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Decomposition of Specifically Carbon-14 Labeled Benzoic and Cinnamic Acid Derivatives in Soil¹

ABSTRACT

Specifically ¹⁴C-labeled benzoic, phenolcarboxylic, and hydroxycinnamic acids were synthesized. The loss of the labeled carbon as ¹⁴CO₂ upon incubation at 100 and 1,000 ppm in a neutral soil with and without the addition of 2% freeze-dried humic acid or 0.5% finely ground peach wood (Prunus persica) was followed over a 12-week incubation period. Under the experimental conditions the phenolic compounds were readily degraded in the soil. Within 1 week about 90% of the COOH carbon of p-hydroxybenzoic, syringic, vanillic, and anisic acids had evolved as CO₂. After 12 weeks this had increased to about 95%. Loss of the ¹⁴COOH carbon of 6-methylsalicylic acid was about 75% at 1 week and 87% after 12 weeks. About 42 to 85% of the side chain carbons of p-hydroxycinnamic acid and caffeic acids evolved as CO₂ and from 66 to 85% of the ring carbon of protocatechuic, benzoic, vanillic, veratric, and caffeic acids was lost over the incubation period. The addition of peach wood or humic acid exerted very little effect on the decomposition rate and total decomposition of the phenols and the phenols did not influence the decomposition rate or total decomposition of the peach wood. The percentage distribution of the residual activity from 3-¹⁴C p-hydroxycinnamic acid, ring-¹⁴C benzoic acid, and O¹⁴CH₃ syringic acid varied from 14 to 21, 17 to 32, and 23 to 59% for the humic acid, fulvic acid, and residual soil fractions, respectively. Linkage into model phenolase polymers greatly retarded decomposition rate. Loss of ring carbon varied from 3 to 6% and side chain and COOH carbons from 8 to 75%. The higher losses occurred from COOH groups of single hydroxybenzoic acids linked into model phenolase polymers from hydroxytoluenes and hydroxyphenols.

¹ Contribution from the Dep. of Soil Science & Agricultural Engineering, Univ. of California, Riverside 92502, and the Institut für Biochemie des Bodens, Forschungsanstalt für Landwirtschaft, Braunschweig, Germany. The authors thank J. O. Ervin, and Miss H. Lemke for technical assistance.

² Biochemist, Institut für Biochemie des Bodens and Professor of Soil Science, respectively.

Received for publication November 11, 1974. Accepted for publication February 12, 1975.