Comparative metabolism of 3,5-di-tert-butyl-4-hydroxytoluene (BHT) in mice and rats

Developmental toxicity and skin sensitization potential of synthetic phenolic antioxidants and butylated hydroxytoluene transformation products: Insights from human embryonic stem cell models

Synthetic phenolic antioxidants (SPAs) are commonly used in food, cosmetics, and other products for their antioxidant properties and stability. However, increasing evidence links excessive SPA use to adverse effects, including developmental issues in animals. Given the widespread use of SPAs in cosmetics, there is a growing need to assess their potential health risks, particularly whether safe to be used during pregnancy. This study investigates the early developmental toxicity of SPAs using a human embryonic stem cell (hESC) monolayer differentiation model. Results show that SPAs and butylated hydroxytoluene transformation products (BHT-TPs) up-regulated neural ectoderm and neural crest genes while down-regulated surface ectoderm and primitive streak genes during differentiation. Furthermore, in a skin-specific differentiation model, SPAs and BHT-TPs disrupted keratinocyte differentiation, inhibiting the differentiation of keratinocyte progenitors into more mature keratinocytes. They also led to the up-regulation of genes associated with psoriasis, pro-inflammatory cytokines, and chemokines, suggesting the potential of SPAs to act as skin sensitizers. These findings suggest that SPAs may affect early embryonic development at an early germ layer specification stage, as well as during skin development, potentially increasing skin sensitivity. Thus, excessive SPA use in cosmetics could pose risks to fetal development and adult skin health.

Developmental and toxicological effects of butylated hydroxytoluene metabolites on zebrafish larvae

Butylated hydroxytoluene (BHT) is among the most widely used synthetic phenolic antioxidants. However, BHT and its metabolites have been detected in aquatic ecosystems, posing potential risks to aquatic organisms. The present study aimed to investigate the effects of BHT metabolites on embryonic development in zebrafish. To this end, embryos were exposed to BHT metabolites, including 3,5-di-tert-butyl-4 hydroxybenzaldehyde (BHT-CHO), 2,6-di-tert-butyl-4-(hydroxymethyl) phenol (BHT-OH), 3,5-di-tert-butyl-4 hydroxybenzoic acid (BHT-COOH), 2,6-di-tert-butyl-P-benzoquinone (BHT-Q), and 2,6-di-tert-butyl-4-hydroxy-4-methylcyclohexa-2,5-dien-1-one (BHT-quinol), from 1-120 h post-fertilization (hpf). BHT-CHO, -OH, -COOH, -Q, and -quinol were toxic to zebrafish larvae with 96 h LC50 values of > 0.10, 15.85, 4.51, > 1.30, and 3.46 mg/L, respectively. Moreover, the acute toxicity of BHT metabolites to zebrafish larvae was indicated by morphological abnormalities, changes in heart rate, and alterations in locomotory behavior. The results indicated that exposure to BHT-COOH and BHT-OH caused intestinal developmental abnormalities, blood coagulation, tail deformities, and pericardial edema. Exposure to BHT-Q and BHT-quinol resulted in abnormal swim bladder development. Moreover, alterations in heart rate and locomotory behavior were observed in zebrafish larvae exposed to BHT-COOH, BHT-OH, and BHT-quinol. These findings demonstrate that exposure to BHT metabolites significantly affects the early growth and developmental stages of zebrafish larvae.

Occupational exposure of nail technicians to industrial chemicals: A pilot study

Previous studies have observed the use of complex industrial chemicals in beauty products. However, occupational exposure of beauty practitioners to various chemicals has not been sufficiently assessed. Our study recruited 37 female nail technicians from 28 nail salons in South China and investigated the abundances and profiles of more than 60 industrial chemicals or their metabolites in indoor dust, hand wipes, and urine of nail technicians. Thirty female college students were also recruited for comparison. The results revealed broad exposure of nail technicians to 42 target chemicals or their metabolites, with mono-phthalate esters (mono-PAEs) exhibiting the highest concentrations (median 284 ng/mL), followed by parabens (median 57.9 ng/mL) and antioxidants (median 19.6 ng/mL) in urine. The urinary concentrations of mono-PAEs, parabens, triclosan (TCS) and triclocarban of nail technicians were significantly higher than those of college students. Pre-shift and post-shift urine did not exhibit significant differences for most chemicals, likely reflecting continuous and long-term exposure. Hand wipe levels of TCS and 2,6-di-tert-butyl-4-methylpheno were significantly associated with urinary levels of these chemicals or their metabolites, while such a pattern was not observed between dust and urinary levels. This highlights the influence of dermal contact or hand-to-mouth transfer on the intake of these chemicals. Collectively, our pilot study demonstrates the occupational exposure of nail technicians to industrial chemicals in beauty products and calls for vigilant self-protection measures to mitigate exposure risks in beauty practitioners.

Seasonal variations and the prevalence of phenolic profiles in ambient fine particulate matter and their impact on oxidative potential

Exposure to fine particulate matter (PM2.5) poses numerous health risks, with oxidative potential (OP) serving as a critical marker of its toxicity. Synthetic phenolic antioxidants (SPAs) and bisphenols (BPs) influence reactive oxygen species (ROS) levels in PM2.5, and exposure to these compounds induces oxidative stress in organisms, thereby potentially affecting the OP of PM2.5. We detected 26 phenols (including 12 SPAs, 5 transformation products (TPs), and 9 BPs) in PM2.5 sample collected from October 2018 to September 2021 in Wuhan, China. Among them, 19 substances were detected at a detection frequency greater than 50 % in PM2.5 sample. AO 2246 and BHT were the main components of SPAs, and BHT-Q and BPA had the highest concentrations in TPs and BPs, respectively. PM2.5 mass concentrations and phenolic levels were higher in winter and autumn. Substances within groups were strongly correlated, suggesting the same or similar source of exposure. This finding aid in more precise pollution source identification and is crucial for comprehensively evaluating their combined health effects. Furthermore, we determined the OP of PM2.5 and found that BPs were related to increased OP and ROS. This suggests that the toxicity of PM2.5 is influenced not only by its concentration but also by its chemical composition, with BPs potentially enhancing its toxic effects. These factors should be fully considered when assessing the health impacts of PM2.5.

Poisoning by butylated hydroxytoluene quinone methide acting as a superwarfarin: first reported case in humans

Superwarfarins are anticoagulant rodenticides nearly 100-fold potent than the parent compound. Since their development, accidental and intentional cases of superwarfarin poisoning have been reported. We report the first human case of poisoning by butylated hydroxytoluene (BHT) quinone methide acting as a superwarfarin otherwise reported to be a well tolerated food additive and preservative and used as an antioxidant, stabilizer, anti-skinning agent in various industries. We aim to highlight the possible underlying cause of this previously unreported and potentially lethal BHT-related complication in the human.

44-Year Retrospective Analysis of Ultraviolet Absorbents and Industrial Antioxidants in Seabird Eggs from the Canadian Arctic (1975 to 2019)

Ultraviolet (UV) absorbents and industrial antioxidants are contaminants of emerging concern (CECs), but little is known about their distribution in Arctic wildlife, as well as how these contaminants vary over time, across regions, and between species. We used archived egg samples to examine the temporal patterns of 26 UV absorbents and industrial antioxidants in three seabird species (black-legged kittiwakes Rissa tridactyla, thick-billed murres Uria lomvia, northern fulmars Fulmarus glacialis) sampled in Arctic Canada between 1975 and 2019. Various synthetic phenolic antioxidants, aromatic secondary amines, benzotriazole UV stabilizers, and organic UV filters were detected in the seabird eggs. Overall, kittiwakes had higher levels of several UV absorbents and industrial antioxidants. Most target contaminants reached their peak concentrations at different points during the 44-year study period or did not vary significantly over time. None of these contaminant concentrations have increased in recent years. The antioxidant 2-6-di-tert-butyl-4-methylphenol (BHT) was the most frequently detected contaminant in seabird eggs, and its level significantly declined over the course of the study period in kittiwake eggs but did not change in the eggs of murres and fulmars. Future research should examine the effects of these CECs on the health of avian species, the sources, and exposure pathways of these contaminants.

Prenatal Exposure to Emerging Plasticizers and Synthetic Antioxidants and Their Potency to Cross Human Placenta

Gestational exposure to environmental chemicals and subsequent permeation through the placental barrier represents potential health risks to both pregnant women and their fetuses. In the present study, we explored prenatal exposure to a suite of 46 emerging plasticizers and synthetic antioxidants (including five transformation products of 2,6-di-tert-butyl-4-hydroxytoluene, BHT) and their potency to cross human placenta based on a total of 109 maternal and cord serum pairs. Most of these chemicals have rarely or never been investigated for prenatal exposure and associated health risks. Eleven of them exhibited detection frequency greater than 50% in maternal blood, including dibutyl fumarate (DBF), 2,6-di-tert-butylphenol (2,4-DtBP), 1,3-diphenylguanidine (DPG), methyl-2-(benzoyl)benzoate (MBB), triethyl citrate (TEC), BHT, and its five metabolites, with a median concentration from 0.05 to 3.1 ng/mL. The transplacental transfer efficiency (TTE) was determined for selected chemicals with valid measurements in more than 10 maternal/cord blood pairs, and the mean TTEs exhibited a large variation (i.e., 0.29-2.14) between chemicals. The determined TTEs for some of the target chemicals were comparable to the predicted values by our previously proposed models developed from molecular descriptors, indicating that their transplacental transfer potency could be largely affected by physicochemical properties and molecular structures. However, additional biological and physiological factors may influence the potency of environmental chemicals to cross human placenta. Overall, our study findings raise concern on human exposure to an increasing list of plastic additives during critical life stages (e.g., pregnancy) and potential health risks.

Synthetic phenolic antioxidants: Metabolism, hazards and mechanism of action

Synthetic phenolic antioxidants can interact with peroxides produced by food. This paper reviews correlation between BHA, BHT and TBHQ metabolism and harms they cause and provides a theoretical basis for rational use of BHA, BHT and TBHQ in food, and also put some attention on the transformation and metabolic products of PG. We introduce BHA, BHT, TBHQ, PG and their possible metabolic pathways, and discuss possible harms and their specific mechanisms responsible. Excessive addition or incorrect use of synthetic phenolic antioxidants results in carcinogenicity, cytotoxicity, oxidative stress induction and endocrine disrupting effects, which warrant attention. BHA carcinogenicity is related to production of metabolites TBHQ and TQ, and cytotoxic effect of BHA is the main cause of apoptosis induction. BHT carcinogenicity depends on DNA damage degree, and tumour promotion is mainly related to production of quinone methylation metabolites. TBHQ carcinogenicity is related to induction of metabolite TQ and enzyme CYP1A1.

Tissue distribution, excretion, and metabolism of 2,6-di-tert-butyl-hydroxytoluene in mice

As one typical synthetic phenolic antioxidant, 2,6-di-tert-butyl-hydroxytoluene (BHT) has been widely adopted in food and other human products, and considered as an emerging contaminant due to its toxic effects. Understanding bioaccumulation and metabolism of BHT is crucial to evaluate its environmental fate and toxicity. In this study, the tissue distribution, excretion, and metabolism of BHT in mice were investigated. It was shown that BHT was prone to be accumulated in metabolism-related organs (i.e., liver and kidney) with AUC_{0-120 h} (area under the concentration-time curve from 0 to 120 h) values of 206 h·μg/g in liver and 162 h·μg/g in kidney. For metabolites, 2,6-di-tert-butyl-4-hydroxy-4-methyl-2,5-cyclohexadione (BHT-quinol) was preferentially accumulated in liver, while 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) was the major metabolite in excreta. The major excretion of BHT and metabolites was through feces with a value of 25.1 ± 0.16% of the initial dose compared with urine of 1.27 ± 0.05%. The possible metabolic pathways of BHT were elucidated as the oxidation of the para-methyl, tert-butyl groups, and aromatic ring based on the known and identified unknown metabolites by HPLC-Q-TOF-MS/MS. The preferred accumulation of BHT and metabolites in liver implies their potential hepatotoxicity. Results here also suggested that considering the distribution and excretion of metabolites can better assess BHT's fate and risk in mammals.

Synthetic Phenolic Antioxidants: A Review of Environmental Occurrence, Fate, Human Exposure, and Toxicity

Synthetic phenolic antioxidants (SPAs) are widely used in various industrial and commercial products to retard oxidative reactions and lengthen product shelf life. In recent years, numerous studies have been conducted on the environmental occurrence, human exposure, and toxicity of SPAs. Here, we summarize the current understanding of these issues and provide recommendations for future research directions. SPAs have been detected in various environmental matrices including indoor dust, outdoor air particulates, sea sediment, and river water. Recent studies have also observed the occurrence of SPAs, such as 2,6-di-tert-butyl-4-methylphenol (BHT) and 2,4-di-tert-butyl-phenol (DBP), in humans (fat tissues, serum, urine, breast milk, and fingernails). In addition to these parent compounds, some transformation products have also been detected both in the environment and in humans. Human exposure pathways include food intake, dust ingestion, and use of personal care products. For breastfeeding infants, breast milk may be an important exposure pathway. Toxicity studies suggest some SPAs may cause hepatic toxicity, have endocrine disrupting effects, or even be carcinogenic. The toxicity effects of some transformation products are likely worse than those of the parent compound. For example, 2,6-di-tert-butyl-p-benzoquinone (BHT-Q) can cause DNA damage at low concentrations. Future studies should investigate the contamination and environmental behaviors of novel high molecular weight SPAs, toxicity effects of coexposure to several SPAs, and toxicity effects on infants. Future studies should also develop novel SPAs with low toxicity and low migration ability, decreasing the potential for environmental pollution.

Prevalence, Biotransformation, and Maternal Transfer of Synthetic Phenolic Antioxidants in Pregnant Women from South China

Synthetic phenolic antioxidants (SPAs) have been identified as an emerging group of contaminants in recent years. However, there are significant gaps in our knowledge of human prenatal exposure to these synthetic chemicals. In this study, a set of eight SPAs and four major transformation products (TPs) were systematically analyzed in matched samples of maternal plasma, cord plasma, and placenta from a population of pregnant women. Five of the eight target SPAs and all four target TPs were frequently detected in the maternal-placental-fetal unit, indicating prenatal exposure to SPAs and the transfer of SPAs across the placenta. In the three matrices, 2,6-di-tert-butyl-hydroxytoluene (BHT), 2,4-di-tert-butylphenol (DBP), and 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (AO 2246) were identified as the most abundant SPAs, while 2,6-di-tert-butyl-1,4-benzoquinone (BHT-Q) and 2,6-di-tert-butyl-4-hydroxy-4-methyl-2,5-cyclohexadienone (BHT-quinol) were identified as the predominant TPs of BHT. In the maternal plasma, concentrations of both BHT-Q and BHT-quinol were significantly correlated with BHT (p < 0.001), suggesting that the two TPs mainly originated from the biotransformation of BHT itself in pregnant women. The transplacental transfer efficiencies (TTEs) of the SPAs and TPs were structure-dependent and generally less than 1. Significantly higher TTEs for four target TPs than their parent BHT were identified. To our knowledge, this study provides the first evidence that SPAs and TPs transfer across the placenta in pregnant women.

Distribution, transformation and toxicity evaluation of 2,6-Di-tert-butyl-hydroxytotulene in aquatic environment

2,6-Di-tert-butyl-hydroxytotulene (BHT), as a significant synthetic phenolic antioxidant (SPA), has received increasing attention in the environmental field. In the present study, the BHT is confirmed to be mainly distributed in the liquid phase in the environment base on the Aspen PLUS simulation results. The mechanism and kinetics of BHT transformation initiated by OH radicals were conducted in aquatic environment using density functional theory (DFT) method. Briefly, seven initiation reactions and three detailed transformation pathways of BHT were reported. The H atoms in the t-butyl and methyl group were found more favorable to be abstracted. The C1 site of the BHT was susceptible to addition by OH radicals. Rate constants of different initial reactions were calculated and they were inhibited by temperature rise. Meanwhile, the acute and chronic toxicities of BHT and its metabolites were evaluated at three different trophic levels using the ECOSAR program. During the degradation process, the toxicities of these metabolites gradually decreased, but the toxicities of the final product 2,6-di-tert-butyl-2,5-cyclohexadien-1,4-dione (BHT-Q) were significantly increased. These results could help to reveal the transformation mechanism and risk assessment of BHT in aquatic environment, and further design the experimental and industrial applications of SPAs.

Synthetic phenolic antioxidants and transformation products in dust from different indoor environments in Toronto, Canada

Synthetic phenolic antioxidants (SPAs) are a class of anthropogenic antioxidants that are widely used in a large variety of commercial products. Although several SPAs have been listed as targets for risk assessment by Environment and Climate Change Canada, little data are available on the occurrence of SPAs in the Canadian environment. In this study, eighty-three indoor dust samples were collected from offices and homes in Toronto. Eight SPAs were detected at concentrations ranging from 67.2 to 1.55e4 ng/g, with a geometric mean (GM) concentration of 1.49e3 ng/g, among which 2,6-di-tert-butyl-4-methylphenol (BHT) was the primary congener and had a GM concentration of 658 ng/g. Four BHT transformation products (TPs) were also detected in the indoor dust samples, with concentrations ranging from 40.4 to 1.27e4 ng/g and a GM concentration of 883 ng/g. No significant concentration difference was observed between the office and home dust samples for either the summed target SPA or TP concentrations (p > 0.05). The calculated estimated daily intakes of these chemical contaminants (0.004-10.0 ng/kg BW/day) suggest that they pose no immediate health risk to the Canadian population. To the best of our knowledge, this is the first report of the occurrence of these chemical contaminants and their transformation products in Canadian indoor environments, and furthermore the first detection of 4-tert-butyl-phenol in an environmental sample.

Synthetic phenolic antioxidants and their major metabolites in human fingernail

Synthetic phenolic antioxidants (SPAs) have been widely used in foods, polymers, and cosmetics, but very limited information is available about their occurrence in human tissues. In this study, five SPAs, namely 2,6-di-tert-butyl-4-methylphenol (BHT), 2-tert-butyl-4-hydroxyanisole (BHA), propyl-, octyl-, and dodecyl-gallate (PG, OG, and DG), and four major metabolites of BHT, including 3,5-di-tert-butyl-4 -hydroxybenzaldehyde (BHT-CHO), 2,6-di-tert-butyl-4-(hydroxymethyl) phenol (BHT-OH), 3,5-di-tertbutyl-4-hydroxybenzoic acid (BHT-COOH), and 2,6-di-tert-butyl-1,4-benzoquinone (BHT-Q), were determined in human fingernail samples collected from Nanjing, China. Total concentrations of the nine target analytes (∑₉SPAs) were 523-14,000 ng/g. BHT was the predominant SPA compound and detected in all samples at a range of 309-11,400 ng/g. The ∑₉SPAs was negatively correlated with age of fingernail donors (p < 0.05). In addition, indoor dust samples from the living places of the fingernail providers were collected with aim to better understand the SPA exposure pathways. A positive correlation (p < 0.05) was found only for DG concentrations between paired fingernail and dust samples, while not for other SPAs, suggesting that SPAs accumulated in fingernails may not be mainly from indoor dust. SPAs were measured for the first time in human fingernail, and the elevated concentrations in fingernail suggest that the health risk of SPAs should be paid more attention due to their bioaccumulation potential in human body. Further studies are warranted about exposure pathway, distribution and metabolism of SPAs in human body.

Synthetic Phenolic Antioxidants and Their Metabolites in Sediments from the Coastal Area of Northern China: Spatial and Vertical Distributions

Synthetic phenolic antioxidants (SPAs) are widely used in foodstuffs, cosmetics, plastics, and rubber products. Little is known about their spatiotemporal distribution in the marine environment. In this study, a total of 144 surface sediments and three sediment cores were collected from the coastal areas of northern China to determine the spatial and vertical distributions of SPAs. For surface sediments, the total concentrations of five SPAs and their four metabolites (∑₉SPAs) ranged from 133 to 4800 (mean: 588) ng/g dry weight (dw). The ∑₉SPAs in surface sediments showed a decrease trend with the distance from the coast to the open sea. For sediment core samples, the ∑₉SPAs in the inner-shelf mud (core-1 and core-3) showed a slight increase trend from the bottom to upper layers, whereas that in the central-shelf mud (core-2) did not. The principal component analysis suggests that the composition profiles of SPAs in both surface sediment and sediment core samples were similar, while the sediments close to the coast were obviously affected by the human activities. This is the first study to report the spatial and vertical distributions of SPAs and their metabolites in sediments from the coastal marine environment.

Synthetic Phenolic Antioxidants and Their Metabolites in Mollusks from the Chinese Bohai Sea: Occurrence, Temporal Trend, and Human Exposure

Synthetic phenolic antioxidants (SPAs) are a group of chemicals widely used in various daily necessities and industrial supplies. Little is known about the occurrence and bioaccumulation potential of SPAs in marine biota. In this study, five commonly used SPAs and their four metabolites were detected in mollusk samples ( n = 274) collected from the Chinese Bohai Sea during 2006-2016 and the spatiotemporal distribution and bioaccumulation of SPAs in mollusks were examined. The concentrations of 2,6-di- tert-butyl-4-hydroxytoluene (BHT) ranged from 383 to 501000 ng/g (geometric mean: 3450 ng/g), accounting for 79.4% of the total concentrations of SPAs and their metabolites (∑₉SPAs). The mollusk species, Rapana venosa (RAP), contained higher levels of BHT than other species, suggesting that Rap could be used as a potential bioindicator for monitoring of the BHT pollution in the investigated region. The ∑₉SPAs concentrations in mollusks gradually increased with years and a significant positive correlation ( r = 0.900, p < 0.05) was found between ∑₉SPAs concentration and trophic level of the mollusks. The trophic magnification factor value of ∑₉SPAs was calculated as 16.1, suggesting a high biomagnification potential of SPAs in mollusks in the Chinese Bohai Sea. The estimated daily intake of ∑₉SPAs through dietary ingestion of mollusks was up to 602 and 789 ng/kg bw/day for adults and children and teenagers, respectively. The principal component analysis result suggests that there exists a common source for three gallates (OG, DG, and PG), and BHT metabolites in mollusks were mainly derived from degradation of BHT. This is the first study to report the occurrence and bioaccumulation potentials of SPAs and their metabolites in invertebrate species from coastal marine environments.

Determination of 2,6-di-tert-butyl-hydroxytoluene and its transformation products in indoor dust and sediment by gas chromatography-mass spectrometry coupled with precolumn derivatization

We developed an analytical method to simultaneously determine 2,6-di-tert-butyl-hydroxytoluene (BHT) and its four transformation products in indoor dust and sediment samples. BHT, 2,6-di-tert-butylcyclohexa-2,5-diene-1,4-dione (BHT-Q), and 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO) were measured by gas chromatography-mass spectrometry (GC-MS) after ultrasonic extraction with hexane/dichloromethane (1:3), while 2,6-di-tert-butyl-4-(hydroxymethyl) phenol (BHT-OH) and 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) were derivatized using N, O-bis (trimethylsilyl) trifluoroacetamide before GC-MS analysis. The limits of detection (LODs) and quantification (LOQs) of the developed method were 0.02-0.34 and 0.08-1.14ngg^-1. The recoveries for BHT and its transformation products were 71.1-118% with relative standard deviations <10.6% at different spiking levels. The method was applied to indoor dust and sediment samples, showing that BHT was found in all samples with concentrations being 0.22-47.37μgg^-1 in dust and 0.09-6.93μgg^-1 in sediment. BHT-Q was the dominant transformation product, followed by BHT-CHO, BHT-OH, and BHT-COOH. Different metabolite profiles for BHT indicated various transformation pathways, making it necessary to study their transformation mechanism and environmental behaviors in the future studies.

Synthetic Phenolic Antioxidants and Their Metabolites in Indoor Dust from Homes and Microenvironments

Synthetic phenolic antioxidants (SPAs), including 2,6-di-tert-butyl-4-hydroxytoluene (BHT), are extensively used in food, cosmetic and plastic industries. Nevertheless, limited information is available on human exposures, other than the dietary sources, to SPAs. In this study, occurrence of 9 SPAs and their metabolites/degradation products was determined in 339 indoor dust collected from 12 countries. BHT was found in 99.5% of indoor dust samples from homes and microenvironments at concentrations that ranged from < LOQ to 118 μg/g and 0.10 to 3460 μg/g, respectively. This is the first study to measure BHT metabolites in house dust (0.01-35.1 μg/g) and their concentrations accounted for 9.2-58% of the sum concentrations (∑SPAs). 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO), 2,6-di-tert-butyl-4-(hydroxymethyl)phenol (BHT-OH), 2,6-di-tert-butyl-1,4-benzoquinone (BHT-Q) were the major derivatives of BHT found in dust samples. The concentrations of gallic acid esters (gallates) in dust from homes and microenvironments ranged from < LOQ to 18.2 and < LOQ to 684 μg/g, respectively. The concentrations and profiles of SPAs varied among countries and microenvironments. Significantly elevated concentrations of SPAs were found in dust from an e-waste workshop (1530 μg/g). The estimated daily intake (EDI) of BHT via house dust ingestion ranged from 0.40 to 222 ng/kg/d (95th percentile).

Occurrence of synthetic phenolic antioxidants and major metabolites in municipal sewage sludge in China

Synthetic phenolic antioxidants (SPAs) are one group of widely used additive chemicals, which have not yet had focused attention except for a few compounds such as 2,6-di-tert-butyl-4-methylphenol (BHT). In this study, the occurrence and composition profiles of 12 frequently used SPAs and three BHT metabolites were investigated in fifty-six sludge samples collected from individual wastewater treatment plants in China. Eleven SPAs were positively found in the sludge samples, in which, to our knowledge, eight SPA compounds were identified for the first time in the environment. BHT, 4-tert-octylphenol (4-tOP), and 2,4,6-tri-tert-bultylphenol (AO 246) were the most dominant SPAs in the sludge at mean concentrations of 4.14 μg/g, 374 ng/g, and 98.1 ng/g d.w. (dry weight). Meanwhile, three BHT metabolites, including 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO), 2,6-di-tert-butyl-1,4-benzoquinone (BHT-Q), and 2,6-di-tert-butyl-4-hydroxy-4-methyl-2,5-cyclohexadienone (BHT-quinol), were also found in most of the samples (>98.2%) with mean concentrations of 141, 562, and 225 ng/g d.w., respectively. The activated sludge system (anaerobic, anoxic, and oxic tanks) of a wastewater treatment plant was further investigated for the removal efficiencies of the SPAs. High removal efficiencies (80.1-89.2%) were found for the six detected SPAs in the aqueous phase, while generation of large proportions of the three BHT metabolites was also observed.

2,6-Di-Tert-Butyl-Hydroxytoluene and Its Metabolites in Foods

2,6-Di-tert-butyl-hydroxytoluene (BHT, E-321) is a synthetic phenolic antioxidant which has been widely used as an additive in the food, cosmetic, and plastic industries for the last 70 y. Although it is considered safe for human health at authorized levels, its ubiquitous presence and the controversial toxicological data reported are of great concern for consumers. In recent years, special attention has been paid to these 14 metabolites or degradation products: BHT-CH₂ OH, BHT-CHO, BHT-COOH, BHT-Q, BHT-QM, DBP, BHT-OH, BHT-OOH, TBP, BHQ, BHT-OH(t), BHT-OH(t)QM, 2-BHT, and 2-BHT-QM. These derived compounds could pose a human health risk from a food safety point of view, but they have been little studied. In this context, this review deals with the occurrence, origin, and fate of BHT in foodstuffs, its biotransformation into metabolites, their toxicological implications, their antioxidant and prooxidant properties, the analytical determination of metabolites in foods, and human dietary exposure. Moreover, noncontrolled additional sources of exposure to BHT and its metabolites are highlighted. These include their carryover from feed to fish, poultry and eggs, their presence in smoke flavorings, their migration from plastic pipelines and packaging to water and food, and their presence in natural environments, from which they can reach the food chain.

Oxidation of synthetic phenolic antioxidants during water chlorination

The degradation of seven phenolic antioxidants and metabolites during chlorination was investigated. Under strong chlorination conditions (10 mg L(-1) chlorine, 24h), five of the target compounds were significantly degraded, while only BHT-Q (2,6-di-tert-butylcyclohexa-2,5-diene-1,4-dione) and BHT-CHO (3,5-di-tert-butyl-4-hydroxybenzaldehyde) were stable. The effect of the presence of bromide to the sample was only significant for BHA (butylated hydroxyanisole) resulting in increased disappearance rate as it is increased. Moreover, the disappearance kinetics were investigated at different concentrations of chlorine and pH of sample using a factorial experimental design. It was observed that the pH of the sample was a significant factor for BHT (butylated hydroxytoluene) and BHA, and chlorine concentration was significant for BHT, resulting in increased disappearance kinetics as they are increased. The degradation of these compounds has revealed two main processes: hydroxylation and oxidation of the aromatic system. The hydroxylated derivatives in some cases (e.g. from BHT-OH (2,6-di-tert-butyl-4-(hydroxymethyl)phenol) and BHT-COOH (3,5-di-tert-butyl-4-hydroxybenzoic acid)) are formed via the chlorinated and/or brominated intermediate. Moreover, the oxidation of the aromatic system leads to the quinone derivatives. The investigation of these by-products in real samples by solid-phase extraction-gas chromatography-mass spectrometry (SPE-GC-MS) showed that derivatives of BHT, BHT-OH and/or BHT-COOH occurred in wastewater and drinking water samples analysed.

Radical-scavenging activity of butylated hydroxytoluene (BHT) and its metabolites

To clarify the radical-scavenging activity of butylated hydroxytoluene (BHT), a food additive, stoichiometric factors (n) and inhibition rate constants (kinh) were determined for 2,6-di-tert-butyl-4-methylphenol (BHT) and its metabolites 2,6-di-tert-butyl-p-benzoquinone (BHT-Q), 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHA-CHO) and 3,5-di-tert-butyl-4-hydroperoxy-4-methyl-2,5-cyclohexadiene-1-one (BHT-OOH). Values of n and kinh were determined from differential scanning calorimetry (DSC) monitoring of the polymerization of methyl methacrylate (MMA) initiated by 2,2'-azobis(isobutyronitrile) (AIBN) or benzoyl peroxide (BPO) at 70 degrees C in the presence or absence of antioxidants (BHT-related compounds). The n values declined in the order BHT (1-2) > BHT-CHO, BHT-OOH (0.1-0.3) > BHT-Q ( approximately 0). The n value for BHT with AIBN was approximately 1.0, suggesting dimerization of BHT. The kinh values declined in the order BHT-Q ((3.5-4.6) x 10(4) M(-1)s(-1)) > BHT-OOH (0.7-1.9 x 10(4) M(-1)s(-1)) > BHT-CHO ((0.4-1.7 x 10(4) M(-1)s(-1)) > BHT ((0.1-0.2 x 10(4) M(-1)s(-1)). The kinh for metabolites was greater than that for the parent BHT. Growing MMA radicals initiated by BPO were suppressed much more efficiently by BHT or BHT-Q compared with those initiated by AIBN. BHT was effective as a chain-breaking antioxidant.

Monitoring of the antioxidant BHT and its metabolite BHT-CHO in German river water and ground water

The behavior of anthropogenic polar organic compounds in ground water during infiltration of river water to ground water was studied at the Oderbruch area on the eastern border of Germany. Additionally, waste water sewage treatment works (STWs) discharging their treated waste water into the Oder River and rain water precipitation from the Oderbruch area were investigated. The study was carried out from March 2000 to July 2001 to investigate seasonal variations of the target analytes. Samples were collected from four sites along the Oder River, from 24 ground water monitoring wells located close to the Oder, from one rain water collection station, from two roof runoffs, and from four STWs upstream of the Oderbruch. Results of the investigations of the antioxidant 3,5-di-tert-butyl-4-hydroxy-toluene (BHT) and its degradation product 3,5-di-tert-butyl-4-hydroxy-benzaldehyde (BHT-CHO) are presented. BHT and BHT-CHO were detected in all samples of the Oder River with mean concentrations of 178 and 102 ngl(-1), respectively. BHT and BHT-CHO were also detected in effluent waste water samples from municipal STWs at mean concentrations of 132 and 70 ngl(-1), respectively. Both compounds are discharged into river water directly via treated waste water. In the rain water sample, 308 ngl(-1) of BHT and 155 ngl(-1) of BHT-CHO were measured. Both compounds were detected in roof runoff with mean concentrations of 92 ngl(-1) for BHT and 138 ngl(-1) for BHT-CHO. The median values of BHT and BHT-CHO in ground water samples were 132 and 84 ngl(-1), respectively. The chemical composition of ground water from parts of the aquifer located less than 4.5 m distant from the river are greatly influenced by bank filtration. However, wet deposition followed by seepage of rain water into the aquifer is also a source of BHT and BHT-CHO in ground water.

Final report on the safety assessment of BHT(1)

BHT is the recognized name in the cosmetics industry for butylated hydroxytoluene. BHT is used in a wide range of cosmetic formulations as an antioxidant at concentrations from 0.0002% to 0.5%. BHT does penetrate the skin, but the relatively low amount absorbed remains primarily in the skin. Oral studies demonstrate that BHT is metabolized. The major metabolites appear as the carboxylic acid of BHT and its glucuronide in urine. At acute doses of 0.5 to 1.0 g/kg, some renal and hepatic damage was seen in male rats. Short-term repeated exposure to comparable doses produced hepatic toxic effects in male and female rats. Subchronic feeding and intraperitoneal studies in rats with BHT at lower doses produced increased liver weight, and decreased activity of several hepatic enzymes. In addition to liver and kidney effects, BHT applied to the skin was associated with toxic effects in lung tissue. BHT was not a reproductive or developmental toxin in animals. BHT has been found to enhance and to inhibit the humoral immune response in animals. BHT itself was not generally considered genotoxic, although it did modify the genotoxicity of other agents. BHT has been associated with hepatocellular and pulmonary adenomas in animals, but was not considered carcinogenic and actually was associated with a decreased incidence of neoplasms. BHT has been shown to have tumor promotion effects, to be anticarcinogenic, and to have no effect on other carcinogenic agents, depending on the target organ, exposure parameters, the carcinogen, and the animal tested. Various mechanism studies suggested that BHT toxicity is related to an electrophillic metabolite. In a predictive clinical test, 100% BHT was a mild irritant and a moderate sensitizer. In provocative skin tests, BHT (in the 1% to 2% concentration range) produced positive reactions in a small number of patients. Clinical testing did not find any depigmentation associated with dermal exposure to BHT, although a few case reports of depigmentation were found. The Cosmetic Ingredient Review Expert Panel recognized that oral exposure to BHT was associated with toxic effects in some studies and was negative in others. BHT applied to the skin, however, appears to remain in the skin or pass through only slowly and does not produce systemic exposures to BHT or its metabolites seen with oral exposures. Although there were only limited studies that evaluated the effect of BHT on the skin, the available studies, along with the case literature, demonstrate no significant irritation, sensitization, or photosensitization. Recognizing the low concentration at which this ingredient is currently used in cosmetic formulations, it was concluded that BHT is safe as used in cosmetic formulations.

Analysis of the antioxidant butylated hydroxytoluene (BHT) in water by means of solid phase extraction combined with GC/MS

The antioxidant 3,5-di-tert-butyl-4-hydroxy-toluene (BHT) is widely used as an additive to increase the tenability of food and plastics. BHT is degraded to 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO) in mammals, as well as in the natural environment such as in water and soils. BHT-CHO has been studied extensively in terms of their potential toxicities. The present investigation was carried out to quantify BHT and BHT-CHO in river, ground, rain and drinking water obtained from several locations in Germany. Apart from the compounds mentioned above, 1,2-bis-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane (2-BHT), which is a dimer of BHT, was also detected in the extracts of some ground water samples. The applied analytical method is based on solid phase extraction (SPE) to concentrate trace compounds from water samples followed by gas chromatography/mass spectrometry (GC/MS) of the extracts. A total of 51 of the respective water samples were used for extraction purposes and analyte recoveries were all > or = 80%. The determination limit for BHT was 5 ng l(-1) and for BHT-CHO 16 ng l(-1). The standard deviations for the analytical procedure were 6% for BHT and 10% for BHT-CHO. The use of the antioxidant BHT in Germany has resulted in water concentrations of 7-791 ng l(-1) in the rivers Rhine, Elbe, Main, Oder, Nidda and Schwarzbach. The degradation product BHT-CHO was also detected in the river water samples at concentrations between 29 and 223 ng l(-1). The concentrations of BHT measured in German rivers are lower compared to values measured in the USA and Japan 20 years ago. In ground water, levels for BHT varied from non-detectable up to 2156 ng l(-1) and for BHT-CHO from non-detectable up to 674 ng l(-1). Both compounds were also detected in rain water in Frankfurt/Main at a concentration of 1797 ng l(-1) for BHT and 59 ng l(-1) for BHT-CHO.

Oxidative DNA damage and apoptosis induced by metabolites of butylated hydroxytoluene

DNA damage by metabolites of a food additive, butylated hydroxytoluene (BHT), was investigated as a potential mechanism of carcinogenicity. The mechanism of DNA damage by 2,6-di-tert-butyl-p-benzoquinone (BHT-quinone), 2,6-di-tert-butyl-4-hydroperoxyl-4-methyl-2,5-cyclohexadienone (BHT-OOH), and 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO) in the presence of metal ions was investigated by using 32P-labeled DNA fragments obtained from the c-Ha-ras-1 proto-oncogene and the p53 tumor suppressor gene. BHT-OOH caused DNA damage in the presence of Cu(II), whereas BHT-quinone and BHT-CHO did not. However, BHT-quinone did induce DNA damage in the presence of NADH and Cu(II). Bathocuproine inhibited Cu(II)-mediated DNA damage, indicating the participation of Cu(I) in the process. Catalase also inhibited DNA damage induced by BHT-quinone, but not that induced by BHT-OOH. The DNA cleavage pattern observed with BHT-quinone plus NADH was different from that seen with BHT-OOH. With BHT-quinone plus NADH, piperidine-labile sites could be generated at nucleotides other than adenine residue. BHT-OOH caused cleavage specifically at guanine residues. Pulsed field gel electrophoresis showed that BHT-OOH and BHT-quinone induced DNA strand breaks in cultured cells, whereas BHT-CHO did not. Both BHT-quinone and BHT-OOH induced internucleosomal DNA fragmentation, which is the characteristic of apoptosis. Furthermore, flow cytometry analysis revealed an increase of peroxides in cultured cells treated with BHT-OOH or BHT-quinone. These results suggest that BHT-OOH participates in oxidative DNA damage directly, whereas BHT-quinone causes DNA damage through H2O2 generation, which leads to internucleosomal DNA fragmentation.

Measurement of synthetic phenolic antioxidants in human tissues by high-performance liquid chromatography with coulometric electrochemical detection

The antioxidants, 2-tert.-butyl-4-methoxyphenol (BHA) and its oxidative peroxidation product 2,2'-dihydroxy-3,3'-di-tert.-butyl-5,5'-dimethoxybiphenyl (di-BHA), 3,5-di-tert.-butyl-4-hydroxytoluene (BHT) and propyl gallate, were measured in plasma and tissue homogenates by HPLC and electrochemical detection, with a sensitivity down to 0.2 (BHA), 0.1 (di-BHA), 0.4 (BHT) and 1 (propyl gallate) ng ml(-1) of plasma or tissue homogenate. The data demonstrate that in man, at the current level of exposure to dietary antioxidants, significant amounts of BHA, BHT and propyl gallate are accumulated in the omentum. Furthermore, they provide the first evidence that the peroxidase-catalysed oxidation of BHA is operative in man.

DNA cleavage by metabolites of butylated hydroxytoluene

The effect of butylated hydroxytoluene (BHT) and its metabolites on DNA cleavage in vitro was studied with supercoiled plasmid DNA, pUC18, by agarose gel electrophoresis. Among several BHT metabolites, 2,6-di-t-butyl-p-benzoquinone (BHT-quinone) caused cleavage of supercoiled DNA (form I) at a concentration as low as 1 x 10(-6) M. The relative amount of linear form (form III) was increased with increasing concentration of BHT-quinone. 2,6-Di-t-butyl-4-hydroperoxy-4-methyl-2,5-cyclohexadienone (BHT-peroxyquinol) and 3,5-di-t-butyl-4-hydroxybenzaldehyde (BHT-CHO) also cleaved DNA, but to a lesser extent than BHT-quinone. No DNA cleavage was detected by BHT, 2,6-di-t-butyl-4-hydroxymethyl phenol (BHT-OH), 3,5-di-t-butyl-4-hydroxybenzoic acid (BHT-COOH), 2,6-di-t-butyl-4-hydroxy-4-methyl-2,5-cyclohexadienone (BHT-quinol) or 2,6-di-t-butyl-4-methylene-2,5-cyclohexadienone (BHT-quinone methide). The DNA cleavage by BHT-quinone was inhibited by oxygen radical scavengers including superoxide dismutase (SOD), catalase, polyethylene glycol, t-butyl alcohol, dimethyl sulfoxide, sodium azide, sodium benzoate, bovine serum albumin and methionine, while it was enhanced by the addition of FeCl2. The production of superoxide radical in a solution of BHT-quinone was confirmed by cytochrome c reduction assay. Superoxide was not produced by BHT or other BHT metabolites except for BHT-quinone. These results suggest that BHT-quinone, one of the principal metabolites of BHT, cleaves DNA strands via its generation of oxygen radicals.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition of single oral doses of butylated hydroxytoluene in man and rat

The kinetics and metabolism of butylated hydroxytoluene (BHT) in man and rats have been compared. Single oral doses of 200, 63 or 20 mg BHT/kg body weight were administered to rats and a single oral dose of 0.5 mg/kg body weight was ingested by human volunteers (non-smoking males). In rats, kinetic parameters (area under the plasma concentration-time curve, plasma BHT peak levels) showed a dose-dependent increase. Plasma BHT levels after oral administration were about four times higher than those that have been reported for another synthetic food antioxidant, butylated hydroxyanisole (BHA; Verhagen et al., Fd Chem. Toxic. 27, 151-158). This may be a reflection of a smaller volume of distribution for BHT, since there were no differences in plasma elimination half-life or plasma clearance between BHT and BHA. In man, the mean plasma concentration-time profile after oral BHT intake was well below the BHT profiles observed for rats and closely followed plasma BHA kinetics in man. In rats, the simultaneous administration of BHT (200 mg/kg body weight) and BHA (200 mg/kg) significantly decreased the absorption of BHT from the gastro-intestinal tract in the first few hours after treatment; the plasma kinetics of BHA were not influenced by the simultaneous administration of BHT. In human female volunteers no alterations in plasma BHT or BHA profiles were seen after the simultaneous ingestion of BHT (0.25 mg/kg body weight) and BHA (0.25 mg/kg). Rats excrete about 10% of an oral dose of 200 mg BHT/kg as unchanged BHT in the faeces, whereas in man no BHT could be detected in the faeces. Urinary excretion of (un)conjugated 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) accounts for only a small percentage of the administered dose in both rats and humans. It is concluded that the plasma BHT concentrations reached after the administration of a single medium to high dose of BHT to rats or a single low dose to man are very different.

Extent of cutaneous metabolism during percutaneous absorption of xenobiotics

In vitro percutaneous absorption studies generally do not determine whether biotransformation occurs during passage of a substance through the skin. Since it has recently been demonstrated that several chemicals are metabolized during skin permeation, we investigated the metabolism of five additional compounds (14C-labeled) after application to fuzzy rat skin: caffeine, p,p'-DDT, butylated hydroxytoluene (BHT), salicylic acid, and acetyl ethyl tetramethyltetralin (AETT). The viability of skin was maintained with a tissue culture medium. Radioactivity of each substrate and any metabolites in skin and receptor fluid was measured so that the absorption and metabolism of water-insoluble compounds would be accurately determined. Percutaneous absorption ranged from a low of 13% of the applied dose for BHT to a high of 49% for DDT. BHT was metabolized in skin to 4-hydroxy-BHT and an unknown metabolite. Of the absorbed radioisotope, 6.6% was isolated in biotransformed products found mainly in the receptor fluid. AETT was also metabolized during absorption, with 1.9% of the absorbed radioisotope found in two unknown peaks. Caffeine, DDT, and salicylic acid were not metabolized during skin permeation. Skin and liver microsomal metabolism was measured for all compounds except DDT. Metabolism in skin was observed only for the compounds also biotransformed in the diffusion cell; BHT and AETT were metabolized at 113 and 2.5 pmol/min/mg protein, respectively. In this study, as in others, skin metabolism was substantially less than the corresponding metabolism in liver. Therefore, a low rate of liver metabolism such as that found for caffeine, salicylic acid, and DDT might often be predictive of the absence of measurable metabolism during skin permeation. It seems likely that for many compounds, the biotransformations in skin will be small in terms of the percentage of absorbed material that is metabolized. Nevertheless, with potent compounds, even small quantities of a metabolite can be important and for pharmacokinetic studies, viability of skin must be maintained.

Metabolic aspects of antioxidants and preservatives

The use of chemical preservatives serves to ensure the nutritional adequacy, palatability and safety of processed foods and beverages. The toxicity of some of the more ubiquitous antimicrobial agents (sorbic acid, p-hydroxybenzoates, sulphur dioxide) and antioxidants (propyl gallate, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT] is reviewed together with the role of metabolic data in assessing the 'safety-in-use' of these and other food-additives.

Specificity of induction of cancer protective enzymes by analogues of tert-butyl-4-hydroxyanisole (BHA)

Protection by 2(3)-tert-butyl-4-hydroxyanisole (BHA) and related phenols against chemical carcinogens, mutagens and other toxins has been attributed to the elevation of tissue levels of non-oxygenative detoxification enzymes. To analyze the mechanisms and specificity of these enzyme inductions, we synthesized a series of mono- and dialkyl ethers of tert-butylhydroquinone (R1O-[(CH3)3C-C6H3]-OR2) and its dimer. The abilities of these compounds to elevate the cytosolic specific activities of glutathione S-transferases (measured with 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene) and of NAD(P)H: quinone reductase in liver, upper small intestine and forestomach of female CD-1 mice were evaluated. The animals were fed five daily doses of 50 mumoles of each monomer (or 25 mumoles of each dimer). The structures of the monomers examined were: R1 = H and R2 = CH3 (I), R2 = C2H5 (VI), R2 = (CH2)2CH3 (VIII), R2 = CH(CH3)2 (X); R1 = CH3 and R2 = C2H5 (VII), R2 = (CH2)2CH3 (IX), R2 = CH(CH3)2(XI); R2 = CH3 and R1 = C2H5(III), R1 = (CH2)2CH3(IV) and R1 = CH(CH3)2 (V). In addition, the monomethyl (XIII), monoethyl (XIV) and mono-n-propyl (XV) ethers of BHA dimer (XII; 2,2'-dihydroxy-3,3'-di-tert-butyl-5,5'-dimethoxybiphenyl) were also prepared. Under the conditions tested, all compounds were ineffective as enzyme inducers in the forestomach but produced coordinate induction of enzymes (generally 2- to 6-fold) in the cytosols of liver and mucosa of proximal small intestine. Increases in bulk of R1 and R2 beyond methyl groups tended to decrease the inductive potency of both monomers and dimers. The lack of strict structural specificity suggests that the induction depends on metabolic conversion of the analogues to common types of metabolites.

Carcinogenicity and modification of the carcinogenic response by BHA, BHT, and other antioxidants

Carcinogenicity tests showed that addition of the antioxidant BHA to the diet of F344 rats induced high incidences of papilloma and squamous cell carcinoma of the forestomach of both sexes. Male hamsters given BHA for 24 weeks also developed papilloma showing downward growth into the submucosa of the forestomach. These results indicate that BHA should be classified in the category of "sufficient evidence of carcinogenicity" as judged by IARC criteria. The 3-tert isomer of BHA seemed to be responsible for the carcinogenicity of crude BHA in the forestomach of rats. BHT was not found to be carcinogenic in rats or mice. In two-stage carcinogenesis in rats after appropriate initiation, BHA enhanced carcinogenesis in the forestomach and urinary bladder of rats, but inhibited carcinogenesis in the liver. BHT enhanced the induction of urinary bladder tumors and inhibited that of liver tumors, but had no effect on carcinogenesis in the forestomach. BHT could be a promoter of thyroid carcinogenesis. Sodium L-ascorbate enhanced forestomach and urinary bladder carcinogenesis. Ethoxyquin enhanced kidney and urinary bladder carcinogenesis, but inhibited liver carcinogenesis. Thus, these antioxidants modify two-stage chemical carcinogenesis in the forestomach, liver, kidney, urinary bladder, and thyroid, but show organ-specific differences in effects.