Following a request from the European Commission, the Panel on Food Additives and Nutrient Sources added to Food (ANS) was asked to deliver a scientific opinion on the re-evaluation of butylated hydroxytoluene (BHT) (E 321) as a food additive.
BHT (E 321) is a synthetic antioxidant authorised as a food additive in the EU that was previously evaluated by the EU Scientific Committee for Food (SCF) in 1987 and the Joint FAO/WHO Expert Committee on Food Additives (JECFA) several times, the latest in 1996.
The SCF established an ADI of 0-0.05 mg/kg bw/day based on thyroid, reproduction and haematological effects in the rat. At its last evaluation JECFA allocated an ADI of 0 0.3 mg/kg bw/day for BHT, based on effects in the reproduction segments and hepatic enzyme induction, seen in two separate 2-generation studies in rats. These studies were probably not available at the time of the SCF evaluation.
Specifications have been defined in the EU legislation Directive 2008/48/EC and by JECFA (JECFA, 2006). The purity is specified to be not less than 99%.
Absorption, distribution, metabolism and excretion of BHT have been studied in mice, rats, rabbits, chickens, monkeys and humans. Overall, these studies show that BHT is rapidly absorbed from the gastrointestinal tract. Upon absorption BHT is distributed to the liver and body fat, while excretion is mainly via urine and faeces. The metabolism of BHT is complex and there may be important species differences. It is not known, for example, whether humans are capable of forming the quinone methides, metabolites that were found in rats and mice. In addition, biliary excretion seems not to be as significant in man as it is in rats, rabbits and dogs.
The acute toxicity of BHT is low with oral LD50 values of 1700-1970 mg BHT/kg bw in rats, 2100-3200 mg BHT/kg bw in rabbits, 10 700 mg BHT/kg bw in guinea pigs, 940-2100 mg BHT/kg bw in cats, and 2000 mg BHT/kg bw in mice.
In general, the genotoxicity studies on BHT indicate a lack of potential for BHT to induce point mutations, chromosomal aberrations, or to interact with or damage DNA. The Panel recognised that positive genotoxicity results obtained with BHT in vitro may be due to pro-oxidative chemistry giving rise to formation of quinones and reactive oxygen species and that such a mechanism of genotoxicity is generally considered to be subject to a threshold.
The Panel noted that the SCF established an ADI of 0-0.05 mg/kg bw/day based on thyroid, reproduction and haematological effects in the rat. However, a NOAEL of 25 mg BHT/kg bw/day was derived from a study in rats where electron microscopy of the thyroid glands of rats exposed to 500 mg BHT/kg bw/day for 28 days showed an increase in the number of follicle cells.
The Panel noted the discrepancy between the ADIs allocated by the SCF and JECFA. In 1987 the SCF reviewed all available studies on BHT, among them metabolic data from several species including man, mutagenicity studies, carcinogenicity studies in rats and mice, special studies on the thyroid, blood, and post-natal development and behaviour. Taking all these effects into account, the SCF considered that the likely NOAEL for BHT is approximately 100 mg/kg in the diet, equivalent to an intake of about 5 mg/kg bw/day. In the view of the nature of the effects, a safety margin of 100-fold was considered appropriate to establish an ADI of 0-0.05 mg/kg bw based on thyroid, reproduction and haematological effects in the rat. The studies used by JECFA to define the ADI were published after the last SCF evaluation and these studies have been included in the present evaluation.
After the last SCF evaluation, two new 2-generation studies have been reported. One study has been published by Olsen et al. in 1986. The other study is an unpublished report by Price in 1994 that was included in the JECFA evaluation published in 1996 and also submitted to EFSA after a public call for data.
The Panel considered that the effects of BHT on tumour formation reported in the Olsen et al. study in 1986 are subject to a threshold since the genotoxicity studies generally indicate a lack of potential for BHT to induce point mutations, chromosomal aberrations, or to interact with or damage DNA. The BMD analysis performed by the Panel on the incidence of hepatocellular carcinoma in male rats induced by BHT as reported by Olsen et al. in 1986 gave a BMDL10 of 247 mg/kg bw/day.
Both two new studies indicated a NOAEL of 25 mg/kg bw/day. In the Olsen et al. study this NOAEL of 25 mg/kg bw/day is based on effects on litter size, sex ratio and pup body weight gain during the lactation period in the reproduction segment of the study. The Panel agreed with the NOAEL of 25 mg/kg bw/day derived by JECFA from the study reported by Price in 1994.
Overall, the Panel concluded that the present database does give reason to revise the ADI of 0-0.05 mg/kg bw/day set by the SCF.
Based on the NOAEL of 25 mg/kg bw/day, derived from both new 2-generation studies, and an uncertainty factor of 100 the Panel established an ADI for BHT of 0.25 mg/kg bw.
The NOAEL of 25 mg/kg bw/day for the reproductive effects is below the BMDL10 value of 247 mg/kg bw/day derived by the Panel from the data of Olsen et al. for the incidence of hepatocellular carcinoma in male rats. The Panel concluded that this NOAEL of 25 mg/kg bw/day also covers the hepatocellular carcinomas observed in the long term studies with BHT.
Using a worst-case scenario of combined exposure to BHT from the food categories where use as a food additive is authorised, the Panel estimated potential exposure for adults to be on average 0.01-0.03 mg/kg bw/day and 0.03-0.17 mg/kg bw/day at the 95th percentile. For children, the Panel estimated potential exposure in the range of 0.01-0.09 mg/kg bw/day at the mean and in the range of 0.05-0.30 mg/kg bw/day at the 95th percentile, The Panel noted that at the mean exposure of adults to BHT is unlikely to exceed the newly derived ADI of 0.25 mg/kg bw/day and at the 95th percentile. For exposure of children to BHT from its use as food additive, the Panel noted that it is also unlikely that this ADI is exceeded at the mean, but is exceeded for some European countries (Finland, The Netherlands) at the 95th percentile.
The Panel noted that the JECFA specification for lead is ≤ 2 mg/kg whereas the EC specification is ≤5 mg/kg.