There is undoubtedly a narrow margin of safety between current occupational blood lead suspension limits and subclinical effect. As a result, the lead users have produced a voluntary Code of Practice with suspension limits significantly below those seen in some national legislation, particularly the Control of Lead at Work Act 2002.

The immunological status of individuals occupationally exposed to low levels of inorganic lead has been examined and compared with that of non-exposed, age and sex-matched controls. At the time of testing the exposed population had a mean (+/- SD) blood lead concentration of 38.4 +/- 5.6 micrograms X 100 ml-1 (n = 39) compared with a mean value of 11.8 +/- 2.2 micrograms X 100 ml-1 (n = 21) for the control group. No differences in the serum concentrations of IgG, IgA and IgM between the populations were observed and there existed no correlation between blood lead concentration and serum immunoglobulin levels. In addition assessment was made of the capacity of peripheral blood mononuclear cells to respond to the mitogen phytohaemagglutinin (PHA), a correlate of T cell function, and to spontaneously lyse cells of the erythroleukaemic cell line K562, a measure of NK cell function. In neither case was there a difference between exposed and control populations and no correlation between reactivity and blood lead concentration. Although previous studies in rodents have indicated that exposure to inorganic lead resulting in similar blood lead concentrations may compromise immune competence our data suggest that no similar effect occurs in man.

Biochemical and haematological data for two consecutive years are presented on about 2000 people from the workforce of a large chemical company. The data are examined for the influence of sex, age, season, time of blood sampling, and patterns of work on the various indices. In addition to the results confirming previously published work relating to the effects of age and sex, they provide interesting new information on the possible influences of seasons and patterns of work, that is, whether the subjects were shift or day workers. Further studies on the influence of these various factors are required, and our on-going survey will perhaps provide more definite data in due course. The findings show the importance of quantifying these variables, particularly in an industrial workforce where minor changes may be of significance.

SUMMARY. Biochemical and haematological data obtained over five consecutive years are presented on the male workforce of a large chemical company. The data have been subjected to statistical analysis and quantify the influence of age and the month of the year in which the samples were taken. The red cell count, white cell count, serum y-glutamyl transferase, alanine transaminase and creatinine show significant and consistent seasonal variations. The previously published work on the influence of age on several indices is confirmed. Biochemical screening may be a method of detecting early signs of toxicity in man but such factors as age, sex and season must be taken into account when comparing the results obtained from exposed and non-exposed groups.This study has been performed on data derived from the analysis of blood samples taken from the male workforce of a large chemical company and is an extension of previously published work.1 As part of an annual medical examination offered to each member of the workforce, blood samples were taken for haematological and biochemical analysis for five consecutive years, 1979-83. When undertaking the screening of our workforce the aims were to provide early evidence of target organ damage following exposure to substances known to be potentially toxic and to monitor workers being exposed to new substances for early evidence of any toxic effects.Previous published work 2 -7 has shown the influence of age and sex on reference ranges. We have extended our studies and investigated the possible influence that the month of the year in which the analyses were performed might have upon the results obtained. It has been known for some time that there are seasonal variations in many hormone assays'': 9 but information on seasonal variations in haematological and biochemical parameters is scanty and inconsistent. Method and quality control