Exposure to Lead and its Particles Size Distribution

Transcription

1 J Occup Health 2004; 46: Case Study Exposure to Lead and its Particles Size Distribution Park DONGUK 1 and Paik NAMWON 2 1 Department of Environmental Health Korea National Open University and 2 Department of Environmental Health School of Public Health Seoul National University Korea Key words: Lead size distribution Size-selective sampling Small lead particle It has been recognized that particle size is a primary determinant of the inhalation and deposition of particulate matter in the human respiratory tract. In this regard most aerosols have dual Threshold Limit Values (TLV) such as total and respirable particulate mass in order to consider the difference in absorption due to particle size 1). It is generally accepted that measurements of airborne lead an aerosol that could have a diverse size distribution are taken by means of total mass sampling without particle size selective criteria. Although the Occupational Safety and Health Administration s Permissible Exposure Limits (OSHA PEL) promulgated in 1978 have contributed to reductions of airborne lead concentrations since their adoption workers exposure to lead in the workplace still remains a major occupational problem 1 2). Froines et al.(1986) demonstrated that OSHA PEL did not adequately take into account the effects of the size distribution of the lead aerosol on the absorption of lead 3). The OSHA model developed by Ashfold et al. 4) was based on a theoretical particle size distribution of lead aerosols as predicted in lead-acid battery manufacturing. Several previous studies had reported that the particle size distribution assumed in the OSHA model was likely found to be incorrect for not only battery plants 5) but also for primary smelter plants 3) capacitors and lead powder plants 6). If the OSHA model was to be directly applied to the actual particle-size distributions significantly lower levels of lead in the blood would be predicted for a given air lead exposure ). It is known that fine lead particle fumes generated in high temperature operations are more easily absorbed into the body than coarse lead particles. Our previous work Received Aug ; Accepted Jan Correspondence to: P. Namwon Department of Environmental Health School of Public Health Seoul National University Yeonkun-dong Jongro-ku Seoul Korea ( nwpaik@snu.ac.kr) concluded that the contribution of respirable lead particles to lead absorption would be greater than that of PbA 9). The present study is designed to compare the size characteristics of lead particles generated in four major lead industries. Our ultimate aim is to suggest that measurement of the respirable fraction of lead is necessary. The specific objectives to obtain this were: 1) to evaluate the worker s exposure to inhalable (Pb I ) thoracic (Pb T ) respirable (Pb R ) and fine lead particles smaller than 1 µm (Pb 1µ ) 2) to examine the difference between lead size fractions (Pb I ) with respect to PbA by industry and 3) to compare the relationship between PbA and fractions of lead size (Pb I Pb T ) in PbA by industry. Methods 1) Industry selection The secondary smelting lead powder and battery manufacturing industries were chosen for this study because workers exposure was known to be higher than in other industries 10). In addition the radiator manufacturing industry in which lead size distribution has not been studied was included because it has operations generating fine lead particles. 2) Air sampling and analysis Not only operations and worker s tasks but also sampling and the analytical methods in these four industries were described in our previous study 9). 3) Lead particle size distribution One hundred-seventeen personal cascade impactor samples reported in a previous study were re-analyzed by focusing on the characterization of the lead particle size fraction by industry. Pb I and fine particle 1 µm (Pb 1µ ) fractions for each impactor stage size interval were estimated from the regression equation of respective mass collection efficiencies and AD as defined by ACGIH and Hind s methods 1 10). Fine lead particles less than 1 µm (Pb 1µ ) in diameter are used in the OSHA model to determine the PEL for lead. It is assumed to be respirable and able to be deposited in the alveolar region with 37% deposition efficiency and 100% absorption efficiency 3). 4) Statistical analysis Size distribution and concentration of PbA as reported in our previous paper 9) as well as Pb I included in this study were analyzed. Statistical testing was carried out with the standard version of SPSS. Scheffe s pair-wise multiple comparison analysis was performed to identify industry groups with similar lead particle size characteristics. The t-test was performed to compare the average concentrations of Pb R by

2 226 J Occup Health Vol Table 1. MMD and exposure to Pb I by industry Industry No of Operation MMD µm Lead concentration GM (µg/m 3 ) (GSD) type sample (GSD) PbA Pb I Pb T Pb R Pb 1µ Secondary smelting Furnace 1.6 (5.0) (1.6) 645.7(1.5) (1.2) (1.2) (1.5) 6 Scrap and furnace 14.5 (1.9) (1.8) 323.6(1.9) (2.2) 97.7 (2.7) 16.6 (3.0) Subtotal 4.9 (5.0) (1.7) 457.1(1.8) (2.2) (2.8) 72.4 (5.9) Dipping 2.5 (5.6) 12.9 (1.9) 10.5(1.8) 7.1 (1.7) 5.3 (1.7) 4.5 (1.7) Soldering 1.4 (8.9) 20.4 (2.1) 17.0(2.2) 12.0 (2.2) 8.5 (2.2) 6.9 (2.2) 42 Soldering after 0.1(21.4) 25.1 (2.2) 22.4(2.2) 19.1 (2.1) 16.2 (2.2) 15.1 (2.2) leak test Subtotal 1.3 (9.6) 19.1 (2.1) 16.2(2.1) 11.5 (2.1) 8.3 (2.2) 6.9 (2.2) Casting 13.5 (1.2) (2.8) 97.7(2.8) 46.8 (2.3) 15.5 (1.8) 5.9 (1.2) Plate off-bear 16.6 (1.4) (4.1) 60.3(2.0) 25.1 (1.9) 8.9 (2.1) 10.0 (2.6) Paste 13.5 (1.4) 85.1 (2.0) 182.0(3.9) 85.1 (3.2) 26.3 (2.8) 4.6 (2.1) Encapsulation 15.1 (1.4) (2.4) 537.0(2.2) (1.9) 57.5 (1.6) 15.5 (1.6) Battery 44 Caste on strap 15.1 (1.2) (5.5) 371.5(5.4) (4.9) 42.7 (4.1) 12.3 (2.9) (COS) Soldering 13.2 (2.5) (3.2) 173.8(3.4) 81.3 (3.2) 39.8 (2.8) 32.4 (4.1) Grinding 12.3 (1.2) (1.4) (1.3) (1.3) (1.3) 40.7 (1.4) Subtotal 14.1 (1.5) (4.7) 239.9(4.7) (4.3) 33.9 (3.7) 12.0 (2.9) Reaction 14.5 (1.6) (7.2) 245.5(7.1) (7.1) 44.7 (6.0) 9.6 (6.3) Lead Cracking 12.3 (1.9) 36.3 (3.6) 26.9(3.4) 14.8 (2.6) 8.7 (2.1) 2.1 (2.4) 25 powder Packing 22.4 (2.0) (4.4) 269.2(4.1) 81.3 (2.4) 24.0 (1.7) 8.3 (3.6) Subtotal 15.1 (1.7) (6.9) 195.0(6.8) 91.2 (6.3) 33.1 (5.1) 7.9 (5.5) Total (6.3) (7.1) 89.1(6.6) 47.9 (5.7) 22.4 (4.4) 9.8 (3.6) Abbreviation: MMD=mass median diameter; GM=Geometric Mean; GSD=Geometric Standard Deviation; Pb I =Inhalable Particulate Mass; Pb T =Thoracic Particulate Mass; Pb R =Respirable Particulate Mass; Pb 1µ =particles 1 µm. industry. Simple linear regression analysis was constructed to compare the relationship between PbA and the fractions of lead size (Pb I ) by industry. Results and Discussion 1) Exposure to Lead Concentration by Size (PbA Pb I Pb T ) In all industries except for the radiator industry worker s exposure to concentrations of PbA as well as Pb I greatly exceeded 50 µg/m 3 the Korean PEL (Table 1). In particular the secondary smelting industry showed that worker s exposure to Pb 1µ was much higher than the PEL. In the battery and lead powder manufacturing industry worker s exposure to Pb I also considerably exceeded the PEL. Workers who ground lead plates in the battery plants were exposed to the highest level µg/m 3 of Pb I µg/m 3 of Pb T and µg/ m 3 of Pb R. Since the lead plate was pasted with a mixture composed of lead lead oxide and sulfuric acid most of the particles generated from the grinding operations such as polishing and buffing would be lead based which caused exposure to high lead concentrations. Secondary smelting battery and pigment manufacturing were identified by OSHA as lead industries that had a significant proportion of workers exposed to airborne lead concentrations above 100 µg/m 3 11). The geometric mean (GM) of PbA concentration (19.1 µg/m 3 ) in the radiator plants was much lower than the PEL. Since lead particles in these plants were very fine with 1.3 µm of MMD it could be estimated that PbA concentrations were low when compared to other industries. Therefore workers who are exposed to fine lead particles could be excluded from monitoring and inspection 12). 2) Size fraction of lead particle The fractions of each of Pb I relative to PbA in the battery and lead powder manufacturing industries were relatively small when compared with average fractions in the secondary smelting and radiator

3 Park DONGUK et al.: Lead Size Distribution 227 Fig. 1. Comparison of average size fractions with respect to PbA among four industries (IPM=Pb I TPM=Pb T RPM=Pb R particles 1 µm=pb 1µ ). manufacturing industries (Fig 1). In particular the average fractions of Pb R were found to be much smaller. The respirable fraction in the lead powder industry (18.9%) was a little higher than the 5 15% range that Tsai et al. reported for the same industry 6). The average of 10.9% of Pb R to PbA in battery plants was lower than the average of 34.6% (range; 28.1% 38.1%) as reported by Hwang et al. who investigated lead exposures of 96 lead battery assembly workers in Taiwan 13). Pb 1µ accounted for more than 50% of Pb R in high temperature operations such as the secondary smelting and radiator manufacturing industries. A T-test demonstrated that the concentrations of Pb R were not significantly different in the secondary smelting (p=0.2720) and radiator manufacturing industries (p=0.2394). This result indicated that fine lead particles accounted for most of the Pb R in high temperature operations such as the secondary smelting and radiator manufacturing industries. Scheffe s multiple comparison tests found that four industries were categorized into two groups with similar size characteristics as to not only mass median diameter (MMD) but also the fractions of Pb I in PbA (Table 2). One group included the secondary smelting and radiator manufacturing industries which produced larger percentages of Pb R. The other group included the battery and lead powder manufacturing industries which generated much coarser lead particles. Significant differences at the 95% confidence level were found between the two industry groups for five dependent variables related to lead particle size distribution. It would be very interesting to find the same classification for the 4 lead industries in spite of the fact that MMD and size fractions indicate their own size characteristics. Spear et al. found that the percentage of respirable fraction in terms of PbA in the blast furnace was 12.4% and in the other work sites was lower than 5.1% 7). The authors demonstrated that lead particle size distribution (i.e. % thoracic % respirable % thoracic/inhalable and % respirable/inhalable) in the sinter plant and the blast furnace operations in the lead smelter was significantly different 14). These results demonstrated that the size characteristic of lead particles such as MMD and size fraction varied not only from operation to operation within the same industry but also from industry to industry. Even in indoor environments of the seven households the dust mass and lead mass distribution as functions of particle size differed significantly 15). Like the smelter and radiator manufacturing industries we studied there are many high-risk activities associated with lead dust and fumes among bridge and structural steel workers: abrasive blasting sanding burning and cutting or welding on steel structures coated with lead paint in construction 16 20). These operations typically produce fumes with very small particle sizes and are likely to lead to great alveolar particle deposition. Levin et al. suggested that to reduce exposures to lead in construction settings blood lead determinations need to be utilized because current air monitoring does not offer sufficient information about exposure to lead 16). This suggestion is thought to be caused by the fact that workers exposure to fine lead particles might not be effectively monitored by the current PbA sampling without consideration of lead particle size. 3) Relationship between PbA and Lead size Fractions (Pb I ) by industry Lead size fractions such as Pb I were regressed against PbA respectively (Table 3). These relationships were all significant with high R 2 in the battery and lead powder industries. Thus PbA significantly accounted for the variations in Pb I Pb R concentrations in the operations which generated coarse lead particles and similar size distribution. In particular the variations in Pb 1µ concentrations significantly predicted by PbA were no less than 38% in the battery and 75% in the lead powder industries respectively. These values were much higher than those of the other industries with fine lead particles. Tsai et al. reported that the respirable lead concentration was correlated with the PbA concentration in battery and lead powder plants (R 2 =0.89) 9). Hwang et al. who studied 96 personal exposures in the battery plant found that the

4 228 J Occup Health Vol Table 2. Results of ANOVA and multiple pair-wise comparison for lead particle characteristics Dependent Independent ANOVA ANOVA variable variable F-ratio p-value Similar industry group by Sheffes significant differences (α=0.05) I II Sheffes p-value MMD Industry ndary smelting Battery Pb I /PbA % Industry ndary smelting Battery Pb T /PbA % Industry ndary smelting Battery Pb R /PbA % Industry ndary smelting Battery Pb 1µ /PbA % Industry ndary smelting Battery Abbreviation: MMD=mass median diameter; Pb I =Inhalable Particulate Mass; Pb T =Thoracic Particulate Mass; Pb R =Respirable Particulate Mass; Pb 1µ =particles 1 µm. Table 3. Simple linear regression analysis for predicting Pb I concentration by industry (Independent variable=pba) Dependent variable Coefficient ± SE Intercept ± SE R 2 p-value Secondary melting Pb I 0.76 ± ± Pb T 0.45 ± ± Pb R 0.38 ± ± Pb 1µ 0.37 ± ± Battery Pb I 0.69 ± ± Pb T 0.28 ± ± Pb R 0.07 ± ± Pb 1µ 0.01 ± ± Pb I 0.75 ± ± Pb T 0.38 ± ± Pb R 0.19 ± ± Pb 1µ 0.13 ± ± Pb I 0.76 ± ± Pb T 0.44 ± ± Pb R 0.19 ± ± Pb 1µ 0.04 ± ± Abbreviation: Pb I =Inhalable Particulate Mass; Pb T =Thoracic Particulate Mass; Pb R =Respirable Particulate Mass; Pb 1µ =particles 1 µm). plot of respirable lead against PbA levels was significant with an R 2 of 0.98 for the regression line. These results were similar to our results indicated in Table 3. By contrast in the other two industries that generated fine lead particles with distinctly different size distributions PbA significantly reflected only the variations in Pb I in the secondary smelting industry. In the radiator manufacturing industry the variation in Pb R concentrations that were accounted for by PbA were 18% and 14% which were much lower than those in the battery and lead powder industries. PbA significantly accounted for the variations in Pb I concentrations in all industries. These results indicated that controlling lead exposure according to total mass sampling methods will not necessarily provide adequate protection to workers exposed to lead with significant proportions of fine aerosol mass. Knowledge of the lead mass as a function of particle size could be critical in improving our ability

5 Park DONGUK et al.: Lead Size Distribution 229 to assess workers exposure to lead. Conclusions In summary our study concluded that the fractions each of Pb I relative to PbA varied greatly among the four industries. In high temperature operations such as secondary smelting and radiator plants the variations in fine lead particles such as Pb R predicted by the PbA concentration were either not significant or very low while they were significant in other industries with coarse lead particles. These results indicated that workers exposure to fine lead particles might not be effectively monitored by the current PbA sampling without consideration of lead particle size. The importance of the measurement of respirable fractions should be discussed to protect workers from exposure to fine lead particles generated by numerous lead operations. References 1) American Conference of Governmental Industrial Hygienists (ACGIH). Threshold Limit Values and Biological Exposure Indices. Cincinnati. OH: ACGIH ) PJ Papanek CE Ward KM Gilbert and SA Frangos: Occupational lead exposure in Los Angeles county: an occupational risk surveillance strategy. Am J Ind Med (1992) 3) JR Froines WC Liu WC Hinds and DH Wegman: Effect of aerosol size on the blood lead distribution of industrial workers. Am J Ind Med (1986) 4) Ashford NA Gecht RD Hattis DB Katz JI. The effects of OSHA medical removal protection on labor costs of selected lead industries. Cambridge. MA: Massachusetts Institute of Technology. Center for Policy Alternatives ) Hodgkins DG. The effect of lead-in-air particle size on the lead-in-blood levels of lead-acid battery workers. A dissertation submitted in partial fulfillment of the requirement for the degree of Doctor of Philosophy (Industrial Health) in the university of Michigan ) DG Hodgkins DL Hinkamp TG Robins MA Schork and WH Krebs: Influence of high past lead-in-air exposures on the lead-in-blood levels of lead-acid battery workers with continuing exposure. J Occup Med (1991) 7) DG Hodgkins TG Robins DL Hinkamp MA Schork and Krebs WH: A longitudinal study of the relation of lead in blood to lead in air concentrations among battery workers. Br. J Ind Med (1992) 8) CJ Tsai TS Shih and RN Sheu: Characteristics of lead aerosols in the different work environments. Am Ind Hyg Assoc J (1997) 9) DU Park and NW Paik: Effect on blood lead of airborne lead particles characterized by size. Ann Occup Hyg (2002) 10) Hinds WC. Chapter 3 Data Analysis In: Lodge JP and Chan TL(Ed.): Cascade Impactor Sampling and Data Analysis. American Industrial Hygiene Association Arkon OH ) JR Froines S Baron DH Wegman and S O Rourke: Characterization of the airborne concentrations of lead in U.S. Am J Ind Med (1990) 12) L Rudolph DS Sharp S Samuels C Perkins and J Rosenberg: Environmental and biological monitoring for lead exposure in California workplaces. Am J Pub Health (1990) 13) YH Hwang KY Chao CW Chang FT Hsaio HL Chang and HZ Han: Lip lead as an alternative measure for lead exposure assessment of lead battery assembly workers. Am Ind Hyg Assoc J (2000) 14) TM Spear MA Werner J Bootland E Murray G Ramachandran and J Vincent: Assessment of particle size distribution of health-relevant aerosol exposures of primary lead smelter workers. Ann Occup Hyg (1998) 15) EY Wang RD Willis TJ Buckley GG Rhoads and PJ Lioy: The relationship between the dust lead concentration and the particle sizes of household dusts collected in Jersey City residences. Appl Occup Environ Hyg (1996) 16) S Levin M Goldberg and JT Doucette: The effect of the OSHA lead exposure in construction standard on blood lead levels among iron workers employed in bridge rehabilitation. Am J Ind Med (1997) 17) Osorio AM Melius J. Lead poisoning construction. In: Construction Safety and Health. Ringer K et al (eds.). Occup Med. state of the Art Reviews 1995; 10: ) SJ Reynolds LJ Fuortes RL Garrels P Whitten and NL Sprines. Lead poisoning among construction workers renovating a previously deleaded bridge. Ame J Ind Med (1997) 19) M Goldberg SM Levine JT Doucette and G Griffin: A tak-based approach to assessing lead exposure among iron workers engaged in bridge rehabilitation. Ame J Ind Med (1997)