removal is defensible. A room air cleaner sold on PCN grounds is not.
• Testing your home or mattress for PCNs. Congener-level analysis needs GC-HRMS or APGC-MS/MS with ¹³C-labelled standards, which is research-laboratory work rather than a consumer kit. Even a valid result could not be interpreted, because no inhalation reference value or indoor guideline exists to compare it against.
• Throwing out mothballs because of PCNs. Mothballs are naphthalene, CAS 91-20-3, a different substance with its own IARC Group 2B classification. There are good reasons to keep naphthalene out of a bedroom. PCNs are not among them.
• Changing your diet on PCN grounds. Diet is the dominant exposure route, and EFSA still concluded with at least 99 percent certainty that dietary exposure to hexachloronaphthalenes does not raise a health concern for any population group assessed, including breast-fed infants at the highest consumption.
• Borrowing a hazard number from naphthalene or from dioxin. IARC has never evaluated PCNs, no long-term carcinogenicity study of them exists, and EFSA could not derive toxic equivalency factors for them. Reading a classification across from a related compound would be inventing a number, not finding one.

Open research questions

• No PCN concentration has ever been measured in an ordinary bedroom. EFSA 2024 reports very little information in the literature about PCNs in indoor air and dust, and the only congener-resolved indoor dataset comes from e-waste recycling hubs in Pakistan. A single study of settled dust in normal homes would be the highest-value missing measurement here.
• There is no published inhalation reference value. No IRIS, PPRTV, ATSDR MRL or CalEPA REL. PCNs belong in the Dose Gap denominator: present in dust and in serum, prohibited in three jurisdictions, with no number for the air a person breathes for eight hours a night.
• IARC has never evaluated PCNs, and the reason is that no long-term carcinogenicity study exists. The absence of a classification is an absence of study, not a finding of safety.
• PCNs sit outside the WHO-TEQ framework. EFSA accepted that some congeners show clear dioxin-like activity but could not establish toxic equivalency factors, citing missing persistence and repeat-dose data. Routine dioxin monitoring therefore does not capture them.
• Where the recent releases come from is unresolved. Seo and colleagues concluded that Detroit soil and street-dust patterns imply ongoing or recent releases decades after manufacture ceased. Whether the source is combustion, chlor-alkali processes or PCB co-contamination determines whether PCNs are a closing legacy or a live problem.
• Australia's IChEMS status is unconfirmed here. Secondary reporting places PCNs in Schedule 7, but the Register and legislation.gov.au could not be opened to check it, so we have not stated it as fact.
• The Stockholm Convention exemption wording is unconfirmed here. A specific exemption for producing polyfluorinated naphthalenes appears on the Secretariat's listing page. We have not read it in the text of decision SC-7/14 and do not quote it.

Citations

1. European Parliament and Council of the European Union (2019). Regulation (EU) 2019/1021 on persistent organic pollutants (recast), Annex I Part A. Official Journal of the European Union, consolidated text 02019R1021-20260101. Source Regulatory
2. Government of Canada, Environment and Climate Change Canada (2025). Prohibition of Certain Toxic Substances Regulations, 2025 (SOR/2025-270), made under the Canadian Environmental Protection Act, 1999. Canada Gazette, Part II, Volume 159, Number 27, 31 December 2025. Source Regulatory
3. Howe PD, Melber C, Kielhorn J, Mangelsdorf I (2001). Concise International Chemical Assessment Document 34: Chlorinated Naphthalenes. World Health Organization, International Programme on Chemical Safety, under the joint sponsorship of UNEP, ILO and WHO. Source Regulatory
4. EFSA Panel on Contaminants in the Food Chain (CONTAM); Schrenk D, Bignami M, Bodin L, et al. (2024). Risks for animal and human health related to the presence of polychlorinated naphthalenes (PCNs) in feed and food. EFSA Journal 22(3):e8640. DOI: 10.2903/j.efsa.2024.8640 Regulatory
5. Fernandes AR, Kilanowicz A, Stragierowicz J, Klimczak M, Falandysz J (2022). The toxicological profile of polychlorinated naphthalenes (PCNs). Science of the Total Environment 837:155764. PMID 35545163. DOI: 10.1016/j.scitotenv.2022.155764 Peer-reviewed
6. Suzuki G, Someya M, Takahashi S, Tanabe S, Sakai S, Takigami H (2010). Dioxin-like activity in Japanese indoor dusts evaluated by means of in vitro bioassay and instrumental analysis: brominated dibenzofurans are an important contributor. Environmental Science & Technology 44. PMID 20860407. DOI: 10.1021/es102021c Peer-reviewed
7. Waheed S, Khan MU, Sweetman AJ, Jones KC, Moon HB, Malik RN (2020). Exposure of polychlorinated naphthalenes (PCNs) to Pakistani populations via non-dietary sources from neglected e-waste hubs: A problem of high health concern. Environmental Pollution 259:113838. PMID 32023785. DOI: 10.1016/j.envpol.2019.113838 Peer-reviewed
8. Seo SH, Xia T, Islam MK, Batterman S (2025). Polychlorinated naphthalenes (PCNs) and polychlorinated biphenyls (PCBs) in surface soils and street dusts in Detroit, Michigan. Science of the Total Environment 964:178582. PMID 39842294. DOI: 10.1016/j.scitotenv.2025.178582 Peer-reviewed

Frequently asked questions

• Are polychlorinated naphthalenes in my mattress?

  No. PCNs were technical waxes used for cable insulation, capacitor dielectrics, lubricants and wood, paper and fabric preservatives, made from roughly 1910 to 1980. No modern mattress, foam, cover fabric or flame-retardant treatment contains or generates them. Manufacture, sale and use are prohibited in the EU under Annex I Part A of Regulation (EU) 2019/1021, in Great Britain under the same assimilated Regulation, and in Canada under SOR/2025-270. A product advertised as PCN-free is marketing against a hazard its category does not have.

• Are PCNs the same as the naphthalene in mothballs?

  No, and this is the most likely mistake to make. Mothballs are naphthalene, CAS 91-20-3, a single compound that IARC classified in Group 2B. Polychlorinated naphthalenes are a group of up to 75 chlorinated congeners registered under the class identifier CAS 70776-03-3. IARC has never evaluated PCNs at all. Naphthalene's classification does not carry across, and there are separate reasons to keep mothballs out of a bedroom.

• How do PCNs get into house dust?

  Two indirect routes. They are one strand of the dioxin-like background already sitting in settled dust, alongside dioxins and furans, coplanar PCBs and brominated dibenzofurans. Suzuki and colleagues measured PCNs in Japanese house dust as a minor contributor, 0.10 percent of the calculated dioxin-like TEQ against 17 percent from brominated dibenzofurans. They are also tracked in on shoes: Seo and colleagues found a geometric mean of 61 ng/g total PCNs across 19 Detroit surface-soil and street-dust sites.

• Has anyone measured PCNs in a bedroom?

  Not that we can find. EFSA's 2024 review states that there is very little information reported in the literature about PCNs in indoor air and dust. The only indoor dataset with congener-level detail comes from e-waste recycling hubs in Pakistan, an occupational setting rather than a normal home. There is also no published inhalation reference value for PCNs: no IRIS, PPRTV, ATSDR MRL or CalEPA REL. Even a valid bedroom measurement would have no benchmark to compare against.

Related compounds

• Naphthalene — the unchlorinated parent compound and the mothball chemical, CAS 91-20-3, with its own IARC Group 2B classification. Different substance, different evidence
• Dioxins and furans — the chlorinated dioxin-like classes in the same house dust, at 14 and 8.8 percent of its TEQ against 0.10 percent from PCNs, and the framework PCNs sit outside because no equivalency factors exist for them
• PCBs — the other chlorinated legacy class in the same dust, with the coplanar congeners driving the same AhR mechanism
• Hexachlorobenzene — a chlorinated aromatic POP with a full IARC evaluation, which is exactly the contrast PCNs lack
• Pentachlorobenzene — another Stockholm POP prohibited under the same EU Annex I Part A
• PBDEs — the brominated flame retardants of the same house dust, where brominated dibenzofurans carried 17 percent of the dioxin-like TEQ against 0.10 percent from PCNs

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.