Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Stability

Isotianilis regarded as degradable by photolytically induced processes in air with an estimated half-life for the reaction with OH-radicals of 4.47 days (24 h day; OH-concentration 0.5E+06 OH/cm³).

Studying the phototransformation in water resulted in half-lives of 1.8 to 2.3 days in natural water under experimental conditions corresponding to 7.4 to 9.4 real days in Tokyo spring. Isotianilwas rapidly and extensively degraded during aqueous photolysis at 25 ± 2 °C. The photolysis produced a complex mixture of components from both the natural water and distilled water solutions. The major degradate was anthranilonitrile amounting for up to 14.5% of the applied radioactivity via amide cleavage. A number of minor degradates were also formed and they were gradually mineralized to 14CO2. Based on the results of this study, photolysis will be a major route of elimination of Isotianil from the aquatic environment.

Photodegradation in soil resulted in a DT50 value of 17.6 days for irradiated samples and 10.7 days for the dark controls. Based on the experimental DT50 value of 17.6 days for irradiated samples, the DT50 of Isotianil under kind of extreme environmental conditions is calculated to be 50.5 solar summer-days at Phoenix, Arizona, USA. There was no difference in the degradation pathway of dark and irradiated soil samples, despite the fact that Isotianil in dark samples degraded much faster and formed higher amounts of the degradation products, i.e. of DCIT-acid. From this study, it is evident that photo-transformation of Isotianil on soil surface does not contribute to the elimination of this compound from the environment. No metabolites of Isotianil formed exclusively by sunlight irradiation on soil surface have to be considered for risk assessments.

Based on a study performed according to OECD 111, the hydrolysis of Isotianil is considered as slow to moderate under environmental conditions (25 °C) with specific half-lives of 60.8 – 71.4 days (pH 7) and 53.7 – 55.0 days (pH 9).

Biodegradation

Isotianil is not readily biodegradable in water with 6% degradation after 28 days. However, simulation tests in water and sediment and soil biodegradation tests under aerobic and anaerobic conditions show that Isotianil and its degradation / transformation products have no potential for accumulation. The half-lives for the degradation of Isotianil in the total water/sediment system and in soil are 2.0 to 3.1 days and 0.1 to 1.2 days, respectively. Consequently, Isotianil will not persist in the environment.

Bioaccumulation

Isotianil is not bioacumulative with BCFs of 121 (based on whole fish, wet weight) and 72 (normalised to 5% lipid content) for two loading rates.

Transport and distribution

The low Henry’s law constant for the substance of 5.22*10-9 Pa m³/mole at 25 °C (HENRYWIN v3.2) shows that the test material is not volatile and will not evaporate into the atmosphere from water surfaces. Experimentally derived log Koc values of 3.0 to 3.6 indicate a strong potential to adsorb to soil and sediment.

As the test substance has a low water solubility (0.5 mg/L) it is expected that the aquatic environment is only exposed to small amounts of the substance even though the test material is not eliminated immediately through biotic or abiotic degradation when present in the aquatic environment.

Due to its structural properties Isotianil has the potential to dissociate under environmental conditions. However, the pka of 8.92 indicates that Isotianil will be present mainly as undissociated form in the relevant environmental pH range (5-9).