Document VJEgMM6a6xXrBXpvwQk3p6208

1 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 jn the Chemical and Development Department at Abadan, dated 30tla January 1943. \ COLLECTION OF SAMPLES. One of the greatest practical difficulties is that of obtaining samples that are wholly free from contamination. Workmen in general and persons without \p chemical or technical training always fail to appreciate the significance of 'the V. manifold opportunities for introducing lead compounds into such samples, and even technically trained persons commonly fail to realise that lead compounds in one'V'S 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 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 serious 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 axe substantially ubiquitous. Since nothing has been said in the report of the Principal Chemist concerning the 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 water available for renal secretion when other factors remain constant. A highly 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. For 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 24-hour perio4 or more, so as to equalise the hour-to-hour variability of samples. Nevertheless there is likely to be a significan seasonal variation ir. the lead concentration of the urine where there are large seasonal variations in temperature. Extreme r- elevation of temperature is certain to be an important factor in this matter. Therefore samples of urino obtained from normal persona without unusual exposure o to lead may show lead concentrations well above the limits commonly regarded as normal for such persons. These facts must be taken Into account not only in the o issuance of instructions for the collection of samples of urine, but also in the o interpretation of analytical results. ANA i i-njjj. 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 are described in the comparatively rocent literature on the subject. It would OOJJJ'A/TJL U1M Ul OaiSrJb&Q 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'yeh technically trained persons commonly fail to realise that lead compounds in one'hs 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 par 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 urinu 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 remain-, constant. A highly 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 volmca of water was taken. For 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 24-hour period or more, so as to equalise the hour-to-hour variability of samples. Nevertheless there is likely to be a slgnifican seasonal variation in the lead concentration of the urine where tliers 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 ba 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 N5TH0S. The method of analysis described iy 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 seem that it would give SsatiMy satisfactory results in the hands of a component and experienced analyst. One ^rould require analytical data on samples of variable 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, is 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. K 0010.148 The method assumes that bismuth i'llII not he present as an interfering elom3nt. One would require information on the extent of the therapeutic use of bismuth comp oil rils 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 tho 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 Courtauld Laboratory of Biochemistry of Middlesex Hospital Medical School, and for warded to Mr. C.J."'fright by Mr. 3svan in his letter of 14th July 1943, my be regarded as entirely satisfactory for such s purpose. i.'pufvrj' t.r AVJUj . y Jii * October 1943. 0010149