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.

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A rapid, convenient and accurate method, based upon an enzyme linked immunosorbent assay (ELISA), is described for the determination of paraquat residues in soil. Polystyrene plates, coated with paraquatkeyhole limpet haemocyanin (KLH) conjugate, are incubated with the test samples and a known amount of monoclonal antibody. Residual antibody that has not reacted with free paraquat in the sample combines with paraquat -KLH on the plate. The determination of the fixed antibody is achieved by the addition of peroxidase labelled rabbit anti-mouse immunoglobulin G followed by reaction with a chromogenic substrate. The enzyme activity of the solid phase is determined from the absorbance measurements, which are inversely proportional to the concentration of paraquat. The method shows high specificity and correlates well with the traditional ion exchangespectrophotometric method for the determination of paraquat.

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