Lead poisoning and lead absorption

by Sir Thomas Morison Legge; Kenneth Weldon Goadby

[B] These numbers for the half-year only, the inspection being taken over in June, 1905.

Meillère[4] goes to considerable trouble to show that absorption of lead dust by the lung is hypothetical; that it may take place, but that it is not a channel of absorption of practical importance. He cites a number of opinions and experiments by various observers on the absorption of lead through the mucous membrane of the mouth, alimentary canal, conjunctiva, etc., and he regards the absorption of lead as one peculiarly confined, in the majority of instances, to the intestinal canal.

The usual view is that, in the passage of the respired dust-laden air through the nose, the larger particles of dust are deposited first of all upon the mucous membrane in the interior chambers of the nose; further, a second deposit takes place on the posterior wall of the pharynx and in the throat, where the eddies produced by the current of air inhaled through the nostrils allow the finer particles to become more easily deposited. Finally, should a small trace gain access to the larynx, it is said to be deposited there upon the mucous membrane, to be subsequently ejected, and only a very small proportion of the total may ever find its way into the lung.

In all arduous labour, directly the respiration rate rises through extra calls made upon the muscles of the body, an increase in the depth of respiration takes place; yet even under these circumstances Meillère and others incline to the view that the dust is deposited on the mucous surfaces of the mouth and swallowed. Experimental evidence is entirely opposed to these suppositions. In the first place, unless particles of dust readily find their way into the lung, it is difficult to understand how the lung itself becomes the site of so much deposit of carbon, and of flinty material in stonegrinder’s pneumokoniosis. The staining of the lung by means of carbon particles, particularly in dwellers in cities, is too well known to warrant more than a passing reference. Moreover, experimental work has shown that fine powders suspended in the air easily reach the lung. Armit[5] has shown that the nickel in nickel carbonyl poisoning gains direct access to the lung, and becomes deposited there, the metallic particles being readily demonstrated in the lung tissue itself. Further, the experiments (see [p. 84]) demonstrate that white lead dust and other forms of lead dust definitely gain access to the lung, and thus inhaled produce all the symptoms of lead poisoning in animals subjected to the inhalation. White lead, litharge, or red lead, are not easily suspended in water, and long-continued mixing is necessary to make a suspension. Great difficulty is found in “laying” lead dust by water, as the following experiment demonstrates: Five wash-bottles are arranged in series; in the first ground dry white lead is placed, and the other three bottles are filled with water, and a tube laid under the surface of the water in such a way that the air from the first bottle must pass the whole of the water seals in each subsequent bottle. In the last bottle is dilute nitric acid saturated with sulphuretted hydrogen. If the series is now attached to an aspirating jar, and air drawn slowly over at the rate of ordinary respiration, the white lead powder in the first bottle being at the same time shaken so that the air is fully charged with finely powdered dust, lead is quickly detected in the air passing through the last bottle of the series, by the darkening of the solution. In this way the presence of lead dust has been demonstrated after passing through four 2-inch water seals and 8 feet of ¹⁄₄-inch wet rubber tubing. Such an experiment negatives the theory that all, or even a large quantity, of a finely divided powder becomes deposited on the upper portion of the respiratory tract.

Particles of lead present in the air in industrial processes are exceedingly minute, and even in ground white lead the average size of the particle is under 1 μ. Finally, Tanquerel[6] and Stanski[7] succeeded in producing lead poisoning experimentally by blowing lead dust through a tube inserted in a tracheotomy opening. There remains, therefore, no room for doubt that the lung is the pre-eminent portal for lead absorption, particularly in industrial processes; from which it follows, as has been extensively shown in actual practice, that the diminution of dust in workshops and factories by means of exhaust ventilation is invariably followed by a diminution in the number of cases of plumbism.

Gastro-Intestinal.

—We have dealt with absorption by way of the lung, and have insisted that such inhalation of dust is of greater importance in giving rise to industrial lead poisoning than gastro-intestinal absorption. Gastro-intestinal absorption can take place, and is by no means negligible, in ordinary industrial conditions. One of the most interesting and important confirmatory evidences of the absorption of lead by the gastro-intestinal canal is to be found in the large outbreaks of poisoning in which water-supplies have been contaminated, either at their source or locally. We have already seen that electrolysis may play an important part in the solution of lead in water, and also learnt from Gautier[8] that the carbon dioxide content of water is not necessarily the sole predisposing element in the solution of lead. In this connection an important case is described by Thresh[9], where water by no means soft, but holding some 30 degrees of hardness, produced lead poisoning in an isolated family. The water in question was distinctly acid to litmus-paper, and contained a very high percentage of nitrates; the compound or salt of lead present was therefore one easily absorbed from the alimentary canal (see [p. 86]).

In all instances of water-borne lead poisoning the amount of lead present in the water was small; but as such lead would not be removed by boiling, the amount of water consumed per person from the contaminated source was probably large. As the signs of poisoning did not appear until a considerable time had elapsed, a much larger quantity of lead was probably absorbed than would appear from the simple statement that the water contained ¹⁄₁₀ grain per gallon.

A number of cases have been reported from use of diachylon as an abortifacient, and the symptoms in these cases are invariably those which occur in other severe forms of poisoning such as are met with in industrial processes. In nearly every case colic was the first symptom, followed later by paresis of various types—amaurosis, albuminuria, albuminuric retinitis, melancholia, encephalopathy—and not a few of the persons succumbed. In most of the reported cases abortion was produced, but in some, particularly in one[10], three dozen pills containing diachylon were taken in a month, producing acute lead poisoning, colic, and paresis, but not abortion.

In fifteen recorded cases of the use of diachylon, fourteen showed a lead line, in many cases distinct and broad. This point has considerable interest, as such a line cannot have been produced by oral contact. The drug in the form of pills would be rapidly swallowed, and little opportunity afforded for particles to remain in the mouth. Its presence, therefore, suggests excretion from circulating blood of lead which has been absorbed in the intestine. The blue line will be referred to again later (see [p. 122]).