Distribution and skewness of occupational exposure sets of measurements in the Norwegian industry.

Aggregated occupational sets of exposure measurements from the Norwegian industry registered in the exposure database EXPO at The National Institute of Occupational Health, Oslo were examined with respect to distributions and skewness. Data for lead in blood show a truncated almost normal distribution because of regulations for workers with high lead in blood concentrations. The styrene, dichloromethane and acetone measurements show quasi log-normal distributions possibly because of over-representation of worst-case measurements. The other personal and stationary measurements are relatively good fitted to a log-normal model. The stationary measurements indicate generally lower mean levels than the corresponding personal measurements. The statistical parameter skewness is valuable in connection with an exposure database as a distribution test for raw data and log-transformed data.

Occupational exposure to styrene in Norway, 1972-1996.

Occupational exposure to styrene has been of special concern in Norway since the beginning of the 1970s, especially the exposure in the reinforced plastic industry. Campaigns have been carried out by the Norwegian Directorate of Labour Inspection and various measures have been set forth to reduce the workers' exposure to styrene. Alongside the campaigns, extensive monitoring programs were carried out. The measurement results are compiled in the database EXPO at the National Institute of Occupational Health (Norway). This article presents a statistical analysis of the measurement data to assess the occupational exposure to styrene in Norway since the 1970s. Results from 7,011 measurements carried out in 234 enterprises covering the period 1972-1996 are included in the database. The analyses show occupational exposure to styrene of 33.0 ppm (median) (mean: 49.4 ppm) for this period. The analyses show a decrease from a median of 62 ppm in the 1970s to 7.1 ppm in the 1990s. The analyses do not disclose any crucial impact from any single preventive measure implemented by the authorities to reduce exposure level. The reduction in the level is probably due to a contribution from different measures. The decline in the styrene exposure coincides with a similar reduction in other countries, and it may be that international concern and technical improvements in the manufacturing process have been an important factor in the exposure level reduction in the Norwegian plastic reinforced industry as well.

In vitro screening for metabolic interactions among frequently occurring binary mixtures of volatile organic chemicals in Norwegian occupational atmosphere.

Surveys of Norwegian industrial occupational atmosphere between 1983 to 1996, have identified the 12 most frequent occurring binary combinations of volatile organic chemicals. These combinations were tested in vitro for mutual inhibition or enhancement of metabolism by the head space vial equilibration technique with liver S9 obtained from in vivo untreated or pretreated (with the binary mixture) rats. The in vitro system responded to in vivo pretreatment by increasing the metabolic rate of several potentially toxic organic chemicals such as toluene, xylene, styrene, and dichloromethane. In untreated liver S9, the metabolism of several of the tested binary pairs was inhibited when coexposed in vitro to their most prevalent follower as shown for instance for ethanol (with ethyl acetate), dichloromethane (with styrene) and mutually between toluene and xylene. This inhibitory effect disappeared, however, for several of the solvents when combined with the in vivo induced liver S9, a situation which may be the most relevant for occupational exposure. It is concluded that several metabolic interactions occur between low-molecular weight volatile chemicals found in occupational air. These are both inductive and inhibitory in nature and a further mechanistic evaluation including a higher number of differentiated dosage levels, must be performed before a possible health hazard can be confirmed or rejected for the investigated combinations.