INVESTIGATIONS ON THE IMPORTANCE OF THE F ORMIC-ACID EXCRETION IN URINE FROM AN ENVIRONMENTAL AND OCCUPATIONAL MEDICAL POINT-OF-VIEW

The suitability of the formic acid excretion in the urine as a paramet er for the biological monitoring of inhalational exposure to formaldeh yde is discussed controversially. We investigated persons not occupati onally exposed to formaldehyde (n = 70) to determine possible influenc ing factors on the physiological excretion of formic acid. Following t his we carried out a study on medical students (n = 30), who during an anatomical dissection course were exposed to a short but intensive in halational exposure to formaldehyde, as well as investigations on empl oyees of a pathological-anatomical laboratory (n = 8) in order to obse rve the course of the formic acid excretion in the urine during a work ing week with a continuous exposure to formaldehyde below or within th e range of the MAK value (0.5 ppm). It was seen that the formic acid e xcretion in the urine with non-exposed persons is subject to considera ble inter and intraindividual fluctuations (at a maximum by a factor o f 30). In addition to differences in the endogenous formation of forma tes an important influencing factor is probably the uptake of food con taining formic acid or its precursors. A value of 23 mg formic acid/g creatinine is given as the upper norm level (95th percentile) of adult s. In the groups who were exposed to formaldehyde, in some cases consi derably above the MAK value, we were able to detect no significant inc rease in the formic acid concentration in the urine. After a short but intensive exposure to formaldehyde (0.32-3.48 ppm) the formic acid co ncentration in the urine did not change significantly with an average formic acid concentration in the urine before exposure of 6.5 mg/g cre atinine (central 50% range: 3.5-14.2 mg/g creat.) and after exposure o f 6.0 mg/g creatinine (central 50% range: 4.4-10.9 mg/g creat.). There was no significant relationship between the individual change in the formic acid concentration in the urine (in mg/g creatinine) and the in halational exposure to formaldehyde determined through personal air sa mpling (r = 0.079). In the course of a working week with a continuous exposure toformaldehyde (0.03-0.83 ppm) there was after relating the v alues to creatinine a continuous increase in the median to 22.3 mg/g c reat. with a starting value of 8.7 mg/g creat. The change proved, howe ver, for the number of cases investigated not to be significant. In pa rticular there was no linear correlation detectable between the indivi dual changes in the formic acid excretion in the urine and the formald ehyde concentrations in the breathing zone determined by personal air sampling. Already stoichiometrical considerations are cause for doubt about the possibility of the determination of an inhalational exposure to formaldehyde. In an occupational or environmental medical diagnosi s with the suspicion of an inhalational exposure to formaldehyde, acco rding to the results of our investigation the determination of the for mic acid excretion in urine cannot be recommended. Due to the consider able inter and intraindividual fluctuations it is nor possible with th e occurrence of an increased formic acid concentration in a spontaneou s urine sample to deduce an individual exposure to formaldehyde.