Biological monitoring of MDA.

4 Wagner JC. Asbestos dust exposure and malignancy. Proceedings of 14th congress on occupational health. Madrid: 1963. 5 Hourihane DO'B, Lessof L, Richardson PC. Hyaline and calcified pleural plaques as an index of exposure to asbestos. A study of radiological and pathological features of 100 cases with the consideration of epidemiology. Biological monitoring of MDA Sir,-4,4'-methylenedianiline (MDA) is a primary aromatic amine usually made via the reaction of aniline and formaldehyde. It is used as a hardener in epoxy resin systems. The product produces cholestasis and hepatic necrosis in many animals and caused the so called Epping jaundice when 84 persons ate bread contaminated with it. In industry hepatitis developed in 12 young male workers exposed to MDA.' Studies from the National Toxicology programme (NTP)2 showed that the dihydrochloride salt of MDA is carcinogenic in both sexes of rats and mice, and found cancer of the liver, the thyroid gland, and the haematopoietic system; MDA is structurally similar to benzidine, a known human bladder carcinogen. The objective of the current study was to measure free and conjugated MDA in the urine of workers as an assessment of exposure. Method Urine was collected at the end of a workshift. Until June 1989 MDA was measured in hydrolysed urine with a liquid. chromatographic method and UV detection (210 nm). The detection level was 100 ppb (100 jug/l). In May 1990 the method was changed. After reaction with hydrochloric acid, MDA was measured by high performance, liquid chromatography with electro-chemical detection using ethylene-dianiline as an internal standard. The detection limit was 2ppb (2 pg/l). The concentration of urinary creatinine was photometrically estimated with a commercial kit (creatinine-Boehringer Mannheim). Results below the detection limit were handled as the half of the detection limit.3 Results These are presented in the table. Discussion Measurements of MDA were carried out at five different times. With many results below the detection limit it is a problem to calculate an average. Here I used the detection limit/2, a method described by Horning and Reed for use when data are highly skewed and with non-detectable values of more than 30%.3 The real average must be somewhere between the two results given in parentheses (see table footnote). After August 1988 working conditions were changed: masks, gauntlets, and disposable paper overalls became obligatory. Results for October 1988 showed a distinct improvement. Nevertheless the management took the decision to totally rebuild the unit. …