Chapter 7: Disinfectants and antibacterials · Part 4: Toilet blocks and mothballs
Paradichlorobenzene (PDCB)
- Poison schedule (Australia)
- Made from a hazardous chemical
- Contaminant risk
The worst fact: in a US study of 953 adults (1988–94 data), people with the highest blood levels had 153 mL lower lung function (FEV1) on average. It was the only one of 11 common solvents measured in blood still linked after allowing for smoking. Its breakdown product was in about 98% of Americans' urine. The WHO cancer agency rates it "possibly carcinogenic to humans", and the EU banned it at 1% or more in air fresheners and toilet deodorisers from June 2015.
Why brands use it: it slowly turns to vapour, masking toilet smells and repelling moths.
Take care if: you have children, or use it in living areas. In Australia it's Schedule 5 (Caution) at any strength. US mothball labels say to use them only in airtight containers, never where children can reach.
Comes from: benzene reacted with chlorine. Australia classes benzene as "May cause cancer". That doesn't mean it's in the product, but it's not a great starting point for something you clean with.
Myth check: "Toilet blocks clean the toilet": PDCB blocks are deodorisers. EU law describes them as air fresheners or deodorisers, not cleaners.
Contaminants: other chlorobenzenes. Pure grade has under 0.05% chlorobenzene and trichlorobenzene. They're unlikely to matter in a well-made product, but it's a factor you can't see on the label.
Fair to say: the rat kidney tumours aren't relevant to people (the "possible carcinogen" rating rests on liver tumours in mice), and levels in Americans' urine halved between 2003 and 2010.
Correct as of November 2026. What the badges mean
Sources
- Australian Government. Poisons Standard October 2026 (SUSMP), F2026L01327: didecyldimethylammonium salts; quaternary ammonium compounds; triclosan; o-phenylphenol; chlorocresol; p-dichlorobenzene; thymol; methanol; Appendix B.
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for each chemical, and for benzene and benzyl chloride.
- European Union. Regulation (EU) 474/2014 (1,4-dichlorobenzene); Implementing Decision (EU) 2016/110 (triclosan); Regulation (EU) 358/2014 (triclosan in cosmetics); Regulation (EU) 2019/831 (chlorophene); Regulation (EU) 2014/866 (cetrimonium chloride).
- IARC. Monographs vol. 73 (1999): ortho-phenylphenol; dichlorobenzenes.
- Elliott L et al. Volatile organic compounds and pulmonary function in NHANES III. Environ Health Perspect 2006;114:1210.
The full source list is at the end of Chapter 7.