Eleven samples of alcohol products were collected by one of the authors (PTHA) from local markets in Vietnam and subsequent chemical analyses were conducted; all samples were locally produced, see Table 1 for details. Collection of alcohol products was based on a convenient sampling procedure aimed at obtaining products most popular with the population. Samples V03 and V05 are from the biggest, most popular manufacturers in the country, while V08 and V09 were homemade (traditionally produced) and are very popular in Vietnam. The designation “homemade” in this context does not mean that individuals prepared the alcohol for personal or family consumption. There are in fact some rural regions around Hanoi famous for producing specific homemade alcohols and providing them to the capital city via a system of commercial outlets, including local street markets, tea shops, or restaurants. Sample V11 was exceptional because it contained whole bodies of snake and scorpion soaked in alcohol (Figure 1); it was also homemade. Small, local companies produced the other samples.

The parameters for chemical analysis were selected on a risk-oriented basis as described in previous studies [16,25,28]. Alcoholic strength was determined by Fourier Transform Infrared (FTIR) spectroscopy [29]. The analysis for volatile components was based on the European Community Reference Methods for the Analysis of Spirits using gas chromatography (GC) with a flame-ionization detector (FID) [30]. Additional details on the GC-FID procedure are published elsewhere [31]. Ethyl carbamate (urethane) was determined using GC with tandem mass spectrometry (GC-MS/MS) [32]. Anionic composition was analyzed using ion chromatography [33]. Conductivity was measured using the procedure outlined in Lachenmeier et al. [34]. Inorganic elements were analyzed using semi-quantitative inductively coupled plasma mass spectrometry (ICP-MS) after evaporation of the sample and re-constitution in ultrapure water. Furthermore, all samples were screened for unknown substances using GC with mass spectrometry (GC-MS).

Alcoholic strength is indicated by ‘percent by volume’ (% vol). In accordance with the procedure described in the European Community Reference Methods for the Analysis of Spirits, volatile compounds contained in the samples are expressed by the unit ‘g/hL of pure alcohol’ or ‘g/hL of 100% vol alcohol’ (i.e., the concentrations are standardized in relation to alcoholic strength) [30]. This approach is superior to reporting in mg/L because the samples can be directly compared irrespective of their individual alcoholic strength. For clarity, we use the abbreviation ‘g/hL pa’. The results for the non-volatile components are presented as ‘mg/L’.

The majority of samples (72%) had an alcohol content between 30% vol and 40% vol, which is in accordance with the typical strength of international commercial spirits. The only abnormalities were the homemade samples V09 (45.0% vol) and V10 (49.7% vol), as well as the notable snake/scorpion-alcohol sample V11 with the highest strength of 76.7% vol. From a public health perspective V10 appears to be the most troubling of the samples as the labeling gave an alcoholic strength of 30% vol, whereas 49.7% vol were in fact contained in the sample - nearly 60% more alcohol than what was labeled, which could lead to severe intoxication and overdose [2].

The snake/scorpion sample V11 is discussed in greater detail below, however it should be noted in this case that the high alcoholic strength may be needed in order to preserve the pickled animals and subsequently increase the product’s shelf life. The alcoholic strength was not labeled on the sample; yet according to the local people we questioned, the common consumers are principally comprised of alcohol-dependent people of the lower socio-economic classes, who are well aware of the very high alcohol potency. Nevertheless, such a high strength alcoholic beverage may have more pronounced detrimental health effects explained entirely by the presence of ethanol [2].

Besides ethanol, our samples contained a number of volatile compounds, which are expected in products derived from alcoholic fermentation. Of these, methanol is the substance most often associated with the toxicity of surrogate and other alcohols [15]. As its presence was relatively low (i.e., lower than the European Union (EU) limit of 10 g/hL pa for vodka [35] in V01–V10), it would appear that in our samples, methanol content did not pose a threat to public health.

Acetaldehyde is a substance considered by the International Agency for Research on Cancer as ‘possibly carcinogenic to humans’ (IARC Group 2B) [38]. It is also regarded as an undesirable substance in spirits because of its unpleasant flavor. The acetaldehyde level in some of the samples was higher than the EU limit of 0.5 g/hL pa for vodka, but typical for spirits distilled under retention of the organoleptical properties of the raw materials (e.g., brandy, whisky, rum) [39]. The highest concentration of 19 g/hL pa, found in the homemade sample V10, can be considered typical for an artisanally produced spirit, as average acetaldehyde residues between 12 g/hL pa and 18 g/hL pa have been found, for example, in artisanal German fruit spirits [40].

Alcohol containing more than two carbon atoms is commonly called ‘higher’ or ‘fusel’ alcohol. Most higher alcohols are created as a byproduct of yeast fermentation and are an important flavor compound. In the EU, some spirits must have minimum contents of higher alcohols, whereas neutral alcohols such as vodka should be almost entirely free of higher alcohols (max. 0.5 g/hL pa) as well as of esters (max. 1.3 g/hL pa) [35]. In this sample group, two of the commercial vodkas (V04, V05) and the two homemade rice alcohols (V09, V10) were above the EU requirement for higher alcohols; the two homemade alcohols also above the requirement for esters. Conversely, the brandy (V01) and rum (V07) samples, were below the minimum EU requirements of 140 or 225 g/hL pa of higher alcohols, for the two groups of spirits respectively. In terms of higher alcohols, sample V10 was the most peculiar, as it had an extremely high content of higher alcohols. The high concentration of esters and ethyl lactate in this sample indicates probable hygienic deficiencies during fermentation (e.g., spoilage with acetic acid or lactic acid bacteria). The other homemade samples showed a surprisingly clean alcohol quality. In conclusion, none of the samples pose a public health risk due to the contents of higher alcohols [41].

Because elements and ions are generally non-volatile, most of the inorganic content found in the spirits is derived from the dilution water used to adjust the distillate to drinking strength. Inorganic contamination may also occur during the use of the distillation equipment. Other than the snake sample discussed below, all the alcoholic beverages conformed to the EU drinking water requirements [37]. The conductivities of the samples and the contents of ions were relatively low, which suggests an overall sufficient water quality or treatment process. No toxic anions such as nitrates, or toxic metals including lead, cadmium, copper, antimony, or arsenic, were found in health relevant concentrations.

The sample that was significant in nearly all analyzed parameters was sample V11, the alcohol containing pickled snakes (cobras) and a scorpion. Typically, the production of such products is comprised of the purchase of a live snake, usually from a street vender/shop or by pre-order, the snake is killed and then placed in a desired glass pot, which depends in volume, shape and style on the size of the snake. This process is carried out by both individuals in their homes, as well as by vendors in local markets in the presence of their customers, so usually there is no bottle label provided.

The use of snakes (e.g., cobras or other snakes) as human food is traditional in Asia [42]. The pickling of snakes in vinegar or in alcohol has been described as a common practice in China, mostly in and around Guangzhou (Canton) and in Taiwan; here the snake meat is used for dishes, while the liquid is seemingly only used for preservation purposes [43]. In the case of our sample however, the snake is not used for eating, but is used, along with the scorpion (including venomous ones), in order to provide an essence for purported medicinal benefit. This practice has its roots in Traditional Chinese Medicine (TCM), popular in Vietnam, where such an alcoholic beverage is used as a treatment for rheumatism and arthritis. In this system, it is believed that the more toxic the snake, the more beneficial; an example of this is “Dragon and Phoenix Wine”, a popular beverage in China, which is made using a venomous snake and a pheasant soaked in a distilled high-proof spirit [43].

There is only sparse information in the literature and there are no systematic studies, regarding whether the snake or scorpion venoms consumed orally as TCM (or during food use) pose a threat to public health. It is unlikely that the venom glands have been separated before infusion in the alcohol, yet the venom might be denatured by the high-proof alcohol. Snake venom has also been described as being much less toxic when administered orally rather than intravenously because it may be broken down by the digestive enzymes of the gastrointestinal tract, as well as hydrolyzed by the acidic conditions [44,45]. Recent research has shown that the use of animal products as TCM may be justified, but little research has been done to prove the claimed clinical efficacy [46].

In our screening analysis of the sample, we only found constituents of the animal fat (e.g., fatty acid esters or cholesterol). However, as we did not know the exact species of the snake or scorpion, we could not search specifically for the venom. The complex proteins in snake venoms would most likely not have been identifiable with our analytical methodologies anyway. Therefore, the slight possibility for a health risk of the product remains, even if intoxications of humans from snakes and scorpions in the food chain, to our knowledge, have never been reported. Besides the animal constituents, the sample contained a comparably high concentration of methanol, which, however, is still much below toxic concentrations [47]. Another exceptional characteristic of the snake/scorpion sample was the high conductivity and chloride level, which may be explained by the diffusion of chloride and other ions from the animals into the liquid or insufficient water quality. However, no anions or metals posing health risk were found in the snake sample (e.g., nitrate, lead, antimony, arsenic were below the EU maximum levels [37]).

An important finding is that the snake/scorpion alcohol also contained ethyl carbamate (urethane), a ‘probably carcinogenic’ substance (IARC Group 2A) [48], in relatively high concentrations above the Canadian limit [36]. Ethyl carbamate may contribute to carcinogenicity of alcoholic beverages [49] due to the synergistic effects between ethanol, ethyl carbamate and other possible carcinogenic contaminants of foods that are co-ingested with alcoholic beverages [50]. This is a surprising finding as ethyl carbamate is generally found in such high concentrations only in stone-fruit spirits [51]. The possibility cannot be excluded that some constituent of the snake or scorpion (e.g., nitrogen compounds or amino acids) may react with ethanol to form ethyl carbamate. The formation mechanism in this special kind of alcoholic beverages is far from clear, and requires further investigation.