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Overview and Recommendations Overview
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Overview and RecommendationsOverviewFormaldehyde (CAS No. 50-00-0) was declared a Priority Existing Chemical on 5 March 2002 in response to occupational and public health concerns. Formaldehyde occurs naturally in the atmosphere through a variety of biological and chemical processes. As a result of various metabolic processes, formaldehyde is naturally present in the human body at very low concentrations. It is also produced incidentally in the course of natural processes and human activities that involve the combustion of organic materials, such as bush fires and fuel. Formaldehyde is manufactured in Australia as aqueous solutions known as ‘formalin’, at approximately 55 000 tonnes per annum (calculated as 100% formaldehyde). Formalin and products/mixtures containing formaldehyde are also imported at approximately 90 tonnes (100% formaldehyde) per year. In addition, approximately 700 tonnes per year of paraformaldehyde (a significant source of formaldehyde) is imported. UsesThe main industrial use of formaldehyde and paraformaldehyde is for the manufacture of formaldehyde-based resins, which are widely used in a variety of industries, predominantly the wood industry. Formaldehyde is also used directly or in formulations in a number of industries including medicine-related industries (such as forensic/hospital mortuaries and pathology laboratories), embalming in funeral homes, film processing, textile treatments, leather tanning, and a wide range of personal care and consumer products. The concentrations of formaldehyde in these products range from 40%, such as in embalming and film processing solutions, to < 0.2%, such as in the majority of cosmetics and consumer products. Environmental exposure, effects and risksFormaldehyde is water soluble and biodegradable. Its major environmental release is to the atmosphere, where it breaks down in a short period of time. Direct release to the aquatic compartment and soil is expected to be minor and significant removal occurs through biodegradation. The short atmospheric lifetime of formaldehyde and worst-case predicted environmental concentrations indicate that no significant risks to non-human organisms through atmospheric exposure to formaldehyde are expected. A low environmental risk to terrestrial organisms is also predicted due to likely low concentrations of formaldehyde in aquatic systems and soil. Health effectsIn humans and experimental animals, formaldehyde is readily absorbed by all exposure routes. When inhaled, it reacts rapidly at the site of contact and is quickly metabolised in the respiratory tissue. Following acute exposure via inhalation, dermal and oral routes, formaldehyde is moderately toxic in animals. Humans experience sensory irritation (eye, nose and respiratory tract irritation) at levels in air of 0.5 ppm formaldehyde and above. Evidence clearly indicates that formaldehyde solution is a skin irritant and a strong skin sensitiser. The available human and animal data indicate gaseous formaldehyde is unlikely to induce respiratory sensitisation. Lung function tests suggest that asthmatics are no more sensitive to formaldehyde than healthy subjects. Limited evidence indicates that formaldehyde may elicit a respiratory response in some very sensitive individuals with bronchial hyperactivity, probably through irritation of the airways. No systemic toxicity was observed following repeated exposure to formaldehyde in animals and humans. Effects at the site of contact show clear dose-related histological changes (cytotoxicity and hyperplasia). A no-observed adverse-effect level (NOAEL) of 1 ppm (1.2 mg/m3) by inhalation and a NOAEL of 15 mg/kg bw/day by oral administration were identified for histopathological changes to the nasal tract and the fore- and glandular stomach in the rat, respectively. Formaldehyde is clearly genotoxic in vitro, and may be genotoxic at the site of contact in vivo. Overall, formaldehyde is considered to have weak genotoxic potential. The possible relationship between formaldehyde exposure and cancer has been studied extensively in experimental animals and humans. There is clear evidence of nasal squamous cell carcinomas from inhalation studies in the rat, but not in the mouse and hamster. Although several epidemiological studies of occupational exposure to formaldehyde have indicated an increased risk of nasopharyngeal cancers, the data are not consistent. The postulated mode of action for nasal tumours in rats is biologically plausible and considered likely to be relevant to humans. There are also concerns of an increased risk for formaldehyde-induced myeloid leukaemia, however, the data are not considered sufficient to establish a causal association. In addition, there is currently no postulated mode of action to support such an effect. NICNAS will maintain a watching brief on the issue of leukaemia and formaldehyde exposure. Based on the available nasopharyngeal cancer data, formaldehyde should be regarded as if it may be carcinogenic to humans following inhalation exposure. Formaldehyde meets the National Occupational Health and Safety Commission’s (NOHSC) Approved Criteria for Classifying Hazardous Substances (NOHSC, 2004) as a Category 2 carcinogen (Risk phrase R49, may cause cancer by inhalation). This classification should replace the current classification of Carcinogen, Category 3 (R40, limited evidence of a carcinogenic effect) in the Hazardous Substances Information System (DEWR, 2004). Other classifications that remain applicable are: toxic by inhalation, in contact with skin and if swallowed (R23/24/25), causes burns (R34), and may cause sensitisation by skin contact (R43). Based on animal and limited epidemiology data, formaldehyde is unlikely to cause reproductive and developmental effects at exposures relevant to humans. The critical health effects of formaldehyde for risk characterisation are sensory irritation, skin sensitisation and carcinogenicity. Although gaseous formaldehyde is a known eye and upper respiratory tract irritant in humans, the limitations of the available data and subjective nature of sensory irritation do not allow identification of a definitive no- observed-effect level (NOEL). The lowest-observed-effect level (LOEL) for sensory irritation in humans is 0.5 ppm. Formaldehyde solution is also a strong skin sensitiser. A 2-stage clonal growth model was developed by the Chemical Industry Institute of Toxicology (CIIT) in the United States to assess the respiratory carcinogenic risk of formaldehyde to humans. This is a biologically-based, dose-response model that incorporates mechanistic data. The model takes into account respiratory tract physiology and regional air flow in animals and humans. It is considered a more reliable estimate of cancer risk than the use of standard default assumptions, due to the incorporation of all available biological data. The table below shows key estimates of the human carcinogenic risk for public and occupational exposure (for non-smokers) using the CIIT model. Exposure Concentration Predicted Additional Respiratory Cancer Risk
1.00 ppm (1000 ppb) ≈33 in 1 million ≈50 in 1 million Public exposure and health risksFormaldehyde is naturally present in the air we breathe and in the food and water we eat and drink. In addition, a wide range of human domestic and industrial activities is responsible for both direct and indirect release of formaldehyde into the atmosphere from diffuse and point sources. The principal route of public exposure is by inhalation, via indoor and outdoor (ambient) air. The estimated environmental exposures to formaldehyde using modelling techniques indicate that the maximum annual average concentration of formaldehyde in urban air is 5.5 ppb and the maximum 24-h average is 23.5 ppb. Based on the CIIT carcinogenic risk estimates of formaldehyde to humans (see table above), the public health risk of respiratory tract cancer after repeated exposure to formaldehyde levels in ambient air is low (less than 1 in a million). The risk of sensory irritation to the public is also low based on the comparison of the NICNAS proposed ambient air standard (80 ppb, see Recommendation 17) and the estimated formaldehyde levels in ambient air. Formaldehyde concentrations in indoor air are generally higher than outdoor levels. Formaldehyde levels in established conventional homes and buildings are generally low at average levels of 15-30 ppb. However, limited monitoring data indicate that mobile homes and possibly relocatable buildings have higher levels of formaldehyde [average of 29 ppb with a range from 8 to 175 ppb in occupied caravans; average of 100 ppb with a range from 10 to 855 ppb in unoccupied caravans; average of 710 ppb with a range from 420 to 830 ppb in relocatable offices (1992 data)]. This is primarily due to the higher usage of products that emit formaldehyde in these buildings, relatively low ventilation rate and /or small internal volume, and other potential sources of formaldehyde such as from combustion of gas used in cooking and refrigeration. There is a potential risk of sensory irritation for people living in these types of buildings, but the risk of nasal cancer is estimated to be low. Due to public concern of childhood chemical exposure and cancers, together with the findings of relatively high levels of formaldehyde in mobile homes and relocatable buildings, a worst-case scenario risk estimation incorporating higher exposures during childhood has been conducted using the CIIT model. The worst-case scenario was identified to be children who live in mobile homes and spend all their schooling time in relocatable classrooms up to 17 years of age. The predicted additional risk of respiratory tract cancer for a full 80-year lifetime, including childhood exposure to formaldehyde under the worst-case scenario is low, at 0.45 in a million. The general population may also come into skin contact with formaldehyde solutions due to its use in a wide range of cosmetics and consumer products. However, the majority of the products contain formaldehyde at low concentrations (< 0.2%). Because formaldehyde solutions may induce skin sensitisation and even very low concentrations of formaldehyde in solution may elicit a dermatological reaction in individuals who have been sensitised, dermal exposure should be minimised or prevented wherever possible. Occupational exposure and health risksOccupational exposure during importation, transportation and storage of formaldehyde is limited, except in cases of accidental spills or leaks of the chemical. The principle occupational exposure route for formaldehyde is inhalation. Workers may be exposed to formaldehyde vapours during resin manufacture, product formulation, and end use. During repackaging, formulation and end use of formaldehyde products, workers are likely to be exposed by skin and eye contact during handling of formaldehyde solutions, such as in manual operations and cleaning of equipment. The risk characterisation identified concerns in a number of use scenarios based on sensory irritation. The risk of sensory irritation in embalmers and workers in medicine- related industries, such as forensic/hospital mortuaries and pathology laboratories, is high due to high concentrations of formaldehyde products handled and relative long exposure durations. The risk of sensory irritation also exists during formaldehyde and formaldehyde resin manufacture (when formaldehyde vapour replacement occurs and where there is a need to break open or enter the enclosed system), product formulation (during raw material weighing and transfer, open mixing process, and equipment cleaning and maintenance), and end use (when formaldehyde product is heated and/or in contact with high humidity, use of formaldehyde resins that contain high levels of free formaldehyde, and during certain modes of application that may generate formaldehyde vapour e.g. spraying). Skin sensitisation of workers can occur as a result of manual handling of formaldehyde products during formaldehyde and resin manufacturing, formulation, repackaging, and end uses. The likelihood of skin contact in some end use scenarios, such as spraying or brushing, is high. Because formaldehyde solutions may induce skin sensitisation and even very low concentrations of formaldehyde in solution may elicit a dermatological reaction in individuals who have been sensitised, dermal exposure should be minimised or prevented wherever possible. The CIIT carcinogenic risk estimation of formaldehyde to humans indicates that the risk for respiratory tract cancer is low (less than 1 in a million) after 40 years repeated occupational exposure to ≤0.6 ppm formaldehyde. Limited monitoring data indicate that formaldehyde levels at the majority of workplaces are < 0.2 ppm. Consequently, the occupational risks for respiratory tract cancers after repeated exposure to formaldehyde by inhalation is likely to be low. The occupational risks can be managed by a number of control measures to reduce workers’ exposure to formaldehyde, such as elimination, process improvements (e.g. use of an automated or enclosed system), effective ventilation, and proper use of personal protective equipment. The current national exposure standard is 1 ppm 8h time-weighted average (TWA) and 2 ppm short-term exposure limit (STEL). It is recommended that the occupational exposure standard be lowered to 0.3 ppm 8h TWA and 0.6 ppm STEL. This recommended standard not only provides adequate protection against discomfort of sensory irritation (the health endpoint on which the proposed standard is set), but also provides a high level of protection for cancer. 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