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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

The substance undergoes slow primary degradation in sediment and water under anaerobic conditions.

Key value for chemical safety assessment

Half-life in freshwater:
1 780 d
at the temperature of:
298.15 K
Half-life in freshwater sediment:
1 780 d
at the temperature of:
298.15 K

Additional information

The biodegradation in sediment study is a Klimisch-1, GLP-compliant study, sponsored by Ciba-Geigy and carried out in 1993 by PTRL-West Inc. (Skinner WS) according to EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism) [equivalent or similar to OECD 308 (Aerobic and anaerobic transformation in aquatic sediment systems), EC C.24], but with only one sediment instead of two. The objective of the study was to evaluate the nature and extent of metabolism of the test substance in anaerobic water and sediment over a 360-day period. Sediment (clay loam - USDA classification) and water collected from a eutrophic rice field in Washington county, Mississippi was used without prior drying or sieving, but was organically amended (glucose) 15 days prior to the water phase being fortified with 9.87μg/mL (ppm) of 14C-labelled test substance. The transformation of the test substance was followed via periodic radio analysis of the water, the sediment (extractable and non-extractable radiocarbon) as well as for 14CO2 and volatile organics. Selected samples were further analyzed by HPLC and two-dimensional TLC to confirm the identity of 14C-residues. The percentage of applied radiocarbon in water decreased from 25% on Day 0 to 2% by Day 90 as 14C-residues adsorbed to the sediment. The model metabolites GS-11354 (2-amino-), GS-34048 (6-hydroxy-), and GS-34161 (Prometryn) were identified in both sediment and water. The water also contained G-30888 [4,6-dihydroxy- (or 4,6-dione-)]. In the entire system, several transient minor unidentified metabolites were also observed, each representing < 0.4% of the applied radiocarbon on a replicate average basis. Intact test substance or its hydrolysis product(s) were successfully released from bound residues by reflux under acidic and basic conditions to a level below 10% of the applied radiocarbon. The major 14C-residue throughout the study was the test substance. The identity of the test substance and the GS-11354 and GS-34048 transformation products were confirmed by HPLC, two-dimensional TLC and GC-MS. The test substance was shown to have an estimated half-life of 1780 days in anaerobic water and sediment.