Document wD9pZBQw4VZZMxDmydqydXOLo

'*... .. -> i ........ DON'T SAV IT-WRIT* IT lwio*----- NEMOURS 7^51 .L..o.c.a..ti.o.n. .J... 'LiO'U.VIIEt:'' RS 30E17 V"^ ir^Ul^Z raeetingdXa8tnThursdaY^ ^ "hiCh Please CaXX e ,.u hav6 any addltlonal conmenta iiii^li^i*iiiiii*^isBiliSii8sM?itisWisiiiiiiiiiiiiiiiia_ i^^i * '$$$$ cc: D. R. Diggs C. F. Reinhardt MMM ..... ,,'...... D. W. Marquardt J. M, Lucas 11* ai mlllmifml M KEEP COMPANY INFORMATION UNDER LOCK AND KEY TEH 0470472 f % ARGUMENTS SUPPORTING AN- AMBIENT AIR Pb STANDARD OF 10 pg/m3 1. An Ambient Air Pb Standard of 10 pg/m3 Represents an 80/6 Reduction (i.e. Safety Factor of 5) from the Occupational Air Pb Standard An Air Pb standard of 10 pg/m3 represents approximately an 80% reduction from the occupational Air Pb standard of 200 pg/ms for 8 hours, which is equivalent to a 24-hour standard of approximately 48 pg/m3, Hence, there is a safety factor of approximately 5 associated with an air Pb standard of 10 pg/m3 (see below), Air Pb Concentration (uq/m3) On Duty (40 hrs/wk) Off Duty (128 hrs/wk) Total % Safety Exposure Reduction Factor 200 2 49 1 4-8 79 4.8 0 48 150 2 37 1 36 72 3.6 0 36 100 2 25 1 25 60 2.5 0 24- - The safety factor is defined here as the ratio of the occupational standard (24-hour equivalent) to the proposed ambient standard of 10 pg/m3 (eq 48/10=4-.8). The Current Air Pb Levels Do Not Exceed 10 u,q/m3 The first step in arriving at an air Pb standard should be to access the current situation, determine what the current air Pb levels are, and whether the current air Pb levels are producing any adverse health effects. The maximum air Pb levels observed in the US have been those measured in California. The high California air Pb levels are due in large part to the interactions of large population centers being located in basins where the mountains prohibit the air masses from moving freely,thereby forcing air pollutant concen trations to increase. A review of studies in the literature shows that the air Pb concentrations in California are generally less than 10 pg/m3 (see below and Table 1). TEH 0470473 DUP050083291 N42462.01 2 Study Seven Cities Azar et al. Azar et al. Calif Sampling Stations Site Pasadena LA Cab Drivers LA Office Workers Lennpx Date Air Pb (liq/m3) On Off Duty Duty Total 3.39 11/70 9.42 4.22 6.10 2/71 3.05 3.02 3.06 11/74 8.32 Blood Pb 17.5 24.6 19.9 The data from the California Air Sampling Stations (Table 1) indicate that the air Pb levels in California are decreasing. This decrease is due in part to the introduction of unleaded gasoline required by the cars with catalytic mufflers. The average air Pb of 6.10 pg/m3 observed for the Los Angeles Cab Drivers is the Azar et al. study and the 8,32 pg/m3 air Pb observed at Lennox in November 1974 need special comment. Both of these measurements represent air Pb levels which the general population is not exposed to. The cab drivers represent an occupationally exposed group. The average on-duty air Pb exposure of the cab drivers was 9*42 pg/m3. The average off-duty exposure was 4.22 pg/ma. The Lennox sampling station is along a freeway and is not representative of air that people would be exposed to for a 24-hour period. . 3. The Blood Pb's of the General Population are Well Within Normal Limits Ci.e. ^ 40 u.q/100 ml) ______ . Now that we have established that the ambient air Pb concentrations do not exceed 10 pg/m3 for any length of time, we can conclude that 10 pg/m3 is a good air Pb standard if we can demonstrate that no adverse health effects have been observed in the general popula tion exposed to air Pb's * 10 pg/m3. The best single measure of lead poisoning is the lead Concentration of the blood. The upper limit on the normal range of blood Pb concentrations in humans is generally accepted to be 40 pg/100 ml. The group average blood Pb's of 17.5, 24.6, and 19,9 for Pasadena, Los Angeles Cab Drivers, and Los Angeles Office Workers are, respectively, 56#, 39%, and 50# less than the upper limit of 40 pg/100 ml. These differences represent group average safety margins of approximately 2.0 (i.e, 2.3, 1.6, 2.0). The blood Pb's of the individual subjects in the general population are also less than 4o pg/100 ml. In the Azar et al. study the air Pb concentrations of the 150 subjects ranged from .22 to 9*12 pg/m3. TEH 0470474 DUP050083292 3 The Los Angeles Cab Driver with the 9.12 pg/m3 air Pb had a blood Pb of 21 pg/100 ml. ' The maximum blood Pb of the Los Angeles Cab Drivers, which was the group in the Azar et al. study with the highest average air Pb (6.10 pg/ms) , was 33 pg/100 ml. Only one of the 150 subjects had a blood Pb > 40 pg/100 ml. His high blood Pb of 53 pg/100 ml was attributed to his drinking illicit moonshine whiskey. Of the remaining 1^9 subjects, none had blood Pb's greater than 40 pg/100 ml,, and only 3 had blood Pb's greater than 35 pg/100 ml (the 3 blood Pb's were 36, 37, and 40). In the Albany Study a group of subjects were exposed to an air Pb concentration of 3.2 pg/m3 for 23 hours/day. Of the seven subjects with complete blood Pb records over the 19-week exposure period, only one subject reached a peak blood Pb level of 35 pg/100 ml. The maximum values for the 7 subjects were 26, 35, 27, 30, 25, 27, 31, and 28 pg/100 ml. The peak of the group average curve was 28 pg/100 ml. A second group of subjects was exposed to an air Pb concentration of 10.9 pg/m3 for 23 hours/day over a 12-week period. The maximum blood Pb concentration reached by any of the eight subjects with complete blood Pb records was 43 pg/100 ml. The peak levels of the individual subjects were 32, 43, 39, 40, 41, 32 , 39, and 38 pg/100 ml, respectively. The peak concentration of the group-average curve was 37 pg/100 ml. The Albany Study has been criticized because it did hot use Pb particles which were representative of auto exhaust. Several years earlier Kehoe had exposed two subjects to an air Pb concentration of 10.7 pg/ms for a 28-day period. The average blood Pb's of Subjects L.D. and J.S. were well within normal limits, being' 26.0 and 28.5 pg/100 ml, respectively. This suggests that the peak blood Pb's of 40 pg/100 ml for the group in the Albany Study exposed to an air Pb of 10,9 pg/m3 could be due in part to the lead particulate used in the study. In any event, the Kehoe experiment represents another instance in which subjects, exposed to air Pb concentrations of approximately 10 pg/m3, had blood Pb's well within normal limits. 3,1 There is a Large Analytical Variation Associated with Blood Pb Determinations ................... ................. ......... It should be noted that while 40 pg/100 ml is the upper limit of the normal range, blood Pb's in the 40-80 pg/100 ml range are generally considered acceptable and not necessarily indicative of Pb poisoning. Blood Pb's over 80 pg/100 ml are generally considered cause for alarm. The undetermined health significance of the 40-80 pg/100 ml "gray area" is easy to understand when one considers the within-subject and analytical variations associated with single blood Pb determinations. Results of the AIHA Interlaboratory Studies of blood Pb analyses indicate that the standard deviation of the within-laboratory variation associated with blood Pb analyses is 12%, To understand the significance of this large variation, consider a blood sample with a Pb content of 40 pg/100 ml. TEH 0470475 DUP050083293 4 The AIHA Interlaboratory Studies indicated that if replicate determinations were made on this blood sample in a typical laboratory, 95% of the determinations would fall between 28 and 57 pg/100 ml. 3.2 More than 85% of the Random Variation in Single Blood Pb Determinations Is Due to Within-Subject and Analytical Variations__________________ ___________________ - McLaughlin, Linch, and Snee reported a study in Which blood Pb determinations were made on a large population over a five-year period. Analysis of this study showed that more than 85% of the random variation in blood Pb determinations was due to within subject and analytical variation. The significance of the withlnsubject and analytical variations is apparent when one considers the fraction of blood Pb values > 40 pg/100 ml. A total of 217 subjects participated in the study for all five years. Over the five-year period approximately 4% of the blood Pb's of these subjects exceeded 4o pg/100 ml as shown below. McLaughlin. Linch, and Snee Longitudinal Pb Study Ye.gr No Subjects Blood Pb's > 40 u.g/100 ml Humber Percent 67 217 15 , 6.9 68 217 4 1.8 69 217 9 4.1 70 217 7 3.2 71 217 8 3.7 Total Determinations 1085 43. 4.0 (average) A study of the five-year average blood Pb for each of the 217 subjects showed that none of the subject average blood Pb's exceeded 40 pg/100 ml, only 3, of1.4%, exceed 35 pg/100 ml (35, 37, and ' 38 pg/100 ml) and an additional 8, or 3.'7%, exceeded 30 pg/lOO ml. Hence, where single determinations indicate that 4% of these subjects had blood Pb's out of normal limits, the average blood Pb's, which are.not as greatly affected by within-subject and analytical variation, indicate that all subjects were within normal limits. This should be expected, since these 217 subjects were representative of the general population and, to our knowledge, had no occupational exposure to Pb. In the Seven Cities Study blood Pb's were obtained from approxi mately 2000 women who had no known occupational Pb exposure. Only three blood Pb's in this sample were > 40`pg/100 ml. The maximum blood Pb observed was 43 pg/100 ml. TEH 0470476 DUP050083294 5 The Data in the Literature Support an Air Pb Standard of 10 uq/m9 After a review of the studies reported in the literature,' one has to conclude that (i) The air Pb levels in California are declining. (ii) The current air Pb levels, even in the most highly congested areas, are less than 10 pg/m3. (iii) A 23-hour exposure to 10.9 pg/m8 raises a subject's blood Pb to, at most, the upper limit of the normal range. (iv) An air Pb standard of 10 pg/ma would result in most areas having air Pb concentrations well below 10 pg/m3, This statement is based on the fact that only the highly congested areas have air Pb's approaching 10 pg/m3. Hence, a small fraction of the population would be exposed to, at most, 10 pg/ma for eight hours/day, five days/week. We found that the Los Angeles Cab Drivers exposed to this air Pb level had blood Pb's which were within normal limits, the maximum blood Pb concentration being 33 pg/100 ml. (v) The blood Pb levels of the general population are within normal limits. This evidence indicates that current air Pb levels are not producing any adverse health effects. Hence, an air Pb standard of 10 pg/m3, which represents a safety factor of five less than the occupational exposure TLV, is sufficient to ensure that air ' Pb concentrations will not present a health hazard. R. D. Snee 10/27/75 chm. * TEH 0470477 DUP050083295 TABLE 1 California Air Sampling Stations Maximum Monthly Air Pb Concentration Site Anaheim Azusa Bakersfield Fresno La Habra Lennox Los Angeles Pasadena Sacramento San Diego San Jose Santa Barbara Valejo I973 3.21 3.18 3.35 if. 50 2.73 14.45 6.45 4.85 1.96 4.45 2.99 1.56 2.54 I21it ' 3.76 2.72 3.32 2.17 3.67 8.32 4.85 3.18 1.26 2.72 2.17 2.63 1.96 % Change -17 -14 -1 -52 34 -42 -25 -34 --36 -39 -27 69 -23 TEH 0470478 DUP050083296