Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

General discussion of environmental fate and pathways

Stability

Phototransformation in air:

The test substance (diflufenzopyr sodium salt) degrades in the atmosphere with a DT50 value of 0.233 days (24-hr day; corresponding to 5.593 hours). As the test substance contains no olefinic carbon-carbon double and acetylic triple bonds, it is not expected to react with ozone.

Hydrolysis:

The hydrolysis rate of the test substance (diflufenzopyr) was determined at 1 ppm concentration in pH 5.0, pH 7.0, and pH 9.0 buffered aqueous solutions at 25 °C. The hydrolysis rate was 0.0538 ± 0.0038 day-1 at pH 5.0, 0.0290 ± 0.0011 day-1 at pH 7.0 and 0.0270 ± 0.0015 day-1 at pH 9.0. Thus the half-life of the test substance's hydrolysis was determined to be 12.9 days at pH 5.0, 23.9 days at pH 7.0 and 25.6 days at pH 9.0

Phototransformation in water:

Photolysis of 14C-labelled test substance (diflufenzopyr) (pyridine and phenyl labels) was conducted in aqueous buffer of pH 5, 7 and 9 at 22 ± 1° C under sterile conditions. The average degradation half-lives were about 16 days (pH 5), 27 days (pH 7) and 22 days (pH 9). The test substance also degraded in the dark control buffers of pH 5, 7 and 9. The average degradation half-lives were about 24 days (pH 5), 39 days (pH 7) and 41 days (pH 9). The test substance degraded to a large number of products (>14). The test substance, M1, M2, M6, M7, M23, M24, P2, P5 and P11 were major degradation products. Rest of the degradation products were minor and none exceeded ~6% TAR.

Phototransformation in soil:

A photolysis study with 14C-labelled test substance (diflufenzopyr) (phenyl and pyridine labels) was conducted on soil at 22 ± 1° C for 15 days for phenyl label and for about 18 days for pyridine label. The test substance degraded with a moderate rate under photolytic conditions with a half-life of about 10 days. The test substance in dark control samples degraded slowly compared to photolyzed samples and had a half-life about 20 days. The test substance degraded to a large number of products. M1 and M6 were the only degradation products found in excess of 10% TAR. The test substance itself was the largest radioactive residue at every sampling interval with the exception of the last sampling interval in the case of pyridine label in which M6 was the largest product.

Biodegradation

Biodegradation in water: screening tests

There are several higher tier biodegradation studies available assessing the biodegradation of the test substance in water and sediment, and in soil showing a moderately fast degradation/dissipation. However, in the light of the principle of precaution and the worst case the substance is thus regarded to be not readily biodegradable.

Biodegradation in water and sediment: simulation tests

The anaerobic aquatic metabolism of 14C-labelled test substance (diflufenzopyr) was studied in sediment and pond water. During the study the primary metabolite (difluoroaniline metabolite) reached a maximum concentration of 22% TAR (total applied radioactivity) by day 61 and decreased to 1% TAR by 187 DAT. The DT50 of the metabolite difluoroaniline was 27.4 days. The intermediate metabolite BH 654-5 ranged from 0.6% to 8% TAR and at 187 DAT accounted for less than 1% TAR. The present study showed that the test substance is rapidly degraded under anarobic conditions. The DT50 of the test substance was reported to be about 7.5 days. The half-lives in water and sediment were determined to be 5.75 d at 25 °C and 7.87 d at 25 °C, respectively.

Biodegradation in soil

The test substance (diflufenzopyr) degraded with a moderate rate under aerobic conditions with a half-life of about 18 days. The test substance degraded to a number of products. Metabolites M1 (8-Methyl-5-hydroxy-pyrido(2,3 d)-pyridazinone), M9 (8-Methylpyrido(2,3-d)pyridazine-2,5(1H,6H)-dione) and CO2 were the only degradation products found in excess of 10% TAR (total applied radiation) during the course of the study.

Bioaccumulation

Bioaccumulation: aquatic / sediment

The performance of a test for bioaccumulation in aquatic species, preferably fish, is scientifically unjustified.

REACH Regulation No. 1907/2006, Annex IX, Sect. 9.3.2, Col. 2, states as follows:

“9.3.2 The study need not be conducted if:

- the substance has a low potential for bioaccumulation (for instance a log Kow <= 3) and/or a low potential to cross biological membranes, or

- direct and indirect exposure of the aquatic environment is unlikely. ”

The Log Pow of the test substance (Diflufenzopyr sodium salt) was calculated to be -0.59 at 25 °C. Therefore, the test substance was considered to have no bioaccumulation potential.

Transport and distribution

Adsorption / desorption

The adsorption and desorption characteristics of 14C-labelled test substance (diflufenzopyr sodium salt) were examined in seven soils (5 US soils and 2 EU soils) by the batch equilibrium method. The adsorption Koc for the loam soil are generally higher than that of soils with higher sand content. However, the desorption Koc values of all soils are considerably greater than the corresponding adsorption Koc values indicating a stronger affinity to soil once adsorbed.

Average Koc value of all US soils for the adsorption based on the linear model is 60, without silt loam the Koc value is reduced to 40. The corresponding average Koc values from the Freundlich model are 68 and 47, respectively. For the EU soils Loamy Sand and Sandy Clay Loam the adsorption Koc values from the Freundlich model and the linear isotherm model are reported to be 30 and 53 and 24 and 41, respectively.

Henry's Law constant

The Henry's Law constant of the test substance (diflufenzopyr sodium salt) was calculated to be 2.11E-013 Pa-m3/mole using HENRYWIN (v3.20) Program (EpiWIN software).