Ethyl carbamate (urethane, C2
, CAS # 51-79-6) is a recognized genotoxic carcinogen, of widespread occurrence in fermented foods and beverages [1
]. Public health concerns about the presence of this substance in alcoholic beverages began in 1985, when relatively high levels were detected by Canadian authorities in imported alcohol products, including German fruit spirits [7
]. Canada proceeded to establish an upper limit of 0.15 mg/L for ethyl carbamate in distilled spirits and 0.4 mg/L for ethyl carbamate in fruit spirits [8
]. However, currently there are no harmonised maximum levels for ethyl carbamate provided by the Codex Alimentarius, the European Union, nor the two countries under study.
The International Agency for Research on Cancer (IARC) recently upgraded its classification of ethyl carbamate to group 2A (probably carcinogenic to humans). This reflects increasing evidence on the significant similarities between rodents and humans regarding the metabolic pathways of the activation of ethyl carbamate, whereby the formation of proximate DNA-reactive carcinogens, hypothesized to play a major role in ethyl carbamate-induced carcinogenesis in rodent cells, is also likely to occur in humans [9
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has concluded that exposure to ethyl carbamate in food is of low concern [10
]. However, the inclusion of alcoholic beverages into this model sets the estimated Margin of Exposure (MOE) to 3,800, a value of concern that necessitates mitigative measures for the reduction of ethyl carbamate concentrations in certain alcoholic beverages (for summary of mitigation measures see Ref. [9
]). The European Food Safety Authority (EFSA) recently confirmed this evaluation, also noting that the MOE for high consumers of fruit spirits was less than 600, indicating an even greater public health concern [8
]. The JECFA evaluation was based on data from the USA, the UK and Japan, whereas the EFSA evaluated data from Europe and North America. Evidence in the international literature (as summarized in Ref. [9
]), which is generally restricted to European-style alcoholic beverages, indicates that the ethyl carbamate problem may be limited to certain fruit spirits (mainly stone-fruit spirits).
The alcohol market in Mexico ranges from international commercial alcohol including spirits and beer, to locally produced alcohol such as tequila, mezcal, and pulque (all agave based). While the Mexican Tequila Regulatory Council (TRC) monitors tequila, there are many small-scale independent and unrecorded alcohol operations producing mezcal and other local spirits (see 2.1).
There is currently no systematic data available on ethyl carbamate levels in locally produced alcoholic beverages from Mexico and Central America, including Guatemala. Our interest in ethyl carbamate in alcoholic beverages in this region comes from evidence of high rates of liver cirrhosis in Mexico [11
]. This public health concern cannot be accounted for by volume of alcohol consumption, which is lower in Mexico when compared to many other countries with markedly lower liver cirrhosis rates, nor alternative explanations [11
]. An exception is limited evidence pointing to water contamination in locally produced alcohol pulque (fermented agave juice) [13
]. Liver cirrhosis rates have been found to vary with consumption of pulque [14
Ethyl carbamate is not only carcinogenic but also a known liver toxic agent in humans [16
]. Animal experiments point to complex interactions between ethanol and ethyl carbamate, e.g. in decreased first-pass hepatic clearance [17
]. This study investigates ethyl carbamate in agave spirits from Mexico and sugarcane spirits from Guatemala and the possible risk to public health with special regard to liver damage.
The incidence of ethyl carbamate in different types of spirits from Mexico and Guatemala is detailed in Table 1
. There were no statistically significant differences in ethyl carbamate between the different categories in the Mexican samples (p=0.589), nor between clandestinely and commercially produced cuxa from Guatemala (p=0.775). The estimated exposure for agave spirit drinkers in Mexico and cuxa drinkers in Guatemala based on the ethyl carbamate concentrations for the entire collection of samples is summarized in Table 2
The number of tequila samples allowed us to investigate its categories and sub-groups in greater detail. First, tequila sampled in Germany did not show significant differences from the tequila purchased on the domestic Mexican market (p=0.214). Second, “100% agave” tequila did not differ from “mixto” tequila (mixed, less than 100% agave) (p=0.580). Finally, there were no differences between “blanco”, “joven u oro”, “reposado” and “añejo” tequila (p=0.192) (for details on the tequila categories, see Refs. [18
]). Because of the evident absence of differences in sub-groups of tequila, we did not make a distinction between categories in Table 1
The incidence for ethyl carbamate contamination was higher in Mexico than in Guatemala. However, only four samples in total (two mezcals, one tequila, one bacanora) were above the Canadian limit of 0.15 mg/L for distilled spirits. None of the samples were above the limit for fruit spirits of 0.4 mg/L. The larger number of Mexican samples along with the sampling in different states allowed for a more detailed exposure estimation for drinkers of this category of spirits. Based on an average per capita consumption of 1 litre of pure alcohol in the form of spirits, with the assumption that only agave spirits are consumed, we provide a whole population exposure scenario in Table 3
. Here, the average exposure is 6 ng/kg bw/day with a corresponding MOE of 52,560. Additionally, we provide exposure scenarios for individual drinkers, showing exposures for different numbers of drinks per day and for different ethyl carbamate concentrations (Table 4
). The corresponding MOEs for these exposures are shown in Table 5
. For mean ethyl carbamate content in the beverages, the MOE ranges between 14,400 for one drink per day and 2,880 for five drinks per day.
The ethyl carbamate concentrations in all Guatemalan beverages were below the Canadian limit of 0.15 mg/L for distilled spirits. In twelve of the samples, no ethyl carbamate was detected. Three samples were below the limit of quantitation, and only one had a quantifiable content of ethyl carbamate detected (0.06 mg/L). The focus of our study on one Mayan town in Guatemala did not allow us to assess the public health risk of ethyl carbamate on a countrywide scale. Of significance, in cases of daily consumption of one drink (125 mL at 18% vol) of the sample with the highest concentration would result in an exposure of 125 ng/kg bw/day and a MOE of 2,400.
Our risk assessment is in line with the estimates of the EFSA for Europe [8
]. For example, an ethyl carbamate exposure of 60 ng/kg bw/day was estimated for spirit consumers in Europe resulting in a MOE of 5,000 [8
]. Comparatively, the ethyl carbamate intake from the consumption of the beverages under study does not differ from that in other countries where the incidence of cirrhosis of the liver is lower, therefore, it seems unlikely that ethyl carbamate is a contributing factor. The ethyl carbamate exposure due to alcoholic beverages in the ng-range was also considerably lower than dosages (2.5–7.6 g/day) known to lead to liver damage, based on instances when ethyl carbamate was used as medicine [16
For these reasons, the author’s are inclined to reject the hypothesis that ethyl carbamate is a likely cause for the more pronounced incidence of liver diseases in Mexico than in other parts of the world. Ethyl carbamate may also not be a major health factor in alcohols produced using completely or partially refined sugarcane materials.
Future research should focus on studying a larger range of constituents and contaminants to explain liver disease incidence in Mexico. Several likely candidates for this line of research were recently pointed out in our pilot study in Lithuania and Hungary [39
]. Acetaldehyde, is a particularly interesting research topic, as we found this compound in relatively high concentrations in our earlier study of Mexican agave spirits [18
], and a recent risk assessment has shown that acetaldehyde constitutes a potential public health risk - even without consideration for the metabolically produced acetaldehyde [40