Study of Lead Levels in Experimental Animals Discussions Follow Ralph G . Smith, Joanne Szajnar, and Lawrence Hecker Department of Occupational and Environmental Health, Wayne State University, Detroit, Mich. 48207
A large number of rodents were maintained in chambers breathing air from a n intersection in central Detroit. A comparable group of animals were maintained in identical fashion, but breathed filtered air, and as a consequence were assumed to have inhaled no lead compounds. Tissues from animals in each of the two groups were analyzed for lead content, and although lead levels tended to be higher in the exposed group, the difference was significant only in the case of bone levels. Both rabbits and guinea pigs displayed significantly increased bone lead levels, and on the basis of the data, it was concluded that the increased levels resulted from the inhalation of approximately 2.5 pg./m.3 for a period of nearly 4 years. Estimates indicated that although the lead intake cia ingestion was considerably greater than that by inhalation, the more efficient absorption of the inhaled lead accounted for the reported difference.
A
t the conclusion of a n air pollution study in which a large number of rodents had been maintained in environments which were identical except for air pollution exposure, the surviving animals were sacrificed and frozen for subsequent trace metal analyses. The protocol of the study and principal findings have been reported elsewhere (Smith, 1968), but of concern with respect to the present study is the observed difference in the quantity of particulate matter in the air which the animals breathed. The exposed animals spent their entire lives (periods up to 4 years) breathing air typical of Detroit and similar large cities, containing on the average about 225 pg. of suspended particulate matter per m. ,3 (Table I). By contrast, the control animals, originally litter-mates of the exposed animals, spent identical lengths of time breathing air containing virtually no particulate matter, the result of filtration through prefilters and absolute filters. The animals were raised on identical diets, drank the same
Table I. Total Suspended Particulate Matter High Volume Samplers Wayne State University-Air Pollution Study Detroit, Michigan Maximum Daily Mean Loading Year
I962 1963 1964 1965 -.
~g./m.~
179 200 263 202
m/m.
818 457 502 381
water, lived in nearly isothermal identical rooms, experienced the same number of hours of light and darkness, were subjected to the same noise levels, and were tended by the same caretakers. So far as can be determined, the only variable which could influence the trace metal burdens of the animals was the inhaled particulate matter which was retained in the animals’ lungs. These animals afford a unique opportunity to study several trace metal levels in relation to urban air pollution, and a number of different analyses are being performed. This paper describes the analytical studies related to lead levels. The suspended particulate matter which was collected and analyzed throughout the several years of exposure proved to contain a small quantity of lead as expected, and values were comparable with other published data. The mean level of 2.46 ~ g . / m .based ~ , on the analysis of conventional highvolume fiber glass filter samples, was remarkably close to the mean of 2.41 pg./m3 obtained during a 3-month study in which membrane filters were employed (Table 11). All samples extended over periods of 24 hours or more, so short-term concentrations could have been substantially higher. Analysis of the fiber glass filters was performed by cutting a measured area of each filter, transferring to a borosilicate flask, and adding 5 ml. of 2 to 1 nitric-perchloric acid mixture. The samples were next heated until fumes of perchloric acid were evolved, cooled, and diluted with distilled water, then filtered and adjusted to known volume. Aliquots were analyzed by the dithizone procedure. Tissue Analyses
On the basis of previously performed analyses of lung tissue, obtained spectrographically (Elton, Szajnar, et al., 1968), tissue from exposed animals contained somewhat more lead as well as several other metals, indicating a contribution by airborne particulate matter. As noted in Table 111, however, the range of values found was great, and statistically
Weekday Weekend Total
Table 11. Air Lead Analyses March 1960-June 1966 Number of Range of Samples Values Analyzed d m . 48 O.C)0-5 .30 15 0.20-2.03 63 0.20-5 .30
Mean
Values d m . 2.67 I .57 2.46
During a special lead study conducted by the University of Michigan for the USPHS, Nov. 1, 1962-Jan. 31, 1963, the mean concentration was 2.41 p g . / m 3 During an inversion period extending from Nov. 26, 1962, to Dec. 4, 1963, a high value of 11.5 pg./m.3was found.
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A1 Ba Be Bi Cd Cr
co
Table 111. Concentrations of the Elements in Lungs of Two Exposure Groups of Animalsa Clean Air Ambient Air Range Mean Range p.p.m. ash p.p.m. ash 40-952 170.0 20-925
