Document MLJLEyM6maLpoZgxx94dJKx7

ao o l o g y [vol. 25, no. 2 onship between clinical aspects of and the lead content of blood and icd. Wchnschr., 59; 1065,1933. \n d Taeg er , II.: Quantitative of urinary lead elimination in id-poisoned individuals, by means iocarbazone, Ztschr. f. d. ges. 3:282, 1935, Lu c as , C. C.: A new method for ion of minute amounts of lead in Chem., Hi: 285, 1935. ctraethylleadpoisoning: clinical erics of nonfatal cases, J. A.M. 25. Tetraethyl lead intoxication and elated compounds of lead, J. A. 1935. f j 'j t . I \ i i \ i i $. MEASUREMENT OF I1TOUSTRIAL LEAD EXPOSURE BY ANALYSES OF BLOOD AND EXCRETA OF WORKMEN* Ja c o b Ch o l a k a n d Ka r l Ba a ib a c h From the Kettering Laboratory of Applied Physiology, College of Medicine, University of Cincinnati, Cincinnati, Ohio ARLIER papers from this laboratory have E given the occurrence of "normal" lead (1, 2, 3) and have shown the relationship precision unless atmospheric dusts are eliminated by means of an efficient dust-removal system in tbe laboratory. of the concentration of lead in the blood and ex In the case of blood specimens, it has been found creta of workmen to their lead exposure in a num necessary to employ all-stainless steel needles and ber of industries (4, 5, 6). Since the publication Pyrex glass syringes, sterilized in all-glass vessels, of these papers, similar observations have been in order to avoid frequent and serious contamina made in other industries and additional data have tion. The chief source of this contamination was been collected on some previously studied. Dur traced to the use of the generally available needles ing this period also the precision of the analytical made by pressing a steel tube into a hub of screw methods has been increased, the general methods cutting brass. The friction of the stylet against of study have been improved, and the physiological the opening in the hub frequently loosened minute background of human lead absorption and excre particles of brass which were carried by the blood tion has been explored in some detail. Therefore into the container. Other opportunities for signif the data now available may be expected to give a icant contamination occur as the result of slight clear presentation of relationships which hitherto faults in the technique of drawing and handling could be seen only in outline. blood samples, and it has been found to be a good An a l y t ic a l Me t h o d s practice to take two samples for analysis. In case of marked disagreement between the two results, As the reliability of the data depends partly the lower value is generally considered the true one upon the analytical methods employed and partly since losses of lead are of much rarer occurrence upon the manner of collecting samples, a brief dis than contaminations. If need be, additional cussion of these aspects of the work will be pre samples are obtained. sented, special attention being given to factors Several excellent analytical methods are availa which are frequently overlooked. In order to ble, but for best results that chosen should have reduce opportunities for contamination with lead general rather than specific applicability. The to a minimum, it is essential to scrutinize carefully dithizoiie (7, 8), spectrographic (9,10), and polaro- every detail of the collection and preparation of graphic (11, 12) methods that we have developed samples. In addition to the purely chemical and described have approximately equal sensi factors, the type of containers used and their tivity and precision. Two of them, the spectro chemical cleansing must be considered and also graphic and dithizone methods, have been used the care taken in the actual collection of the speci interchangeably for a number of years, while the mens. The latter should never be collected in the recent use of the polarographic method has added working areas or while the subject is in his working clothes. Contamination from factory dusts is frequently very serious; in one instance which has a further source of parallel results. The choice of any of the above methods for a particular problem is largely a matter of convenience, based come to our attention, a laboratory had to dis upon the availability of equipment and the continue urinary lead determinations because of experience and preference of the analyst, (The this factor. Indeed difficulties associated with recent statement of Fairhali and Keenan (13) dusts from almost any source are considerable and are of such importance generally as to make it impossible to carry out analytical work of high ^Received for publication August 15, 1942. A paper presented at the April, 1942 meeting of the American Industrial Hygiene Association. that "the usual diphenylthiocarbazone procedure as carried out with small samples of urine gives high results," is at variance with the experience of competent analysts employing methods described by Wilkins, Willoughby and co-workers (14, 15), Clifford and Wichman (16), Hubbard (7), and </ / fk *t- Ayf ^ J*- LS 1*43 N40753 if,-i.U 48 JOURNAL OF INDUSTRIAL HYGIENE AND TOXICOLOGY [vol. 25, no. 2 Bambach (8). Since the details of the dithizone method that yielded high results in the hands of Fairhall and ICeenan were not given, it is not posable to determine the reason for these high results.) Justification for the use of these methods inter changeably is given in Tables 1 and 2 In Table 1 are listed the findings obtained by the spectro- results obtained by this technique, following isola tion of the lead by two different methods, are compared with the spcctrographic and dithizone findings from the same samples of human tissues. When three methods, based bn entirely different principles, yield such closely concordant results, one can only conclude that the methods are specific and precise as applied. TABLE 1 Le a d De t e r min at io n s o n Co n s ec u t iv e We e k l y Bl o o d Sa mpl e s o f Tw o Su b j ec t s Ha d e b y Sp e c TROGRAPHJC (10) AND BlTHIZONE (8) METHODS KG. Pb/100 GM. SUBJECT M. R. FREQUENCIES SUBJECT E. B. FREQUENCIES Spectro graphic Dithizone Spectro graphic Dithizone 0,0250-0.0299 53 0.0300-0.0349 3 1 0 2 0.0350-0.0399 12 3 7 5 0.0400-0.0449 26 6 8 3 0.0450-0.0499 25 16 4 9 0.0500-0.0549 24 38 17 10 0,0550-0.0599 19 31 16 15 0.0600-0.0649 20 24 22 24 0.0650-0.0699 13 14 4 12 0.0700-0.0749 8 16 5 12 0.0750-0.0799 3 4 5 3 0.08000.0849 1 0 8 5 0.0850-0.0899 0 2 1 0.0900-0.0949 0 0 1 0.0950-0,0999 0 1 0.1000-0.1049 2 0 Total........ . 156 156 103 103 TABLE 2 Le a d De t e r min at io n s o n Hu ma n Tis s u e s Ma d e b y t h e Sp e c t r o g r a p h ic , Dit h iz o n e , a n d Po l a r o g r a p h ic Me t h o d s LEAD IN MILLIGRAMS PER 100 GRAMS TISSUE By Polarp- graphic Method WEICHT 0 By <12) in car. Spectro graphic Method (10) zone Method (8) Electro lytic Isola tion and Com bined Extrac tion and Concen Elec tration trolysis Spleen........... . Heart...... . . ... Suprarenal.____ Stomach............. Lung.----------... Muscle............... Thyroid............ Small intestine... Rib bone.,..,... 28.4 30,1 6.0 26,5 49.0 29.0 4,5 18.5 6,5 1.05 1.18 1.12 1.10 0,050 0.032 0.035 0.045 0.24 -- . 0.20 0.085 0,095 0.080 0.070 0.39 0.40 0.36 0.35 0.045 0.03 0.025 0.035 0.62 0.57 ,-- 0.070 0.060 0.06 0.065 16,85 17.7 17.1 18.2 Note that in most cases the aliquants employed rep resent very small quantities of material, so that the differences between the results often amounted to no more than 1 microgram. Mean............. 0.054 0.058 0.058 0.059 Probable error. 0.001 0.001 0.001 0.001 Standard de viation. ..... 0.012 0.010 0.014 0.013 Coefficient of variability... 23% 17% 25% 21% Median.______ 0.053 0.057 0.058 0,061 Mode......... 0.051 0,055 0.058 0,065 graphic and dithizone methods on duplicate weekly blood samples from two subjects under experimental study. The general .agreement be tween the two sets of results is apparent and offers convincing proof of the adequacy, not only of the analytical methods but also of the precautions taken in collecting and preparing the samples. The suitability of the polarographic method for this work may be gauged from Table 2 where Re s u l t s a n d Dis c u s s io n The interpretation of analytical results must be based upon reliable information on the concentra tions of lead in the blood and excreta of persons without any industrial lead exposure. Illustra tive data of this type are detailed in Table 3. Several groups of people of different nationalities have been studied by random sampling, and a number of individuals have been followed for long or short periods. For the sake of simplicity the probable errors and standard deviations are given only for the combined group. The mean value for the entire group has been influenced unduly by inclusion of a large number of samples from a few individuals. However, this figure is not far from that obtained in the case of random samples from a large number of individuals. The mean values DUP050058606 XICOLOGY [vol.25}no.2 * this technique, following isolaby two different methods, are e spectrographic and dithizone ?ame samples of human tissues. >ds, based on entirely different ich closely concordant results, de that the methods are specific led. TABLE 2 >ss o n Hu man Tis s u e s Ma d e b y GRAPHIC, DlTUIZONE, AND ^g r a ph ic Me t h o d s . LEAD IN MILLIGRAMS PER 100 GRAMS By Polaro- grapbic Method IGUT CM. 02) D?t&zone Method C8) Electro lytic Isola- tlonand Com bined Extrac tion and Concen Elec tration trolysis 1,4 1.05 1.18 1.12 1.10 U O.OSO 0.032 0.035 0.045 i.Q 0.24 -- -- 0.20 ..s; 0,085 0.095 0.080 0.070 ',0 0.39 0.40 0.36 0.35 .0 0.045 0.03 0.025 0,035 >5 0.62 ' 0.57 5 0.070 0.060 0.06 0.065 .5 16.85 17.7 17.1 18.2 :ases the aliquants employed repantities of material, so that the ie results often amounted to no im. s a n d Dis c u s s io n i of analytical results must be information on the concentrablood and excreta of persons rial lead exposure. IHustrav*Pe are detailed in Table 3. -Opie of different nationalities by random sampling, and a Is have been followed for long or the sake of simplicity the standard deviations are given d group. The mean value for s been influenced unduly by lumber of samples from a few cr, this figure is not far from case of random samples from ulividuals. The mean values i i \ i *\ j ti 1 I i t \ * * TABLE 3 Me a n Le ad Co n c e n t r a t io n in t h e Bl o o d , Ur in e , a n d Fe c e s , in t h e Ca s e op No r mal In d iv id u a l s a n d Gr o u p s URINE DESCRIPTION Number ofPersons or Samples Mg. Pb/L Group A Frenchmen................ ............................... ............................... Mexicans. ,....................................................................... Americans..................*............................. ..................... Germans.................................................. ............... .......... 33* 29 30 13 0.030 0.022 0.029 O.Q27 BLOOD FECES . Number of Per sons or Samples Mg./100 mb Number of Per sons or Samples Mg. Pb/24 hr. 30 0.023 30 0.027 Group B Normal Subject E. B........................... ,...................... Normal Subject M. R....................................................... Normal Subject H. t>________________..... 56 30 551 310 0.031 0.021 0,021 0.038 9 6 76 37 0.029 0.038 0.034 0.031 54 21 537 213 0.346 0.436 0.265 0.244 Combined Groups and individuals Number.........______......--------...... ............... Mean............,............... .... .....................,.................. ,.. Probable error------ -----------------------------Std. deviation............................................ 1,052 0.027 d=0.0003 <=t0.014 188 0.030 d=O.OOQ5 sfc0.009 825 0.270 0.003 dbQ.145 on individuals merely illustrate the variabiHty encountered thus far among normal persons. The origin of most of this lead in "normal" persons has been discussed in detail in previous papers (1, 2, 3). Other sources are indicated in Table 4, in which are given some of the data of an incomplete study of the composition of air and fallen soot from a number of locations in Cincin nati. These results are merely illustrative and are not necessarily representative of atmospheric environment of cities in general of even, of this community, since the range of values may shift considerably when more extensive data are available. Comparison of the results obtained on normal persons with those arrived at in industrial studies (Table 5) is particularly illuminating, since there is a definite trend toward higher concentrations of lead in the urine, feces, and blood as the severity of known exposure increases. The increase in the urinary lead is obviously much more regular than that observed in the case of feces, and it is apparent that urinary and blood findings provide better criteria of lead exposure than fecal, especially under conditions of exposure to volatile and finely divided lead compounds (fume). On the other hand, when the predominant lead exposure occurs through the inhalation of dusts, the greater portion of the lead finds its way into the feces and gives evidence of the severity of the exposure. As is illustrated by the results (Table 5), the fecal values are likely to be spotty, only those in industries definitely associated with, lead dusts showing TABLE 4 Pa r t ic u l a t e Le a d in Cin c in n a t i Air a n d To t a l Le ad in Cin c in n a t i So o t f a l l ELECTROSTATIC AIR SAMPLES (1941- ) SOOTPALL (1941-* r Mg./lO Cu.M, 0.000-0,019 0.020-0.039 0.040-0.059 0.060-0.079 0.080-0.099 0.100-0.119 0.120-0.139 0.140-0.159 0.160-0.179 0.180-0.199 0.200-0.219 0.220-0.239 0.240-0.259 0.260-0.279 Number 16 37 11 5 6 2 1 1 1 1 1 1 0 1 % Pb per Ton of Soot 0.000-0,039 0.040-0.079 0.080-0.119 0.120-0459 0.160-0.199 0.200-0.239 0.240-0.279 0.280-0.319 0.320-0.359 0.360-0.399 0.40(H).439 0.520-0.559 0.600-0.639 0.720-0,759 Number 10 14 5 7 8 6 2 .5 0 1 1 1 1 1 Total.......... 84 Total................ 62 Mean.............. 0.051 Mean....... . . 0.161 0.004 0.012 Standard devi Standard devi ation ............. 0.051 ation.............. 0.145 Coefficient of Coefficient of variability .. . 99.52% variability.... 90.06% Mean sootfall per square mile for 1932-1939 equalled 15.3 tons DUP050058607 50 JOURNAL OF INDUSTRIAL HYGIENE AND .TOXICOLOGY \vol 25, no. 2 marked elevation of the fecal'lead. In a few instances (Table 5), insufficient material was available to establish stable mean values so that the results are tentative. The blood value listed for the white-lead group may be considered to be somewhat low since the mean was calculated from findings on blood samples taken at variable inter vals after the exposure had ceased. In spite of the significant differences between the means for unexposed and exposed persons, there is an overlapping of the results. The lead, and men engaged in the manufacture of lead shot, respectively, are below 0.04 mg. lead per liter of urine. In the ease of the results on the blood of the same groups, 90%, 80%, 50%, and 18%, respectively, are found at or below 0.04 mg. per 100 g. blood, while in the case of feces, the respective percentages for the same groups are 92%, 65%, 70%, and 17% at or below 0.45 mg. lead per sample of feces.. A somewhat correspond ing range of variability can be expected to occur as the result of repeated observations on the same TABLE 5 Me an Va l u es f o e Le ad in Ur in e , Bl o o d , a n d Fe c e s o f Gr o u ps o f Pe r s o n s u n d e r Va r y in g Co n d it io n s o f Le a d Ex p o s u r e MEAN VALUES OCCUPATION Urine Feces Blood Number of Person? Mg. Pb/L or Samples Number of Persons or Samples Mg. Pb/24 hr. Number of Persons or Samples Mg. Pb/ 100 g. No occupational lead exposure ........................ . 1,052 0.027 859 0.280 188 0.030 Applying insulation........ ................. . 23 0.037 27 0.037 Garage mechanics..... ........ .............................. 654 0,050 463 0,486 145 0.039 Paint manufacture.............. ............................. 20 0.067 20 0.505 20 0.048 Soldering......... ............................. ................. 74 0.074 15 0.050 Gasoline pump repair............ ............ . <......... 17 0.074 17 0.041 Manufacture of insecticides.......................... .. 27 0.079 26 0,546 Manufacture of tetraethyl lead....................... . 762 0,093 750 0.458 136 0.045 Manufacture of lead shot.--__________ 38 0.124 38 1.421 13 0,062 Manufacture of pigments............... .............. 12 0.124 6 0,500 7 0.086 Brass foundrymen.................. ,.................. .. 60 0.161 55 0,592 Manufacture of storage batteries....--.......... 69 0.182 71 2.530 Manufacture of white lead--moderate ex posure Manufacture of white lead--severe expo sure .. 86 10 0.241 0.336 85 3.760 / 21 0.086 10 7.600 interpretation of individual findings within the overlapping range is' always a matter of doubt, but the occurrence of overlapping is not remark able, if viewed in the light of Figure 1. Here the data on large representative groups of unexposed persons and on employees in three industries are plotted so as to show the distribution percentage of each group within certain levels of concentration. The curves vary in height and shape. From the mean values and standard deviations obtained for the normal group, concentration ranges are ob tained which can be used as bases of comparison with other groups. Thus in the case of urine it is seen that 90%, 50%, 14%, and 5% of the results in the case of unexposed persons, garage mechanics, men employed in the manufacture of tetra-ethyl individual, and therefore, by means of a sufficient number of observations, any person or group can be fitted into the proper place with respect to the level of the current lead exposure. Only a small number of observations are required if the in dividual in question belongs in either the unex posed or the heavily exposed groups. The atypical character of exposure to tetraethyl lead, as contrasted with that associated with in organic lead dusts, is shown best by the fecal find ings, the percentage of values below 0.45 mg. being almost as great as in the case of persons without any industrial lead exposure. A stable mean value for the urinary lead usually serves as a satisfactory measure of the overall exposure in an established industry, but much DUP050058608 irii's:,until M OOLOGY [iol.25.no. 2 i \ ; ed in the manufacture of lead .re below 0.04 mg. lead per ie case of the results on the roups, 90%, 80%, 50%, and re found at or below 0.04 mg. rule in the case of feces, the cs for the same groups are d 17% at or below 0.45 nag. es. A somewhat correspondty can be expected to occur as :d observations on the same acps o p Pe r s o n s j '1 f Feb. tH3\ 7UVB5 res Blood Mg. Pb/24 hr. Number of Persons or Samples Mg. Pb/ 100 g. 0.280* 0.4S6 0.505 0.546 0.458 1.421 0,500 0.592 2.530 188 27 145 20 15 17 136 13 7 0.030 0.037 0.039 0.048 0.050 0.041 0.045 0.062 0.086 3.760 - 21 7.600 0.086 >re, by means of a sufficient ms, any person or group can per place with respect to the ead exposure. Only a small ions are required if the inbelongs in either the unexexposed groups, cter of exposure to tetraethyl vith that associated with inshown best by the fecal findu values below 0.45 mg. being t the case of persons without posure. ie for the urinary lead usually tore measure of the overall Wished industry, but much */ * LEAD EXPOSURE BY ANALYSES OF BLOOD AND EXCRETA 51 DUP050058609 52 JOURNAL OF INDUSTRIAL HYGIENE AND TOXICOLOGY [vol 25, no. 2 additional information may be gained by setting up the data in the form of histograms as indicated in Figure 2. The histograms recorded here char acterize the total exposure of a certain plant (Curve V), and that associated with each of a series of individual occupations within the plant (Curves IV, III, II, and I). The histogram for the entire industry is fairly regular, but there is some skew ness, which shows that several degrees of exposure are present. The composite character of this tawi j - rr . . .7f / 2 s. . y~ severe type. In Curve I, two modal groups are seen, as a clear indication that there are two universes of exposure. This may be due to two types of occupation within the group, or to the fact that some individuals were more careful in following precautions, thereby reducing the se verity of their exposure. Finally, such data, particularly the mean con centrations calculated from analytical results of periodic examinations of suitable numbers of representative workmen, can be used to detect changes in the exposure in a plant and also to compare different plants in the same industry. rT Thr anau: - rPr - J-TT 1 - - l\ JL JP m..n i a O iL -d -f *05 .10 i >IZbrtt:.20rtl, zs M9-lAD UTER OP UflINS Fig . 2. Lead exposure in an entire plant and in in dustrial occupations within the plant as demonstrated by urinary lead excretions of representative workmen. histogram is analyzed by means of the lower curves. The majority of the workmen have a relatively slight exposure, as is indicated by the close-to-normal distribution obtained for workers represented in Curves II and IV. However, other occupations in the plant are accompanied by greater exposure. (The severity of the exposure may also be affected by the personal habits of the men.) In the case of the men represented in Curve HI, the high variability is an expression of irregularly occurring exposures of a relatively Fig . 3. Comparison of lead exposure in two plants of Industry A. An example is given in Figure 3 where the mean values for lead in the urine and feces of workmen from two plants of the same type are plotted on a semi-annual basis for a number of years. The means for urinary lead in employees of plant No. 1 which has been in operation for a long time, are practically stable, at a level of 0.095 mg. per liter. On the other hand, the corresponding means for the workmen from the more recently opened plant No. 2, progressively increased for almost three years until finally the level approached that of plant No. 1, where it also may be expected to become stable. The initial mean urinary lead iMrV;rf` *$'*'?* DUP050058610 XOLOGY lvol.25;t.2 rve I, two modal groups are Jication that there are two c\ This may be due to two within the group, or to the nduals were more careful in s, thereby reducing the sc are, particularly the mean con- id from analytical results of ns of suitable numbers of men, can be used to detect >sure in a plant and also to lants in the same industry. / r/ \ ___I* ini Kin 1 - Plant No.2 ii >939 1940 1941 YEARS i of lead exposure in two plants i in Figure 3 Where the mean e urine and feces of workmen the same type are plotted on for a number of years. The id in employees of plant No. 1 ^ration for a long time, are . a level of 0.095 mg. per liter, the corresponding means for he more recently opened plant v increased for almost three the level approached that of it also may be expected to /- initial mean urinary lead Feb, 1943] LEAD EXPOSURE BY ANALYSES OF BLOOD AND EXCRETA 53 concentration of the workmen in plant No. 2 at the start of operation is somewhat Higher than that obtained for unexposed persons, in keeping with our observation that industrial employees in gen eral yield somewhat higher values than office workers. From the study of the conditions of exposure as well as the precautions observed in these plants, it can be assumed that the degree of lead exposure was about the same in both of them. Therefore, the rise in the mean concentration of lead in the urine (plant No. 2), is the result of the cumulative absorption of lead during a period of essentially constant lead exposure, while the stable maximum level is characteristic of this industry with the safeguards that have been instituted. An additional practical point of some importance is illustrated by the curve for plant No. 2, in that it may be seen that the maximum effects of occupa tional lead exposure are not reached for some time. The length of time required depends upon the type and severity of the exposure, and therefore lead determinations must be made periodically until stable mean values have been attained, if they are to reveal the maximum level. The fact that the means for fecal lead in the two plants are practically in agreement and are at a constant level only slightly above the value of 0.45 mg., the upper limit for persons without industrial lead exposure, indicates that the ex posure to lead dust is not great. Co n c l u s io n s In the case of normal persons with no occupa tional lead exposure the mean lead concentrations are found to be 0.030 mg. per 100 g. blood, 0.027 mg. per liter of urine, and 0.27 mg. per 24-hour fecal sample. Exposure to lead,in industry causes a definite increase in the mean lead concentration in these materials, in proportion to the severity of the exposure. The lead content of either the urine or the blood serves as a better criterion of lead exposure than does that of the feces. Analy tical data from large representative groups of workmen may be set up in the form of histograms in order to determine the character of the exposure in a plant and particularly to show, from the modal groups, whether the exposure is uniform in type and severity. The distribution of results and the mean values obtained over extended periods of time can be used as a measure of the uniformity and efficacy of the means employed to control the lead exposure. REFERENCES (1) Ke h o e , R. A., Th a ma n n , F., a n d Ch o l ak , J.: On the normal absorption and excretion of lead. I. Lead absorption and excretion in primitive life. II. Lead absorption and lead excretion in modern American life. HI. The sources of normal lead absorption. TV. Lead absorption and excretion in infants and chil dren, Th is j., 15: 257-306, 1933. (2) Ke h o e, R. A., Th a man n , F., a n d Ch o l ak , J.: Normal absorption and excretion of lead, J.A.M. A.,104:90,1935. (3) Ke h o e , R. A., Ch o l ak , J., a n d St o r y , R. V.: A spectrocbemical study of the normal ranges of concentration of certain trace metals in biologi cal materials, J. Nutrition, 19: 579, 1940. Editorial review. Manganese, lead, tin, aluminum, copper and silver in normal bio logical material, Ibid, 20:85,1940. (4) Ke h o e, R. A., Th a ma n n , F., a n d Ch o l ak , J.: Lead absorption and excretion in certain lead trades, Th is J., 15; 305, 1933. (5) Ke h o e, R. A., Th a man n , F., a n d Ch o l ak , J.: An appraisal of the lead hazards associated with the distribution and use of gasoline con taining tetraethyl lead. Part 1, Th is J., 10: 100, 1934. (6) Ke h o e , R. A., Th a man n , F., Aim Ch o l ak , J.: An appraisal of the lead hazards associated with the distribution and use of gasoline con taining tetraethyl lead. H. The occupational lead exposure of filling station attendants and garage mechanics, Th is J., 18:42,1935, (7) Hu bbar d , D, M.: Determination of lead: A photometric dithizone method as applied to certain biological material, Ind. Eng, Chem., Anal. Ed., 9: 493,1937, (8) Bambac h , K.: Determination of lead by dithizone: modifications and improvements of the Hubbard-Clifford-Wichmann method as ap plied to biological material, Ind. Eng. Chem., Anal. Ed,, 11:400,1939. (9) Ch o l ak , J,: Quantitative spectrographic deter mination of lead in biological material, Ind, Eng. Chem., Anal. Ed., 7: 287, 1935. (10) Ch o l ak , J., an d St o r y , R. V.: Spectrographic analysis of biological material. III. Lead, tin, aluminum, copper and silver, Ind. Eng. Chem., Anal. Ed., 10; 519, 1938. (11) Bambac h , K., an d Ch o l ak , J.: Electrolytic deposition of lead from biological material, Ind. Eng. Chem., Anal. Ed., 13:504,1941. DUP050058611 - it*.*. 54 JOURNAL OF INDUSTRIAL HYGIENE AND TOXICOLOGY [vol 25, no. 2 (12) Ch o l a k , J., a n d Bambac h , K.: Determination of lead in biological material. A polarographic method, Ind. Eng. Chem., Anal. Ed., IS: 533, 1941. (13) Fa iRh a l l , L. T., an d Ke e n a n , R. G.: A rapid method for tlie microanalysis of lead, J. Am. Chem. Soe., 63: 3076, 1941, (14) Wil k in s , E. S., Jr ., Wil l o u g h b y , C. E., Kr a eme r , E. O., a n d Smit h , F. L. 2n d : Determina tion of minute amounts of lead in biological materials: a titrimetric-extraction method, Ind. Eng. Chem., Anal. Ed., 7:33, 1935. (15) Wil l o u g h b y , C. E., Wil k in s , E. S., Jr ., an d Kr aemer , E. O.: Determination of lead, Ind. Eng. Chem. Anal. Ed., 7:285,1935. (16) Cl if f o r d , p. A., a n d Wic h ma n n , H. J.: Ditlih zone methods for the determination of lead, J. Assoe. Off. Agric. Chem., 19:130,1936. j Fr; i if ki de as tli re al 50 of h< g` sc w n d* b d s< a r s c r 1 J l i t r DUP050058612