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Biodegradation in water: screening tests

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biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study was conducted in accordance with recognized scientific methods and procedures. The study meets national and international scientific methods and provides sufficient information to support the conclusion.
equivalent or similar to guideline
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
BOD5 method
Principles of method if other than guideline:
The method followed the recommendations as laid down in the Her Majesty's Stationery Office publication "5 Day Biochemical Oxygen Demand (BOD5) Second Edition 1988 (with Dissolved Oxygen in Waters, Amendments 1988), Methods for the Examination of Waters and Associated Materials".  Method is very similar to OECD 301.
GLP compliance:
yes (incl. QA statement)
GLP for COD method: yes
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Inoculum: Sewage works final effluent, Severn Trent Water Plc., Belper sewage treatment works, Belper, Derbyshire.  Date of collection 2 April 1992. The sample was allowed to settle for 30 minutes and the supernatant withdrawn for test.
Duration of test (contact time):
5 d
Initial conc.:
120 mg/L
Based on:
other: Test substance
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
BOD bottles were filled by siphon and firmly stoppered to exclude all air bubbles. Sufficient bottles were prepared to allow a single oxygen determination per bottle to be made at day 0 and day 5 for each test medium (duplicate bottles at each sampling time). Bottles were incubated in a water bath at 20 degrees C for 5 days. 

Chemical Oxygen Demand (COD) was determined using a semi-micro sample digestion (Hach) technique. Reaction vials containing premeasured amounts of sulfuric acid, potassium dichromate, silver catalyst plus 2 ml water sample were heated at 150 degrees C for 2 hours and the COD values read from a Hach DR/2000 Direct Reading Spectrophotometer.
Reference substance:
other: glucose/glutamic acid (1:49)
Remarks on result:
other: refer to BOD results
15.1 other: mg/L
66 other: mg O2 per litre, for the 60% aqueous solution.
Results with reference substance:
BOD5 240.1 mg O2/L (at nominal test concentration 105 mg/L)
Validity criteria fulfilled:
DOC variation in the blank fulfilled the requirements
Interpretation of results:
other: Not readily biodegradable
It was determined in a reliable BOD5 study conducted in compliance with GLP that HEDP is not readily biodegradable.

Description of key information

The substance is not readily biodegradable, based on the results of the BOD5 test.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The ready biodegradability study using HEDP acid was selected as the key study (Handley & Mead, 1992). This study followed the 5 day Biological Oxygen Demand (BOD5) method (similar to OECD 301). The study is considered to be a reliable study to demonstrate that the substance is not readily biodegradable.

A very large number of supporting studies are available for the acid form and for the sodium salt of HEDP associated with WWTP simulation, aerobic and anaerobic studies using radiolabelling etc. The potassium salt can be expected to have equivalent properties. All of the available evidence supports a lack of biodegradability even where pre-adapted inoculum is used, though in some cases removal from the system by adsorption processes has occurred.