E-numbers / Preservatives / E232
also: Sodium 2-phenylphenate · Sodium o-phenylphenate · Sodium ortho-phenylphenol · SOPP
A synthetic fungicide sprayed or dipped onto citrus fruit peel after harvest to stop mould. No longer permitted as a food additive in the UK or EU.
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The sodium salt form has caused bladder and kidney tumours in rats at high doses and is classed by IARC as possibly carcinogenic to humans (Group 2B).
Why it’s worth knowing. The sodium salt form has caused bladder and kidney tumours in rats at high doses and is classed by IARC as possibly carcinogenic to humans (Group 2B). It is not a permitted food additive in the UK or EU, but may appear on imported citrus from countries where post-harvest use continues. Look for 'sodium orthophenyl phenol' or 'E232' on a 'surface treatment' label declaration on waxed citrus.
Sodium orthophenyl phenol (also written sodium ortho-phenylphenate or SOPP) is the sodium salt of 2-phenylphenol, a synthetic aromatic phenol compound. It appears as a white powder, dissolves readily in water, and belongs to a group of related citrus post-harvest fungicides that also includes 2-phenylphenol (E231) and biphenyl (E230).
It works as an antifungal agent by disrupting the cell membranes of mould fungi, particularly Penicillium species that cause green and blue rot on citrus during storage and transport. Fruit is either dipped in a solution or treated via impregnated wrapping paper. The compound penetrates the peel surface and remains as a residue.
Historically applied post-harvest to the outer peel of citrus fruits including oranges, lemons, grapefruits and mandarins. As a food additive it is no longer permitted in the UK or EU, but residues may be present on imported citrus from countries where it remains in use as a pesticide. Where declared, it appears on packaging or retail price labels as 'surface treatment: E232' or 'preservative: sodium orthophenyl phenol'.
IARC evaluated the sodium salt specifically in its 1987 Supplement 7 and again in Volume 73 (1999), concluding there is sufficient evidence of carcinogenicity in animals and classifying it as Group 2B, possibly carcinogenic to humans. The parent compound ortho-phenylphenol is Group 3 (not classifiable). No human cancer data were available at either evaluation.
Sodium ortho-phenylphenate is classified as possibly carcinogenic to humans (IARC Group 2B) based on sufficient evidence of carcinogenicity in experimental animals.
Dietary administration produced tumours of the urinary bladder and renal pelvis in male rats in two separate studies, and a marginal increase in bladder tumours in female rats in one study. No carcinogenicity was observed in mice.
In the earlier Supplement 7 assessment, the sodium salt was also noted to increase liver haemangiomas and hepatocellular carcinomas in male mice following oral administration.
Animal studies indicate the sodium salt acts through a non-genotoxic mechanism. High doses raise urinary pH and produce toxic metabolites including phenylhydroquinone and phenylbenzoquinone, which cause urothelial cell damage and persistent inflammation, leading to regenerative cell proliferation. Tumours develop only at doses that first produce this hyperplasia. No DNA adduct formation was detected in rat bladder tissue, which suggests the carcinogenic pathway does not involve direct genetic damage.
No evidence of direct DNA adduct formation was found in rat bladder urothelium exposed to ortho-phenylphenol or the sodium salt, supporting a non-genotoxic mode of action.
The higher urinary pH induced by the sodium salt, compared with the parent compound, may enhance urothelial toxicity; formation of abnormal urinary crystals was not part of the mechanism.
Reactive quinoid metabolites, particularly phenylbenzoquinone, have been identified as the likely drivers of cytotoxicity and subsequent cell proliferation in rat bladder epithelium.
Toxicologists have debated whether the rat bladder tumour findings translate to humans. The dominant view in the regulatory literature is that the effect is species-specific and dose-dependent, occurring only at levels far above any food residue exposure, and involving a threshold-based non-genotoxic pathway. JECFA set an ADI of 0 to 0.4 mg/kg bodyweight for 2-phenylphenol (the active form the sodium salt converts to), reflecting this threshold view. No human epidemiological data have linked dietary exposure to cancer.
Bladder tumours in rats and male mice are considered high-dose, sex- and species-specific phenomena based on non-genotoxic mechanisms, and conventional margin-of-safety approaches are judged appropriate for human risk assessment.
JMPR (1999) established an ADI of 0 to 0.4 mg/kg bodyweight for 2-phenylphenol; the sodium salt was not given a separate ADI because it dissociates rapidly to the parent compound.
No data were available to the IARC Working Group on carcinogenicity of either ortho-phenylphenol or its sodium salt in humans.
Neither the EU Regulation 1333/2008 Annex II nor the current UK FSA approved-additives list includes E232. E230, E231, E232 and E233 all have a gap in the permitted preservatives series, with the list jumping from E228 to E234. Some EU member states retained E232 as a post-harvest plant protection product under separate pesticide law after it was removed as a food additive, regulated by maximum residue levels rather than additive authorisation.
E232 is absent from the UK FSA approved-additives list and from Annex II of EU Regulation 1333/2008; it is not a permitted food additive in the UK or EU.
A provisional MRL of 5 mg/kg was set for 2-phenylphenol residues on citrus fruits under EU Regulation 396/2005, covering post-harvest use as a plant protection product in countries where it remains authorised.
E232 is not present in UK or EU-produced food as a permitted additive. People concerned about residues on imported citrus should check packaging for 'surface treatment' declarations, wash citrus thoroughly before use, and avoid using the peel of treated fruit. Those who are pregnant or limiting chemical residue exposure may wish to choose organically grown citrus, which prohibits synthetic post-harvest fungicides. Look for 'E232', 'sodium orthophenyl phenol', or 'surface treatment' on the price label or packaging of imported citrus.
The key fact is that E232 is not a permitted food additive in the UK or EU, so it should not appear in any food produced or sold here under that authorisation. The IARC Group 2B classification for the sodium salt is a genuine signal, but it is based entirely on animal studies at high dietary doses with no human cancer data. The scientific debate has largely settled on a non-genotoxic, threshold-dependent mechanism, which regulators treat as meaning the residue levels that might realistically reach consumers carry a much smaller risk than the rat studies alone suggest. That debate is not fully closed. Residues on imported citrus peel are the realistic exposure route for UK consumers, not food additives. The science here is animal-based and extrapolated, not settled at the human level.
E232 is not a permitted food additive in the UK. It does not appear on the UK FSA approved-additives list or in EU Regulation 1333/2008 Annex II, which the UK retained after Brexit. It was permitted in older UK regulations but was subsequently removed. It may still be present as a pesticide residue on imported citrus fruit treated post-harvest in countries where it remains authorised.
IARC classifies sodium ortho-phenylphenate (the sodium salt form, E232) as Group 2B, possibly carcinogenic to humans, based on sufficient evidence of bladder and kidney tumours in rats. No human cancer data exist. The tumours occurred at high dietary doses in rats, and the prevailing view among regulatory toxicologists is that the mechanism is species-specific and threshold-dependent, not directly applicable to low residue exposures in humans. However, the IARC Group 2B classification stands and has not been revised.
As a permitted food additive, none in the UK or EU. Historically it was used as a post-harvest surface treatment on citrus fruits including oranges, lemons, grapefruits and mandarins. Residues may still be present on imported citrus from countries where the compound remains registered as a pesticide for post-harvest use. Where applied, it must be declared on packaging or retail labels as a surface treatment.
Yes, sodium orthophenyl phenol is a synthetic compound with no animal-derived ingredients. It is suitable for vegans and vegetarians on that basis.
Last reviewed: 20 June 2026
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