Pyrene

Pyrene is a polycyclic aromatic hydrocarbon (PAH) that appears as a colorless or sometimes yellow crystal-like solid. 

Formed during the incomplete burning of materials like coal, oil, gas, and garbage, pyrene is part of a group of chemicals with over 100 different compounds, commonly occurring together. 

PAHs, including pyrene, are found naturally and through human activities, such as industrial processes and vehicle emissions. Humans are exposed to PAHs via air, food, water, and skin contact, especially in certain occupations. 

Pyrene is mainly used in research and the production of dyes, plastics, and pesticides. It can enter the body through inhalation, ingestion, or skin contact, but is typically excreted within days. 

While animal studies link pyrene exposure to kidney disease, liver changes, and potential blood alterations, human studies have primarily focused on its association with cancer risk.

The U.S. Environmental Protection Agency (EPA) states there isn't enough information to classify pyrene as a carcinogen.

What is Pyrene? [6.] 

Pyrene is a polycyclic aromatic hydrocarbon (PAH), a group of chemicals often found together in various combinations. There are over 100 different PAHs, but the most common are treated as a group of 15. PAHs occur naturally in the environment and can also be man-made. Pyrene appears as a colorless, crystal-like solid or sometimes yellow. It forms during the incomplete burning of products such as coal, oil, gas, and garbage.

What are Polycyclic Aromatic Hydrocarbons (PAHs) [4.]

PAHs are a group of chemicals with two or more fused benzene rings, known for their diverse physical, chemical, and toxicological properties. They are found in air, water, soil, and sediment, and are formed both naturally and through human activities, such as the incomplete burning of fossil fuels, industrial processes, and vehicle emissions.

Human Exposure to PAHs [4.]

Humans are exposed to PAHs through several routes:

Air: breathing in ambient air contaminated with PAHs from industrial emissions, vehicle exhausts, and cigarette smoke.

Food and Water: consuming food and water contaminated with PAHs from environmental sources, industrial processing, and certain cooking methods like grilling and smoking.

Occupational Exposure: working in industries like coke production, roofing, oil refining, coal gasification, and automotive services where PAHs are prevalent.

Contact: skin contact with contaminated soil, oils, coal tar, and other materials.

These exposures can occur in both occupational and non-occupational settings, making PAHs widespread environmental pollutants with potential health risks.

Uses of Pyrene [6.] 

Most PAHs, including pyrene, are used in research. Pyrene is also used in the production of dyes, plastics, and pesticides, and it is a precursor for another PAH called benzo(a)pyrene.

Exposure to Pyrene [6.] 

Pyrene can enter the body through inhalation of contaminated air, ingestion of contaminated food and water, or skin contact with contaminated soil or products like coal tar and creosote. 

It can spread throughout the body, targeting the kidneys, liver, and fat tissues, but it is typically excreted within a few days through urine and feces.

Health Effects of Pyrene [6.] 

Animal studies indicate that exposure to pyrene can cause kidney disease (nephropathy), liver changes, and slight blood alterations. 

Some PAHs have caused tumors in lab animals and reproductive issues in pregnant mice. While these effects haven't been observed in humans, exposure to PAHs is associated with cancer risk. [4., 6.] 

The U.S. Environmental Protection Agency (EPA) states that there is not enough information to classify pyrene as a carcinogen.

Signs and Symptoms of Polycyclic Aromatic Hydrocarbon (PAH) Exposure [1., 5.]

Acute Exposure

Acute Toxicity: PAHs generally have low acute toxicity in humans. [1.] 

Some symptoms reported with acute exposure include: 

• Headache

• Nausea

• Respiratory irritation

• Dermal irritation

Chronic Exposure [1., 5.] 

Some known effects of chronic exposure to PAHs include:

Pulmonary System

Chronic bronchitis, cough irritation, bronchogenic cancer.

Gastrointestinal System

Leukoplakia, buccal-pharyngeal cancer, lip cancer.

Renal System

Kidney-related issues

Dermatologic System

Dermatitis, cutaneous photosensitization, pilosebaceous reactions.

Hematopoietic System

Potential effects on blood cells (inconclusive).

Immune System

Potential suppression and dysfunction.

Reproductive and Developmental Systems

Adverse effects on reproduction and development.

Neurologic System

Possible neurological effects.

Specific Health Effects Associated with Chronic Exposure to Coal Tar and Its By-Products (PAHs): [1., 5.] 

Skin

Erythema, burns, warts on sun-exposed areas, progressing to cancer

Eyes

Irritation and photosensitivity

Respiratory System

Cough, bronchitis, bronchogenic cancer

Gastrointestinal System

Leukoplakia, buccal-pharyngeal cancer, cancer of the lip

Hematopoietic System

Leukemia (inconclusive), lymphoma

Genitourinary System

Hematuria, kidney, and bladder cancers

Testing for PAHs Including Pyrene

Direct Biological Measurement [5.] 

Direct biologic measurement of PAHs is neither cost-effective nor clinically useful. Direct measurement refers to testing directly for the parent compound (or specific PAHs exposed to), not the metabolites.

Although researchers have examined PAHs directly in the blood and tissues of experimental animals, these methods have not been widely used for human samples. The high costs of testing and limited knowledge of the significance of background levels in humans limit the clinical usefulness of such tests.

Indirect Biological Measurement

The most common tests for determining exposure to PAHs involve examining tissues, blood, and urine for the presence of metabolites.

Pyrene is commonly found in PAH mixtures, and its urinary metabolite, 1-hydroxypyrene, has been used as an indicator of exposure to PAH chemicals. [1., 5., 7.]

The ACGIH recommends measurement of 1-hydroxypyrene in the end-of-shift, end-of-work-week urine samples as a biological exposure index (BEI) for assessment of exposure to mixtures containing PAHs. This practice may help identify workplaces requiring improved industrial hygiene measures [5.]

In the Third National Report on Human Exposure to Environmental Chemicals, urinary levels of hydroxylated metabolites of PAHs were measured in a subsample of the National Health and Nutrition Examination Survey (NHANES) participants aged 6 years and older during 1999–2002. [5.] 

The geometric mean for 1-hydroxypyrene (ng/g of creatinine) for the U.S. population aged 6 years and older during 1999–2002 was 74.2, with a 95% confidence interval of (61.6–89.3). [5.]

These data provide physicians with a reference range so that they can determine whether people have been exposed to higher levels of PAHs than are found in the general population. 

As well, the data help scientists plan and conduct research on exposure to PAHs and health effects.

Laboratory Testing for Pyrene

Test Information, Sample Collection and Preparation

1-Hydroxypyrene levels, a metabolite of pyrene, are commonly tested in urine. Urine samples may be collected from the comfort of home. 

It is important to consult with the ordering provider prior to sample collection, as fasting, or adjustments in supplementation or medication use may be recommended. Do not adjust your medication dose without consulting a licensed healthcare professional. 

Interpretation of Laboratory Results

Optimal Levels of 1-Hydroxypyrene Levels

1-Hydroxypyrene is a urinary metabolite of the polyaromatic hydrocarbon pyrene.Optimal levels of urinary 1-hydroxypyrene are undetectable, or very low. 

Different studies have demonstrated different amounts of urinary 1-hydroxypyrene levels in urine. 

One study found that pre- and peri-pubertal girls in Northern California had high detection rates of urinary PAH metabolites, with exposure primarily linked to environmental tobacco smoke and grilled food consumption. [2.]  

The participants of this study did not have any apparent symptoms or illnesses associated with 1-hydroxypyrene levels. 

The geometric mean for 1-hydroxypyrene in the study sample was 74.2 ng/L, with a 95% confidence interval of 68.9–80.0 ng/L. [2., 5.] 

Clinical Significance of Elevated 1-Hydroxypyrene Levels

Elevated levels of 1-hydroxypyrene could suggest increased body burdens of PAHs, which may result in higher health risks associated with PAH exposure.

High urinary 1-hydroxypyrene levels have been strongly linked with an increased risk of cancer. PAHs are known carcinogens, and 1-hydroxypyrene serves as a proxy for overall PAH exposure.

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