Monitoring of formic acid in urine of humans exposed to low levels of formaldehyde.

This study documented the formaldehyde exposures of a group of veterinary medicine students. It also investigated the feasibility of biologically monitoring the exposures. The biological monitoring was based on the fact that the formaldehyde is metabolized in the body to formic acid, and may then be excreted in the urine. Therefore, exposures to formaldehyde could theoretically create a shift in the formic acid levels in the urine. Normal baseline levels of urinary formic acid were first established for each subject. The baselines of most students were quite variable. Very few exhibited a "tight variability" in their baseline. Next, three sets of pre- and post-exposure urine samples were taken. A series of paired t-tests were run on these "pre" and "post" sets. The results indicated that no significant formic acid shift was seen. A subset of the samples was "corrected" for specific gravity. However, this adjustment did not have an effect upon the relative formic acid levels. In addition, no significant formic acid shift was seen in the adjusted group. Exposure levels of the students were less than 0.5 ppm of formaldehyde. Therefore, the main conclusion of the study was that biological monitoring of formaldehyde exposures (via formic acid shifts) at these low levels was not a feasible technique.