Plasma porphyrin levels were determined in a group of 50 workers exposed to lead. The mean value obtained (0·7 μg./100 ml.) was found to be higher than that obtained from a control group (0·2 μg./100 ml.). Although urinary porphyrin levels in the lead workers were also higher than in the control group, no correlation was found between plasma porphyrin levels and urinary porphyrin levels.

Chromatography of the plasma porphyrins from lead workers showed that some protoporphyrin was present in addition to the coproporphyrin found in plasma from the control group.

The findings of a diagnostic blood test for the presence of hexachloro-epoxy-octahydro-dimethanonaphthalene (H.E.O.D.) performed on whole blood obtained from operatives of plants manufacturing two chlorinated hydrocarbon insecticides, aldrin and dieldrin, and formulating products containing them and from dogs experimentally exposed to dieldrin have been reported. When clinical signs of poisoning were present, the concentration of H.E.O.D. in the blood was more than 16·0-17·0 μg./100 g. blood. In the absence of clinical signs of intoxication the concentration of H.E.O.D. found in the blood was less than these values. However, the concentration of H.E.O.D. found in several operatives and in two dogs who were without signs of intoxication was above these values. It is suggested that there is a concentration of H.E.O.D. in the blood of man and dog which is a threshold for intoxication. The value for the threshold concentration may be near 15·0-20·0 μg./100 g. blood. An individual man or dog with a concentration of H.E.O.D. in the blood greater than the threshold is in a critical condition requiring some factor or factors not yet determined to precipitate intoxication. The use of this blood test will assess the severity of occupational exposure and support the diagnosis in suspected intoxication.

The suggestion that inhalers might on average leave a greater length of cigarette unsmoked was supported in a study of miners and ex-miners aged 35 to 64 years living in the Rhondda Fach. Non-inhalers, detected in an earlier random sample survey, were matched with inhalers, for age, radiological category of pneumoconiosis, and number of cigarettes smoked daily. Cigarette ends were collected for one day from all the men. The ends were measured by one observer who knew nothing about the smoking habits of the men submitting them. In each ten-year age group, the length of unsmoked cigarette was slightly shorter in non-inhalers than in inhalers, and the difference of 1·28 mm. was just significant (p = 0·05). The biological implications of this small difference are discussed.

In view of the increased importance attached to the gravimetric sampling of airborne dust in mines and other working places, it was recently decided to start regular gravimetric sampling in the experimental animal dusting rooms in this Unit. As no suitable sampling instrument was available, a Hexhlet dust sampler was modified by fitting it with a probe in place of the elutriator. This instrument has also been used to collect samples of airborne particulate matter from within chimney stacks and exhaust ducts and also unelutriated samples of dust from the air in working places.

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The kinetics of the distribution and excretion of lead (210Pb) were studied in rats for 14 days after single intravenous injections of 100 μg. of lead per rat.

The results show that in the blood the lead is bound mainly to the cells, and that the ratio of lead in the cells and plasma is constant throughout the whole period. 210Pb is rapidly distributed in the tissues, the highest concentrations being in the kidneys, liver, and bones.

The kinetics of the disappearance of 210Pb from the organs and tissues follow the pattern of first order reactions. The disappearance curves in the blood, plasma, haematic cells, and some other tissues can be expressed as sums of exponential functions. In contrast, the removal of metal from the bone tissue occurs at a constant and extremely slow rate.

The metal is excreted by the faeces and urine. The rates reach their maxima within 24 hours and decrease asymptotically afterwards. More 210Pb was excreted in the faeces (35·7%) than in the urine (15·9%) during the 14 days of observation.

Associations between exposure to asbestos and carcinoma of the lung, diffuse mesothelioma of the pleura, and diffuse abdominal tumours have been demonstrated. Only by an epidemiological approach can the total risks of exposure to asbestos be estimated, and such a study is reported here. This suggests that white asbestos (chrysotile) may not be a serious hazard as far as mesothelioma or abdominal tumours are concerned, though there is some evidence of an excess in the number of deaths from carcinoma of the lung and bronchus.

In the manufacture of zinc oxide the raw material normally used in zinc metal plates. In a factory in which old aeroplane batteries containing zinc mercury amalgam were substituted, it was not realized that mercury vapour was being produced. Of 25 workers exposed, seven developed serious chronic mercury poisoning and were admitted to hospital. The clinical findings in the affected workers are described. They were first treated with penicillamine D, but in all but one case this had to be stopped because of rashes. Little improvement followed a switch to B.A.L. It is suggested that if penicillamine D is used in the treatment of mercury poisoning, steroid cover should be given from the start.

Volatilization of mercury has been observed from various biological media (tissue homogenates, infusion broth, plasma, urine) containing mercuric chloride. That micro-organisms were responsible was indicated by the finding that the rates of volatilization were highly variable, that a latent period often preceded volatilization, that toluene inhibited the process, and that the capacity to volatilize mercury could be transferred from one biological medium to another. Two species of bacteria when isolated and cultured from these homogenates were able to volatilize mercury. Two other bacteria, one of which was isolated from the local water supply, were also highly active. The volatile mercury was identified as mercury vapour. The importance of these findings in relation to the storage of urine samples prior to mercury analysis is discussed.