Another parent of 1,2,4-triazole? - Fate and transformation of 4-amino-1,2,4-triazole (ATC) in soil

Nitrification inhibitors (NI) and urease inhibitors (UI) have been used in agriculture since the 1970s to inhibit key microbial and enzymatic nitrogen transformation processes in soil. When mixed into nitrogen-fertilizer, they reduce nitrate (NO₃^-) leaching, extend nitrogen availability in the form of ammonium (NH₄⁺) and decrease ammonia emissions. But are there side-effects of this “magic” compounds?

In a soil column study, the leaching and transformation of five inhibitors (3,4-dimethylpyrazole phosphate [DMPP], dicyandiamide [DCD], 4-amino-1,2,4-triazole [ATC], reaction mass of N-((5-Methyl-1Hpyrazol-1-yl)methyl)acetamide, N-((3-Methyl-1H-pyrazol-1-yl)methyl)acetamide [MPA] and N-(2-nitrophenyl)phosphoric triamide [2-NPT])  were examined in two different field topsoils at two temperatures (13 and 19 °C). After 280 days, ATC showed the highest persistence among all examined NI and UI, with 15 - 30% of the applied mass remaining in the soil. The recovery rate depended on soil temperature, indicating biodegradation as a dominant process. The recovery rates of the other inhibitors were substantially lower (DMPP: 1.1 – 6.7%, DCD: 0.1 – 0.3%, MPA & 2-NPT < 0.1%). Also, evidence was found, that a compound in the soil was transformed into 1,2,4-triazole (TZ), as the masses of TZ increased by a factor of 8.2 - 9.8. Possible parent compounds were identified to be either ATC or pesticides which might have been in soil before the experiment and are known to transform into TZ.

To confirm ATC as a parent compound of TZ, we designed an aerobic transformation study following OECD Test Guidelines 307 for 90 days, with two different soils, two temperatures (16/30 °C) and two soil moistures (20/60% WHC). First preliminary results show that TZ is formed while ATC is degraded.

A second soil column study in which field subsoil was used, identical temperatures and the same masses of inhibitors without fertilizer were applied. The results indicate that at least 60% of the applied ATC mass (90 µg) was transformed into TZ. Only 0 - 0.02% of the applied ATC mass was found in the percolation water, while no ATC was detectable in the soil after 316 days.

Overall, ATC transport showed differences between topsoil and subsoil conditions. At a lower organic carbon content in the subsoil (C_org= 0.16%, 0.36%) compared to topsoil (C_org= 1.10%, 1.36%) no leaching of ATC was observed, and ATC was completely transformed. The clear formation of TZ across all studies confirms ATC as a relevant parent compound of a ubiquitously found metabolite.