Wood dust – aspiration fraction Documentation of proposed values of occupational exposure limits (OELs)
Authors: D. PAKULSKA Daria , Soćko Renata 
Published: July 2020

Wood is the raw material of the wood industry, which is used in the form of solid wood or in the processed form. Occupational exposure to wood dusts occur during processing and woodworking. The highest levels of wood dust concentrations in the work environment were recorded in the furniture and carpentry industries. The number of workers exposed to wood dust in Poland estimated during WOODEX project (2000-2003) amounted to 310 000, of which 79 000 workers were exposed to wood dust at concentrations < 0.5 mg/m3, 52 000 workers at concentrations: 0.5 ÷ 1 mg/m3, 63 000 workers at concentrations: 1 ÷ 2 mg/m3, 72 000 workers at concentrations: 2 ÷ 5 mg/m3 and 44 000 workers at concentrations > 5 mg/m3. According to data from selected sectors of the economy in Poland in the years 2001-2005, developed in collaboration with the Chief Sanitary Inspectorate at the Institute of Occupational Medicine in Łódź, the arithmetic mean value of inhaled wood dust concentrations in the wood and wood products sector (excluding furniture) was 2,08 mg/m3. This concentration was calculated on the basis of 8 602 measurements. In the case of hardwood dust, exceeded values of NDS at worksites were reported in more than 20% of the measurements, whereas in case of softwood – in less than 10% of measurements. Exposure to hardwood dust (mainly oak and beech wood) or in mixture with conifer species (softwood) is correlated with nasopharyngeal adenocarcinomas, whereas non-neoplastic respiratory symptoms, excluding asthma, are not correlated with the specific type of wood. Occupational asthma is most often the result of action of the biologically active compounds present in some wood species (both hardwood and softwood). One of the better-known species of wood and source of knowledge about occupational asthma is the dust of red cedar wood. Both dust hardwood and softwood may impair clear airway, resulting in chronic lung disease. The health effects of exposure to wood dust concern the upper or lower respiratory tract depending on the size of the wood particles. Occupational exposure to wood dust causes: chronic bronchitis, rhinitis and conjunctivitis and skin irritation, also allergic skin reactions. Spirometry has shown the reduction of the lung function index as a result of mechanical or chemical irritation of the lung tissue. It should be noted that changes in pulmonary function and the occurrence of occupational asthma was found in the woodworking industry workers, mainly employed in furniture industry (with no history of atopy) at concentrations below 1 mg / m3 of wood dust. A review of the studies in humans and in experimental animals show that wood dusts exhibit mutagenic and genotoxic effects. Analysis of DNA taken from people with cancer of the paranasal sinuses, employed in exposure to wood dusts showed mutations, mainly in the gene k-ras, which is one of the most frequently activated oncogenes in human cancers. Furthermore, h-ras mutations in adenocarcinoma patients, chromosomal aberrations in carpenter peripheral blood lymphocytes, damage to DNA strands in rats' hepatocytes, increase in micronuclear frequency in cells of mouse intestine and rats' nasal epithelium have been found. Based on results of epidemiological studies, including case-control studies showed the relationship between the incidence of the nose and paranasal sinuses cancer and the exposure to the wood dust. The risk of adenocarcinoma was a significantly higher compared to the risk of squamous cell carcinoma. The International Agency for Research on Cancer concluded that there was sufficient evidence of carcinogenicity of wood dust in humans and assigned them to Group 1 - a substances with proven carcinogenic effects in humans. The Commission of the European Union has included works related to exposure to hard and mixed wood dusts to technological processes classified as carcinogenic to humans (Directive 2004/37 / EC) and has established a BOELV value for the inhalable wood dust fraction on a level of 5 mg/m3 indicating that if there is a mixture of hardwood dust with other wood dusts then NDS refers to the total wood dust present in the mixture. SCOEL Scientific Committee resigned from the division into hard and soft wood and proposed the exposure limit value for wood dust, taking into account not only its irritating effects on upper and lower respiratory tract but also carcinogenicity (inhalable fraction: 1 mg/m3, total dust 0.5 mg/m3). The health effects of exposure to wood dust and the socio-economic conditions have alsobeen considered by the Committee on Safety and Health at Work (ACSHW), which has proposed a BOELV value for hard wood dusts of 3 mg/m3, taking into account that the lower value would result in the closure of many companies, mostly small, employing 1 to 9 employees. Establishment of the hygienic standards of wood dust is complicated by the fact that we never expose to the wood dust itself. At the same time, we are exposed to naturally occurring chemicals in wood (most of them are irritating and sensitizing). In addition, the biological fraction (bacteria, mold) found in wood dust, mainly fresh, as well as wood preservatives such as organic solvents or formaldehyde, increase the health risk. Another variable considered when assessing risk associated with exposure to wood dust is the particle size emitted during wood processing, which varies according to the type of wood and its treatment. Aerodynamic diameter of the particles is generally in the range of 10 to 30 m, which classifies them into an extra thoracic fraction (penetrating head area) or thoracic fraction (penetrating the trachea bronchial area). Percentage of respirable fraction is usually 15 ÷ 20%. When setting the NDS value for wood dusts, data from a cross-sectional survey of 161 people employed in wood dust exposure in 54 furniture companies were used. Nasal patency was examined after exposure to mixed wood dust at a low concentration (0.17 ÷ 0.74 mg/m3), mean (0.74 ÷ 1.42 mg/m3) and high (1.42 mg/m3). With regard to nasal patency before commencement of the work, exposure to medium and high concentration of wood dust significantly increased nasal congestion, reduced nasal cavity capacity and reduced nasal cross-sectional area as a result of 4-7 hours exposure. There was a statistically significant relationship between the concentration of wood dust and the nasal obstruction grade determined by the method of acoustic rhinometry and the subjective assessment. These symptoms also occurred when the dust concentrations were small, but these symptoms were not statistically significant. Furthermore, patients in the control group had significant differences in nasal passivity before commencement of work compared to the post-work period, thus undermining the observed changes at low concentrations (0.17 ÷ 0.74 mg/m3) of wood dust. Taking into account the above data as well as socioeconomic factors discussed with wood industry representatives in Poland, the Interdepartmental Commission on NDS and NDN at its 84th meeting on 4 November 2016 adopted a concentration of 3 mg/m3 for the maximum permissible concentration (NDS) for the inhalable fraction of all wood dust. Socioeconomic considerations were also taken into account in determining the BOELV value for the inhalable wood dust fraction (3 mg/m3) in the European Union. The adoption of this value without distinction for hard and soft wood is a compromise between current NDS values for wood dust with the exception of dust oak and beech (4 mg/m3) and beech and oak dust (2 mg/m3). The proposed value of NDS is at the level proposed by the European Commission for BOELV for the hard wood dust inhalable fraction (3 mg/m3), which takes into account socio-economic conditions of enterprises. Due to the fact that wood dusts have been shown to be carcinogenic, mutagenic and cause pneumoconiosis, the determination of NDSCh values is unjustified. It is proposed to mark the wood dust notation: "Carc. – category 1 carcinogen, according to the classification of the International Agency for Research on Cancer and, by reason of possible sensitization, the letter "A ".