Acrylamide is an industrial chemical used in the manufacturing of many types of polymers. These polymers can then be used in water treatment systems (and wastewater treatment, too) and in the synthesis of various grouts, cements, cosmetics, plastics, pesticides and paper (and more). The United States used over 250 million pounds of acrylamide in industrial processes in 2007. Acrylamide is also used in molecular biology laboratories as a reagent in the synthesis of electrophoretic gels .
Twenty years ago construction workers on a tunnel site in Sweden began complaining of nausea, dizziness and numbness in their fingers. In areas around the tunnel project, cows were found paralyzed and ponds were full of dead fish. Researchers found that acrylamide, a component of the grout that the workers were using to seal the tunnel wall, was poisoning the workers (it is rapidly absorbed through exposed skin) and was also leaking out into the surrounding pastures and ponds. Acrylamide, even back in the 1990’s, was known to have neurotoxic and carcinogenic properties. What surprised researchers, though, as they tried to determine the magnitude of the construction workers’ acrylamide exposure, was that everyone whose blood they tested, even people who had not been exposed to the acrylamide grout of the tunnel project, had acrylamide in their blood.
Where was this acrylamide coming from?
It turns out that acrylamide is formed when carbohydrate-rich foods are heated (or cooked) at very high temperatures (above 120 degrees C (or, 248 degrees F). It is a by-product of the Maillard reaction in which amino acids in a food react with reducing sugars (like glucose or fructose) to form the browned (and extremely flavorful) surface layer of the food. Toasting bread, grilling steaks, frying potatoes, or roasting coffee beans are all ways to generate a Maillard reaction. One of the twenty, naturally occurring amino acids (asparagine) is thought to be essential in the specific Maillard reaction that forms acrylamide as a by-product. Raw foods or foods that have been boiled do not contain acrylamides.
These observations led to a number of investigations that explored the possible connection between dietary acrylamide and cancers. Large studies conducted primarily in the early 2000’s found some evidence that certain cancers (like ovarian and endometrial cancers) might have a correlation with dietary intake of acrylamide, but these connections were not confirmed in later studies. Researchers stress that one of the problems in these studies is accurately quantifying an individual’s dietary intake of acrylamide since it is not just certain foods that contain it but the method of cooking those foods that causes it to be synthesized. Measured serum levels of acrylamide did not, however, correlate with the increased incidence of either of these cancers.
This is a very good time to go from this qualitative discussion of acrylamide to one that is more quantitative in nature. Numbers really do matter here, and the numbers I use in the following discussion come from The World Health Organization (WHO).
For example, it is very clear at what level acrylamide will cause neurological symptoms. This value is based on a daily accumulation of acrylamide per kg of body mass. Anyone who takes in 0.5 mg of acrylamide per each kg of their body mass per day will develop neuropathies. This means that an 80 kg (176 pounds) person must absorb 40 mg or acrylamide a day to generate these types of symptoms (the tunnel workers, mentioned above, for example, reached and probably exceeded these levels of exposure). Acrylamide can also cause infertility, and this response occurs when an individual is exposed to about four times the level that would cause neuropathies. So, our 80 kg test subject would have to be exposed to 160 mg of acrylamide per day. The connection of acrylamide to cancer, though, is still not clear and, therefore, has not been quantified. Logically, though, if acrylamide is carcinogenic the potential impact level exposure would be chronic and could be substantially less than 0.5 mg exposure per kg body weight per day that causes neurological symptoms.
The average amount of acrylamide absorbed from dietary sources is 1.0 microgram per kg body weight per day. A microgram is one thousandths of a milligram (1000 micrograms = 1 milligram). This means that our 80 kg person will absorb 80 micrograms (or 0.08 mg) of acrylamide every day from their consumption of French fries, burned toast, coffee, etc. This value is 0.2 % of the acrylamide needed to generate neurological symptoms. It is still an unresolved question, though, as to whether this value approaches a chronic exposure level that could have potential carcinogenicity, but most studies feel that these levels of dietary acrylamide intake are not inherently harmful.
There is another source of acrylamide, though, that can elevate serum acrylamide levels significantly: cigarette smoke. The processing of tobacco causes the synthesis of acrylamides and the subsequent burning of the tobacco generates even more. Smoking cigarettes, according to a study published in the Annals of Agricultural and Environmental Medicine in 2016, exposes the average adult smoker to 0.17 micrograms of acrylamide per kg body weight per day. For our 80 kg example subject, this would be almost 14 more micrograms of acrylamide absorbed per day.
An article in The Scientist (April 1, 2017) presented a concise overview of the history and current status of the medical research concerning acrylamide. Most scientists feel that other areas of chemical exposure control would generate more significant cancer reductions than regulation of dietary acrylamides. It is logical, though, that foods that are deep fried or excessively browned are, in fact, potential sources of this toxin, and that they should be eaten in moderation. It is also logical, as if we needed more evidence about this, that avoiding cigarettes and cigarette smoke is an excellent way to maintain better health.