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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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According to the REACH regulation Annex IX column 2, studies on the biodegradation in water and sediment do not need to be conducted if the test item is readily biodegradable.

However, additional data obtained from different wastewater simulation tests conducted in accordance of OECD Guideline 314 are available. The results of these studies were used to calculate the degradation kinetic constant k for STP, surface water and soil.

In three die-away studies performed in accordance with OECD Guideline 314 A and 314 B the biodegradation potential of AES (C14, 3EO) in wastewater was investigated. For testing raw sewage and activated sludge (collected on different dates) from a municipal waste water treatment plant receiving predominantly domestic wastewater was used. The removal of AES (C14, 3EO) in raw sewage was 98.8% after 24 h and 98.0% in activated sludge after approx. 5 h.

Using raw sewage as inoculum, the test substance was converted to metabolites and incorporated into solids. Mineralisation did not occur. Using activated sludge as inoculum the test substances was mineralized, converted to metabolites and incorporated into solids (P&G, 1988).

In a further wastewater simulation study Marks (P&G, 1994) investigated the degradation of AES (C14, 3EO) under aerobic conditions in accordance with OECD Guideline 314 B. Using activated sludge of a sewage treatment plant fed predominately with domestic sewage AES (C14, 3EO) was mineralized to 88.3% after 28 days of exposure.

In a test conducted similarly to OECD Guideline 314 C AES (C14, 3EO) was incubated in anaerobic digester sludge. After 21 h 91% of the radiolabelled test substance was mineralized. The half-life for primary degradation was determined as 2.6 h while the half-life of ultimate degradation was 3 h (P&G, 1994).

This result was supported by a similar test with AES (C14, 3EO) according to OECD Guideline 314 C. After 14 days 88% of the applied radioactivity was recovered in evolving gases. The half-life was determined to be 0.67 d (P&G, 1994).

Biodegradation of AES (C14, 3EO) directly discharged into surface water was simulated in a test following the procedures of OECD Guideline 314 D. In surface water (89% river water, 10% sewage treatment plant effluent and 1% activated sludge), 39.7% of AES (C14, 3EO) were mineralized after 48 hours. Remained parent compounds and metabolites were not found. However, 60.3% were determined as non-extractable residues (P&G, 1996).

In another simulation test in surface water in accordance to OECD Guideline 314 D a mineralization rate > 87% was observed after 28 days of exposure (P&G, 1994).

Taking into account all available results obtained from the different simulation tests conducted according to OECD Guideline 314, it was demonstrated, that alkylethoxysulfates are not persistent in water and are ultimately removed under aerobic and anaerobic conditions.