Acrolein

Acrolein (structural formula: CH2=CH-CHO ), a simple unsaturated, highly reactive aldehyde compound, is formed mainly during the incomplete combustion of fuels, wood, waxes or plastics, animal and vegetable oils. The typical acrolein smell occurs, for example, immediately after a candle has gone out.

In the exhaust gases of engines 0.05 - 27.7 mg/m3 acrolein has been detected. Commercial canteen kitchens, in which cooking oil is heated to temperatures above 180 °C during frying/frying, are a significant source of inhaled acrolein exposure at the workplace. When heating e.g. 3 kg oil, 5 to 250 mg acrolein may be released depending on the conditions (e.g. oil type, temperature, time). For example, concentrations of up to 0.55 mg/m3 air can be measured in the ambient air of kitchens when heating frying fat (Schuh C 1992). The traffic-induced pollution of the air we breathe is estimated to be about 1.8 t acrolein per year, that of commercial kitchens at 7.7 t/year (Ho SS et al. (2006).

Acrolein in tobacco smoke:

• Tobacco smoke can also contribute to the inhalation of acrolein. The acrolein content in cigarette smoke is about 3-220 μg/cigarette (International Agency for Research on Cancer 1995). In the mainstream smoke of cigarettes, 56-118 μg acrolein per cigarette was detected. Acrolein formation increases with increasing glycerol and sugar content of the tobacco (Talhout R et al. (2006).

Acrolein in the atmosphere:

• The average acrolein content of the atmosphere is estimated at 14.3 μg per m3 (EPA 2003). However, the persistence of acrolein in the environment and the exchange between different environmental compartments is low due to the instability of the molecule.

Acrolein and food:

• Acrolein can be formed from fats, amino acids and carbohydrates when food is heated (Stevens JF et al. 2008). Heat-induced formation from glycerides or glycerol in the fat phase of foods, thermal decomposition of amino acids such as methionine and threonine, or heating of carbohydrate-containing foods (Yaylayan V A et al. 2000) may also lead to the formation of acrolein. Hardly any data are available on the occurrence of acrolein in fresh, untreated food. These few data indicate that acrolein can be found in small amounts in fruits and vegetables, but also in animal foods such as fish [and cheese.
• The formation of acrolein when heating oils depends on the fatty acid composition, the heating time and the temperature (Ewert A et al. 2011). Used deep-frying fats, on the other hand, showed strongly increased acrolein contents in the range of 0.2 - 1.4 mg/kg (ppm) (KuballaT et al. 2012)

Endogenous exposure to acrolein:

• There are no data on endogenous exposure of the organism to acrolein. However, it has been described that acrolein can be formed as a by-product of certain metabolic pathways, e.g. during lipid metabolism, glycolysis, amino acid conversion or by oxidative deamination of polyamines.
• Acrolein in the metabolism of cyclophosphamide : Cyclophosphamide is a prodrug which is only metabolised in the liver to 4-hydroxy-cyclophosphamide. 4-Hydroxy-Cyclophosphamide then reaches all organs via the bloodstream where it is converted into the alkylating agent phosphoric acid amide -Lost by splitting off acrolein, which has a strong alkylating effect due to the electron pressure of the negatively charged O atom.

Acrolein and environment:

• The environmental exposure of humans to acrolein is mainly by inhalation. Smokers (approx. 20 cigarettes/day) can expect an additional exposure (50-100 μg/cigarette) of up to 2 mg corresponding to 0.03 μg/kg bw per day. Smokers have twice as high levels of the acrolein main metabolite 3-HPMA in their urine as non-smokers.

Toxicity/carcinogenicity of acrolein:

• Acrolein essentially causes irritation and inflammation of exposed mucous membranes. Inflammation and necrosis of the lung tissue are observed in inhalation exposure, while oral exposure causes inflammation and necrosis in the fore stomach of rats.
• Various committees have classified the carcinogenicity of acrolein as follows:
  • IARC Category 3 (not classifiable as to its carcinogenicity to humans, based on insufficient evidence in humans and in experimental animals for the carcinogenicity of acrolein)
  • MAK Commission of the DFG: Category 3B (justified suspicion)

However, the data available to date indicate that toxicity and possibly genotoxicity may be expected if doses are high enough. There is also sufficient evidence for an endogenous formation of acrolein in the intermediate metabolism.

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