Abstract
Radioisotopes carbon 14 and chlorine 36 were used to elucidate the environmental role of trichloroacetic acid (TCA) formerly taken to be a herbicide and a secondary air pollutant with phytotoxic effects. However, use of
14C-labeling posed again known analytical problems, especially in TCA extraction from the sample matrix. Therefore—after evaluation of available methods—a new procedure using decarboxylation of [1,2-
14C]TCA combined with extraction of the resultant
14C-chloroform with a non-polar solvent and its subsequent radiometric measurement was developed. The method solves previous difficulties and permits an easy determination of amounts between 0.4 and 20
kBq (10–500
ng
g
−1) of carrier-less [1,2-
14C]TCA in samples from environmental investigations. The procedure is, however, not suitable for direct [
36Cl]TCA determination in chlorination studies with
36Cl. Because TCA might be microbially degraded in soil during extraction and sample storage and its extraction from soil or needles is never complete, the decarboxylation method—i.e. 2
h TCA decomposition to chloroform and CO
2 in aqueous solution or suspension in closed vial at 90
°C and pH 4.6 with subsequent CHCl
3 extraction—is recommended here, estimated
V
<
7%. Moreover, the influence of pH and temperature on the decarboxylation of TCA in aqueous solution was studied in a broad range and its environmental relevance is shown in the case of TCA decarboxylation in spruce needles which takes place also at ambient temperatures and might amount more than 10–20% after a growing season. A study of TCA distribution in spruce needles after below-ground uptake shows the highest uptake rate into current needles which have, however, a lower TCA content than older needle-year classes, TCA biodegradation in forest soil leads predominatingly to CO
2.