Chromosome aberrations in peripheral lymphocytes of workers employed in the plywood industry.

Chromosome tions in peripheral lymphocytes of workers employed in the plywood industry. Scand J Work Environ Health 1993;19:132-4. Workers employed in sawmills and in the manufacture of plywood are ex posedto potentially mutagenic chemical aromatic emissions from wood. However, very little is known about the exposure to these natural wood components. In an attempt to determine whether such expo sure could have clastogenic effects, a group of 13 male nonsmoking employees mainly from the be ginning of the wood-processing line of three plywood mills and 15 matched nonsmoking referents were studied for chromosome aberrations in blood lymphocytes. A statistically significant elevation of the frequency of cells with chromatid-typebreaks (mean 2.1%), as compared with the correspond ing frequency of the referents (mean 1.0%),was observed for the lymphocytes of the wood workers. These results lend support to previous studies which suggested that wood-dryingfumes may be carci nogenic.

Workers in the plywood indu stry are expo sed to various suspected or kno wn carcinog ens ( I). In addition, co mplex uncharacterized emi ssions from mechanical wood processing have been reported to cau se coug hing, throat irrit ati on, and a slight decline in lung function (2,3).
In a Finnish case-referent study ( I), an ass ociation was found between resp iratory cancer and work in the mech anic al wood indu stry. Exposure to terp enes and oth er products from the he ating of coniferous timber was significantly associa ted with an increa sed risk of re spiratory cancer when the duration of exposure exceeded five years. In addition, exposure to pesticides and phenol see med to increase the risk. A sim ilar association had not been ob served for exposure to wood dust or form aldehyde (I, 4). Wood workers who are in contact with fresh wood are also suspected to be at an elev ated risk for chronic lymphati c leukemia, while no such relation has been found for persons working with dried wood (5) . Fum es from spruce and birch were observed to be mut ageni c in the Ames' Salmonella mammalian microsome assay, but no mutagenicity was ob ser ved with wood du sts of these speci es (6) . The se studi es suggest that compounds em itted from fres h wood or formed from it by heating may be a carcinogen ic hazard to exposed human s.
In our study, workers exposed to natur al em ission s from wood (pine, spruc e, and birch ) proce ssin g during veneer production were examined for chromosome abe rrations in their blood lymphocyte s.

Subjects and methods
Fift een male plywood workers [mean age 47 (SD 5) years ] from three factor ies in eastern Finland formed the exposed group. They had been employe d in venee r produ ction for an average of 20 (SD 7) years and were selected from non smokers wor king primarily at the beginning of the pro cess in tasks such as barking , c utting, and peeling logs (table I). Thus they were supposedly exposed to the heating products and oth er compounds emitted from wood. Five of the workers (numbers 11-15) were employed in activitie s such as loading (gluing department ), pressing, sawing, and sorting plywood, with pot ent ial exposure to glues and formaldehyde , in additio n to the em issions from wood. The exposed workers were employe d at wood processing mill s that had earlier been incl uded in a study of chemical exposure in the plywood ind ustry (7) .
The referents [mean age 47 (SD 5) yea rs ] were men who were non smokers and matched for age with the exposed workers. The y were from the same town and were empl oyed by a municipal energy plant, a loading company, or a health care center.
Before the blood sampling, all of the subjec ts filled out a que stionnaire which included qu estion s about their age , present and previous j obs, chemical exposures, diseases, hospitalizations, X-ray ex posures , recent virus infections, medi cat ion , rece nt vaccination s, alcohol cons umption, diets, and pre sent and previous smoking habits. The q uestionnaire confirmed that all of the persons studied, except one exposed worker , were nonsmokers. In the final results, the only smoker and another expose d person whose lymphocyte cultures did not yield enough metaphases for analysis were excl uded. The questionnaire revealed no other condition or exposure among the subjects that would be known to influence chromosome aberration analysis.
To minimize possible interference by culture conditions, we collected all of the blood samples and used them for the lympho cyte cultu res durin g a sin-Scand J Work Environ Health 1993. vo1 19, no 2 gle day. The venous blood samples were collected into tubes containing lithium heparin (Terumo Venoject, Leu wen, Belgium). The whole-bl ood lymphocyte cultures, two from each sample, were set up as previously described (8) and were cultivated for 48 h. The cells were harvested, fixed, put on slides , and stained as reporte d earlier (9,10). The dupl icate cultures were united at harvest. The slides were coded, and metaph ases were located with the use of automated metaphase finding (Cytoscan Cytogenetics Image Analysis System CS2, Warrington , United Kingdom). The found metaphases were recalled with  Scand J Work Environ Health 1993, vol 19, no 2 inranking set "off. " Using the Cytoscan microscope, a microscopist analyzed 100 metaphases per person for the presence of structural chromosome aberrations. The mean number of aberrant cells among the exposed and reference group s were statistically compared with the Mann-Whitney u-test (2-tailed).

Results and discussion
The workers employed in plywood production showed about a two times higher frequency of cells with chromatid-type aberrations than the referents (table I ). The difference was statistically significant (P < O.OI) . All of the excess aberrations were singlecell chromatid breaks.
An association has been shown in mechanical wood processing between increased risks for respiratory cancers and exposure to pesticides and the heating products of wood ( I) . The subjects of this study were selected mainly from the beginning of the wood-processing line where expo sure to pesticides can be estimated to be insign ificant. Therefore, the emission s from wood itself were the most likel y cause of the clastogenic effec ts observed in this study.
The fumes from wood drying consist mostly of monoterpenes ( I I) . The total concentration of airborne monoterpenes durin g veneer proce ssing has varied from 1 to 30 mg . rrr? ( I I , 12), values far below the Finni sh occupational exposure limit of turpentine (560 mg . rrr" ). The increase in aberrant cells amon g the plywood workers indicates exposure to clastogenic chemical s. These findings are interesting in light of the results of previous studies in which increa sed risk for respiratory cancers and chronic lymphatic leukemia were sugges ted to be caused by work with wood (1 , 5). In general, increa sed chromosome aberrations are interpreted as biological effects possibly associated with an elevated risk of cancer (13,14). Action should thus be taken to provide a better characterization of the agents responsible for the observed effect and, subsequently, to decrease the causative exposure.