Human Exposure
Formaldehyde is found in outdoor and indoor air. Daily, most people take in some form and dose of formaldehyde. Formaldehyde is used to produce a wide array of products, particularly building materials. It is emitted from many sources, including power plants, cars, gas and wood stoves, and cigarettes. It is a natural product in some foods and it is naturally present in the human body as a metabolic intermediate.
Much research has been conducted on the health effects of exposure to formaldehyde (IRIS, 2011). Formaldehyde comes in contact with in large parts of society almost everyday due to its countless sources. Many governments and agencies around the world have accordingly issued a series of standards to regulate its exposure in homes, office buildings, workshops, public places, and food. (Kim et al., 2011).
Formaldehyde is an organic compound, also called methanal. It is a gas that is flammable at room temperature. Formaldehyde is also highly toxic and colorless (NIOSH, 2018). It is used for building material and household products. These include fertilizer, plywood, paper, medicines, and cosmetics (NIOSH, 2018). When a human is exposed to formaldehyde their skin, throat, lungs, and eyes can get irritated.
When exposed to the skin it can cause an irritation or even allergic dermatitis. Although many people are exposed to formaldehyde daily, it is usually in a very small amount and not intense enough to produce a reaction (Formaldehyde, 1980).
In regard to human eyes, the chemical acts as a mucous -membrane irritant to cause conjunctivitis and lacrimation (Committee on Toxicology, 1980). Eye irritation is very common among construction workers. Eye irritation is a common complaint and has been reported at airborne concentrations of 0.3–0.9 ppm in industrial workers. Severe eye irritation can develop in the range of 4–20 ppm (Committee on Toxicology, 1980).
Formaldehyde can also affect the respiratory system. This causes dryness of the nose and throat. Symptoms of this could be coughing, wheezing, and chest tightness (Committee on Toxicology, 1980). High doses of formaldehyde can also affect sense of smell. Upper airway irritation attributed to formaldehyde at 1–11 ppm occurred in employees handling nylon fabric coated with urea-formaldehyde resin (Committee on Toxicology, 1980).
Repeatedly being exposed to this chemical can cause cancer (NIOSH, 2018). Products with formaldehyde can be found in many occupational environments such as agriculture and construction. As well as among morticians and beauticians. Formaldehyde can be found in glues and resins, dyes, textiles, disinfectants, building materials, automobile parts, embalming, and laboratories (NIOSH, 2018). Workers exposed to these products can potentially be at risk.
A pregnant woman is also more at risk from exposure to formaldehyde. The human placenta has a chorionic villus (Guillaume et al., 2015). This allows the mother to exchange nutrients with the baby. Processes and other organs reliant on this exchange are sensitive to pollutants and chemicals. The human placenta can accumulate formaldehyde and eventually allow the organic compound to enter the fetal compartment (Gillaume et al., 2015).
Formaldehyde is a well-known airborne contaminant causing eye, nose, and throat irritation as well as airway irritation and slight neuropsychologic changes (Ezratty et al., 2007). It is thought that this can cause asthma in a human being. A study done by Lang et al., 2006 examined human volunteers who were exposed to formaldehyde in the workplace. The setup of the study included formaldehyde exposures and evaluation of the influence of personality factors (i.e. neuropsychological changes).Testing was conducted in 21 healthy volunteers over a 10-week period using a repeated measures design. Each subject was exposed for 4 hours to each of the 10 exposure conditions on 10 sequential working days. Measurements consisted of eye redness, blinking rate, nasal flow and resistance, pulmonary function, and reaction times. Subjective ratings of discomfort as well as the influence of personality factors on the subjective scoring were examined (Lang, et al., 2006). These factors were tested both before and after the treatment.
The results of this study indicated no significant treatment effects on nasal flow and resistance, pulmonary function, and reaction times. Blinking frequency and conjunctival redness, ranging from slight to moderate, were significantly increased by short-term peak exposures of 1.0 ppm that occurred at a baseline exposure of 0.5 ppm formaldehyde. Nasal irritation was reported at concentration levels of 0.5 ppm. Those being observed who rated their personality as ‘anxious’ tended to report complaints at a higher intensity therefore showing some indication of neuropsychological changes; not significant, but worth noting for future neuropsychological studies (Lang, et al., 2006). Overall the study signified eye irritation as the most profound factor.
Another study done by Ellenhorn et al. (1997) examined a tragic story of a 41-year-old woman who ingested 120 ml of 37% formaldehyde solution. Her original formaldehyde blood concentration was 4.8 mg/ml, but dropped quickly and remained within a range of 1-2 mg/ml over the next 15 hours; however, she suffered of hypotension, apnea, and acidosis and died. Her blood formic acid concentrations rose and fell within a range of 250-500 mg/ml. Ingestion of as little as 30 ml of 37% (approximately 2 tablespoons) formaldehyde solution has been reported to cause death in an adult. The minimum lethal exposure in men is 477 mg/kg and in women is 108 mg/kg (Ellenhorn, 1997).
Due to its triggering properties, irritating effects and potential cancer hazard status, this substance is of huge environmental health concern. Numerous studies in humans and experimental animals demonstrated that inhaled formaldehyde produced toxicity, genotoxicity, and cancer at distal sites (Costa et al., 2011).
Distribution, Biotransformation, Storage, & Elimination
Inhaled formaldehyde is absorbed primarily in the upper airways because of its high-water solubility, metabolism, and reactivity (IRIS, 2011). When formaldehyde is inhaled in the nasal cavity it first touches the mucus layer lining the epithelium. Once in the mucus layer, formaldehyde undergoes an alterable reaction with water to form methanediol, also known as formaldehyde monohydrate (IRIS, 2011). Diffusion is the dominant transport mechanism for formaldehyde through the mucus layer. Some inhaled formaldehyde passes through the mucus layer to reach the epithelium where its transformation and removal occur by enzymatic reactions with the nasal tissue and nonenzymatic reactions with glutathione and macromolecules, including proteins and DNA.
Formaldehyde is a genotoxic (DNA-reactive) chemical (IRIS, 2011). Formaldehyde-induced DNA damage is postulated to lead to mutations and clastogenesis, critical cytogenetic events in the carcinogenic mode of action. The studies of genotoxicity of formaldehyde, particularly those involving in vivo exposures of humans and animals, have provided strong evidence that formaldehyde genotoxicity occurs in the nasal mucosa and peripheral (circulating) blood lymphocytes (IRIS, 2011).
Formaldehyde is present at low levels in most living organisms. Physiological quantities of formaldehyde are endogenously formed from serine, glycine, and methionine (Liteplo 2002; IARC, 1995). The overall uptake of inhaled formaldehyde by the nasal passages at resting minute volume airflow rates has been predicted to be 76% in humans. In humans, accumulative airflow leads to a reduced percentage uptake in the nasal passages with concomitant shift of flux to postnasal areas (ATSDR, 1999a). Formaldehyde can enter your body from breathing it in, consuming it, or when it touches your skin. Formaldehyde is quickly absorbed through all those methods. After it is absorbed, formaldehyde is also very quickly broken down. Almost every tissue in the body has the capability to break down formaldehyde. It is usually converted to a non-toxic chemical called formate, which is excreted in the urine. Formaldehyde can also be altered to be made carbon dioxide and exhaled. Another form of elimination is that it also can be broken down so the body can use it to make larger molecules needed in your tissues. Formaldehyde is not stored in fat (Agency for Toxic Substances and Disease Registry ATSDR, 1999a).
The enzymatic metabolism of formaldehyde results in detoxification and is considered a defense mechanism against endogenous and exogenous levels of formaldehyde (BfR-Wissenschaft, 2006). This process is located in all tissues of the body as a product of endogenous development of formaldehyde. The formate formed by biotransformation is then rapidly removed by the supporting blood supply. Due to its ability to rapidly metabolize, storage is not a considerable factor in its toxicity. Very small amounts of formaldehyde reach the systemic circulation because it is able to metabolize so rapidly at the site of absorption. The formate is then excreted in the urine or oxidized to carbon dioxide and exhaled (Lunn et al., 2009). Formaldehyde dehydrogenase is the primary metabolic enzyme involved in the biotransformation of formaldehyde in the human body, which is also widely distributed in animal tissues – specifically the glutathione adduct of formaldehyde (ATSDR, 1999b). Several other enzymes, including nonspecific aldehyde dehydrogenase, can catalyze the oxidation reaction that results in formic acid. In addition, the unmetabolized formaldehyde can act locally, forming cross linkages between proteins, protein and single stranded DNA, or bind with tetrahydrofolate to enter intermediary metabolism (Landrigan & Etzel, 2013). Formaldehyde dehydrogenase, however, is specific to formaldehyde and remains the main enzyme responsible for biotransformation. An increase in formaldehyde exposure does not result in increased formaldehyde dehydrogenase activity therefore there is no increase in metabolism (ATSDR, 1999b).