| Abstract |
This study examined the association between respiratory disease and exposure to fungicides used to combat sap-staining moulds on softwood lumber products. A retrospective cohort study was conducted of 11,745 British Columbia sawmill workers employed in 14 mills between 1979 and 1994. Non-fatal respiratory disease was identified using provincial hospital discharge records using the respiratory disease. Exposure to fungicide was estimated as none, low and high by industrial hygienists based on observations made at the mills and interviews with senior employees. Cumulative exposure for each participant was calculated by summing the products of exposure level and duration of employment at each job held. Standardized mortality ratio analyses were conducted for fatal respiratory disease. Respiratory hospitalization rates among exposed workers were compared to unexposed workers and rates among sawmill workers were compared to the general population using Poisson regression. Nine mills used fungicides during the study period. Of the non-using mills, two processed only Western red cedar and three were located in the interior of the province. Four fungicides were commonly used in the participating mills: DDAC (didecyldimethyl ammonium chloride), IPBC (3-iodo-2-propynyl butyl carbamate), TCMTB (2[thiocyanomethylthio] benzthiazole) and borates. Relatively few workers had been exposed to the four fungicides: 553 to TCMTB, 322 to borates, 359 to IPBC, and 478 to DDAC. Record linkage to the Canadian Mortality Database identified 720 deaths between 1950 and 1995. There were 41 deaths due to respiratory disease and no evidence of an association with fungicide exposure was observed. Overall, 1,136 persons were hospitalized with a diagnosis of respiratory disease between April 1985, and July 1997, including 261 for chronic obstructive pulmonary disease (COPD) and 105 for asthma. The hospitalization rates for overall respiratory disease, COPD, and asthma in the fungicide-using mills were similar to those for the cedar mills and significantly less than those for the interior mills, which did not use fungicides. The risk of COPD was elevated among workers who had been employed for 10 or more years in all three types of mills but did not appear to increase with further duration of employment. Overall respiratory disease, COPD, and asthma did not appear to be associated with exposure to any of the fungicides, but very few COPD and asthma cases were observed among exposed workers. After adjustment for sex, age group, and region of the province, workers from all three types of sawmills had somewhat increased rates of hospitalization for respiratory disease compared to the general BC population. The rate ratios (RRs) were 1.4 for fungicide using, 1.3 for cedar, and 1.5 for interior sawmills. Hospitalization rates for COPD were also elevated for all three types of sawmills with rate ratios 1.3, 1.5, and 1.8, respectively. Asthma rates were elevated for fungicide-using (RR=2.2) and interior mills (RR=27), but no excess was observed for cedar mills (RR=0.8) In summary, this study did not find any evidence for an association between respiratory disease and DDAC, IPBC, TCMTB, and borates. This could be due to a true lack of effect, low levels of exposure, or limitations in the study's design. An elevated risk of hospitalization for overall respiratory disease and COPD was observed for all types of sawmills that could not be explained by differences in smoking rates. An increased risk of asthma was also observed for all but the cedar mills. The lack of an excess among cedar workers could be explained by good management of asthma cases, but the cause for the excess among other types of sawmill workers warrants further investigations. |
