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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water and sediment: simulation testing, other
Type of information:
experimental study
Adequacy of study:
key study
Study period:
July 17 to September 18, 2006
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study has a high relevant, is adequate and performed under GLP.
Qualifier:
no guideline available
Principles of method if other than guideline:
"Die-away of Radiolabeled Semi-Volatile Organic Compounds in Activated Sludge or River Water (draft)"; A Standard Operating Procedure developed by the testing laboratory and the company Procter & Gamble.
GLP compliance:
yes (incl. certificate)
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: Natural water with activated sludge added at a level of 10 mg AS/litre.
Details on source and properties of surface water:
River water was collected from the Choptank River in Denton, Maryland. The pH, total suspended solid concentration, total hardness and total organic carbon concentration of the river water was measured:
pH 6.5, Total Suspended Solids 13 mg/l, Hardness 36 mg CaCo3/l, TOC 6.2 mg C/l, Total Plate count 1.9 * 10^3 CFU/ml
Details on inoculum:
Activated sludge mixed liquor was collected from the Cambridge Wastewater Treatment Facility, Cambridge, Maryland. The sludge was sieved through a 2 mm mesh and the total suspended solids concentration of sludge was measured to supplement the river water. River water contained 13 mg ds/l. It was supplemented with activated sludge solids at a rate of 10 mg ds/L.
Duration of test (contact time):
28 d
Initial conc.:
5 µg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
Compartment:
other: water / sediment, material (mass) balance
Remarks on result:
other: See the section remarks for the detailed mass balance.
Remarks on result:
not measured/tested
Compartment:
water
DT50:
9 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: r2 = 0.999.
Other kinetic parameters:
other: initial first-order loss rate 0.004 ± 0.0004 hr-1... (see attached file)
Transformation products:
not specified
Remarks:
A range of metabolites was formed at different rates, however the identity of the transformation products is not specified.
Details on transformation products:
More polar degradation products were formed, see field 'Details on Results'
Evaporation of parent compound:
yes
Volatile metabolites:
not specified
Residues:
yes
Details on results:
Rad-TLC of the solvent extracts from the abiotic treatment revealed one major peak associated with the parent material at a retention factor (Rf) of 0.62 to 0.69 that remained consistent throughout the experiment. The parent material eluted with Rf 0.63-0.69 in the biotic treatments. The Rf of the standard ranged from 0.62 to 0.68. The total recovery for the individual samples ranged between 83 and 93%.

Rad-TLC of the solvent extracts from the biotic treatment revealed four distinct peaks. The disappearance of parent was associated with the appearance of three polar peaks. The peak (Rf 0.63-0.69) associated with the parent material was present at 84.02% of the initial activity at the 5 minutes sampling interval and declined to 28.87% by the termination of the test on day 28. Three polar peaks eluted in the following manner: The first peak with a Rf range of 0.44 to 0.51 was detected at 4.04% of initial activity on day 7, increased to a maximum level of 4.86% by day 14 and was detected at 4.70% on day 28. The second peak with a Rf range of 0.28 to 0.34 was detected at 6.12% of initial activity on day 7 and increased to a maxium level of 9.79% on day 28. The third peak that remained at the origin of the plate (Rf<0.00-0.06) was detected at 4.75% of initial activity on day 7, increased to a maximum level of 6.75% by day 21 and was detected at 5.82% on day 28. For the biotic treatment, the level of activity associated with the extracted solids was variable and ranged from 0.63 to 1.01%. For the abiotic treatment, the amount of material associated with the extracted sludge solids increased over time from 0.79% at the 5 minute sampling interval to 5.30% on day 28. The kinetic analysis was as follows: The loss of parent test material was described by 2 compartment model which included an initial first-order loss followed by a second first-order loss. 58.9% +/- 6.4% of parent degraded at a rate constant of 0.004 +/- 0.0004 (hrs-1); 25.2% +/- 6.5% of parent degraded at a rate constant of 7.14 x 10(-7) +/- 0.0003 (hrs-1).

Mass balances were made for the components in the test medium:

Time

5 min

Day 7

Day 14

Day 21

Day 28

Abiotic Day 28

14C-AHTN , 5 mg/l, river water + 10 mg AS/l* 

% recovered in extracts with solvent

                  As parent

84.0

54.6

39.5

32.2

28.9

44.2

                  As metabolite

0

14.9

19.3

21.2

20.3

0

% recovered in aqueous

0.93

0.46

0.83

0.84

0.79

0.15

% not extractable from solids

0.63

0.99

0.80

1.0

0.84

5.3

% volatilised

n.a.

15.9

26.4

33.8

40.4

42.6

Total recovery %

85.6

86.8

86.8

89.1

91.2

92.2

* AS: Activated sludge

Validity criteria fulfilled:
yes
Conclusions:
AHTN steadily disappeared with an overall half-life of 200 hours (9 days). A range of metabolites was formed at different rates and with increasing polarity in time.
Executive summary:

The objective of the study was to determine the extent and rate of primary and ultimate biodegradation of AHTN (radiolabeled) in river water. The test apparatus consisted of two, amber glass 1 gallon (3.8 liter) jugs (test vessels) each containing 2 liters of biologically active (biotic) or abiotic river water adjusted to a target TSS level of 13 mg/l and supplemented with activated sludge solids at a rate of 10 mg/l. The abiotic control was identical to the biologically active treatment with the exception that it was amended at a nominal concentration of 1 g/l with mercuric chloride. 14C test material was dosed to both biotic and abiotic test vessels at a nominal concentration of 5 ug/l. Samples were removed from the test vessels over a 28 day period. Dissappearance of parent and the formation of metabolites were determined by radio thin layer chromatography (Rad-TLC). The solids were combusted to determine the amount of radioactivity remaining in the solids. Sampling of biotic test vessels was conducted at 5 minutes, Days 7, 14, 21, 28 and abiotic test vessels at 5 minutes and Day 28. Results were calculated as percent recovered in extracts (parent or metabolite), percent recovered in aqueous and solids, and percent volatilized. Percentages are the average of the three replicates at each sampling interval.

 

Rad-TLC of the solvent extracts from the abiotic treatment revealed one major peak associated with the parent material at a retention factor (Rf) of 0.62 to 0.69 that remained consistent throughout the experiment. The Rf of the standard ranged from 0.62 to 0.68. Rad-TLC of the solvent extracts from the biotic treatment revealed four distinct peaks. The disappearance of parent was associated with the appearance of three polar peaks. The peak (Rf 0.63-0.69) associated with the parent material was present at 84.02% of the initial activity at the 5 minutes sampling interval and declined to 28.87% by the termination of the test on day 28. Three polar peaks eluted in the following manner: The first peak with a Rf range of 0.44 to 0.51 was detected at 4.04% of initial activity on day 7, increased to a maximum level of 4.86% by day 14 and was detected at 4.70% on day 28. The second peak with a Rf range of 0.28 to 0.34 was detected at 6.12% of initial activity on day 7 and increased to a maxium level of 9.79% on day 28. The third peak that remained at the origin of the plate (Rf0.00-0.06) was detected at 4.75% of initial activity on day 7, increased to a maximum level of 6.75% by day 21 and was detected at 5.82% on day 28. For the biotic treatment, the level of activity associated with the extracted solids was variable and ranged from 0.63 to 1.01%. For the abiotic treatment, the amount of material associated with the extracted sludge solids increased over time from 0.79% at the 5 minute sampling interval to 5.30% on day 28. The kinetic analysis was as follows: The loss of parent test material was described by 2 compartment model which included an initial first-order loss followed by a second first-order loss. 58.9% +/- 6.4% of parent degraded at a rate constant of 0.004 +/- 0.0004 (hrs-1); 25.2% +/- 6.5% of parent degraded at a rate constant of 7.14 x 10(-7) +/- 0.0003 (hrs-1).

In conclusion, the overall half-life of AHTN in this study with river water was shown to be 200 hours (9 days) and the biological degradation after 28 days was 42%. With 10 mg suspended solids from activated sludge, the conditions in the river die-away test simulate the situation after release of AHTN in effluent into river with respect to the concentration and origin of suspended solids in the receiving river. The sediment downstream of a STP is formed by settlement of suspended solids that will originate at least partly from the solids discharged with the effluent (30 mg/l). Therefore the conditions are environmentally relevant but do not correspond with standard biodegradation simulation tests in surface water, where an amendment with sediment from the same site is allowed, but not with suspended solids derived directly from an STP. With 5 microgram/liter is the AHTN concentration in the test still relatively high.

Description of key information

Aquatic degradation has been assessed in three studies, i.e. Continuous activated sludge, a die-away study in activated sludge and a die-away study in river water. The test item is almost completely removed in sewage treatment plants and the half-life in water in a river water die-away study was less than 9 days (200 h).

Key value for chemical safety assessment

Half-life in freshwater:
200 h
at the temperature of:
20 °C

Additional information

The continuous activated sludge (CAS) study showed almost complete removal of the parent test item. Half of the test item biotransformed into more polar metabolites. The other half was removed by sorption. Volatilisation played a minor role.

In the die-away study in activated sludge, the parent test item had a half-life of 12 to 24h and was largely transformed into more polar metabolites within 20 days.

The die-away study in river water showed the disappearance of the test item. The test item in association with the appearance of more polar metabolites. The overall half-life is 9 days (200 h).

The studies were considered highly relevant and the topic has been carefully studied as is reflected in the various available reviews (see EU Risk Assessment Report AHTN). The test item does not show significant biodegradation in the screening tests, but is biotransformed into more polar metabolites, which are predicted to be less bioaccumulative and toxic than the parent compound.

The EU Risk Assessment Report adopted the key value "inherent biodegradable, not fulfilling specific criteria", that was based on all the available information about the environmental degradation of the test item.