Formaldehyde exposure in work and the general.:environment Occurrence and possibilities for prevention

Formaldehyde in environment: and possibilities for Formaldehyde is extensively used for many different purposes. For this reason, serious concern has been expressed about the health hazards related to its potent irritating and sensitizing properties. Recently published information about the potential car cinogenicity of formaldehyde has generated further discussion of the potential health hazards of this compound. This article briefly reviews the health hazards of formaldehyde, the occurrence of formaldehyde in the environment, and general aspects of the prevention of existing hazards.


Irritating and sensitizing properties
Forma'ldehyde, the simplest of tJhe aldehydes, is 'chemlcally more reacti'Ve Ithan its higher homologues. It is used extensi'Vely in a wide spectrum of commercial processes.
Exposure to low atmospheric concentrations of formaLdehyde Oa1l!SBS i>rritation, especially of the eyes and respiratory tract alt concentraJUODIs abov,e 0.3 cm 3 /m 3 (0.38 mg/m 3 ). A clear dose~respoiU'se relationship has been observed (17). A conceni'l"atlion as ,low as 0.5-1 cm 3 /m 3 (0.63-1.25 mg/m 3 ) causes iniltaJtion of the mucOf\liS membT'anes in some individuals. A!bout 17 Ofo of the workers exposed to a concentration of 2 ems/m s (2.5 mg/m 3 ) experiences moderate to strong irritarfiion. A formaldehyde con- tolerated on,ly wi1lh difficulty; expooure to concentrations above this level caus,es severe difficul:ty in breathing, burning of the 'eyes, nose and 'trachea, intense l'acrimation, and severe coughing (14). Direct contact wii1Jh so'lutions, solids, or resins oonta:ilniJng free formaldehyde has been shown to c,ause bo.th inflammatory and allergic dermatitis (14). In Finland more than 100 cases of occupational eczema due to formaldehyde have been reported from 1975 to 1979.
Most of ifue cases of eczema have been allergic reactiJons. In addi'llion a few oases of OCcupaitional asthma have annually been reported in Finland. Asthmatic symptoms may be due to allergiIC sensi-tiiIvity to formaldehyde, even at low concellitrations (2). The obstructive symptoms may be of eiJther the acute or the delayed type.
Two neoplasms of the nasal turbinates were identilfied in the mice at 15 cm 3 /m 3 (18.75 mg/m 3 ) exposure levels af,ter 24 months of exposure (WD Kerns, personal c()lmmun~cation). No nasal cancers were observed among the con'troil animals.
Whi'1ethe exposure levels used in the experimental c8Jrdnogenidty studies have been higher than those whioh occur at workplaces (table 1) and Whi[e rodents, in contrClJSt to :hurnans, breaJthe through !ffue nose, the degree and site of carcinogeniciJty may be modified in humans. As an example, biS'(chloromethyl)ether causes nasal tumors in rats~9), whereas oancers of the lungs aTe found in humans (24). Quantitative hUJIIl·an riJsk assessmerut can be a'ohieved oil'ly after careful and exrtensive epidemiioilogiJC stud1es.

Formaldehyde in the work environment
Formaldehyde and its derivatives are used in numerous industria:! oper,ations involving ,the 'manu£aiCture, formu:lartion, commercial distribution, and production of a variety of products. Formaldehyde is used maittllyin phenoliJc, urea, melamine and acetal resins. These l'e&lns are utilized in llhe production of particle board, plywood, ftulation materials, adhesives, paints, t€xtiles, the coatings of papers, etc.
The IMt.1tute of Occupational Health in Finland has measured the level of airborne formaldehyde iJn occupational and nonoccupa'tionalenv,ironments during the last few yearn. The measurements have been made either as a service based on the ol'ders of employers or in conjunction with resea'l'ch projeots. Ai'r samples were collected in midg,et impingers and analyzed by the chromotl'opic add method (7). The results of the measurements of formaldehyde concentratilons are summarized in taMe 1. In Finlland the 1Jh~old limit value (TLV) ooiJmg fur rthe work environment is 2 cm 3 /m 3 (2.5 mg/m 3 ) (12).
The textile industry uses synthetk resins iJn permanent press f'abrics, in fireproofing, and in dying. The concentrat1ons of formaldehyde used are lower than 1 cms/m s (1.25 mg/m 3 ).
In the tlannin'g and shoe manufaclJu['iJng industry, Formalim® (an aqueous solution of formaldehyde) is used in finishing operations ,to gllue substances toge1Jher. It is sprayed onto the surface to be treated. The ev.apO!I"ation of formaldehyde during this operation 15 so great that the TLV for fOI1maldehyde is oiften exceeded.
Synthetd.cresirrl's with £orma'ldehyde as a componenJtare used in the manufac,turing of 'particle hoard and plywood. The most commonly used are urea-rormaldehyde, melamine-formaldehyde and phenol-£ormaldehyde resins. These resins aTe sOiluble in water and always conta.i.n a small ,amount Of free formaldehyde. Phenolic resin is nearly the only plywood adhesive used in FmIanid. Particle boaros are mainlly glued with urea resin, even When melamine~urea-fol'ma}dehyde resin is used in the manufacturing of moisture resistarut particle board. Formaldehyde does not evaporate from phenolic resins as readily as from urea and melamine resins.
For this re-ason the formaldethyde problem is more seriOU!s in the particle board in-duS/try than tn 1Jhe plywood industry.
In the proces!s of manufacturing particle board, formaldehyde is relea'sed during ,the following stages: the mixj>ng of glue, the forming stages, the hot pressin,g stage, the cooling stage. The evaporation of fo!rmaldehyde is especiaUy gl'ea:t during the hot pressing and cooling stages. The concentrations of formaldehyde measured range from 0.1 to 4.9 cm/m 3 (1.25 to 6.13 mg/m 3 (13). A great amount of formaldehyde is clhemiJcally 'bound by the curing process. NevertJheless, a small residue remains in 'the free or loosely bound starte; during 1Jhe 'course of time, this residue is relea'sed in w,arlfuouses ,and even in dwellings.
The ,release of residues of free formaldehyde resulius in 'high concentra,tions during the £1rst year or more. Due to the continuous depoJymerizaHon of formaldehydeurea resin, the release of residues decreases exponentiaJ]ly to a steady concentr<lJtion whidh is higher than th'e ,concentr,ation of 1Jhe natural !background. Grealter amounts of free formaldehyde in boards result if resins with a ,higher content of free formaldehyde are incorrectly applied or if the resins are insufficiently cured during the pressing stage.
The manufacturing of wooden furniture I1equiresa wide rang,e of adhesives, lacquers, paints, and hardeners cOJltaining formaldehyde as a component. Formaldehyde is r,eleased during the mixing, spreading, hOlt pressing and drying operations of glue application. During painting, the highest fOI1maldehyde exposure occurs during \jjhe application and drying process. The formaldehyde concentrations measured have been quite high; 18 Ofo of the measuremenits obtained exceeded the Finnish TLV of 2 em 3 /m 3 (2.5 mg/m 3 ). This valJue was exceeded in an adhesive plant during 'the manufacture of urea resins.
At present, many welding metals are painted or treated with corrosion preven-tiNes cOJlltaining synthetic resins. The product,s of ,thermal decamposirtion may eontain 'formaldehyde. Painting is also a typiJcal work operation in machine shops. Forma;ldehyde exposure may occur if~he pai'!llts used contain forma1dehyde. The formal 1 deihyc1e concentrations measured have usually been below 2 em 3 /m: l (2.5 mg/m 3 ).
In the manufacturing of elec1'rical machinery 'and apparatus, soldering and lac- quel"mg are common work operations. This industry uses a great variety of plastic produots. Many solders contain colophony resins whose pyrolysis during 1lhe solderilng operation produces formaLdehyde (3). The formaldehyde concentrations measured have been very low, below 0.1 em 3 /m 3 (0.13 mg/m 3 ). The formaldehyde concent ra'tJions measured were below 0.5 om 3 /m 3 (0.63 mg/m 3 ) during the preSJSing of melamine-fo:vma1dehyde plastics and the lacquering of transformers. The cold-setting furan resins are used in foundries as binding agents for sand, mainly in the making of oo.res. Furan binder.s contain either urea-formaldehyde or phenol-formaldehyde resins. As a voLantle co,mponent in furan resin, formaldehyde is released into the ,air of the workroom when the sand is mixed and when thecor,e boxes are filLed. According to a study of Finn1sh foundries in [1972][1973][1974][1975]38 Ofo of :the measurements obtained exceeded the TLV (23). Later measuremen.ts, im 1977-1979, based on oJ:1ders from f<>U'llddes showed somewhat lower cc>ncentrations of formaldehyde.
In the construction industry, the hig'hreslt formaldehy;de exposure was found during the :lacquering of parqu,et floors (1). In most cases, carbamide lacquer of two components was used for this purpose. Carbamide lacquer 'always contains some free fol'maldehyde, which evaporaJtes dUTing the application and drying of the lacquer. The aVe1'age concentrati·on of formaldehyde was at the level of 2 em 3 /m 3 (2.5 mg/m 3 ); 40 Ofo of the measurements exceeded the present Finnish TLV. Momentary concentrations we,re found to be many times greater than rthe average figure.
In hospitaLs, formaldehyde is used to preserve tissue specimens and as an agent of chemical sterilldzation. Momerutary form-a1dehyde conceTIJtl'a'tions stemming from autoclaves and disinfection have exceeded the VJaliJd TLV, bUit the time-weighred average 'has remained below 1 ems/m s (1.25 mg/m 3 ). Even th<:mgh particle boaI1d is a COiIIl-mOIl C·OIIlstruOtion malteri'al in offiices and schools, the f.o:vmaldehy;de problems which we have encounter·ed have occur.red only in Ithe pr·eseIlJee of other s<>Urces orr. formaldehyde. Urea-fo:vmaldehyde foam, which irs used for thermal insuJation, has caused problems along with carpet adhesive or 98 parquet lacquer. The fact that particle board has oawed iless complaints in offices and schools than in dwellings is obviously due ,to better veIliti1a1llon. Ul'ea-formaidehyde linsularlion foam may cause iong~term releas€s of fomnaldehyde. Formaldehyde evolves from earpet adhesives and lacquers on!ly during short periods ofappJicaition and drying. Evaporation for a few weeks, howev·er, is possi:ble ifth·e composition of lacquer and hardener is incorrect. The measured concentrations have ranged from 0.05 to 0.77 ·cm 3 /m 3 (0.06 to 0.96 mg/m 3 ).

Formaldehyde in nonoccupational environments
Formaldehyde commonly occurs in non-occupa1:ional environments. It i,s fo:vmed during 1Jhe :thermal decomposition. of many organic substances. The concenwation of aildcl1yde in tthe eX!haust fumes of combustion motors is usuaHy 10-30 em 3 /m 3 (12.5-37.5 mg/m 3 ). C~garette smoke contains even more fOI1IIlJaldehyde than the preViaiEng TLV ' (22). Some drugs used in the treatment of urinary infections (methenamine mantdelJate and methenamine hippurate) are metabolized in a way that fOI'maldehyde is released in the urinary traot (10).
In dwellings, formaLdehyde evaporates from 'construotion materials and :turniJtu.re. The InsUtute of Occupational Health in Finland has measul'ed the formaldehyde concentration in 65 dwellings during the last 4 a. PaI1tic1e boavd was the main soU'oce of formaldehyde in 61 dwellings, urea-formaLdehyde foam iIn 3, and the adhesive of a waH panel in 1. The highest measured concentrat~on was 0.93 em 3 /m 3 (1.16 mg/m 3 ). In F.inland, no indoor air standards for nonoccupational enIYhx>I1ments have heen set. An upper limit for f.ormaldehyde concentration -0.12 em 3 /m 3 (0.15 mg/m 3 ) -has lbeen suggeSited for the indoor home environment in Denmark (6). According 10 Da'IlJish investigatioll1S (4,5), the conceIlltmtion of formaldehyde in dweNings depends on ,the sources of formaldehyde, :the age of the buiJdiIng, verutilation, air !temperature, and ak humidity condiJtions.
The standaro proposal for minimum ven-tilaHon in dwellings put forwavd by the Nordic Commi.1ltee for Buillding Codes is 0.5 air change/h (15). In some modern dwellings today, however, it is as low as 0.1 change/h. These low ventilation rates cause an increase in indoor humidity; in periods when the sun shines through the windows of well-insulated dwellings, the hot-humid indoor environmern and the low rate of ven:ti'lation may cause high indoor concentrations of formaldehyde. 11herefore, the change in building .teohnology caused by inoreases in the cost of energy may aggravate the hazards of formaldehyde.

Control and elimination of formaldehyde hazards
Substituting a less toxic compound for toxk malberial is :jjhe classic propo,sal for reducing risk,s to workers' heaG.rtfu. Formaldehyde is an important and inexpensive chemical it-hat iJs used in many ways, and it is therefore not 'an easy task to find a substitute. However, it has been possvble to reduce the airborne forma,Mehyde concentrations, eg, in the plywood and particle board industries, by rearrang,ing ventilahon, Iby 'lliring new types of glues, and by other simi'lar methods (13).
Any process including the 'hand-ling of formaldehyde should the isolated as completely aJS possible. If total isolation is impossi!ble, then art; least the strongest sources of emission should be enclosed. Spray booths or rooms, as well as drying areas, should be equipped with exhaust systems. In ca:ses of lesser sources of formaldehyde, it is possijble to remove vapors with local exhaust ventilation. If formaldehyde evaporates from large sunEaces, general ventilati'On should be effective enough. In some ca\ses formaldehyde exposure is of short durati'On; i!t is then possible to reduce exposure by ,the use of proper respirators.
The most sertous problems in dwe'llings arise when residents move into a newly constructed 'house wirth unfinished or pOOl" quality 'partide boards. For the reduction of formaldehyde hazards in dwellings, the amount of free formaldehyde in boards must be kept as low as possible. Effective quality control of b(}ards is therefore necessary. The rate of air dhange shou1d be sUlffideIlJt. Treatment with a formalde-hyde~bsor:biJng paint can also reduce evaporation (6).