Document ZBOBwRd95aLERmp5Xp65YExDJ

NOTES ONTHE DETERMINATION OF LEADIN URINE. The following comments apply generally to some extent to methods of analysing samples of biological materials for their content, and specifically to the pro cedures described in the Laboratory Note of the Principal Chemist in the Chemical and Development Department at Abadan, dated 30tla January 1943. ' .V COLLECTIONQg SAMPLES. One of the greatest practical difficulties is that of obtaining samples that are wholly free from contamination. Workmen in general and pel'sons without \ . \ chemical or technical training always fail to appreciate the significance of thep manifold opportunities for introducing lead compounds into such samples, and even technically trained persons commonly fail to realise that lead compounds in oners general surroundings readily find their way into samples through contact of the N latter with tlie air and with any material which is not wholly clean in the chem ical sense. The quantities of lead found in urine are quite small, being only rarely in excess of 0.50 mg.Pb par litre, and usually (in unexposed persons) of an order of magnitude well under 0.10 Pb per litre. The introduction of a few micrograms of lead into a small sample of urine or blood represents a serioiis contamination. Contact of the urine with clothing, fingers, rubber or metal cathetsrs and intermediate containers such as urinals, may result in gross con tamination, since lead compounds are substantially ubiquitous. Since nothing has been said in the report of the Principal Chemi3t concerning ths care taken in . collecting the samples, one hopes for the best while realising that persons who lack experience in this regard usually set up insufficient precautions for the collection of samples of urine. It is possible, even probable, that some of the samples collected from workman were contaminated, and that some of the excess- ' ively high results came about in this maimer. A second point of importance in relation to the collection of samples of urine had to do with the volume of these samples, and the rate of water elimin ation represented by them. The urinary lead concentration varies strikingly with the quantity of v.-ater available for renal secretion when other factors remain constant. Ahighly concentrated sample obtained on a hot day during which little water was consumed may contain lead in ten or more times the concentration that is found in a sample voided by the same individual on a cool day when a consider able volume of water was taken. Por this reason it is advisable to make sure that the urinary secretion is within reasonably normal limits during the period of collection. This is usually assured by collecting a sample over a S4-hour period or more, so as to equalise the hour-to-hour variability of samples. Nevertheless there is likely to be a significan seasonal variation in the lead concentration of the urine where there are large seasonal variations in temperature. Extreme ' 9lsvation of temperature is certain to be an important factor in this matter. Therefore samples of urina obtained from normal persons without unusual exposure to lead may show lead concentrations wall above the limits commonly regarded as normal for such persons. These facts must be taken Into account not only in the issuance of instructions for the collection of samples of urine, but also in the interpretation of analytical results. ANALYTICAL METHOD. The method of analysis described by the Principal Chemist represents a com bination of procedures, the over-all error of which cannot be guessed by the writer. It is not likely any of the standard methods of high precision which asereemdtehsactribietdwionuldthegivceomSspEarr'laytisvaetlyisfraoccteonrtylirteesrualttusreinotnhethehansdusbjoefcta. Icotmwpoonueldnt -  O J J j 'jtTJ L uiM o i a J ir jL C iO One of the greatest practical difficulties is that of obtaining samples that are wholly free from contamination. Workmen in general and persons without ' . chemical or technical training always fail to appreciate the significance of the :., manifold opportunities for introducing lead compounds into such samples, and e'yen technically trained persons commonly fail to realise that lead compounds in onefs general surroundings readily find their way into samples through contact of the latter with the air and with any material which is not wholly clean in the chem ical senee. The quantities of lead found in urine are quite small, being only rarely in excess of 0.50 mg.Pb per litre, and usually (in uaexposed persons) of an order of magnitude well under 0.10 Pb per litre. The introduction of a fev; micrograms of lead into a small sample of urine or blood represents a serious contamination. Contact of the urin3 with clothing, fingers, rubber or metal cathetsrs and intermediate containers such as urinals, may result in gross con tamination, since lead compounds are substantially ubiquitous. Siuce nothing has been said in the report of the Principal Chemist concerning ths' care taken in , collecting the samples, one hopes for the best while realising that persons who lack experience in this regard usually set up insufficient precautions for the collection of samples of urine. It is possible, even probable, that some of the samples collected from workman were contaminated, and that some of the excess ively high results came about in this manner. A second point of importance in relation to the collection of samples of urine had to do with the volume of these samples, and the rate of water elimin ation represented by them. The urinary Stead concentration varies strikingly with the quantity of water available for renal secretion when other factors remainr' constant. Ahighly concentrated sample obtained on a hot day during which little water was consumed may contain lead in ten or more times the concentration that is found in a sample voided by the sain individual on a cool day when a considerable volume of water waa taken. For till a reason it is advisable to make sure that the urinary secretion is within reasonably normal limits during the period of collection, This is usually assured by collecting a sample over a 24-hour period or more, so as to equalise the hour-to-hour variability of samples. Nevertheless there is likely to be a significan seasonal variation in the lead concentration of the urine where tilers are large seasonal variations in temperature. Extreme elevation of temperature is certain to be an important factor in this matter. Therefore samples of urine obtained from normal persons without unusual exposure to lead may show lead concentrations wall above the limits commonly regarded as normal for such persons. These facts must be taken into account not only in, the issuance of instructions for the collection of samples of urine, but also in the interrrotation of analytical results. ANALYTICAL hTJTHOD. The method of analysis described by the Principal Chemist represents a com bination. of procedures, the over-all error of which cannot be guessed by the writer. It is not likely any of the standard methods of high precision which arc described in the comparatively recent literature on the subject. It would asenedmetxhpaetrieintcewdoualdnaglyivset.SstfOiMnye ^sraotuilsdfarcetqouriyrereasnualltysticinalthdeatahanondssaomf palecsoionfpov*aenritable und known lead content as a means of assessing the adequacy of the method. The practice of splitting the samples of urine, taking only portions for analysis, in fraught with grave danger of error, unless the samples are fresh and entirely free from sediment or suspended material. contd R.A.K. Oct. 1943. 0010148 The method assumes that bismuth '.rill not be present as an interfering elom3nt. one would require information on the extent of the therapeutic use of bismuth compoilids among the workmen to be assured that this may not be an important factor in 3ome of the results. The interpretation of the analytical data obtained on the men must depend somewhat on factors which have been mentioned in the foregoing para graphs, and even more upon data obtained on samples on normal (unopposed) persons under comparable conditions with respect to season, consumption of fluids, and general mode of life. It may well be found feasible ana desirable to employ an analytical method that has been found highly sensitive and accurate in a number of laboratories for examining further samples of urine obtained from exposed workmen. The method given in detail by Professor Dodds of the Ccurtauld Laboratory of Biochemistry of Middlesex Hospital Medical School, and for warded to Kr. C.J.fright by Hr. 3svan in his letter of 14th July 1943, my be regarded as entirely satisfactory for such s purpose. ROBERTA. iLLHOE, October 1943. 0010149