COMPREHENSIVE EVALUATION OF LONG-TERM TRENDS IN OCCUPATIONAL EXPOSURE- PART 1 - DESCRIPTION OF THE DATABASE

Objectives-To conduct a comprehensive evaluation of long term changes in occupational exposure among a broad cross section of industries wor ldwide. Methods-A review of the scientific literature identified studi es that reported historical changes in exposure. About 700 sets of dat a from 119 published and several unpublished sources were compiled. Da ta were published over a 30 year period in 25 journals that spanned a range of disciplines. For each data set, the average exposure level wa s compiled for each period and details on the contaminant, the industr y and location, changes in the threshold limit value (TLV), as well as the type of sampling method were recorded. Spearman rank correlation coefficients were used to identify monotonic changes in exposure over time and simple linear regression analyses were used to characterise t rends in exposure. Results-About 78% of the natural log transformed da ta showed linear trends towards lower exposure levels whereas 22% indi cated increasing trends. (The Spearman rank correlation analyses produ ced a similar breakdown between exposures monotonically increasing or decreasing over time.) Although the rates of reduction for the data sh owing downward trends ranged from -1% to -62% per year, most exposures declined at rates between -4% and -14% per year (the interquartile ra nge), with a median value of -8% per year. Exposures seemed to increas e at rates that were slightly lower than those of exposures which have declined over time. Data sets that showed downward (versus upward) tr ends were influenced by several factors including type and carcinogeni city of the contaminant, type of monitoring, historical changes in the threshold limit values (TLVs), and period of sampling. Conclusions-Th is review supports the notion that occupational exposures are generall y lower today than they were years or decades ago. However, such trend s seem to have been affected by factors related to the contaminant, as well as to the period and type of sampling.