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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Diuron has to be regarded as a well dissipating compound from the water phase of water/sediment systems. Degradation from the sediment phase is slower but field conditions are likely to increase degradation rates further.

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The dissipation from the water phase and the kinetics of metabolic breakdown of [phenyl-UL-14C]Diuron were studied in two water/sediment systems; the River Erft (approx. 500 m before flow into the Rhine river), and the Hönniger Weiher Pond (an artificial dammed pond).Diuron was quickly eliminated from the water body, either by translocation into the sediment or by degradation. The calculated DT50values of Diuron for the supernatant water phase in both systems were 4 and 9 days, respectively for the Hönniger Weiher and River Erft. The DT50values for Diuron in the total systems were 48 and 232 days for River Erft or Hönniger Weiher, respectively. The metabolic results demonstrate the existence of two degradation pathways: In the one way demethylation to DCPMU (System River Erft and Hönniger Weiher) and in the other way dechlorination to m-CPDMU (Hönniger Weiher). The water/sediment systems tested showed differences in the metabolism of Diuron which may be explained by differences in the microbial status. Additional biological activities (plants) and light exposure will raise the degradation rates under field conditions (Sneikus, 2001).