Lead poisoning and lead absorption

by Sir Thomas Morison Legge; Kenneth Weldon Goadby

Susceptibility and immunity to poisoning by lead may be considered, according to the type of lead compound absorbed, further in its relation to age and sex. All compounds of lead are not poisonous in the same degree; the more easily soluble compounds are more poisonous than the less soluble. On the other hand, compounds which appear at first sight unlikely to produce poisoning may do so; for instance, fritted lead or lead silicate, a substance largely used in the potteries as a glaze, and manufactured by fusing together litharge and a silicate, would appear at first sight to be quite an innocuous substance. Owing to its method of preparation, however, it is not a pure compound of lead and silica, but contains lead oxide, metallic lead, etc., entangled in its meshes, and experimentally one of us (K. W. G.) has demonstrated that such a compound may be acted on by the tissues of the body, both when injected subcutaneously and even when inhaled, and so gradually produce definite symptoms of lead poisoning, but at a much slower rate than the more poisonous lead compounds. The fineness of division in which the compound of lead exists is another factor affecting its poisonous nature; the more finely divided particles find their way into the lung more easily than the coarser particles. Various subsidiary matters may also determine the susceptibility in a given individual, and of these a certain number require mention, as they probably act as definite predisposing factors. Age and sex may be regarded as predisposing factors to lead poisoning, and certain diseases also.

Age.

—Young persons are regarded as more liable to lead poisoning than adults, although it is difficult to obtain definite figures on the point, the duration of employment acting as a disturbing factor in estimating the susceptibility of young persons. They may have worked in a lead works for a year or more without showing any signs of poisoning, but develop them later in adult life, although it is very likely that absorption had taken place during the earlier period. In the Report of the Departmental Committee on the Use of Lead in the Potteries (Appendix XII.), the attack rate for the period 1899 to 1909 for young persons is 19·3 per 1,000, and for adults 18·8 for the same period, but the figures upon which these attack rates are based are too small to build any conclusion. The general clinical conclusions of appointed surgeons and certifying surgeons in the various lead factories would be, we believe, that the susceptibility of young persons is at least twice that of adults, and there is some ground for supposing that the tissues of an adult when growth has ceased more readily adapt themselves to deal with the absorption and elimination of poisonous doses of lead than do the tissues of a young person.

Sex.

—Women are more susceptible to poisoning by lead than men, and in lead poisoning from drinking water the proportion of women (especially pregnant women) and children attacked is stated to be higher than in men, and one such epidemic is quoted by Oliver where the rise in the number of miscarriages and premature births led to the discovery of the fact that the water-supply was contaminated with lead. The close relationship of lead poisoning to miscarriage has been repeatedly made out, especially by Oliver, in the white lead industry as carried on twenty years ago. Oliver also quotes the effect upon rabbits[9], Glibert upon guinea-pigs[10], and in the experiments of one of us (K. W. G.), referred to on [p. 99], all the animals to which lead was given during pregnancy aborted; and, further, with one exception out of eight animals, all died of lead poisoning, not as the result of the abortion, but some time later, although no further administration of lead was made. This confirms the well-known abortifacient effect of diachylon, and there is no doubt that the lead circulating in the maternal blood determines the abortion. Further, observers who have examined the fœtus in such cases have demonstrated the presence of lead in the fœtus itself. Oliver[11] found that eggs painted with lead nitrate did not hatch out, and on opening the eggs the embryos were found to have reached only a limited stage of development, and to have then died, whereas control eggs painted with lime produced live chicks. From what is stated later with regard to the curious action of lead upon the blood, the mechanism of abortion is easily understood; it is probable that placental hæmorrhages are produced, as in other organs of the body. But the effect of lead on the female is not only apparent during pregnancy. A considerable number of women working in lead processes suffer from amenorrhœa, and often from periods of menorrhagia and dysmenorrhœa, which as a rule is the more striking symptom. The effect of lead on the uterine functions, however, only exists so long as the constant intake of the poison is taking place, and many cases are recorded where women, after having had successive abortions while working in lead factories, have ultimately gone through a normal pregnancy and given birth to a living child. This circumstance bears a strong analogy to the similar train of events in syphilis.

In the Report of the Committee on the Use of Lead in the Potteries, some inquiry was made with regard to the possible association of lead absorption on the male side as a predisposing cause of infant mortality and premature birth. The tables given are not very conclusive, and from our own observations there seems to be very little evidence for supposing that a male lead worker is less likely to beget children, or that his children are more likely to be unhealthy than those of men working in any other industrial process. We are here speaking of the effect of lead under the conditions of its general use in this country now. In the absence of any precautions whatever as to daily absorption of dangerous dust, the effect on the offspring, even in the case of male lead workers, may well be evident, as has been shown by Chyzer[12] in the manufacture of pottery as a home industry in Hungary. One greatly disturbing factor in estimating the greater susceptibility of the female than the male in many lead industries is that the more dangerous work is performed by the women, such, for instance, in the Potteries, as the process of colour-blowing and ware-cleaning.

Predisposing Causes of Lead Poisoning.

—In lead poisoning, as in many other diseases, a number of predisposing and contributory causes may be cited which tend to lower the susceptibility of the individual to the poisonous effect of the metal and its compounds, or to so modify the functions of the body that a smaller dose of poison may produce more profound changes than would otherwise be the case.

Certain diseases may be regarded as predisposing causes by lowering the general resistance of the body tissues to the influence of lead, and a consideration of the chapter on Pathology will at once demonstrate how seriously certain diseases may contribute in this way.

The peculiar effect of lead is upon the blood and the walls of the bloodvessels, and it will therefore follow that any disease which may affect the intima of the bloodvessels may predispose to lead poisoning; and, further, as the elimination of lead takes place to a certain extent through the kidney, any disease which affects either the renal epithelium or the general maintenance of the excretory function of the kidney may predispose that organ to the irritative effects of the lead circulating in the blood. In the same way, the condition of lead absorption in which the balance of absorption and elimination of lead remains in such a ratio that no definite symptoms of lead poisoning appear may have that delicate balance easily upset by the introduction of some secondary cause, which, when operating in association with lead absorption, may precipitate symptoms attributable to poisoning by that metal. Chronic alcoholism especially, producing as it does definite changes in the kidney of itself—changes which it is impossible to distinguish by the naked eye from the effects of lead poisoning—must clearly act as a predisposing, if not even an exciting, cause of lead kidney infection. In experiments upon animals, it was found that the addition of alcohol to the diet of an animal which was the subject of chronic lead absorption precipitated the attack of definite poisoning; in other words, the latent period of lead poisoning—that is to say, the resistance exhibited by the tissues to the toxic influence of lead—was considerably diminished by this addition of a second irritant, alcohol. In several experiments, also, where the form of lead experimented with was one of the least toxic of the lead compounds, the animals subjected to such a compound alone did not become poisoned, but succumbed if alcohol were added to their diet. This experimental work is amply borne out by the clinical evidence of all persons who have had experience of industrial lead poisoning, as cases of colic and wrist-drop are frequently observed in lead workers shortly after alcoholic excesses. Individuals, therefore, who are suspected of the alcoholic habit should not be employed in any process where they are likely to run risk of absorption of lead dust.