Car-making workers 2。6 [16]

Ship engine maintenance workers (ferries)

Ship engine maintenance workers (overall)

0。45 [17]

0。24 [18]

2。2。

Sample analysis

Based on a study conducted by Simpson et al。, oil mist samples lost less than 5% of their weight while the viscosity of the involved mineral oils were greater than 18 cSt (at 40 ◦C) [21]。 In our study, the viscosity of the involved MWF for the formingprocess(115。6 cStat40 ◦C) andthreading process

  (183。7 cSt at 40 ◦C) are much greater than the above mentioned。

Therefore, we considered the loss of mass due to the evaporation could be negligible, and hence gravimetric analysis was used to determine concentrations of oil mist for all collected samples [22]。 To reduce errors associated with moisture adsorption, all filters (before and after field samplings were conducted) were conditioned prior to the weighing process by placing themin a desiccator overnight then weighed by using an electronic balance (Sartorius, Model RC210P, Goettinggen, Germany)。

2。3。Data analysis

2。3。1。Personal inhaled oil mist concentrations

In this study, the log-normality of each concentration pro- file for each exposure group was examined by using the W-test [23]。 The arithmetic mean was used to describe the average con- centration [24]。 The method of the minimum variance unbiased estimate (MVUE) was adopted to estimate the arithmetic mean (AMMVUE) and its 95% confidence interval for a log-normally distributed profile。 Full calculating procedures were described in the study conducted by Attfield and Hewet [25]。 The above method has also been recommended by the American Industrial Hygiene Association (AIHA) Exposure Assessment Strategies Committee for exposure data with various sample sizes and geometric standard deviations (GSDs) [26]。

2。3。2。Particle size distribution of oil mists for each industrial process

For each industrial process, the particle size distribution was obtained by averaging the four collected size-segregating sam- ples。 Both the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) were used to describe a particle size distribution。 Here, GSD can be estimated by cal- culating either d50%/d16% or d84%/d50%, where dn% represents the aerodynamic diameter at dae with a n% cumulative fraction for the given size distribution。

2。3。3。Oil mist concentrations to the different regions of the respiratory tract

In this study, we assumed that the oil mist size distribution found in a given workplace atmosphere was representative to that exposed to workers in the workplace。 Therefore, the ratio of the inhalable fraction, thoracic fraction and respirable fraction could be estimated by using the inhalable, thoracic, and respirable sam- pling criteria which are currently adopted by the International Standards Organization (ISO), the Comite´ Europe´en de Normal- isation (CEN), and ACGIH [27–29]。 Here, aerosols of inhalable, thoracic, and respirable fractions are defined as follows。

Inhalable aerosols: The fraction of particles that is aspirated through the nose and/or mouth during breathing。

Thoracic aerosols: The fraction of inhaled particles that passes into the lung below the larynx。

Respirable aerosols: The fraction of inhaled particles that passes down to the alveolar – or gas-exchanging region – of the lung。

Here, it should be noted that the above definitions for the inhalable fraction simply indicate the fraction of aerosols which can be inhaled into the respiratory tract, and both thoracic and respirable fractions represent aerosols which can penetrate to, as opposed to deposition in the thoracic and alveolar region errs on the side of being conservative。