Registration Dossier

Environmental fate & pathways

Biodegradation in water: screening tests

Administrative data

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1991-1992
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1992
Report Date:
1992

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Details on test material:
The test substance, parachlorometaxylenol, was supplied by Reckin and Colman Products, Dansom Lane, Kingston-upon-H ull.

The sample (Batch number DS7539) was received on 11 July 1991 and was assigned the Brixharn code V540. It was a colourless crystalline solid.

The theoretical oxygen demand of the substance was l.99 g Oif g (Ref 3).

The sample was stored in the dark at ambient temperature in the container in which it was received until required for testing when an appropriate subsarnple was provided for the test operator. Solutions of the test substance were prepared in deionised water.

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
The sample was stored in the dark at ambient temperature in the container in which it was received until required for testing when an appropriate subsarnple was provided for the test operator. Solutions of the test substance were prepared in deionised water.
Duration of test (contact time):
118 d
Initial test substance concentration
Initial conc.:
>= 98 - <= 100 other:
Based on:
other: BOD
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
other: non-purgeable dissolved organic carbon content (NPOC)
Details on study design:
A SCAS unit was dosed with the test substance at a concentration of 5 rng/l for a period of 118 days. The test substance concentration was selected to be below that which had been found to be inhibitory to microorganisms in a previous study (Ref 3) and was too low to allow reliable determinations of biodegradability by carbon removal. Therefore, at fortnightly intervals for a period of 10 weeks, the activated sludge from the SCAS system was used to provide the inoculurn for 5-day (closed
bottle test) determinations of biochemical oxygen demand (BOD5), to indicate whether acclimatisation (adaptation) of the microorganisms had occurred, enabling biodegradation of parachlorometaxylenol. If a positive indication had been obtained,
the intention was to carry out a 28-day closed bottle test (OECD 301D) using the acclimatised seed.

BlA456/B page 7

After 90 days, specific chemical analysis on the feed and effluent from the SCAS unit was carried out. This was repeated on Day 109 and followed by further analyses designed to distinguish between biodegradation, sorption to sludge solids and volatilisation.

Reference substance
Reference substance:
not specified

Results and discussion

Preliminary study:
(SCAS) system (OECD 302A, Ref 1) was used to acclimatise the microorganisms, with 5-day closed bottle tests (based on OECD 301D, Ref 2) and specific analysis to determine biodegradation
Test performance:
The substance had previously been found to be not readily biodegradable by 28-day closed bottle test. A SCAS unit was dosed with the test substance at a concentration of 5 rng/l for a period of 118 days. The test substance concentration was selected to be below that which had been found to be inhibitory to microorganisms in a previous study (Ref 3) and was too low to allow reliable determinations of biodegradability by carbon removal.
% Degradation
Parameter:
other: carbon removal.
Value:
>= 5 - <= 5
Sampling time:
118 d
Details on results:
There was no significant inhibition of either control or acclimatised microorganisms at a test substance concentration of 5 mg/l.

BOD5 / COD results

BOD5 / COD
Parameter:
BOD5
Value:
8.4 other: mg/l
Results with reference substance:
The results of the analyses of the SCAS feed and effluent on Days 90 and 109 are given in Table 4.

Both sets of data indicate that in excess of 96% removal of parachlorometaxylenol was occurring during the 24 hour interval between unit dosing. (Note that the test feed was diluted by a factor of 2 on addition to the SCAS unit).

Because no indication of biodegradation had been obtained from the fortnightly BODs measurements, the experiment to determine the removal mechanism was initiated

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable
Conclusions:
SCAS removal mechanisms

The results of the experiment to distinguish between biodegradation, sorprion to sludge solids and volatility, as mechanisms for the observed removal of parachlorometaxylenol, are given in Table 5 and are plotted in Figure I.

The decline in parachlorometaxylenol concenrrarion in the "active" treatment was 60% in the 24 hour period, less than that in the SCAS test unit (>98% in 24 hours). However, in the "volatility control" the measured concentrations had not declined after 24 hours, eliminating volatility as a significant removal mechanism in the SCAS system. In the "poisoned" treatment, 10% loss of parachlorometaxylenol occurred af ter 24 hours, attributable to sorption to the sludge solids.

It was concluded that the predominant mechanism for the observed removal of parachlorometaxylenol in the SCAS system was biodegradation, and that the substance was inherently biodegradable.
Executive summary:

TABLE 5

PARACHLOROMETAXYLENOL:       INVESTIGATION OF SCAS REMOVAL MECHANISM

Time (hr)       Nominal concen- tration (mg/l)       Measured concentration (mg/l)

             SCAS       "Active"       "Poisoned"       "Volatility control"

0       2.5       (2.0)*       (2.0)*       2.0       2.1

0.5       -       -       -       2.0       -

1       -       1.5       1.6       2.0       2.2

2       -       1.2       1.6       2.0       l.9

4       -       0.57       1.6       2.0       1.8

24       -       <0.022       0.8       1.8       2.2

* Measured concentration of the "poisoned" treatment taken as the initial value for the SCAS and "active" treatments.