Aromatic nitro- and amino-compounds (ANA) are notorious methemoglobin forming substances. From 1987 to 1993, the author surveyed the exposure level to ANA and health status of workers in a chemical industry where they synthetize nitrophenol and anisidine from chloro-nitrobenzene. The ANA exposure indicator was the diazo-reaction positive substance in the worker's urine (Dz) and the biological effect of ANA was monitored through the methemoglobin concentration in the blood (MHb). The following results were obtained from the survey.
1. Both the Dz and MHb values tended to become lower between 1987 and 1993.
2. The MHb levels of the workers were a little higher than the control levels, and the difference between the values was statistically significant (p<0.01); both levels were, however, within the normal range.
3. The MHb value was estimable from a mathematical model:
MHb=(k1-k2/a)×DU×CH, where k1 and k2 were constants and a, DU and CH indicated the activity of glutathion S transferase in erythrocytes (GST), DZ in urine and blood hemoglobin concentration, respectively. The correlation coefficient of the multiple regression was statistically significant (R²=0.263, p<0.01). This model suggets that the biotransformed fraction of ANA in the pulmonary uptake site, the lung, could not penetrate into erythrocytes or act as an MHb former. The model seemed to be consistent and valid when urinary DZ values were less than 1.0 (mg/mg creatinine) and MHb values were less than 2.0 (mg/ml blood). Thus, the upper limit of normal levels for MHb can be considered to be 2.0 (mg/ml blood), or 12-1.6% of total hemoglobin in blood.
4. The significance of the uptake sites, i.e., lung, skin etc., was discussed with refer-ence to the evidence obtained from the longshoremen cases, who were percutaneously exposed to chloronitrobenzene in 1984.
5. Hemolysate solutions from the blood of workers were applied to isoelectric focus-ing electrophoresis (IEF), and Hb species of different valencies were separated; intermediate MHbs, where the heme iron in one of the components of Hb, i.e., in the α or β chain was oxidized and MHb where both the α and β chain heme iron oxidized and Hb X and Y, were separated and easily discernible. The correlation matrix was calculated using the data relevant to IEF and other indicators; MHb estimated spectrophotometrically, GST activity of erythrocytes, Hb and urinary DZ vale. The statistical procedure of principal component analysis was applied to the matrix, and two major principal components were extracted from the calculation. One of the components is relevant to the redox state of erythrocytes explained by MHb and Hb (X, Y) levels in the IEF pattern, and the other is relevant to detoxication by GST. The intermediate MHb values separated by IEF correlated to both of the components.