K. Schmid et al., INVESTIGATIONS ON THE IMPORTANCE OF THE F ORMIC-ACID EXCRETION IN URINE FROM AN ENVIRONMENTAL AND OCCUPATIONAL MEDICAL POINT-OF-VIEW, Zentralblatt fur Hygiene und Umweltmedizin, 196(2), 1994, pp. 139-152
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.