Lead poisoning and lead absorption

by Sir Thomas Morison Legge; Kenneth Weldon Goadby

“Caustic Soda.—One hundred grammes of pure caustic soda dissolved in 250 c.c. of water.

“Sugar.—A saturated solution of sugar in water.

“Sulphuretted Hydrogen.—A saturated solution of sulphuretted hydrogen in water.

“Coloured Solution.—Cotton-wool dissolved in concentrated nitric acid and evaporated to dryness, and the residue dissolved in a little water and filtered; the solution is deep yellow in colour.

“Standard Lead.—A solution of lead acetate or lead nitrate made up to contain exactly 0·0001 gramme of lead per c.c. of solution.

“The bulk of the dust in the filter was removed to a beaker (No. 1), by gently tapping the inverted funnel. The cotton-wool was then removed from the funnel, and the upper one-third, containing the remainder of the dust, was cut off and added to the dust in beaker No. 1. The remainder of the cotton-wool was placed in a second beaker (No. 2); 2¹⁄₂ c.c. of hot nitric acid was dropped on the dust in beaker No. 1 from a pipette, a little water added, and the whole heated. The solution was filtered into a 50 c.c. Nessler glass, and the liquid remaining in the cotton-wool also removed by squeezing the wool with a glass rod against the side of the beaker. The cotton-wool in beaker No. 2 was similarly extracted with 2 c.c. of nitric acid, and the solution added to that remaining in beaker No. 1. The liquid was heated, the cotton-wool macerated in it and filtered as before. The wool was then washed with hot water about three or four times, and the liquid filtered into the Nessler glass. A number of standards were then made up by running into Nessler glasses, from a burette, varying amounts of standard lead solution covering a fair range. Usually five standards were made up, containing 0·5, 0·8, 1·0, 1·2, and 1·4 c.c. lead solution, depending on the volume of the air aspirated and the quantity of lead expected in the known weight of dust found. To each standard 4¹⁄₂ c.c. nitric acid was added, and 5 c.c. of the caustic soda solution and 4 c.c. of the sugar solution were run into all the six solutions—i.e., one test and five standards—from pipettes. It was invariably found that the test was coloured faintly yellow, and if this is not allowed for in the standards high results are obtained. Hence a drop or two of the coloured solution (see solutions required) was added to the standards placed on white paper till they matched the test. Lastly, to the contents of each of the six glasses was added 4 c.c. of sulphuretted hydrogen solution, and the liquid in each made up to the 50 c.c. mark, and the whole well stirred. Usually it was found that the colour of the test came somewhat deeper than that of one standard, and a drop or two of lead solution was added to the standard till its colour matched that of the test. The elaborate method of making up a number of standards was adopted because it was found that any other way gave high results. In the way described many trial experiments were made, and they were invariably correct within half a drop of the standard solution.”

The estimation of the quantity of lead present in organic fluids, with the disturbing influence of the presence of other metals, is a factor which always complicates the use of the sulphuretted hydrogen colorimetric estimation. It is almost impossible, when dealing with fæces, with blood, or, on the other hand, with artificial digests containing bread and milk, to eliminate the disturbing influence of iron. Further, if steps are taken to remove the iron and other metals, so much loss takes place in the manipulations necessary that the results arrived at are not satisfactory. Whenever dealing with organic matter, such as urine and fæces, it is best to make a blank test with a similar quantity of the substance under examination obtained from other sources, and to subtract the error found due to iron, when a rather closer approximation may be arrived at.

So far as can be estimated, the minimal quantity of lead required to produce poisoning is 0·005 gramme per kilogramme of body weight; but, on the other hand, persons who have swallowed much larger doses than this have exhibited no symptoms of poisoning. There is every reason to suppose that lead absorbed through the lung produces a maximum toxic effect, and, from the estimation of the quantity of lead found in the body after death, it is highly probable that exceedingly minute quantities of lead have, when absorbed over long periods, produced changes not only by their actual presence in the tissues, but also have set up degenerative changes which progress even after the elimination of the metal from its local position.

Histological Examination.

—In addition to the chemical examination of tissues from a person who has died of suspected lead poisoning, it is of the highest importance to make histological examinations, as the naked-eye appearance of post-mortem examination is frequently insufficient to give any clue to the cause of the poisoning. Moreover, in a large number of instances the necropsy may exhibit a number of signs of disease, such, for instance, as granular kidney, cirrhosis of the liver, and so forth, which are associated with diseases other than lead poisoning, and, in the absence of any present or past evidence of definite hæmorrhages found associated with the other lesions already mentioned, an ordinary autopsy must be inconclusive. It is true that such pathological conditions are consistent with poisoning by lead; and if the individual has been a lead-worker, it is easy, but frequently erroneous, to conclude that the symptoms owe their origin to the worker’s occupation. We are entirely in sympathy with the remarks of King Alcock[9], who says: