Orthosulfamuron

Endpoint summary

Description of key information

Hydrolysis

Hydrolysis rate of purified active substance at pH values 4, 7 and 9 under sterile conditions in the absence of light was investigated according to EEC method C7. Rate of hydrolysis and half life were found to be 0.0284 d-1 and 24.4 d respectively at 25C and pH7.

Phototransformation in soil

Soil photolysis followed the same pattern as observed under aerobic conditions although much slower. Half life (DT50) of the substance was 18 -40 days under a xenon lamp. There was less than 5% degradation after 15 days. The main degradation products were IR7863 and IR7825.

Biodegradation in water

Under the test conditions the percentage biodegradation of IR5878 was determined to be 0% after 28 days of incubation, based on ThOD_NH4and ThOD_NO3. IR5878 can therefore be considered to be not ready biodegradable. The reference item Aniline was sufficiently degraded to a mean of 72% after 14 days, and to a mean of 91% after 28 days of incubation, thus confirming the suitability of the used activated sludge inoculum. Based on the results of a biodegradability study, IR5878 is not a readily biodegradable substance.

Biodegradation in water and sediment

The biodegradation of IR5878 was studied in a pond system and a river system over 155 days. Several degradation products were separated including IR7825 which exceeded 10% AR. DT50 was 10 days for surface water in pond and river systems. DT50 were 27 and 20 days for the whole system in pond and river systems respectively.

Biodegradation in soil

The degradation if IR5878 was studied in the dark in sandy loam (M1 bis) and silty clay loam (Fer) paddy field soils. IR5878 degraded faster in the M1 bis system than the Fer system. The DT50 values were between 8 and 16 days in surface water, 33 and 83 days in soil and 30 and 75 days in the whole system.

Absorption/Desorption

Preliminary test showed that:

-         the time necessary to reach adsorption equilibrium was 2 hours for all the tested soils;

-         four cycles of desorption were necessary to find negligible amounts to be released;

-         IR5878 was substantially stable during the adsorption step.

Advanced test: based on the results of the Preliminary test, the incubation time was 2 hours for all the tested soils. The amount of adsorbed IR5878 was 43.35%, 54.09%, 46.63% and 46.51% as percentage mean value respectively in B-1, G-2, M-2 and VM-1 soil. At the end of the desorption cycles, the amount of desorbed IR5878 was 50.35%, 51.20%, 39.21% and 73.70% as percentage mean value respectively in B-1, G-2, M-2 and VM-1 soil. The data of adsorption isotherms fitted very well (r²> 0.97) with Freundlich equation. Mass balance was ≥ 93%. The adsorption-desorption study with¹⁴C-IR5878 was carried out in four different soils.The calculated K_oc were 283, 328, 550 and 249, for sandy loam, silt loam, silt loam and clay loam soils, respectively