Document O1MV17mQ060yp17MOqry81ZRv

Delta-Aminolevulinic Acid and Lead in Urine of Lead Antiknock Workers Theodore R. Robinson, MD, IMD, Baton Rouge, La Delta-aminolevulinic acid (ALA) and tabolism. The elevation is thought to lead were measured In the urine ol work ers exposed to organic lead In the form of tetraethyl lead (TEL) and tetramethyl lead (TML). The levels of ALA and lead In urine were found to have a relatively low posi tive correlation of 0.52, These results are qualitatively similar to, but may be quanti tatively different from, results reported by others for persons exposed to Inorganic forms ot lead. The mechanism through result from a partial inhibition by lead of the conversion of ALA into porphobilinogen as one of the steps in the normal biosynthesis of hemoglo bin. Such an elevation is an indication of a biological response to the ab sorbed material. The usual clinical picture associated with intoxication due to inorganic which the absorbed organic lead exerts lead" is quite different from that pro Its effect on urinary ALA Is not Indicated by this study. Urinary ALA was not consid ered to be an adequate replacement for urinary lead In a program of medical monitoring of workers exposed to organic lead In the form of TEL and TML. duced by organic lead in the form of tetraethyl lead (TEL).' The biochem ical mechanisms underlying these dif ferences are not understood. The re ports that have been published concerning the effect of lead on uri nary ALA levels have dealt with ex Elevation of the delta-aminolevu linic acid (ALA) level in urine posures to inorganic forms of lead. An investigation of the possible ef has been reported to be a sensitive fects of absorption of an organic form and specific indication of increased of lead on urinary ALA levels was absorption of lead,1 a except for cer considered to be of interest. tain rare disorders of porphyrin me- Materials and Methods Submitled for publication June 25, 1973; ac cepted Oct 9. From the Medical Department, Ethyl Corpora tion, Baton Rouge, La. Reprint requests to Medical Department, Ethyi Corporation, PO Box 341, Baton Rouge, LA 70821 (Dr. Robinson). Subjects,-One hundred twenty-three men of various ages and lengths of service, all working as operators or maintenance men in an area of production of lead alkyl antiknock compounds, provided the speci mens of urine used in this study. Most of these men have a much greater relative po tential for occupational exposure to or ganic lead in the form of TEL and tet ramethyl lead (TML) than to inorganic forms of lead. Exposures must be consid- Arch Environ Health/Vol 28, March 1974 Delta-Aminolevulinic Acid/Robinson 133 EC4822 0.05 0.10 0.15 0.20 Urinary Lead, mg/liter Fig 1 --Lead and ALA levels in urine of organic lead (TEL, TML) workers. 0.25 0.30 0.35 ered to be a mixture of TEL and TML, with the relative amounts of each compo nent being variable and unknown for a given individual. The subjects were seen as part of a routine program of medical sur veillance of employees working in this area of production. None of the subjects were clinically ill and none were on any type of "deleading" therapy. Urine Specimens.~Each urine specimen consisted of a single voiding of 75 ml or more obtained at some time during the em ployee's normal working day. Most of the specimens were obtained from those work ers thought to have the greatest potential for increased absorption of organic lead, A few specimens were obtained from sub jects whose work was thought to offer rela tively little opportunity for occupational exposure to lead in any form. A small por tion (about 2 ml) of each specimen was set aside for determination of ALA concentra tion and was stored at 15 C until analysis. No measurement or adjustment of urinary pH was done prior to storage. The remain der of each specimen was used for deter mination of specific gravity and of lead concentration. Specimens with a specific gravity of less than 1.011 were not used in this study (and only seven specimens had a specific gravity of less than 1.016). A total of 268 urine specimens were analysed for both ALA and lead. Analyses.-All ALA determinations were done in the clinical laboratory of the plant medical facility, using the modification hy Davis et al' of the method of Mauzerall and Granick.* Disposable ion-exchange chroma tographic columns and reagents were ob tained commercially. Standards were run with each group of specimens analyzed. It should be recognized that the lower ("nor mal") values for urinary ALA indicated by the method used are only in part (10% to 20%) due to ALA, with the remainder pre sumably being due to a residue of amino ketones and glucosamine." However, this method has been shown to be specific for elevated values of ALA found in subjects having a disorder of porphyrin metabo lism,' ' and in subjects having excessive absorption of inorganic lead.1 All lead determinations were done by the Analytical Section of Research and De velopment Services at Ethyl Corporation's Baton Rouge, La, plant by a modification of the dithizone method of Snyder.' This method determines total lead in the urine. Results The values obtained in this study for ALA and lead in urine arc shown in Fig 1. These values are not ad justed for urine specific gravity. The expected (normal) range of each corn- 134 Arch Environ Health/Vol 28, March 1974 Delta-Aminolevulinic Acid/Robinson EC4823 3.0 2.5 E s 2.0 Cn E 1.5 3 < 1.0 wc* C D 0.5 3.0 2.5- 2 % E 1.5 3 < t CO i -0 % D 0.5 1 23456789 Time, mo Fig 2.--Trends in urinary ALA and lead levels over time in certain organic lead (TEL, TML) workers. Encircled X (subject 51) indicates large urine sample with lead level of 0.11 mg/liter. Arch Environ Health/Vol 28, March 1974 Delta-Aminolevulinic Acid/Robinson 135 EC4824 Urinary Lead, mg/liter Fig 3.--Comparison of reported urinary ALA-Lead relationships for exposures to inorganic lead with results of present study Involving organic lead (TEL, TML). ponent for persons not occupationally exposed to lead is indicated. For pur poses of calculation, the lower (nor mal) values for ALA were used as if they were due entirely to ALA. The resulting correlation coefficient is r = 0.52, with a dispersion (standard deviation) of 0.38. Similar calculations were made on values of ALA and lead, adjusted to a urine specific gravity of 1.024. No sig nificant change in the relationships (r = 0.48, SD = 0.31) between urinary ALA and urinary lead resulted. Vari ous combinations of normal and loga rithmic values, adjusted and not ad justed for specific gravity, were investigated. None of these ap proaches yielded results significantly different from the initial one. These results, coupled with the absence of any known physiological reason for making an adjustment for urine spe cific gravity for the two materials in volved (ALA and lead), led to the use of unadjusted values in this report. Fig 2 shows the urinary ALA and lead values over time for each of six workers who have been observed for a number of months. Urinary ALA and lead values are seen to vary con comitantly over time in these work ers. Of the men studied in this man ner, one (Fig 2, No. 70) shows an apparent quantitative difference from the others in his urinary ALA- lead relationships. Comment The degree of dispersion of the re sults reported here is such that no single line or curve is thought to be justified as portraying the relation ship between ALA and lead in the urine of these workers. It is not clear whether this dispersion is primarily due to innate variability of response of individuals to absorbed organic lead, to differences in the composition of the TEL-TML mixture to which in dividuals were exposed, to differences in the exposure/no-exposure time re lationships, to differences in intervals between exposure and sampling, or to 136 Arch Environ Health/Vol 28, March 1974 Delta-Aminolevulinic Acid/Robinson EC4825 other possible variable factors. Be cause of this degree of dispersion, precise quantitative comparison of these results with the results others have reported for exposures involving inorganic lead* "' cannot be made. However, comparison of such results by simple inspection (Fig 3) suggests that a given elevation of urinary lead excretion probably is associated with a lower level of urinary ALA excre tion when exposure is to organic lead (TEL, TML) than when exposure is to inorganic lead. It is not clear whether this difference might be related pri marily to differences in circumstances of exposure or to differences in me tabolism (biotransformation) of the different forms of lead to which expo sure occurred. In vitro and in vivo studies by Cremer" and in vivo studies by Bolanowska12 suggest that TEL is con verted, at least in part, in the body to triethyl lead and that this latter form of lead produces a disturbance in cen tral nervous system function similar to that observed in intoxication due to TEL. Unconfirmed results by Bolanowska indicate that triethyl lead may be excreted as such in urine and feces quite slowly and without evi dence of further degradation by the body. A portion of Bolanowska's work suggests that some part (less than 20%) of absorhed TEL may be con verted directly to inorganic lead by the body. This portion of lead presum ably would behave in a manner physi ologically the same as lead derived from inorganic lead exposures, in cluding effects on porphyrin metabo lism and urinary ALA excretion. This suggests also that the urine of per sons who have absorbed TEL contains organic as well as inorganic lead. In vivo and in vitro studies by Cremer and Callaway" suggest that TML may undergo a relatively slow conversion in the body to (the more toxic) trimethyl lead. No evidence has been reported to indicate whether or not some portion of absorbed TML might be converted directly to inor ganic lead within the body. The ex cretion product(s) of TML is (are) not known. There have been no studies re ported to indicate what effect, if any, triethyl lead or trimethyl lead per se might have on porphyrin metabolism and, hence, on urinary ALA excre tion. It is impossible at present, there fore, to assess the relative importance of TEL and TML (and possible me tabolites, triethyl lead, trimethyl lead, and inorganic lead) in producing the deviations from normal of uri nary ALA values observed in the present study. Further investigation must be done if the roles of the vari ous compounds mentioned are to be understood. An increase in urinary excretion of porphyrins has not been noted follow ing exposure to TEL,* in contrast to the elevation found following absorp tion of inorganic lead. The results of the present study suggest that por phyrin metabolism is affected at the ALA level, ie, prior to the formation of porphyrins, by absorption of one or the other (or perhaps both) of the forms of organic lead (TEL, TML) in volved in this study. Subject 70, whose urinary ALAlead relationship seems to differ from the other subjects in this study (Fig 2), works in the lead recovery (fur naces) area of the plant. His job may entail a greater potential for expo sure to inorganic lead than other job assignments in the organic lead pro duction area. This subject's urinary ALA-lead pattern is quantitatively quite similar to those reported by oth ers for workers exposed to inorganic lead.'None of the other furnace workers seen during the course of the present study exhibited a significant elevation of either urinary lead or uri nary ALA levels and thus do not fur nish information to evaluate this point more definitely. Determination of ALA in urine has been considered by some authors to be of considerable value in the rou tine monitoring of workers exposed to inorganic lead.1 The present study indicates that urinary ALA de terminations would be of uncertain value in a monitoring program where exposure is primarily to organic lead (TEL, TML). Programs of preventive medicine have been in existence for many years at facilities for the pro duction of lead antiknock compounds. These programs have relied heavily on urinary lead determinations. Long experience has shown such programs to be adequate for the prevention of overt intoxication by organic lead. Recent studies (T.R.R., unpublished data) have provided mortality and morbidity data and information on certain other health factors that strongly indicate that at least one such program has been adequate over a period of 20 or more years to pre vent any detectable significant ad verse effects on health. Programs of such proven effectiveness should be significantly altered only for compel ling reasons. As can be seen in the group results (Fig 1) and in results for individuals (Fig 2, subjects 51 and 101), levels of urinary lead shown by long experi ence in the above programs to indi cate the desirability for reduction in continued occupational exposure to lead (ie, a consistent urinary lead level of 0.18 mg/liter or more) may be associated with levels of urinary ALA that are within normal limits. It can not categorically be denied that nor mal urinary ALA levels in such in stances might be an indication that an adequate safety margin still exists for the individual, but there is no ob vious reason to presume this to be the case. It appears very unlikely that this (relatively mild) response of the hemopoietic system would be related in any direct manner to the CNS dys function that is characteristic of in toxication by organic lead (TEL, TML). Due to the serious nature of such intoxication, workers should not be allowed to continue exposures that produce urinary lead values in excess of the established guidelines for the purpose of testing such a possibility. For the present, then, the determina tion of lead in urine must continue to be considered as the most useful labo ratory tool in the routine medical sur veillance (monitoring) of workers who have a potential for exposure to organic lead in the form of TEL and TML. The clinical implication, if any, of an elevation of urinary ALA level is not known at the present time. It does not appear per se to indicate the existence of a disease state. In order Arch Environ Health/Vol 28, March 1974 Delta-Aminolevulinic Acid/Robinson 137 EC4826 to help clarify this matter, and as a relatively early objective indication of a response to increased absorption of (organic or inorganic) lead, consid eration should be given to the inclu sion of urinary ALA determinations as a part of the continuing medical surveillance necessary to protect the health of workers who have a poten tial exposure to lead in any form. In formation obtained thereby should be of value in long-term clinical and epidemiological studies and may be useful in the evaluation of such addi tional indicators of biological re sponse as may be developed in the fu ture. In summary, the present study shows that absorption of organic lead in the form of TEL and TML, as indi cated by increased urinary lead levels, is associated with an increase in uri nary ALA levels. The mechanism through which this effect is produced is not revealed by this study. Urinary ALA determinations should be con sidered for inclusion in any program of medical monitoring of organic or inorganic lead workers in order to clarify the clinical significance of this biological response to lead absorption. Urinary lead determinations continue to be the primary laboratory tool in the medical monitoring of workers having a potential for exposure to or ganic lead in the forms of TEL and TML. References 1. Hmger-Aronsen B: Studies on urinary ex cretion of S-aminolaevulic acid and other haem precursors in lead workers and lead-intoxicated rabbits. Scan J Clin Lab Invent 12(suppl 47): 1128, 1960. 2. Chisolm JJ Jr Disturbances in the biosyn thesis of heme in lead intoxication. J Pediatr 64:174-187, 1964. 3. Johnstone RT: Clinical inorganic lead intox ication. Arch Environ Health 8:250-255, 1964. 4. Sanders LW: Tetraethyllead Intoxication. Arch Environ Health 8:270-277, 1964. 5. Davis JR, et al; Urinary delta-amino levulinic acid (ALA) levels in lead poisoning: II. Correlation of ALA values with clinical findings in 250 children with suspected lead ingestion. Arch Environ Health 17:164-171, 1968. 6. Mauzerall D, Granick S: The occurrence and determination of delta-aminolevulinic acid and porphobilinogen in urine. J Biol Chem 219:435446, 1956. 7. Snyder LJ: Improved dithizone method for determination of lead: Mixed-color micromethod at high pH. Ind Eng Chem Anal Ed 19:684-687, 1947. 8. Stopps GJ: Symposium on air quality crite ria: lead. J Oceup Med 10:550-564, 1968. 9. deKretser AJ, Waldron HA: Urinary delta amino-laevulinic acid and porphobilinogen in lead-exposed workers. Br J Ind Med 20:35-40, 1963. 10. Davis JR, Andelman SL: Urinary deltaaminolevulinic acid (ALA) levels in lead poison ing: 1. A modified method for the rapid determi nation of urinary delta-aminolevulinic acid using disposable ion-exchange chromatography col umns. Arch Enmron Health 15:53-59, 1967. 11. Cremer JE: Biochemical studies on the toxicity of tetraethyl lead and other organo-lead compounds. Br J Ind Med 16:191-199, 1959. 12. Bolanowska W: Distribution and excretion of triethyllead in rats. Br J Ind Med 25:203-208, 1968. 13. Cremer JE, Callaway S: Further studies on the toxicity of some telra and trialkyl lead com pounds. Br J Ind Med 18:277-282, 1961. 14. Gibson SL, Mackenzie JC, Goldberg A: The diagnosis of industrial lead poisoning. Br J Ind Med 26:40-51, 1968. 15. Cramer K, Selander S: Detection of indus trial lead poisoning. Lancet 1:544-545, 1966. 138 Arch Environ Health/Vol 28, March 1974 Delta-Aminolevulinic Acid/Robinson EC4827