Following a request from the European Commission, the Panel on Food Additives and Nutrient Sources added to Food (ANS) was asked to re-evaluate the safety of boric acid (E 284) and sodium tetraborate (E 285) when used as food preservatives.
The Panel was not provided with a newly submitted dossier and based its evaluation on previous evaluations and reviews, additional literature that has become available since then and the data available following a public call for data. The Panel noted that not all original studies on which previous evaluations or reviews were based were available for re-evaluation by the Panel.
Boric acid and sodium tetraborate (borax) are authorised as food additives in the EU. They are authorised for use as preservatives of sturgeon eggs (caviar) up to a maximum concentration of 4 g boric acid/kg food by Commission Regulation (EU) 1129/2011. Previous evaluations relevant for assessing the safety for use in food have been performed by the Scientific Committee for Food (SCF) in 1979, endorsed in 1988 and published in 1992 (SCF, 1992)), the Joint FAO/WHO Expert Committee on Food Additives (JECFA, 1962), EFSA (2004, 2005a, b, 2012) and TemaNord (2002). In addition, boron for use in food and drinking water has been evaluated by the SCF (1979, 1988, 1992, 1998), the Expert Group on Vitamins and Minerals (EVM, 2003) and the World Health Organization (WHO, 2011). The purity criteria for boric acid and sodium tetraborate for use as food additives have been specified in Commission Regulation (EU) 231/2012. Boric acid and sodium tetraborate are also included in Regulation (EU) No 609/2013 regarding substances that may be added for specific nutritional purposes in foods for particular nutritional purposes (PARNUTS).
The Panel noted that the specifications for sodium tetraborate do not contain an assay percentage value.
In 1990, the SCF evaluated boric acid and concluded that boric acid and its salts were toxicologically acceptable for use only as a preservative in genuine caviar. The evaluation noted that a long-term study in rats had demonstrated some accumulation of boric acid in some organs. The evaluation also reported that the compound is nephrotoxic (SCF, 1992).
Studies in animals have shown that boron is readily absorbed following oral exposure in rats (Ku et al., 1991; Usuda et al., 1998), rabbits (Draize and Kelley, 1959), sheep (Brown et al., 1989) and cattle (Owen, 1944; Weeth et al., 1981; EPA, 2004). Absorption of borates is approximately 95 % in rats following ingestion (IPCS, 1998; Vanderpool et al., 1994, as reported in EPA, 2004).
Boron appears rapidly in the blood and body tissues (liver, muscle, colon, testis, epididymides, seminal vesicles, prostate, adrenals) of several mammalian species following ingestion (IPCS, 1998). Most of the boron in blood is associated with the plasma fraction (Moseman, 1994). Boron is distributed throughout the tissues and organs of animals and humans, resulting in concentrations between 0.05 and 0.6 mg/kg fresh weight (Nielsen, 1986, 1989, as reported in EFSA, 2004), with lower levels found in fatty tissues (BfR, 2005). Small quantities of boric acid have also been detected in faeces, saliva, milk and perspiration (Kingma, 1958). The highest levels are found in bone, which possibly represents a second kinetic compartment, as elimination kinetics for bone differ from those of soft tissue and body fluids (EVM, 2003).
The excretion of boron compounds is similar in humans and animals and is predominantly (> 90 %) via urine, regardless of the route of administration (IPCS, 1998). Excretion of boron is relatively rapid and it has a half-life of elimination of 24 hours or less (Nielsen, 1986, 1989; Litovitz et al., 1988, as reported in EFSA, 2004; IPCS, 1998).
In a 90-day study with Sprague–Dawley rats, a pronounced reduction in testicular weights in males of the 87.5 mg boron/kg body weight (bw)/day group was observed (Weir and Fisher, 1972). The effects observed were similar in rats given either boric acid or sodium tetraborate via the diet. The Panel considered 26.3 mg boron/kg bw/day (equivalent to 152 mg boric acid/kg bw/day) as the No Observed Adverse Effect Level (NOAEL) in this study. Female B6C3F1 mice exposed to boric acid in the diet for 90 days appeared to be less sensitive than males to the lethal effects of boric acid: 8/10 males and 6/10 females in the high-dose group died, and 1/10 males in the lower dose group. Histopathological changes included a dose-related increased incidence of extramedullary haematopoiesis in the spleen in males and females, and hyperkeratosis and acanthosis of the stomach in eight males and three females at the highest dose (IPCS, 1998; ECETOC, 1995).
Boric acid or sodium tetraborate fed to beagle dogs for 90 days at 0, 0.44, 4.38 or 43.75 mg boron/kg bw/day demonstrated a significant decrease in testes weight in the mid- and high-dose groups. Four out of 5 high-dose dogs showed complete testes atrophy and the remaining high-dose dog had partial testes atrophy (Weir and Fisher, 1972). Paynter (1963, reported in USDA, 2006) reported similar testes lesions in dogs exposed to 268 mg sodium tetraborate/kg bw/day for 90 days.
Reversibility of testicular lesions was evaluated in F344 rats dosed with boric acid for 9 weeks and assessed for recovery up to 32 weeks post treatment. Inhibited spermiation was exhibited at 5.6 μg boron/mg tissue, whereas inhibited spermiation progressed to atrophy at 11.9 μg boron/mg testes, with no boron accumulation in the testes to levels greater than those found in the blood during the 9-week period. After treatment, serum and testis boron levels in all dose groups fell to background levels. Inhibited spermiation was reversed by 16 weeks post treatment, but focal atrophy was detected that did not show recovery up to 32 weeks post-treatment (Ku et al. 1993).
Genotoxicity studies in bacteria and in mammalian cells in vitro, addressing several genetic end-points (gene mutation, chromosomal aberrations, micronuclei, sister chromatid exchanges), as well as an in vivo micronucleus test in mice, published after the previous EFSA evaluations (EFSA, 2004, 2005a, b), do not provide any indications of genotoxic potential of boric acid and sodium tetraborate. Thus, based on the available evidence, the Panel concluded that boric acid and sodium tetraborate do not raise concern for genotoxicity.
Microscopic changes in the tissues of mice, rats and dogs exposed to boric acid or sodium tetraborate for 2 years involved primarily the kidneys and testes. Glomerular and tubular damage has been noted in the kidneys. Glomerular damage consisted of changes in the permeability of the capillaries, and tubular damage consisted of cellular vacuolisation and shedding of cells into the tubular lumen. In male reproductive organs, the effects of boric acid and sodium tetraborate included inhibition of spermiation in stage IX and X tubules, followed by germ cell loss, changes in epididymal sperm morphology and caput sperm reserves, decreased serum testosterone levels and testicular atrophy. In males, the effects on reproductive organs have been reported in oral exposure studies at doses as low as 29 mg boron/kg bw/day in dogs exposed for 2 years to dietary boric acid or borax (Weir and Fisher, 1972).
Results from animal experiments demonstrate that boric acid adversely affects fertility and development. Feeding studies in different animal species (rats, mice and dogs) have consistently demonstrated that the male reproductive system is the principal target in experimental animals, although effects on the female reproductive system have also been reported. Testicular damage ranging from mildly inhibited spermiation to complete atrophy has been demonstrated following oral administration of boric acid. In a 2-year study in rats, effects on male fertility were observed at lower dose levels compared to dose levels where signs of general toxicity appeared. For this 2-year study, 17.5 mg boron/kg bw/day was considered a NOAEL for male and female fertility (EFSA, 2004).
In 1998, the IPCS concluded that the mechanism by which boric acid and borates induce testicular atrophy is unclear. However, as boron does not accumulate in the testes, it may be possible that decreased testosterone production is due to CNS-mediated mechanisms. It is further reported that it is unlikely that hormone changes cause testicular atrophy as spermatogenesis has been shown to be maintained even in the presence of significantly decreased intra-testicular testosterone levels (ECETOC, 1995).
Developmental toxicity of boric acid was investigated in the rat, the rabbit and the mouse. In the rat, developmental toxicity (decreased fetal weight at 13.7 mg boron/kg bw/day) occurred in the absence of marked maternal toxicity. For developmental toxicity in rats, a NOAEL of 9.6 mg boron/kg bw/day (equivalent to 55 mg boric acid/kg bw/day) has been derived by Price et al. (1996a).
The adverse effects of boric acid on development and fertility observed across species were very similar, both in nature and effective doses. Further, the adverse effects obtained with boric acid are comparable to those obtained from other borates, thus indicating that boron is the toxicologically active species. The available data on toxicokinetics do not indicate differences between laboratory animals and humans. It is not known whether there are significant differences in the toxicodynamics between humans and laboratory animal models and, in the absence of such knowledge, it must be assumed that the effects seen in animals could occur in humans. On the basis of toxicokinetic and toxicodynamic considerations, it is assumed that the animal data are relevant to humans. This is further underlined by the fact that (1) there are indications that boric acid is able to cross the human placenta and that (2) up to now, epidemiological studies in humans are insufficient to demonstrate the absence of an adverse effect of inorganic borates on fertility (ECHA, 2010).
In order to set a group acceptable daily intake (ADI), the Panel considered that this should be expressed as boron equivalents. The Panel identified the study of Price et al. (1996a) as the pivotal study and agreed with the NOAEL defined by the authors of this study. The NOAEL is 55 mg boric acid/kg bw/day (equivalent to 9.6 mg boron/kg bw/day). As the pivotal effect that serves as the basis for the ADI is developmental toxicity, pregnant women are the subgroup of interest in this regard (WHO, 2009). The glomerula filtration rate (GFR) being the critical physiological process for boron toxicokinetics, the default toxicokinetic UF for human variability was adjusted by the EFSA Panel on Nutrition, Dietetic Products and Allergies (NDA) and the EFSA Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids (CEF) on the clearance in pregnant women. This approach leads to a toxicokinetic UF factor of 1.8 instead of 3.2, whereas the intraspecies toxicodynamic UF of 3.2 remained unchanged. This ultimately resulted in an uncertainity factor (UF) of 60 instead of 100.
When applying an UF of 60 (EFSA, 2004, 2005a, b, 2012), the group ADI for boric acid and sodium tetraborate, expressed as boron equivalents, is 0.16 mg boron/kg bw/day.
The results of several human case studies described in the literature and collected from poisoning centres demonstrated that the average dose of boric acid required to produce clinical symptoms is presumed to be within the range 100 mg to 55.5 g, which is far above the ADI established by the Panel.
Exposure to boric acid and sodium tetraborate from its use as a food additive in caviar is based on the assumption that the consumption data from the EFSA Comprehensive Food Consumption Database reported for the food category “fish roe” cover the consumption of caviar. The Panel noted that these estimates are conservative, since it is unlikely that all foods falling into this food category actually are caviar. Although the EFSA Comprehensive Food Consumption Database provides information on food consumption from 32 different dietary surveys carried out in 22 different European countries, only those countries with statistically reliable data on the consumption of the food category “fish roe” were included in exposure estimate calculations at the mean and at the 95th percentile. Using the maximum permitted level (MPL) of 4 g/kg food of boric acid or sodium tetraborate expressed as boric acid, these exposure estimates result in mean exposures to boric acid and sodium tetraborate in the range 0.00–0.21 mg boric acid/kg bw/day for children, 0.00–0.06 mg boric acid/kg bw/day for adolescents, 0.00–0.08 mg boric acid/kg bw/day for adults and 0.00–0.05 mg boric acid/kg bw/day for the elderly. Exposure estimates at the 95th percentile could only be calculated for Denmark and Sweden (Denmark only for the elderly) and are in the range 2.81–3.17 mg boric acid/kg bw/day for children, 1.47–2.11 mg boric acid/kg bw/day for adolescents, 0.72–0.74 mg boric acid/kg bw/day for adults and 0.88 mg boric acid/kg bw/day for the elderly.
The estimates refer to the exposure to boric acid and sodium tetraborate expressed as boric acid. Based on its boron content of 17.5 %, the highest average exposure to boron across European Member States is 0.04 mg/kg bw/day for children, 0.01 mg/kg bw/day for adolescents, 0.01 mg/kg bw/day for adults and 0.01 mg/kg bw/day for the elderly and the very elderly. The exposure to boron from the use of boric acid and sodium tetraborate as food additives at the highest 95th percentile, for consumers only, would be 0.56, 0.37, 0.13 and 0.15 mg/kg bw/day for children, adolescents, adults and the elderly, respectively.
The Panel also noted that this exposure scenario is only valid for its present single authorisation for caviar, whereas a detailed exposure assessment would be needed if the authorisation would be extended to other products (e.g. fish roe other than sturgeon eggs).
The Panel identified a NOAEL of 55 mg boric acid/kg bw/day (equivalent to 9.6 mg boron/kg bw/day). When applying an UF of 60, the group ADI for boric acid and sodium tetraborate, expressed as boron equivalents, is 0.16 mg boron/kg bw/day.
For children and adolescents, at the highest 95th percentile, exposure estimates indicate exceedance of this ADI. However, exposure to boron from its use as a food additive in the form of boric acid and sodium tetraborate in caviar is unlikely to occur on a regular basis. Therefore, the Panel noted that even at high consumption and in consumers only, it is unlikely that a regular exceedance of the ADI occurs.
However, the Panel also noted that exposure to boron from its natural occurrence in the diet and from other sources (food supplements, food contact materials, feed for food-producing animals, cosmetics, oral hygiene products, etc.) may already lead to exposures exceeding the ADI.