Ametryn

Biodegradation in soil

Description of key information

The substance undergoes rapid primary degradation in soil under aerobic conditions, with the endpoint of the pathway being mineralisation to carbon dioxide or incorporation into residues bound to the soil.  The substance is stable under anaerobic conditions.
Aerobic sediment DT50 = 9.2 days at 20°C and 24.3 days at 10°C.

Key value for chemical safety assessment

Half-life in soil:

9.2 d

at the temperature of:

293.15 K

Additional information

The biodegradation in soil study is a Klimisch-1, GLP-compliant study, sponsored and carried out in 1999 by Novartis Crop Protection AG (Glänzel A) in accordance with Commission Directive 95/36/EC of 14 July 1995 amending Council Directive 91/414/EEC: Annex II: 7.1 Fate and Behaviour in soil, 7.1.1. Route and rate of Degradation [equivalent or similar to OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil), but with only one soil type being used for all four test conditions]. The objective of the study was to evaluate the degradation of the test material aerobically in soil at 10°C and at 20°C as well as anaerobically in waterlogged soil at 20°C and aerobically/anaerobically in soil that was waterlogged after an initial aerobic period. The soil (aerobic) or water (anaerobic) was treated with 14C-labelled test substance at a field rate of 4.2 kg active ingredient per hectare. For the aerobic/anaerobic test, the initial aerobic period was 14 days - about one half-life. The soil used was loam (USDA classification) collected from meadows that had not been treated with fertiliser or pesticides, which had been slightly air-dried, sieved through a 2 mm sieve, and adjusted with deionised water to a moisture level 40% of its maximum water holding capacity (MWC). For anaerobic conditions, the soil was waterlogged with deionised water. The test substance was rapidly degraded (half life = 9.2 days at 20°C and 24.3 days 10°C) at a soil moisture content of 40% MWC under aerobic conditions yielding mainly at first the sulfoxide NOA 423271 which was further oxidized to the sulfonic acid NOA 428383. In a second pathway NOA 423271 was degraded by reduction of the sulfoxide group to hydroxyl (G 34048) followed by oxidation of the N-ethyl group to carboxymethyl (NOA 438707). Both NOA 428383 and NOA 438707 are intermediates. The endpoint of the metabolic pathway is the mineralization to carbon dioxide and the formation of bound residues. Under anaerobic conditions, almost no degradation of the test substance was found, and under aerobic/anaerobic conditions only the sulfoxide NOA 423271 was further degraded, yielding the original test substance, G 34048 and bound residues.