Serious Health Risks Associated With Grilling – Part II: Polycyclic Aromatic Hydrocarbons
Michael Garko, Ph.D.
Syndicated Host & Producer – Let’s Talk Nutrition
Some of the best moments of summer can be with family and friends at a holiday barbeque enjoying each other’s company and all of the enticing aromatic smells wafting off the grill. As wonderful as such occasions can be, there is, unbeknown to many, a serious health threat lurking in the food-scented, barbeque smoke permeating the air. How could it be that barbeque generated smoke be harmful to a person’s health?
That question and other health-related issues will be discussed in this July, 2014, issue of Health and Wellness Monthly. This is the second article in a series on the health-threatening risks associated with grilling, one of America’s most favorite methods of cooking. Specific attention will be given to polycyclic aromatic hydrocarbons (PAHs), what they are, their sources, how, other than grilling, people can become exposed to them, their health effects, factors affecting the formation of PAHs when grilling and cooking strategies to reduce the formation and health threats of PAHs.
So as not to mislead the reader by the title of the article, PAHs are not toxic chemical compounds exclusive to grilling or barbequing. It is the case that PAHs represent a widespread related collection of naturally- and humanly-created chemicals constituted of various structures and levels of toxicity (see Lah, 2011).
What Are PAHs?
PAHs constitute a group of over 100 different, ubiquitous and dangerous environmental organic pollutants created by the incomplete combustion or burning of carbon-based organic substances derived from natural and human sources such as tobacco, coal, oil, gas, wood and garbage, among other substances (see Agency for Toxic Substances and Disease Registry, 1995 & 1996). Typically, PAHs do not occur as single compounds but as complex mixtures when found in combustion end-products such as soot and smoke.
In terms of the incomplete combustion of PAHs, the lower the temperature of the fire when carbon-based organic substances are burned and the less oxygen is available, the more incomplete the burning and production of dangerous PAHs (German Federal Environmental Agency, 2012). When there is complete combustion of organic matter, carbon atoms tend not to break apart and bond with oxygen atoms, producing harmless carbon dioxide (CO2), something we exhale when we breathe (see Brown et al., n.d.; German Federal Environmental Agency, 2012).
What is the Nature of PAHs?
Given their complex chemical structure, PAHs tend not to break down so readily (taking weeks to months) and, thus, are persistent and pervasive toxins contaminating the environment, posing a real health threat to humans, other life forms (i.e., plants and animals) and the planet (see Agency for Toxic Substances and Disease Registry, 1995; Perrin, 2012).
In addition to being toxic, globally pervasive and breaking down slowly, PAHs tend to evaporate rather quickly into the atmosphere from surface soils and waters when exposed to heat, travel long distances in the air, attach or stick tightly to soil, dust, soot, smoke and sediment particles, resist dissolving easily in water and resist combustion (high melting and boiling points) or otherwise not burn easily. These different properties of PAHs come into play as they make their way into the air, water and soil of the environment and into the existence and health of people, other animals and plants. One feature of PAHs that illustrates this point is that “[t]he PAH content of plants and animals living on the land or in water can be many times higher than the content of PAHs in soil or water” (Agency for Toxic Substances and Disease Registry, 1995, p.2).
What Are the Sources of PAHs?
PAHs, as chemically-dangerous and environmentally-ubiquitous carbon-based organic compounds, are the result of naturally- and humanly-related sources.
PAHs enter into the environment via naturally occurring phenomena such as forest and grass fires, volcanic eruptions, oil seeps and degradation of organic material involving some saprophytic fungi and bacteria and chlorophyllous plants, resulting in PAHs being formed in sediments and fossil fuels (Agency for Toxic Substances and Disease Registry, 1995; German Federal Environmental Agency, 2012; Lah, 2011; Nagpal, 1993; U.S. Geological Survey, 2014).
Human sources are the major contributors of PAHs contaminating the environment and people. Industrial activities are one of the main human sources of PAHs. The activities at contaminating industrial sites often involve the production or use of fossil fuels or products derived from fossil fuels (e.g., coal tar and creosote) (Lundstedt, 2003). PAHs derived from industrial activities include the burning of fossil fuels, iron smelting, petroleum refining, gasification/liquification of fossil fuels, production of coke, carbon black, coal tar and asphalt, thermal power generation, waste incineration, tar paper production, wood treatment, wood preservation using creosote and electric power generation, among other industrial-related sources (Agency for Toxic Substances and Disease Registry, 1995; German Federal Environmental Agency, 2012; Lundstedt, 2003; Nagpal, 1993; U.S. Geological Survey, 2014).
Other human-related sources activities implicated with humans being put in contact with PAHs include toys and children products, tobacco smoke, vehicle exhaust, leaking motor oil, tire particles, crumbling asphalt, parking lot and driveway sealants, consumer products and food (i.e. contaminated crops and manufactured/processed foods containing PAHs), indoor fireplaces, grilling/barbequing, among other human-related sources (Agency for Toxic Substances and Disease Registry, 1995; Danish Ministry of the Environment, 2012; German Federal Environmental Agency, 2012; Van Metre, 2006).
What is the Reach of PAHs?
The reach of PAHs derived from natural and human sources is far and wide. PAHs are found across the planet polluting the air, water, soil and contaminating a variety of consumer goods and products, including food (i.e., crops and manufactured foods) (see Agency for Toxic Substances and Disease Registry, 1995; Blumer & Youngblood, 1975; German Federal Environmental Agency, 2012; U.S. Geological Survey, 2014).
PAHs in the Atmosphere
PAHs find their way into the environment largely as emissions released into the atmosphere from natural and human sources such as volcanic eruptions, forest and grass fires, waste incineration, residential wood burning, vehicle exhaust and industrial and refining processes, among other routes. PAHs have low vapor pressure, evaporating easily into the air from contaminated soil and surface waters. Once in the atmosphere, they can react with sunlight and other chemicals causing them to breakdown into longer-lasting by-products (see Lundstedt, 2003). PAHs also have the ability to travel fairly long distances in the atmosphere before finding their way back to the earth’s surface by way of rainfall and particulate settling. As they settle to the ground from the atmosphere, PAHs get deposited on soil, bodies of water (e.g., rivers, lakes and streams) and vegetation (Agency for Toxic Substances and Disease Registry, 1995).
PAHs in the Water
PAHs do not dissolve readily in water. Because they have an ability to adhere to surfaces, PAHs attach quite easily to sediment particles, resulting in high sediment concentrations in rivers, lakes and streams. Their ability to cohere to solid particles and settle to the bottom of rivers and lakes is one of the primary characteristics of PAHs (see Perrin, 2012; Agency for Toxic Substances and Disease Registry, 1995). Soil erosion is another way PAHs can be deposited in lakes, rivers and streams. PAHs enter surface water by way of toxic discharges from industrial facilities and waste water treatment plants. (Agency for Toxic Substances and Disease Registry, 1995; Nagpal, 1993).
PAHs in the Soil
In soil, PAHs become sorbed or otherwise strongly attached to organic matter, impeding their degradation, and thereby, causing them to remain in soil for centuries and posing a long-term contamination threat to the environment (Lundstedt, 2003). PAHs are typically released into the soil by way of hazardous industrial waste sites of one type or another. Because they cohere tightly to soil particles, they stay close to the surface of the ground. The PAHs contained in soils also contaminate underground water and any crops growing in soil contaminated with them (Agency for Toxic Substances and Disease Registry, 1995; Brown et al. n.d.; Blumer & Youngblood, 1975).
In terms of their reach into the environment, the Agency for Toxic Substances and Disease Registry (1996) has summarized what happens to PAHs once they find their way into the environment:
- PAHs enter the air mostly as releases from volcanoes, forest fires, burning coal, and automobile exhaust.
- PAHs can occur in air attached to dust particles.
- Some PAH particles can readily evaporate into the air from soil or surface waters.
- PAHs can break down by reacting with sunlight and other chemicals in the air, over a period of days to weeks.
- PAHs enter water through discharges from industrial and wastewater treatment plants.
- Most PAHs do not dissolve easily in water. They stick to solid particles and settle to the bottoms of lakes or rivers.
- Microorganisms can break down PAHs in soil or water after a period of weeks to months.
- In soils, PAHs are most likely to stick tightly to particles; certain PAHs move through soil to contaminate underground water.
- PAH contents of plants and animals may be much higher than PAH contents of soil or water in which they live (p.1).
PAHs in Consumer Goods and Products
Commercially, PAHs are found in medicines, tobacco products (e.g., smokeless tobacco), smoked food products (e.g., liquid smoke food flavorings, smoked cheeses, turkey, pork, chicken, beef, mussels and fish), dyes, protective coats, coatings and adhesives, lubricating materials, products made of rubber or plastics (e.g., tool handles, clogs, beach sandals, toys and childcare products, sports equipment, bicycle handlebars, watch straps, etc.), tattoo inks, electronic products, photographic products, pesticides, asphalt for road construction, tires, sealcoat for pavements and driveways, tar for roofing, wood preservatives and coal briquettes, among various other commercial products (see German Federal Environmental Agency, 2012; Nagpal,1993; Van Metre et al., 2006).
How do Humans Become Exposed to PAHs?
Human exposure to PAHs is nearly inevitable for a relatively large portion of the population because of their characteristics and reach. That is, they are globally pervasive and persistent, derived from a variety of natural and human sources, found in air, soil, water and consumer goods and products, generally resistant to breakdown, with high melting and boiling points and low aqueous solubility, low vapor pressure and easily cohere to particles), how they behave in the environment and relatively large constellation of natural and human sources of PAHs makes
Given that PAHs are present throughout the environment, people can become exposed to them while at home, when they go outside or while at work. Most of the time people are exposed to a mixture of PAHs and not individual PAHs.
Because PAHs exist throughout the environment, they can be found in the air, water and soil. They can exist in the air attached to dust particles or in the soil as solids or sediment. Because they are found throughout the environment, people become exposed most typically to mixtures (and not an individual PAH) of PAHs in their homes, as well as in and outside the workplace (see Agency for Toxic Substances and Disease Registry, 1995).
According to the ATSDR (1995), people are most likely to be exposed to PAHs in the environment via vapors or PAHs which are attached to dust and other particles in the air derived from cigarette smoke, vehicle exhausts, asphalt roads, coal, coal tar, wildfires, volcanoes, agricultural burning, residential wood burning, municipal and industrial waste incineration, and hazardous waste sites (ATSDR, 1995). Further environmental exposure to PAHs can occur when humans become exposed to contaminated soil found at or near hazardous waste sites (e.g., former manufactured-gas factory sites or wood-preserving facilities) and PAH-contaminated drinking water supplies (Agency for Toxic Substances and Disease Registry, 1995).
The Agency for Toxic Substances and Disease Registry (1996) summarizes the ways in which humans can become exposed to PAHs:
- Breathing air containing PAHs in the workplace of coking, coal-tar, and asphalt production plants; smokehouses; and municipal trash incineration facilities.
- Breathing air containing PAHs from cigarette smoke, wood smoke, vehicle exhausts, asphalt roads, or agricultural burn smoke.
- Coming in contact with air, water, or soil near hazardous waste sites.
- Eating grilled or charred meats; contaminated cereals, flour, bread, vegetables, fruits, meats; and processed or pickled foods.
- Drinking contaminated water or cow’s milk.
- Nursing infants of mothers living near hazardous waste sites may be exposed to PAHs through their mother’s milk (p. 1).
What Are The Health Effects and Carcinogenicity of PAHs?
It has been learned from animal studies that exposure to PAHs during pregnancy can cause future problems in reproducing, which can be passed on to offspring. Experiments have established that PAH-contaminated offspring experience higher rates of birth defects and have lower body weights. As of yet, it has not been established that these sorts of effects occur in humans.
Animal studies have also demonstrated that PAHs are associated with having harmful deleterious effects on the skin, body fluids, along with the ability to fend off disease after both short- and long-term exposure. These sorts of effects have not yet been observed in humans.
With respect to the carcinogenicity of PAHs, the Department of Health and Human Services (DHHS) has reported that certain PAHs may reasonably be expected to be carcinogens. Specifically, some individuals have developed cancer after breathing or touching mixtures of PAHs over long periods of time. Some laboratory animals have contracted lung cancer after breathing air containing PAHs, stomach cancer after ingesting PAHs contained in food and skin cancer after coming in contact with PAHs (See Agency for Toxic Substances and Disease Registry, 1996)
Based on the scientific study of PAHs, there is little ambiguity that PAHs are environmentally-ubiquitous chemical compounds that pose a clear and present danger to the health of the environment and humans. They can be found in the air, water, soil, plant life, animals (including humans and human breast milk), food-chain (e.g., cereals, grains, flour, bread, vegetables, fruits, meats, cow’s milk), home and workplace. While they are the result of natural and human sources, human sources are primarily responsible for contaminating the environment, humans and other animal and plant life on the planet.
The purpose of this article was to identify those sources and help raise awareness of PAHs in terms of their chemical nature, reach, pathways of exposure and dangerous effects. What makes PAHs so dangerous to the environment is that they can enter it from a variety of human and naturally occurring sources (e.g., volcanoes, forest fires, burning coal and automobile exhaust), evaporate easily into the air from soil or surface waters and contaminate underground water, among other environmentally destructive features mentioned above.
What makes PAHs such a threat to humans is that they can readily enter the body by breathing PAH-contaminated air from a host of human-derived sources (e.g., cigarette smoke, wood smoke, vehicle exhausts, asphalt roads or agricultural burn smoke) or coming in contact with products, including food and children’s products, containing PAHs, thereby, exposing people to potentially serious health effects, including cancer.
One of the ways by which humans become exposed to PAHs is eating grilled or charred meats or breathing the smoke from grilling. It is unrealistic to expect people to stop grilling. However, it might be prudent if those who enjoy grilling and eating grilled meats did so on a less regular basis. In the April, 2016, issue of Health and Wellness Monthly, the health risks associated with the formation of heterocyclic amines (HCAs) from grilling was featured. It was pointed out in the article that the body of evidence generated from human and non-human research on HCAs, along with the consumption of HCAs over a lifetime and genetic factors predisposing people to convert HCAs into mutagenic (DNA damaging) and cancer-causing agents suggests that people lower their exposure and potential cancer risk due to HCAs (see Garko, 2016). Recommended cooking strategies were presented in the article to minimize the creation of HCAs when cooking foods high in protein and creatine at high temperatures using the methods of grilling, along with broiling and pan frying.
Grilling exposes people to both HCAs and PAHs. It has been clearly shown in the scientific literature that HCAs and PAHs are potentially deleterious to humans. Hence, not grilling on a frequent basis should be considered to minimize the health risks associated with this method of cooking.
Agency for Toxic Substances & Disease Registry (2014). ToxFAQs™ for polycyclic aromatic hydrocarbons (PAHs). Retrieved from http://www.atsdr.cdc.gov/toxfaqs/TF.asp?id=121&tid=25.
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Garko, M.G. (2016, April). Serious health risks associated with grilling – Part I: Heterocyclic amines. Health and Wellness Monthly. Retrieved from www.letstalknutrition.com.
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Suggested Article Citation: Garko, M. G. (2016, May). Serious health risks associated with grilling – Part II: Polycyclic aromatic hydrocarbons. Health and Wellness Monthly. Retrieved (insert month, day, year), from www.letstalknutrition.com.