OECD GUIDELINE FOR TESTING OF CHEMICALS

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301
Adopted:
17.07.92
OECD GUIDELINE FOR TESTING OF CHEMICALS
Adopted by the Council on 17th July 1992
Ready Biodegradability
INTRODUCTION
1. In this Guideline six methods are described that permit the screening of chemicals for ready
biodegradability in an aerobic aqueous medium. They are:
301 A: DOC Die-Away
301 B: CO2 Evolution (Modified Sturm Test)
301 C: MITI (I) (Ministry of International Trade and
Industry, Japan)
301 D: Closed Bottle
301 E: Modified OECD Screening
301 F: Manometric Respirometry
Method 301 A is similar to the ISO Standard 7827-1984 and replaces the Modified AFNOR
method; AFNOR has adopted the ISO standard. Methods 301 B, 301 D and 301 E are modified
versions of the earlier OECD Guidelines adopted in 1981. Method 301 C is virtually identical with
earlier Guideline 301 C (MITI I). Method 301 F is new; it is similar to 301 C differing mainly in the
inocula employed.
2. Much experience has accumulated with the six methods over the years including an OECD
inter-laboratory comparison exercise (ring test) in 1988. The accumulated experience, and the ring
test, have confirmed that the methods may be used for the assessment of ready biodegradability.
However, depending on the physical characteristics of the substance to be tested, a particular method
may be preferred.
3. General considerations including those common to all six methods are given hereafter. Details
of individual methods are given under separate headings (301 A to F). Throughout the text the reader
is referred to the Annexes which contain definitions (Annex I), formulas and useful guidance material.
GENERAL PRINCIPLE OF THE TESTS
4. A solution, or suspension, of the test substance in a mineral medium is inoculated and
incubated under aerobic conditions in the dark or in diffuse light. The amount of DOC in the test
solution due to the inoculum should be kept as low as possible compared with the amount of organic
carbon due to the test substance. Allowance is made for the endogenous activity of the inoculum by
running parallel blanks with inoculum but without test substance, although the endogenous activity of
cells in the presence of a chemical will not exactly match that in the endogenous control. A reference
compound is run in parallel to check the operation of the procedures.
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5. In general, degradation is followed by the determination of parameters such as DOC, CO2
production and oxygen uptake and measurements are taken at sufficiently frequent intervals to allow
the identification of the beginning and end of biodegradation. With automatic respirometers the
measurement is continuous. DOC is sometimes measured in addition to another parameter but this
is usually done only at the beginning and end of the test. Specific chemical analysis can also be used
to assess primary degradation of the test substance and to determine the concentration of any
intermediate substances formed. It is obligatory in the MITI method (301 C).
6. Normally, the test lasts for 28 days. Tests however may be ended before 28 days, i.e. as soon
as the biodegradation curve has reached a plateau for at least three determinations. Tests may also
be prolonged beyond 28 days when the curve shows that biodegradation has started but that the plateau
has not been reached by day 28, but in such cases the chemical would not be classed as readily
biodegradable.
INFORMATION ON THE TEST SUBSTANCE
7. In order to select the most appropriate method, information on the chemical’s solubility,
vapour pressure and adsorption characteristics is essential. The chemical structure or formula should
be known in order to calculate theoretical values and/or check measured values of parameters, e.g.
ThOD, ThCO2, DOC, TOC, and COD. Information on the purity or the relative proportions of major
components of the test material is required in order to interpret the results obtained, especially when
the result lies close to the pass level.
8. Information on the toxicity of the test substance to bacteria (Annex II) may be very useful for
selecting appropriate test concentrations and may be essential for the correct interpretation of low
biodegradation values.
APPLICABILITY AND SELECTION OF METHODS
9. Test substances which are soluble in water to at least 100 mg/l may be assessed by all
methods, provided they are non-volatile and non-adsorbing. For those chemicals which are poorly
soluble in water, volatile or adsorbing, suitable methods are indicated in Table 1. The manner in
which poorly water-soluble chemicals and volatile chemicals can be dealt with is described in Annex
III, but in the MITI method neither solvents nor emulsifying agents are to be used. Moderately
volatile chemicals may be tested by the DOC Die-Away method if there is sufficient gas space in the
test vessels (which should be suitably stoppered). In this case, an abiotic control must be set up to
allow for any physical loss.
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TABLE 1 APPLICABILITY OF TEST METHODS
Test Analytical method Suitability for compounds which are:
poorly
soluble
volatile adsorbing
DOC Die-Away
(301 A)
Dissolved organic carbon - - +/-
CO2 Evolution (301
B)
Respirometry: CO2 evolution + - +
MITI (I)
(301 C)
Respirometry: oxygen
consumption
+ +/- +
Closed Bottle (301
D)
Respirometry: dissolved
oxygen
+/- + +
Modified OECD
Screening
(301 E)
Dissolved organic carbon - - +/-
Manometric
Respirometry (301
F)
Oxygen consumption + +/- +
PASS LEVELS
10. The pass levels for ready biodegradability are 70% removal of DOC and 60% of ThOD or
ThCO2 production for respirometric methods. They are lower in the respirometric methods since, as
some of the carbon from the test chemical is incorporated into new cells, the percentage of CO2
produced is lower than the percentage of carbon being used. These pass values have to be reached in
a 10-d window within the 28-d period of the test, except where mentioned below. The 10-d window
begins when the degree of biodegradation has reached 10% DOC, ThOD or ThCO2 and must end
before day 28 of the test. Chemicals which reach the pass levels after the 28-d period are not deemed
to be readily biodegradable. The 10-d window concept does not apply to the MITI method. The value
obtained in a 14-d window would be acceptable in the Closed Bottle method if it is considered that
the number of bottles necessary to evaluate the 10-d window causes the test to become too unwieldy.
REFERENCE COMPOUNDS
11. In order to check the procedure, reference compounds which meet the criteria for ready
biodegradability are tested by setting up an appropriate vessel in parallel as part of normal test runs.
Suitable compounds are aniline (freshly distilled), sodium acetate and sodium benzoate. These
reference compounds all degrade in these methods even when no inoculum is deliberately added. It
was suggested that a reference compound should be sought which was readily biodegradable but
required the addition of an inoculum. Potassium hydrogen phthalate has been proposed but more
evidence needs to be obtained with this chemical before it can be accepted as a reference compound.
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REPRODUCIBILITY OF TESTS
12. Because of the nature of biodegradation and of the mixed bacterial populations used as inocula,
determinations should be carried out at least in duplicate. It is usually found that the larger the
concentration of micro-organisms initially added to the test medium, the smaller will be the variation
between replicates. Ring tests have also shown that there can be large variations between results
obtained by different laboratories, but good agreement is normally obtained with easily biodegradable
compounds.
GENERAL PROCEDURES AND PREPARATIONS
13. General conditions applying to the methods are summarised in Table 2. Apparatus and other
experimental conditions pertaining specifically to an individual method are described later under the
heading for that method.
Water
14. Deionised or distilled water, free from inhibitory concentrations of toxic substances (e.g. Cu2+
ions) is used. It must contain no more than 10% of the organic carbon content introduced by the test
material. The high purity of the test water is necessary in order to eliminate high blank values.
Contamination may result from inherent impurities and also from the ion-exchange resins and lysed
material from bacteria and algae. For each series of tests, use only one batch of water, previously
checked by DOC analysis. Such a check is not necessary for the Closed Bottle method, but the
oxygen consumption of the water must be low (see 301 D, paragraph 25).
Mineral media
15. Mineral media are prepared from stock solutions of appropriate concentrations of mineral
components, namely, potassium and sodium phosphates plus ammonium chloride, calcium chloride,
magnesium sulphate and iron (III) chloride. Since only a very small inoculum, containing low
concentrations of trace elements and growth factors, is used in the Modified OECD Screening method
(301 E), the medium for this test may need to be fortified with additional compounds. The details of
the stock solutions of mineral salts, trace elements and growth factors and the proportions used are
given under the headings for the separate tests.
Methods of adding the test and reference substances
16. The method used for adding the test and reference substances to the reaction mixture depends
upon the nature of the chemical, especially its water solubility. For substances of adequate solubility,
greater than about 1 g/l, prepare stock solutions at appropriate concentrations and use aliquots to
prepare the final test solution. Dissolve less soluble substances in the mineral medium to avoid
diluting the buffer solution. Add substances which are even less soluble directly to the final mineral
medium. Finally, refer to Annex III for the handling of poorly and insoluble substances, but note that
in the MITI method (301 C) neither organic solvents nor emulsifying agents are to be used.
Inoculum
17. The inoculum may be derived from a variety of sources: activated sludge; sewage effluents
(unchlorinated); surface waters and soils; or from a mixture of these. For the DOC Die-Away (301
A), CO2 Evolution (301 B) and Manometric Respirometry (301 F) methods if activated sludge is used,
it should be taken from a treatment plant or laboratory-scale unit receiving predominantly domestic
sewage. Inocula from other sources, usually yielding lower cell densities, have been found to give
higher scattering of results. For the Modified OECD Screening (301 E) and Closed Bottle (301 D)
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methods, a more dilute inoculum without sludge flocs is needed and the preferred source is a
secondary effluent from a domestic waste water treatment plant or laboratory-scale unit. For the MITI
(I) method, the inoculum is derived from a mixture of sources. Details of the sources and preparation
of inocula are described under the headings of the specific test methods.
Pre-conditioning of inoculum
18. Inoculum may be pre-conditioned to the experimental conditions, but not pre-adapted to the
test substance. Pre-conditioning consists of aerating activated sludge (in mineral medium) or
secondary effluent for 5-7 days at the test temperature. Pre-conditioning sometimes improves the
precision of the test methods by reducing blank values. It is considered unnecessary to pre-condition
MITI (I) inoculum.
Abiotic controls
19. When required, check for the possible abiotic degradation of the test substance by determining
the removal of DOC, oxygen uptake or carbon dioxide evolution in sterile controls containing no
inoculum. Sterilize by filtration through a membrane (0.2-0.45 μm) or by the addition of a suitable
toxic substance at an appropriate concentration. If membrane filtration is used, take samples
aseptically to maintain sterility. Unless adsorption of the test substance has been ruled out beforehand,
tests which measure biodegradation as the removal of DOC, especially with activated sludge inocula,
should include an abiotic control which is inoculated and poisoned.
Number of flasks and samples
20. At least two flasks or vessels containing the test substance plus inoculum, and at least two
containing inoculum only should be used. Single vessels suffice for reference compounds plus
inoculum and, when required, for toxicity, abiotic removal and adsorption controls. The Closed Bottle
and MITI (I) methods have special requirements for the number of flasks. These are given under the
specific headings. It is mandatory to follow DOC and/or the other parameters in the test suspension
and inoculum blanks in parallel. It is advisable to follow DOC in the other flasks in parallel as well.
This may, however, not always be possible.
21. Although it is necessary to ensure that sufficient samples or readings are taken to allow the
percentage removal in the 10-d window to be assessed, it is not possible to specify accurately the
frequency of sampling because of the wide range of the lag phases and rates of degradation. In the
MITI method (301 C) and, if an automatic respirometer is used in the Manometric Respirometry
method (301 F), sampling for oxygen uptake presents no problems. In the latter method, daily
readings are adequate when non-automatic respirometers are employed. Specific advice on sampling
is given under the headings of the other four tests.
DATA AND REPORTING
Treatment of results
22. In the calculation of Dt, percentage degradation, the mean values of the duplicate measurement
of the parameter in both test vessels and inoculum blank are used. The formulas are set out in the
sections below on specific methods. The course of degradation is displayed graphically and the 10-d
window is indicated where applicable. Calculate and report the percentage removal achieved and the
value at the plateau, or at the end of the test, and/or at the end of the 10-d window, whichever is
appropriate. In respirometric methods, N-containing chemicals may affect the oxygen uptake because
of nitrification (see Annexes IV and V). Also, if the ThOD cannot be calculated because the test
material is insufficiently defined, the COD value may be used to calculate the percentage degradation.
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However, it must be borne in mind that the COD is often not as high as the ThOD as some chemicals
are very poorly oxidised in the COD test, resulting in falsely high values for percentage
biodegradation.
23. When specific chemical analytical data are available, calculate primary biodegradation from:
where:
Dt = % primary degradation at time t, normally 28 days;
Sa = residual amount of test chemical in inoculated medium at end of the test (mg);
Sb = residual amount of test chemical in the abiotic control at the end of the test (mg).
Validity of tests
24. A test is considered valid if the difference of extremes of replicate values of the removal of
the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate,
is less than 20% and if the percentage degradation of the reference compound has reached the pass
levels by day 14. If either of these conditions is not met, the test should be repeated. Because of the
stringency of the methods, low values do not necessarily mean that the test substance is not
biodegradable under environmental conditions, but indicates that more work will be necessary to
establish biodegradability.
25. If in a toxicity test, containing both the test substance and a reference compound, less than
35% degradation (based on total DOC) or less than 25% (based on total ThOD or ThCO2) occurred
within 14 days, the test substance can be assumed to be inhibitory (see Annex II for other toxicity
tests). The test series should be repeated, using a lower concentration of test substance (if this can be
done without seriously impairing the accuracy of the DOC determination) and/or a higher
concentration of inoculum, but not greater than 30 mg solids/l.
26. Other conditions for the validity of test results specific to individual methods are set out under
the headings for those tests.
Test report
27. The test report must include the following:
Test substance:
- physical nature and, where relevant, physicochemical properties;
- identification data.
Test conditions:
- inoculum: nature and sampling site(s), concentration and any pre-conditioning
treatment;
- proportion and nature of industrial waste water in sewage, if
known;
- test duration and temperature;
- in the case of poorly soluble test substances, methods of
preparation of test solutions/suspensions;
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- test method applied; scientific reasons and explanation for
any change of procedure.
Results:
- data in tabular form;
- any observed inhibition phenomena;
- any observed abiotic degradation;
- specific chemical analytical data, if available;
- analytical data on intermediates, if available;
- the graph of percentage degradation against time for the test
and reference substances, the lag phase, degradation phase,
the 10-d window and slope (see Annex I for definitions);
- percentage removal at plateau, at end of test, and/or after
10-d window.
Discussion of results.
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TABLE 2: TEST CONDITIONS
TEST DOC DIE-AWAY CO2 EVOLUTION MANOMETRIC
RESPIROMETRY
MODIFIED
OECD
SCREENING
CLOSED
BOTTLE
MITI (I)
Concentrations of test substance:
mg/l 100 2 - 10 100
mg DOC/l 10 - 40 10 - 20 10 - 40
mg ThOD/l 50 - 100 5 - 10
Concentration of inoculum:
mg/l SS < 30 30
ml effluent/l < 100 0.5 < 5
approx. cells/l 107 - 108 105 104 - 106 107 - 108
Concentration of elements in mineral medium (in mg/l):
P
N
Na
K
Mg
Ca
Fe
116
1.3
86
122
2.2
9.9
0.05 - 0.1
11.6
0.13
8.6
12.2
2.2
9.9
0.05 - 0.1
29
1.3
17.2
36.5
6.6
29.7
0.15
pH 7.4 + 0.2 preferably 7
Temperature o C 22 + 2 25 + 1o
DOC = Dissolved Organic Carbon ThOD = Theoretical Oxygen Demand SS = Suspended Solids
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301 A "DOC DIE-AWAY TEST"
INTRODUCTION
1. Matters of general interest concerning the assessment of biodegradability are discussed in
"General Procedures and Preparations" and it is advisable to read this before proceeding. For this
method, the test substance should be non-volatile and have a solubility in water of at least 100 mg/l.
Also the carbon content and, preferably, the purity or relative proportions of major components should
be known. This test is virtually the same as the ISO Standard 7827-1984. It is similar to the
Modified OECD Screening test (301 E) but allows the use of much higher microbial cell densities.
PRINCIPLE OF THE TEST
2. A measured volume of inoculated mineral medium, containing a known concentration of the
test substance (10-40 mg DOC/l) as the nominal sole source of organic carbon, is aerated in the dark
or diffuse light at 22 ± 2oC. Degradation is followed by DOC analysis at frequent intervals over a
28-day period. The degree of biodegradation is calculated by expressing the concentration of DOC
removed (corrected for that in the blank inoculum control) as a percentage of the concentration initially
present. Primary biodegradation may also be calculated from supplemental chemical analysis for
parent compound made at the beginning and end of incubation.
DESCRIPTION OF THE METHOD
Apparatus
3. Normal laboratory apparatus and:
(a) Conical flasks, e.g. 250 ml to 2 litre, depending on the volume needed for DOC
analysis. The flasks must be carefully cleaned with, for example, alcoholic
hydrochloric acid, rinsed and dried before each test;
(b) Shaking machine - to accommodate the conical flasks, either with automatic
temperature control or used in a constant temperature room, and of sufficient power
to maintain aerobic conditions in all flasks;
(c) Filtration apparatus, with suitable membranes;
(d) DOC analyser;
(e) Apparatus for determining dissolved oxygen, to check that the flask contents are
aerobic;
(f) Centrifuge.
Water
4. A description of the water to be used is given in the "General Procedures and Preparations"
(p. 5).
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Stock solutions for mineral medium
5. Prepare the following stock solutions using analytical grade reagents:
(a) Potassium dihydrogen orthophosphate, KH2PO4 . . . . . . . . . . . . . 8.50 g
Dipotassium hydrogen orthophosphate, K2HPO4 . . . . . . . . . . . . 21.75 g
Disodium hydrogen orthophosphate dihydrate,
Na2HPO4.2H2O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33.40 g
Ammonium chloride, NH4Cl . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.50 g
Dissolve in water and make up to 1 litre.
The pH of the solution should be 7.4.
(b) Calcium chloride, anhydrous, CaCl2 . . . . . . . . . . . . . . . . . . . . 27.50 g
or
Calcium chloride dihydrate, CaCl2.2H20 . . . . . . . . . . . . . . . . . . 36.40 g
Dissolve in water and make up to 1 litre.
(c) Magnesium sulphate heptahydrate, MgS04.7H20 . . . . . . . . . . . . 22.50 g
Dissolve in water and make up to 1 litre.
(d) Iron (III) chloride hexahydrate, FeCl3.6H20 . . . . . . . . . . . . . . . . . 0.25 g
Dissolve in water and make up to 1 litre.
Note: In order to avoid having to prepare this solution immediately before use, add one drop
of concentrated HCl or 0.4 g ethylene-diaminetetra-acetic acid (EDTA disodium salt)
per litre.
If a precipitate forms in a stock solution replace with a freshly made solution.
Preparation of mineral medium
6. Mix 10 ml of solution (a) with 800 ml water, then add 1 ml of solutions (b), (c) and (d) and
make up to 1 litre with water.
Stock solutions of test substances
7. When the solubility of the substance exceeds 1 g/l, dissolve 1-10 g, as appropriate, of test or
reference substance in water and make up to 1 litre. Otherwise, prepare stock solutions in mineral
medium or add the chemical directly to the mineral medium, making sure it dissolves.
Inoculum
8. The inoculum may be derived from a variety of sources: activated sludge; sewage effluents;
surface waters; soils; or from a mixture of these.
Inoculum from activated sludge
9. Collect a fresh sample of activated sludge from the aeration tank of a sewage treatment plant
or laboratory-scale unit treating predominantly domestic sewage. Remove coarse particles if necessary
by filtration through a fine sieve and keep the sludge aerobic thereafter.
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10. Alternatively, after removal of any coarse particles, settle or centrifuge (e.g. at 1100 g for 10
minutes). Discard the supernatant. The sludge may be washed in the mineral medium. Suspend the
concentrated sludge in mineral medium to yield a concentration of 3-5 g suspended solids/l.
Thereafter aerate until required.
11. Sludge should be taken from a properly working conventional treatment plant. If sludge has
to be taken from a high rate treatment plant, or is thought to contain inhibitors, it should be washed.
Settle or centrifuge the re-suspended sludge after thorough mixing, discard the supernatant and again
re-suspend the washed sludge in a further volume of mineral medium. Repeat this procedure until the
sludge is considered to be free from excess substrate or inhibitor.
12. After complete re-suspension is achieved, or with untreated sludge, withdraw a sample just
before use for the determination of the dry weight of the suspended solids.
13. A further alternative is to homogenise activated sludge
(3-5 g suspended solids/l). Treat the sludge in a Waring blender for 2 minutes at medium speed.
Settle the blended sludge for 30 minutes or longer if required and decant liquid for use as inoculum
at the rate of about 10 ml/l of mineral medium.
Other sources of inoculum
14. Alternatively, the inoculum can be derived from the secondary effluent of a treatment plant
or laboratory-scale unit receiving predominantly domestic sewage. Collect a fresh sample and keep
it aerobic during transport. Allow to settle for 1 hour or filter through a coarse filter paper and keep
the decanted effluent or filtrate aerobic until required. Up to 100 ml of this type of inoculum may be
used per litre of medium.
15. A further source for the inoculum is surface water. In this case, collect a sample of an
appropriate surface water, e.g. river, lake, and keep aerobic until required. If necessary, concentrate
the inoculum by filtration or centrifugation.
Pre-conditioning of inoculum
16. Inoculum may be pre-conditioned to the experimental conditions, but not pre-adapted to the
test substance. Pre-conditioning consists of aerating activated sludge (in mineral medium) or
secondary effluent for 5-7 days at the test temperature. Pre-conditioning sometimes improves the
precision of the test method by reducing blank values.
Preparation of flasks
17. As an example, introduce 800 ml portions of mineral medium into 2-litre conical flasks and
add sufficient volumes of stock solutions of the test and reference substances to separate flasks to give
a concentration of chemical equivalent to 10-40 mg DOC/l. Check the pH values and adjust, if
necessary, to 7.4. Inoculate the flasks with activated sludge or other source of inoculum to give a final
concentration not greater than 30 mg suspended solids/l. Also prepare inoculum controls in the
mineral medium but without test or reference substance.
18. If needed, use one vessel to check the possible inhibitory effect of the test substance by
inoculating a solution containing comparable concentrations of both the test and a reference substance
in the mineral medium.
19. Also, if required, check whether the test substance is degraded abiotically by setting up a flask
containing a sterilised uninoculated solution of the substance. Sterilise by filtering though a membrane
(0.2-0.45 μm) or by the addition of a suitable toxic substance at an appropriate concentration.
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20. Additionally, if the test substance is suspected of being significantly adsorbed onto glass,
sludge, etc., make a preliminary assessment to determine the likely extent of adsorption and thus the
suitability of the test for the chemical (see Table 1, p. 4). Set up a flask containing the test substance,
inoculum and sterilising agent.
21. Make up the volumes in all flasks to 1 litre with mineral medium and, after mixing, take a
sample from each flask to determine the initial concentration of DOC in duplicate (see Annex IV.4).
Cover the openings of the flasks, e.g with aluminium foil, in such a way as to allow free exchange
of air between the flask and the surrounding atmosphere. To start the test, insert the vessels into the
shaking machine.
Number of flasks
22. In a typical run, the following flasks are used:
Flasks 1 & 2 - containing test substance and inoculum (test suspension);
Flasks 3 & 4 - containing only inoculum (inoculum blank);
Flask 5 - containing reference compound and inoculum (procedure control);
and, preferably and when necessary, also
Flask 6 - containing test substance and sterilising agent (abiotic sterile control);
Flask 7 - containing test substance, inoculum and sterilising agent (adsorption
control);
Flask 8 - containing test substance, reference compound and inoculum (toxicity
control).
PROCEDURE
DOC determinations
23. Throughout the test, determine the concentrations of DOC in samples from each flask in
duplicate at known time intervals. It is mandatory to follow DOC in the test suspension and inoculum
blanks in parallel. It is advisable to follow DOC in the other flasks in parallel as well. This may,
however, not always be possible.
Sampling
24. Take only the minimal volume of test suspension necessary for each determination. Before
sampling make good any evaporation losses from the flasks by adding water in the required amount.
Mix the culture medium thoroughly before withdrawing a sample and ensure that material adhering
to the walls of the vessels is re-dissolved or re-suspended before sampling. Membrane-filter or
centrifuge the sample (see Annex IV.4) immediately after it has been taken. Analyse the filtered or
centrifuged samples on the same day, otherwise store at 2-4°C for a maximum of 48 h or below -18°C
for a longer period.
Frequency of sampling
25. Ensure that a sufficient number of samples are taken to allow the percentage removal in the
10-d window to be assessed. No precise sampling pattern can be described. If analyses are performed
on the day of sampling, assess the next sampling time by considering the result of the analysis. If the
samples are preserved, take samples daily or every two days. Analyse the last samples (28 d) first
and, by a stepwise "backwards" selection of appropriate samples for analysis, it is possible to obtain
a good description of the biodegradation curve with a relatively small number of determinations. Of
course, if the last samples (28 d) show no degradation, no further samples need be analysed.
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DATA AND REPORTING
Treatment of results
26. Data from the test should be entered onto the attached data sheet.
27. The percentage degradation (Dt) at each time a sample was taken should be calculated separately
for both flasks containing test substance (i.e. Flasks 1 and 2) using mean values of duplicate DOC
measurements (see data sheet) in order that the validity of the test can be assessed (see "Data and
Reporting", p. 7). It is calculated using the following equation:
where:
Dt = % degradation at time t,
Co = mean starting concentration of DOC in the inoculated culture medium
containing the test substance (mg DOC/l),
Ct = mean concentration of DOC in the inoculated culture medium containing test
substance at time t (mg DOC/l),
Cbl(o) = mean starting concentration of DOC in blank inoculated mineral medium (mg
DOC/l),
Cbl(t) = mean concentration of DOC blank inoculated mineral medium at time t (mg
DOC/l).
All concentrations are measured experimentally.
28. If the test has complied with the validity criteria, display the course of degradation graphically
using the mean of both flasks containing test substance. Indicate the 10-d window. Calculate and
report the percentage removal achieved at the plateau, at the end of the test and/or at the end of the
10-d window, whichever are appropriate.
29. When specific chemical analytical data are available, calculate primary biodegradation (see
"Data and Reporting", p. 7).
30. When a abiotic sterile control is used calculate the percentage abiotic degradation using:
where,
Cs(o) = DOC concentration in sterile control at day 0,
Cs(t) = DOC concentration in sterile control at day t.
Validity of tests
31. The validity criteria apply given in "Data and Reporting" (p. 7).
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Test report
32. The test report should include the information described in "Data and Reporting" (p. 8).
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DOC DIE-AWAY TEST
DATA SHEET
1. LABORATORY:
2. DATE AT START OF TEST:
3. TEST SUBSTANCE:
Name:
Stock solution concentration: mg/l as chemical
Initial concentration in medium, to: mg/l as chemical
4. INOCULUM:
Source:
Treatment given:
Pre-conditioning, if any:
Suspended solids concentration in reaction mixture: mg/l
5. CARBON DETERMINATIONS:
Carbon analyser:
Flask
no.
DOC after n days (mg/l)
0 n1 n2 n3 nx
Test substance plus
inoculum
1
a1
a2
mean, Ca(t)
2
b1
b2
mean, Cb(t)
Blank, inoculum
without test substance
3
c1
c2
mean, Cc(t)
4
d1
d2
mean, Cd(t)
mean, Cbl(t) = Cc(t) + Cd(t)
2
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6. EVALUATION OF RAW DATA:
Flask no. Calculation of results % Degradation after n days
0 n1 n2 n3 nx
1 0
2 0
Mean* 0
* D1 and D2 should not be averaged if there is a considerable difference.
Note: Similar formats may be used for the reference compound and toxicity controls.
7. ABIOTIC DEGRADATION (optional)
Time (days)
0 t
DOC conc. (mg/l) in sterile control Cs(o) Cs(t)
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8. SPECIFIC CHEMICAL ANALYSIS (optional)
residual amount of test
chemical at end of test % primary degradation
Sterile control Sb
Inoculated test medium Sa
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301 B CO2 EVOLUTION TEST
INTRODUCTION
1. Matters of general interest concerning the assessment of biodegradability are discussed in
"General Procedures and Preparations" and it is advisable to read this before proceeding. For this
method, the test substance should be non-volatile and its carbon content and, preferably, its purity or
relative proportions of major components should be known.
PRINCIPLE OF THE TEST
2. A measured volume of inoculated mineral medium, containing a known concentration of the
test substance (10-20 mg DOC or TOC/l) as the nominal sole source of organic carbon is aerated by
the passage of carbon dioxide-free air at a controlled rate in the dark or in diffuse light. Degradation
is followed over 28 days by determining the carbon dioxide produced. The CO2 is trapped in barium
or sodium hydroxide and is measured by titration of the residual hydroxide or as inorganic carbon.
The amount of carbon dioxide produced from the test substance (corrected for that derived from the
blank inoculum) is expressed as a percentage of ThCO2. The degree of biodegradation may also be
calculated from supplemental DOC analysis made at the beginning and end of incubation.
DESCRIPTION OF THE METHOD
Apparatus
3. Normal laboratory apparatus and:
(a) Flasks, 2-5 litres, each fitted with an aeration tube reaching nearly to the bottom of
the vessel and an outlet (the tube must not interfere with the magnetic stirrer, when
used);
(b) Magnetic stirrers, when assessing poorly soluble chemicals;
(c) Gas-absorption bottles;
(d) Device for controlling and measuring air-flow;
(e) Apparatus for carbon dioxide scrubbing, for preparation of air which is free from
carbon dioxide; alternatively, a mixture of CO2-free oxygen and C02-free nitrogen,
from gas cylinders, in the correct proportions (20%02:80%N2) may be used;
(f) Device for determination of carbon dioxide, either titrimetrically or by some form of
inorganic carbon analyser;
(g) Membrane filtration device (optional);
(h) DOC analyser (optional).
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Water
4. A description of the water to be used is given in the "General Procedures and Preparations"
(p. 5).
Stock solutions for mineral medium
5. Prepare the same stock solutions as detailed in 301 A (paragraph 5).
Preparation of mineral medium
6. Refer to 301 A (paragraph 6).
Stock solutions of test substances
7. Prepare in the same way as described in 301 A (paragraph 7).
For the handling of poorly soluble substances see Annex III.
Inoculum
8. The inoculum may be derived from a variety of sources: activated sludge; sewage effluents;
surface waters; soils; or from a mixture of these.
Inoculum from activated sludge
9. Refer to 301 A (paragraphs 9 to 13) for details on the collection and preparation of inoculum
from activated sludge.
Other sources of inoculum
10. Alternatively, the inoculum can be derived from the secondary effluent of a treatment plant
or laboratory-scale unit receiving predominantly domestic sewage or from surface water. Refer to 301
A (paragraphs 14 and 15) for details.
Pre-conditioning of inoculum
11. Refer to 301 A (paragraph 16).
Preparation of flasks
12. As an example, the following volumes and weights indicate the values for 5-litre flasks
containing 3 litres of suspension. If smaller volumes are used modify the values accordingly, but
ensure that the carbon dioxide formed can be measured accurately. To each 5-litre flask add 2,400
ml mineral medium. Add an appropriate volume of the prepared activated sludge to give a
concentration of suspended solids of not more than 30 mg/l in the final 3 litres of inoculated mixture.
Alternatively, first dilute the prepared sludge to give a suspension of 500-1000 mg/l in the mineral
medium before adding an aliquot to the contents of the 5-litre flask to attain a concentration of 30
mg/l; this ensures greater precision (other sources of inoculum may be used, see paragraphs 14 and
15 of 301 A). Aerate these inoculated mixtures with C02-free air overnight to purge the system of
carbon dioxide.
13. Add the test material and reference compound, separately, as known volumes of stock
solutions, to replicate flasks to yield concentrations, contributed by the added chemicals, of 10 to 20
mg DOC or TOC/l; leave some flasks without addition of chemicals as inoculum controls. Add poorly
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soluble test substances directly to the flasks on a weight or volume basis or handle as described in
Annex III. Make up the volumes of suspensions in all flasks to 3 litres by the addition of mineral
medium previously aerated with CO2-free air.
14. If required, use one flask to check the possible inhibitory effect of the test substance by adding
both the test and reference substances at the same concentrations as present in the other flasks.
15. Also, if required, check whether the test substance is degraded abiotically by using a sterilised
uninoculated solution of the chemical. Sterilise by the addition of a toxic substance at an appropriate
concentration.
16. If barium hydroxide is used, connect three absorption bottles, each containing 100 ml of
0.0125 M barium hydroxide solution, in series to each 5-litre flask. The solution must be free of
precipitated sulphate and carbonate and its strength must be determined immediately before use. If
sodium hydroxide is used, connect two traps, the second acting as a control to demonstrate that all the
carbon dioxide was absorbed in the first. Absorption bottles fitted with serum bottle closures are
suitable. Add 200 ml 0.05 M sodium hydroxide to each bottle. This is sufficient to absorb the total
quantity of carbon dioxide evolved when the test substance is completely degraded. The sodium
hydroxide solution, even when freshly prepared, will contain traces of carbonates; this is corrected by
deduction of the carbonate in the blank.
17. Optionally, samples may be withdrawn for analysis of DOC (see Annex IV.4) and/or specific
chemical analysis.
Number of flasks
18. In a typical run, the following flasks are used:
Flasks 1 & 2 - containing test substance and inoculum (test suspension);
Flasks 3 & 4 - containing only inoculum (inoculum blank);
Flask 5 - containing reference compound and inoculum (procedure control);
and, preferably and when necessary, also
Flask 6 - containing test substance and sterilising agent (abiotic sterile control);
Flask 7 - containing test substance, reference compound and inoculum (toxicity
control).
PROCEDURE
19. Start the test by bubbling C02-free air through the suspensions at a rate of 30-100 ml/min.
CO2 determinations
20. It is mandatory to follow the CO2 evolution from the test suspensions and inoculum blanks
in parallel and it is advisable to do the same for the other test vessels.
21. During the first ten days it is recommended that analyses of CO2 should be made every second
or third day and then at least every fifth day until the 28th day so that the 10-d window period can
be identified. On the days of C02 measurement, disconnect the barium hydroxide absorber closest to
the test vessel and titrate the hydroxide solution with 0.05 M HCl using phenolphthalein as the
indicator. Move the remaining absorbers one place closer to the test vessel and place a new absorber
containing 100 ml fresh 0.0125 M barium hydroxide at the far end of the series. Make titrations as
needed, for example, when substantial precipitation is seen in the first trap and before any is evident
in the second, or at least weekly. Alternatively, with Na0H as absorbent, withdraw a sample of the
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sodium hydroxide solution from the absorber nearest to the test vessel using a syringe. The sample
volume needed will depend on the carbon analyser used, but sampling should not significantly change
the absorbent volume over the test period. Inject the sample into the IC part of the carbon analyser
for analysis of evolved carbon dioxide directly. Analyse the contents of the second trap only at the
end of the test in order to correct for any carry over of carbon dioxide.
22. On the 28th day withdraw samples, optionally, for DOC and/or specific chemical analysis.
Add 1 ml of concentrated hydrochloric acid to each test vessel and aerate them overnight to drive off
the carbon dioxide present in the test suspensions. On day 29 make the last analysis of evolved carbon
dioxide.
DATA AND REPORTING
Treatment of results
23. Data from the test should be entered onto the attached data sheet.
24. The amount of CO2 produced is calculated from the amount of base remaining in the
absorption bottle. When 0.0125 M Ba(OH)2 is used as the absorbent, the amount remaining is
assessed by titrating with 0.05 M HCl. (Thus 50 ml HCl would be needed to titrate 100 ml Ba(OH)2).
25. Since 1 mmol of CO2 is produced for every mmol of Ba(OH)2 reacted to BaCl2 and 2 mmol
of HCl are needed for the titration of the remaining Ba(OH)2, and given that the molecular weight of
CO2 is 44 g, the weight of CO2 produced (mg) is calculated by:
Thus, in this case, the factor to convert volume of HCl titrated to mg CO2 produced is 1.1. Calculate
the weights of CO2 produced from the inoculum alone and from the inoculum plus test substance using
the respective titration values; the difference is the weight of CO2 produced from the test substance
alone. For example, if the inoculum alone gives a titration of 48 ml and inoculum plus test substance
gives 45 ml,
CO2 from inoculum = 1.1 x (50-48) = 2.2 mg
CO2 from inoculum plus test substance = 1.1 x (50-45) = 5.5 mg
and thus the weight of CO2 produced from the test substance is 3.3 mg.
26. The percentage biodegradation is calculated from:
or,
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where 3.67 is the conversion factor (44/12) for carbon to carbon dioxide. Obtain the percentage
degradation after any time interval by adding the percentage of ThCO2 values calculated for each of
the days, up to that time, on which it was measured.
27. When NaOH is used as the absorbent, calculate the amount of CO2 produced after any time
interval from the concentration of inorganic carbon and the volume of absorbent used.
Calculate the percentage degradation from:
28. Display the course of degradation graphically and indicate the 10-d window. Calculate and
report the percentage removal achieved at the plateau, at the end of the test and/or at the end of the
10-d window, whichever is appropriate.
29. When appropriate, calculate DOC removals using the equation given in 301 A (paragraph 27).
30. When an abiotic control is used, calculate the percentage abiotic degradation by:
Validity of tests
31. The IC content of the test substance suspension in the mineral medium at the beginning of the
test must be less than 5% of the TC, and the total C02 evolution in the inoculum blank at the end of
the test should not normally exceed 40 mg/l medium. If values greater than 70 mg CO2/l are obtained,
the data and experimental technique should be examined critically.
32. The other validity criteria given in "Data and Reporting (p. 7) also apply.
Test report
33. The test report should include the information described in "Data and Reporting" (p. 8).
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CO2 EVOLUTION TEST
DATA SHEET
1. LABORATORY:
2. DATE AT START OF TEST:
3. TEST SUBSTANCE:
Name:
Stock solution concentration: mg/l as chemical
Initial conc. in medium: mg/l as chemical
Total C added to flask: mg C
ThCO2: mg CO2
4. INOCULUM:
Source:
Treatment given:
Pre-conditioning, if any:
Suspended solids concentration in reaction mixture: mg/l
5. CO2 PRODUCTION AND DEGRADABILITY:
Method: Ba(OH)2/NaOH/other.
Time (day)
CO2 produced (mg) Cumulative CO2
produced (mg)
test - blank mean
% ThCO2
cumulative CO2 x 100
ThCO2
Test chemical Blank
Flask
1
Flask
2
Flask
3
Flask
4
Mean Flask
1
Flask
2
Flask
1
Flask
2
Mean*
0
n1
n2
n3
n4
28
Note: Similar formats may be used for the reference and toxicity controls.
* Do not take mean if there is a considerable difference between replicates.
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6. CARBON ANALYSIS (optional):
Carbon analyser:
Time (day) Test chemical (mg/l) Blank (mg/l)
0 (Co) (Cbl(0))
28* (Ct) (Cbl(t))
* or at end of incubation
7. ABIOTIC DEGRADATION (optional)
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301 C MODIFIED MITI TEST (I)
INTRODUCTION
1. Matters of general interest concerning the assessment of biodegradability are discussed in
"General Procedures and Preparations" and it is advisable to read this before proceeding. For this
method, the formula of the test substance and its purity, or relative proportions of major components,
should be known so that the ThOD may be calculated. Insoluble and volatile substances may be
assessed provided precautions are taken. Insoluble substances should be dispersed, for example, by
using very finely ground material or ultrasonics, but not solvents or emulsifying agents. For volatile
substances the volume of "dead" gas space in the automatic respirometer should be kept to a minimum.
PRINCIPLE OF THE TEST
2. The oxygen uptake by a stirred solution, or suspension, of the test substance in a mineral
medium, inoculated with specially grown, unadapted micro-organisms, is measured automatically over
a period of 28 days in a darkened, enclosed respirometer at 25 + 1°C. Evolved carbon dioxide is
absorbed by soda lime. Biodegradation is expressed as the percentage oxygen uptake (corrected for
blank uptake) of the theoretical uptake (ThOD). The percentage primary biodegradation is also
calculated from supplemental specific chemical analysis made at the beginning and end of incubation,
and optionally ultimate biodegradation by DOC analysis.
DESCRIPTION OF THE METHOD
Apparatus
3. Normal laboratory apparatus and:
(a) Automatic electrolytic BOD meter or respirometer normally equipped with 6 bottles,
300 ml each and equipped with cups to contain CO2 absorbent;
(b) Constant temperature room and/or water-bath at 25°C + 1°C or better;
(c) Membrane-filtration assembly (optional);
(d) Carbon analyser (optional).
Water
4. A description of the water to be used is given in the "General Procedures and Preparations"
(p. 5).
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Stock solutions for mineral medium
5. Prepare the following stock solutions, using analytical grade reagents:
(a) Potassium dihydrogen orthophosphate, KH2PO4 . . . . . . . . . . . . . 8.50 g
Dipotassium hydrogen orthophosphate, K2HPO4 . . . . . . . . . . . . 21.75 g
Disodium hydrogen orthophosphate
dodecahydrate, Na2HPO4.12H2O . . . . . . . . . . . . . . . . . . . . . . . 44.60 g
Ammonium chloride, NH4Cl . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.70 g
Dissolve in water and make up to 1 litre.
The pH value of the solution should be 7.2.
(b) Magnesium sulphate heptahydrate, MgS04.7H20 . . . . . . . . . . . . 22.50 g
Dissolve in water and make up to 1 litre.
(c) Calcium chloride anhydrous, CaCl2 . . . . . . . . . . . . . . . . . . . . . 27.50 g
Dissolve in water and make up to 1 litre.
(d) Iron (III) chloride hexahydrate, FeCl3.6H20 . . . . . . . . . . . . . . . . . 0.25 g
Dissolve in water and make up to 1 litre. The pH of the solution should be 7.2.
Preparation of mineral medium
6. Take 3 ml of each solution (a), (b), (c) and (d) and make up to 1 litre.
Stock solutions of test substances
7. When the solubility exceeds 1 g/l dissolve 1-10 g, as appropriate, of test or reference substance
in water and make up to 1 litre. Otherwise prepare stock solutions in the mineral medium or add the
chemical directly to the mineral medium. For the handling of poorly soluble substances, see paragraph
11.
Preparation of inoculum
8. Collect fresh samples from no fewer than ten sites, mainly in areas where a variety of
chemicals are used and discharged. From sites such as sewage treatment works, industrial waste-water
treatment works, rivers, lakes, seas, collect 1 litre samples of sludge, surface soil, water, etc. and mix
thoroughly together.
9. After removing floating matter and allowing to stand, adjust the supernatant to pH 7 + 1 with
sodium hydroxide or phosphoric acid. Use an appropriate volume of the filtered supernatant to fill
a fill-and-draw activated sludge vessel and aerate the liquid for about 23.5 h. Thirty minutes after
stopping aeration, discard about one third of the whole volume of supernatant and add an equal
volume of a solution (pH 7) containing 0.1 % each of glucose, peptone and potassium orthophosphate,
to the settled material and re-commence aeration. Repeat this procedure once per day.
10. The sludge unit must be operated according to good practice: effluents should be clear;
temperature should be kept at 25 + 2°C and at pH 7 + 1; sludge should settle well; there should be
sufficient aeration to keep the mixture aerobic at all times; protozoa should be present and the activity
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of the sludge should be tested against a reference substance at least every three months. Do not use
sludge as inoculum until after at least one month’s operation, but not after more than four months.
Thereafter, sample from at least 10 sites at regular intervals, once every three months. In order to
maintain fresh and old sludge at the same activity, mix the filtered supernatant of an activated sludge
in use with an equal volume of the filtered supernatant of a freshly collected ten-source mixture and
culture the combined liquor as above. Take sludge for use as inoculum 18-24 h after the unit has been
fed.
Preparation of bottles
11. Prepare the following six bottles:
Bottle 1 - test substance in water at 100 mg/l;
Bottles 2,
3 and 4 - test substance in mineral medium at 100 mg/l;
Bottle 5 - reference compound (e.g. aniline) in mineral medium at 100 mg/l;
Bottle 6 - mineral medium only.
Add poorly soluble test substances directly on a weight or volume basis or handle as described in
Annex III except that neither solvent nor emulsifying agent should be used. Add the C02 absorbent
to all test vessels in the special cups provided. Adjust the pH in bottles 2, 3 and 4 to 7.0 before
inoculation, if necessary.
PROCEDURE
12. Inoculate vessels 2, 3 and 4 (test suspensions), 5 (activity control) and 6 (inoculum blank) with
a small volume of the inoculum to give a concentration of 30 mg/l suspended solids. No inoculum
is added to Bottle 1 which serves as an abiotic control. Assemble the equipment, check that it is
air-tight, start the stirrers, and start the measurement of oxygen uptake under conditions of darkness.
Check the temperature, stirrer and coulometric oxygen uptake recorder, and note any changes in colour
of the contents of the vessels on a daily basis. Read the oxygen uptakes for the six bottles directly
by an appropriate method, for example, from the six-point chart recorder, which produces a BOD
curve.
13. At the end of incubation, normally 28 days, measure the pH of the contents of the bottles and
determine the concentration of the residual test substance and any intermediates and, in the case of
water-soluble substances, the concentration of DOC (Annex IV.4). Take special care in the case of
volatile substances. If nitrification is anticipated, determine nitrate and nitrite concentrations, if
possible.
DATA AND REPORTING
Treatment of results
14. Data from the test should be entered onto the attached data sheet.
15. Divide the oxygen uptake (mg) by the test substance (mg) after a given time, corrected for that
taken up by the blank inoculum control after the same time, by the weight of the test substance used.
This yields the BOD expressed as mg oxygen/mg test substance, that is,
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The percentage biodegradation is then obtained from:
16. For mixtures, calculate the ThOD from the elemental analysis, as for a single compound. Use
the appropriate ThOD (ThODNH4 or ThODNO3) according to whether nitrification is absent or complete
(Annex IV.2). If however, nitrification occurs but is incomplete, make a correction for the oxygen
consumed by nitrification calculated from the changes in concentrations of nitrite and nitrate
(Annex V).
17. Calculate the percentage primary biodegradation from loss of specific (parent) chemical using
the equation given in "Data and Reporting" (p. 7). If there has been a loss of test substance in Bottle
1, measuring abiotic removal, report this and use the concentration of test substance (Sb) after 28 days
in this bottle to calculate percentage biodegradation.
18. When determinations of DOC are made (optional), calculate the percentage ultimate
biodegradation at time t using the equation given in 301 A (paragraph 27). If there has been a loss
of DOC in Bottle 1, measuring abiotic removal, use the DOC concentration in this vessel at day 28
to calculate the percentage biodegradation.
Validity of results
19. The oxygen uptake of the inoculum blank is normally 20-30 mg 02/l and should not be greater
than 60 mg 02/l in 28 days. Values higher than 60 mg/l require critical examination of the data and
the experimental technique. If the pH value is outside the range 6-8.5 and the oxygen consumption
by the test substance is less than 60%, the test could be repeated with a lower concentration of test
substance.
20. A test is considered valid if the difference of extremes of replicate values of the removal of
the test substance at the plateau or at the end of the test, as appropriate is less than 20% and if the
percentage degradation of aniline calculated from the oxygen consumption exceeds 40% after 7 days
and 65% after 14 days. If either of these conditions is not met, the test should be repeated. Low
values do not necessarily mean that the test substance is not biodegradable under environmental
conditions, but indicates that more work will be necessary to establish biodegradability.
Test report
21. The test report should include the information outlined in "Data and Reporting" (p. 8).
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MODIFIED MITI TEST (I)
DATA SHEET
1. LABORATORY:
2. DATE AT START OF TEST:
3. TEST SUBSTANCE:
Name:
Stock solution concentration: mg/l as chemical
Initial concentration in medium, Co: mg/l as chemical
Volume of reaction mixture, V: ml
ThOD: mg O2/l
4. INOCULUM:
Sludge sampling sites:
1. 6.
2. 7.
3. 8.
4. 9.
5. 10.
Concentration of suspended solids in activated sludge after acclimation with synthetic sewage = mg/l
Volume of sludge added/litre of final medium = ml
Concentration of sludge in final medium = mg/l
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5. OXYGEN UPTAKE: BIODEGRADABILITY
Type of respirometer used:
Time (days)
n1 n2 n3 nx
O2 uptake by test substance (mg):
a1
a2
a3
O2 uptake by blank (mg):
b
Corrected O2 uptake (mg):
a1-b
a2-b
a3-b
BOD (mgO2/mg test substance):
(a1-b)/CoV
(a2-b)/CoV
(a3-b)/CoV
% degradation BOD/ThOD x 100:
123
mean*
Note: Similar formats may be used for the reference compound
* Do not take a mean if there are considerable differences between replicates
6. CARBON ANALYSIS (OPTIONAL)
Carbon analyser:
Flask
DOC %DOC
removed
Mea
n
Measured Corrected
Water + test substance a - -
Sludge + test substance b1 b1-c
Sludge + test substance b2 b2-c
Sludge + test substance b3 b3-c
Control blank c - - -
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7. SPECIFIC CHEMICAL ANALYSIS
residual amount of test
substance at end of test % primary degradation
Blank test with water Sb
Inoculated medium Sa1
Sa2
Sa3
Calculate % primary degradation for bottles a1, a2, and a3 respectively.
8. REMARKS
BOD curve against time, if available, should be attached.
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301 D CLOSED BOTTLE TEST
INTRODUCTION
1. Matters of general interest concerning the assessment of biodegradability are discussed in
"General Procedures and Preparations" and it is advisable to read this before proceeding. For this
method, the formula of the substance and its purity, or relative proportions of major components,
should be known so that the ThOD may be calculated. If the ThOD cannot be calculated, the COD
should be determined, but falsely high values of percentage biodegradation may be obtained if the test
substance is incompletely oxidised in the COD test. Insoluble and volatile substances may be assessed
provided that precautions are taken. Degradation values for insoluble substances may be falsely low
unless the bottles are agitated periodically during the incubation.
PRINCIPLE OF THE TEST
2. The solution of the test substance in mineral medium, usually at 2-5 mg/l, is inoculated with
a relatively small number of micro-organisms from a mixed population and kept in completely full,
closed bottles in the dark at constant temperature. Degradation is followed by analysis of dissolved
oxygen over a 28-d period. The amount of oxygen taken up by the microbial population during
biodegradation of the test substance, corrected for uptake by the blank inoculum run in parallel, is
expressed as a percentage of ThOD or, less satisfactorily COD.
DESCRIPTION OF THE METHOD
Apparatus
3. Normal laboratory apparatus and:
(a) BOD bottles, with glass stoppers e.g. 250-300 ml or 100-125 ml;
It is important that the bottles are thoroughly clean before use. If the Winkler method
for determining dissolved oxygen is used, it is sufficient to rinse the bottle several
times with tap water then deionised water. However, if the electrode method is used,
a more stringent cleaning procedure is required. Add to the empty bottle 5-10 ml of
a wash solution (e.g. 2.5 g iodine plus 12.5 g potassium iodide per litre of 1% w/v
sulfuric acid) shaking well to coat the bottle walls. Leave to stand for 15 min., pour
off the solution and rinse thoroughly with tap water and finally deionised water.
(b) Water bath or incubator, for keeping bottles at constant temperature (+ 1°C/or better)
with the exclusion of light;
(c) Large glass bottles (2-5 litres) for the preparation of media and for filling the BOD
bottles;
(d) Oxygen electrode and meter, or equipment and reagents for Winkler titration.
Water
4. A description of the water to be used is given in "General Procedures and Preparations" (p. 5).
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Stock solutions for mineral medium
5. Prepare the following stock solutions, using analytical grade reagents:
(a) Potassium dihydrogen orthophosphate, KH2PO4 . . . . . . . . . . . . . 8.50 g
Dipotassium hydrogen orthophosphate, K2HPO4