Greetings, dear readers.

In this post I share some considerations about a type of contamination of fossil sources that is present in our homes by the preparation of food.

Introduction

When my professor of environment, development and health in one of her classes began to introduce the subject of Polycyclic Aromatic Hydrocarbons, my attention was caught by the barbecue when she pointed it out among the pyrogenic sources that generate these carcinogenic substances.

In a family sharing where meat, chicken and their rich derivatives are being roasted, millions of biomolecules composed of carbon, hydrogen and oxygen can be produced (to a lesser extent), without downplaying the importance of soot and tar by the combustion of dry wood and coal. My preference for cooking charcoal-grilled meat led me to be interested in knowing this information and sharing it.

Public domain image, hosted on pxhere

When cooking meat at high temperatures or direct fire potential carcinogenic substances are generated, among them Polycyclic Aromatic Hydrocarbons.

Meanwhile, I turned my attention to the studies of Bloch and Dreifuss, who in Zurich (1921) discovered substances with traces of tar responsible for generating malignant tumours in people who had been exposed for considerable periods of time to these compounds, characteristic of the group of polycyclic hydrocarbons.

Years later, the British pathologist Sir Ernest Laurence Kennaway validated his theory of obtaining carcinogenic compounds from the exposure of petroleum, isoprene, acetylene, yeast, cholesterol and even animal tissue and skin to thermal decomposition processes (pyrolysis) and high temperatures.

The pyrolysis of organic matter is a very extended thermochemical process, it is given by lack of oxygen, which implies an incomplete combustion. This anomaly causes the formation of harmful by-products such as carbon monoxide (CO) and the so-called PAH; once the pyrolysis process has been completed, a wide distribution of PAH comes into play in all the components and environmental elements: air, soil, water, sediments, biological tissues, including some foods. At this point, it is of concern for biological diversity and human health.

Subsequent studies will conclude and would serve as a compass to hold benzo[a]pyrene (3, 4-benzopyrene in the old nomenclature) responsible as a potent tumourigenic agent of tar and other fluorescence characteristics that were being investigated in certain fractions.

Polycyclic Aromatic Hydrocarbons

It turns out that this family of compounds spreads daily throughout the environment; they are characterized by being polynuclear structures that manifest photochemical destabilization, or rather, they are susceptible to degradation with light (photooxidation). They originate from the bad combustion of any organic matter whether by natural process, industrial, domestic, transport, tobacco, smoked meat and fish, among others, as stated by the Agency for Toxic Substances and the Registry of Diseases:

Polycyclic aromatic hydrocarbons (PAHs) are a group of over 100 different chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances like tobacco or charbroiled meat. PAHs are usually found as a mixture containing two or more of these compounds, such as soot. Source

Chemical structure of the main PAHs

Polycyclic aromatic hydrocarbons are compounds with a structure of several benzene rings that have been unified by a complex biochemical process. Each vertex of the molecular structure corresponds to a carbon atom, this has 4 links represented by the segments that are interconnected to each vertex; in most of them 3 links are visualized, which means that the remaining link is occupied by a hydrogen atom. As you will see in the animated illustration, the chaining of benzene rings underpins its polycyclic condition.

Own image file [Source]
Data retrieved from here

Benzene is a hydrocarbon whose molecular formula is C₆ H₆ with a characteristic ring appearance, complements its name of benzene or aromatic ring, its smell of benzene. Another interesting aspect is that in this molecular compound each carbon atom occupies the vertex of a regular hexagon, as seen in the three-dimensional image, the cyan color represents carbon, while the white color identifies hydrogen. The main polycyclic aromatic hydrocarbons with a description of their chemical properties are shown below.

Own image file [Source]
Data retrieved from here
Ancetraceno [Anthracene]

Molecular formula: C₁₄ H₁₀ Density: 1280 kg/m³; 1,28 g/cm³ Melting point: 488,8 K (216 °C) Boiling point: 613 K (340 °C)

Own image file [Source]
Data retrieved from here
Benzo[a]pireno [Benzo [a] pyrene]

Fórmula molecular: C₂₀ H₁₂ Density:1240 kg/m³; 1,24 g/cm³ Melting point: 179 K (452 °C) Boiling point: 495 K (768 °C)

Own image file [Source]
Data retrieved from here
Criseno [chrysene]

Fórmula molecular: C₁₈ H₁₂ Density: 1274 kg/m³; 1,274 g/cm³ Melting point: 527 K (254 °C) Boiling point: 721K (448 °C)

Own image file [Source]
Data retrieved from here
Coroneno [Coronene]

Fórmula molecular: C₂₄ H₁₂ Density: 1.371 g/cm³ Melting point: 437.3 °C (819.1 °F; 710.5 K) Boiling point: 525 ° C (977 ° F; 798 K)

Own image file [Source]
Data retrieved from here
Coranuleno [Corannulene]

Molecular formula: C₂₀ H₁₀ Molar mass: 250.29 g/mol

Own image file [Source]
Data retrieved from here
Pentaceno [Pentacene]

Molecular formula: C₂₄ H₁₂ Density: 1.3 g/cm^-3 Melting point: >300 °C/sublimates 372 ºC Boiling point: 40 - 43 ° C

Own image file [Source]
Data retrieved from here
Naftaleno [Naphthalene]

Molecular formula: C₁₀ H₈ Density: 1.45 g/cm^-3 (15.5 ºC) Melting point: 78.2 ° C (172.8 °F; 351.3 K) Boiling point: 217.97 ° C (424.35 °F; 491.12 K)

Own image file [Source]
Data retrieved from here
Fenantreno [Phenanthrene]

Molecular formula: C₁₄ H₁₀ Density: 1180 kg/m³; 1,80 g/cm³ Melting point: 374,15 K (101 °C) Boiling point: 613,15 K (340 °C)

Own image file [Source]
Data retrieved from here
Pireno [Pyrene]

Molecular formula: C₁₆ H₁₀ Density: 1271g/cm³ Melting point: 0.135 (a 25 ° C) Boiling point: 393.5 ° C (666.65 K)

Own image file [Source]
Data retrieved from here
Trifenileno [Triphenylene]

Molecular formula: C₁₈ H₁₂ Density: 1,302 g/cm³ Melting point: 199 °C Boiling point: 438 °C (1013 hPa)

Own image file [Source]
Data retrieved from here
Ovaleno [Ovalene]

Molecular formula: C₃₂ H₁₄ Density:1,302 g/cm³ Masa molar: 398.45 g/mol Scarcely soluble in solvents such as benzene, toluene and dichloromethane.

PAHs as Environmental Pollutants

There are diverse sources of PAH emissions on a global scale, although a significant part comes from natural processes, the main sources are the industrialized centers and urban dynamics; in the latter are those related to transport services, heating, burning of garbage and incineration of synthetic waste.

It was similar in the 1990s in Germany, where low temperatures were accompanied by significant amounts of benzo[a]pyrene from the burning of coal as a heating mechanism, while another considerable volume originates from industrial activity and automobile fleets.

PAH in food

Among the main exogenous sources of genotoxic compounds are food and tobacco. In the case of benzo[a]pyrene, its mutagenic properties and its direct impact on health through the generation and reproduction of carcinogenic cells are striking.

Attribution to jconejo. Public domain image, hosted on pixabay

Process of accumulation and release of PAH by segregation and burning of fat in meat.

There are many ways in which PAH can be produced, taking up the anecdotal development of these chemicals by grilling, it happens that subjecting meat and its derivatives to cooking with firewood, charcoal and even frying in frying pan at high temperatures, makes foods produce large amounts of fat and fat-soluble juices that, When in contact with fire, vapors and smoke charged with PAH emanate and partially adhere and accumulate in food, which are generally ingested without removing these substances with smoked and burned appearance, substances such as amino acids, sugars and creatinine would be the main ingredients that react at more than 120 ºC to synthesize this mutagenic and carcinogenic cocktail.

Other industrially processed foods such as meat and smoked fish have concentrations of benzo[a]pyrene and other PAHs that can cause serious health damage. Organisms such as the Spanish Agency for Consumption, Food Safety and Nutrition warn about the tolerable daily intake of PAH on occasion that they do not represent a risk to health. Many countries have established protective measures by means of advanced legislation on the maximum permissible limits in certain food products; hence the warning is made about the consumption of smoked products and those that are subjected to direct drying.

Polycyclic aromatic hydrocarbons are not only generated by natural sources and industry of hydrocarbons and their derivatives, also, are produced at home during the preparation of some foods that are subjected to cooking with charcoal or firewood at high temperatures; likewise, with exposure that produces smoking and burning.
Benzo[a]pyrene is highly carcinogenic and is present in cigarette smoke, foods subjected to high temperatures for preparation and other nearby sources.
PAHs have rapid effects such as eye irritation, skin and digestive symptoms; however, their greatest damage to health is manifested in the long term by mutagenic and carcinogenic disorders.
The cooking of foods rich in proteins and fats with firewood, charcoal or frying should be done avoiding the burning and generation of smoke due to excessive exposure.

Polycyclic Aromatic Hydrocarbons (PAHs) Link
Polycyclic aromatic hydrocarbon Link
AECOSAN - Agencia española de consumo, seguridad alimentaria y nutrición Link
Agudo, A. (2009). Los Hidrocarburos Aromáticos Policíclicos (HAP) Acercamiento a su problemática como riesgo laboral Link

For the elaboration of the images in gif format, the software ChemOffice 2016, Chemsketch, Easy GIF Animator and photoshop cs6 were used.

𝕿𝖍𝖆𝖓𝖐 𝖞𝖔𝖚 𝖋𝖔𝖗 𝖞𝖔𝖚𝖗 𝖘𝖚𝖕𝖕𝖔𝖗𝖙 @𝖚𝖕𝖒𝖊𝖜𝖍𝖆𝖑𝖊, @𝖘𝖙𝖊𝖊𝖒𝖘𝖙𝖊𝖒, @𝕿𝖍𝖊𝖗𝖎𝖘𝖎𝖓𝖌 @𝖊𝖈𝖔𝖙𝖗𝖆𝖎𝖓, @𝖈𝖚𝖗𝖆𝖓𝖌𝖊𝖑...