Microbial Degradation of Ametryn in Hawaiian Torrox and Hydrandept Surface Soils
1975
Goswami, Kishore P. | Green, Richard E.
Degradation of ring-¹⁴C ametryn in autoclaved and inoculated surface soils with added C and N sources was measured for 60 days in a ¹⁴C balance study. The study involved periodic analysis for (i) total methanol-extractable ¹⁴C, (ii) ¹⁴C-polar products separated from the methanol extract by liquid-liquid partitioning with chlorform, (iii) ¹⁴CO₂ evolution, and (iv) ¹⁴C-nonextractable residue by combustion. The results confirm that unlike the chemical breakdown of chloro-s-triazines, ametryn degradation in soil is predominantly a microbiological process which proceeds mainly through the initial N-dealkylation pathway with some simultaneous formation of hydroxyatrazine. Gas chromatographic analysis showed partitioning of two possible N-dealkylated products of ametryn metabolism into the aqueous phase of the chloroform/aqueous-methanol system. Less than 7% of the applied ametryn was lost in autoclaved soils, but ametryn was rapidly degraded in inoculated soils. Ametryn disappearance was much faster in the Hilo soil (Typic Hydrandept) with 8.7% remaining at 60 days than in the Molokai soil (Typic Torrox) with 63.7% remaining. The extremely high surface area and high organic matter content of the Hydrandept surface soil were considered conducive to higher microbial activity in this soil. The major fraction of ¹⁴C-degradation products was recovered in polar compounds with a lesser quantity residing in a nonextractable fraction; less than 0.2% was evolved as ¹⁴CO₂. Evolution of ¹⁴CO₂ at a given time was not governed either by the quantity of parent ametryn remaining nor by the concentration of polar products.
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