Formaldehyde

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: screening test, other

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

No guideline study but the study appears well conducted and from the reported data no doubts on the validity of the study arise.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Batch-test

GLP compliance:

no

Specific details on test material used for the study:

no data

Oxygen conditions:

anaerobic

Inoculum or test system:

anaerobic sludge

Details on inoculum:

- Source of inoculum/activated sludge: Sewage sludge from anoxic chamber of a treatment plant of a resin-producing factory
- Laboratory culture: no
- Preparation of inoculum for exposure: no data
- Pretreatment: no data
- Initial cell concentration: 2 g/L

Duration of test (contact time):

11 d

Initial conc.:

1 360 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

test mat. analysis

Details on study design:

TEST CONDITIONS
- Composition of medium: medium supplemented with nutrient solution
- Additional substrate: none
- Solubilising agent: none
- Test temperature: thermostatic chamber, 20°C
- pH: Initially 7.5, adjusted with NaHCO3
- Suspended solids concentration: 2 g/L
- Other: Flasks shaken at 200 rpm

TEST SYSTEM
- Culturing apparatus: vials, 300 cm3
- Number of culture flasks/concentration: 1

CONTROL AND BLANK SYSTEM: none
STATISTICAL METHODS: none

Reference substance:

not required

Test performance:

Sludge from the anoxic chamber of the full-scale wastewater treatment plant of a resin-producing factory was used as inoculum. An initial formaldehyde concentration of 1360 mg/l was applied.
The concentrations of formaldehyde as well as the intermediates methanol and formic acid were measured in the medium using a substance-specific analysis. The inhibitory effects of formaldehyde to nitrification were studied by nitrate measurements.
The test was run at 20°C instead of 35°C proposed by the OECD Guideline 311. Instead of CO2 and CH4 evolution, substance-specific measurements of formaldehyde and its metabolites methanol and formic acid were conducted. No reference substance was tested. Instead of predominantly domestic sewage sludge, industrial sludge which was probably preadapted was used as inoculum.

Parameter:

% degradation (test mat. analysis)

Value:

100

Sampling time:

4 d

Details on results:

Formaldehyde removal led to the formation of methanol and formic acid (see attached degradation curve). Degradation of methanol and formic acid began after the exhaustion of formaldehyde in the medium.
Further experiments revealed that addition of methanol (270-950 mg/L) did not inhibit formaldehyde degradation. However, KNO3 (initially 400 mg N/L) was not completely denitrified. The decrease of nitrate concentration occurred simultaneously with the decrease of methanol and formic acid concentrations.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The results of the study indicate that formaldehyde is rapidly eliminated in anaerobic sludge. Elimination is predominantly due to degradation, rather than volatilization or adsorption.

Executive summary:

A batch test was conducted to assess the biodegradation potential of formaldehyde in the presence of methanol under denitrifying conditions. An inoculum of sewage sludge from anoxic chamber with the initial concentration of 2 g/L was exposed to 1360 mg/L of the test item for 11 d under anaerobic conditions. The test item was determined spectrophotometrically, while the products methanol and formaldehyde were measured by GC and HPLC. After 4 d 100 % of the test item were degraded.

In the test medium, the formaldehyde concentration decreased rapidly, after 4 days the test substance was completely biodegraded. Simultaneously to formaldehyde removal, methanol and formic acid were formed as intermediate products. Degradation of both metabolites began after the exhaustion of formaldehyde in the medium.

Further experiments revealed that addition of methanol did not inhibit formaldehyde degradation. However, nitrification was inhibited in the test system. The decrease of nitrate concentration occurred simultaneously with the decrease of methanol and formic acid concentrations. The authors concluded that methanol and formic acid were used as carbon sources for denitrification.

A mass balance for the fate of formaldehyde in the test system was not conducted. However, volatility of formaldehyde from aqueous solutions can be neglected the test was conducted in a closed system. Losses due to adsorption can be neglected, because of its low absorptivity (cf. 5.4.1). Due to the rapid removal of the test item (100 % in 4 d) inhibition of the inoculum can be excluded.

 

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

27.09.2011 - 25.10.2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 A (Ready Biodegradability: DOC Die Away Test)

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

sewage, predominantly domestic, non-adapted

Details on inoculum:

Fresh samples of activated sludge were withdrawn on September 27th, 2011 from the sewage treatment plant Ruhrverband Kläranlage, Sunthelle 6,
57392 Schmallenberg, Germany, which is mainly fed with municipal wastewater.
The concentration used in the test was 29.8 mg dry mass/litre (23.9 mg dry mass/800 mL).

Duration of test (contact time):

28 d

Initial conc.:

10 mg/L

Based on:

DOC

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

Formaldehyde Solution (30 - 55 % W/W) and sodium benzoate, respectively, in concentrations of chemical equivalent to 10 mg DOC per litre mineral medium
were incubated with 29.8 mg dry mass inoculum per litre mineral medium in 2-litre conical glass flasks at a medium volume of 800 mL. The pH value was
checked and adjusted to pH 7.4 ± 0.2, if necessary with H2SO4 (conc. 50 g/L).
Inoculum controls are also prepared in the mineral medium without test or reference substance. Toxicity, abiotic sterile, and adsorption controls are also set up by following the same procedure.
After mixing, a sample was taken from each flask to determine the initial concentration of DOC at least in duplicate. The openings of the flasks were
covered in such a way as to allow free exchange of air between the flask and the surrounding atmosphere. Then the vessels were inserted into a
shaking machine for starting the test. During the test, the medium wes stirred continuously.
Throughout the test, the concentrations of DOC in samples from each flask are determined at least in duplicate at test start and at day 1, 2, 5, 7, 12, 14, 21, and 28 in a TOC analyser.

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (DOC removal)

Value:

99

Sampling time:

28 d

Details on results:

The decrease of Formaldehyde in the static test was found to be 99 % after 28 days. The biodegradation within the 10-day-window was 102 %. The 10-day window started at day two.
No lag phase / adaptation phase was noticeable.
With 3 % decrease of DOC in the adsorption control within the first day of incubation and a maximum of decrease of 10 % in the course of the study, no
significant adsorption of Formaldehyde occurred. According to Beek et al. (2001), adsorption can be neglected when DOC decrease is < 20 % within the first
day. With a maximum of 13 % decrease of DOC in the abiotic sterile control at the end of the incubation, no significant abiotic degradation of Formaldehyde
occurred. Consequently, the decrease in the test suspension and toxicity control can be assumed to be due to biotic degradation.

Results with reference substance:

The reference item sodium benzoate was degraded to 104 % within the first 14 days.

The biodegradation of the item mixture in the toxicity control was found to be 106 % after 14 days of incubation. Thus, the demanded threshold value of 35 % is exceeded and the test item Formaldehyde Solution (30 - 55 % W/W) can be identified as not toxic under the chosen test conditions.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

Due to the results, the test item can be identified as readily biodegradable according to OECD criteria.

Executive summary:

The biodegradation of the test substance (aqueous solution) at a concentration of 10 mg DOC per liter was investigated over a 28-day period in a DOC Die-Away Test according to OECD guideline 301A and GLP regulations. The test medium was inoculated with microorganisms from a digester of a sewage treatment plant mainly treating municipal wastewater.

The test solutions were stirred in flasks at 22 °C for 28-days. The rate of degradation was monitored by measuring the DOC of the solutions over a 28-day period. The amount of DOC, corrected for the amount in the blank inoculum run in parallel, was expressed as a percentage of the initial DOC. In order to check the procedure, sodium benzoate was used as a degradable reference item at a concentration of 10 mg DOC per liter, along with a toxicity control at the same concentration of the test item and sodium benzoate.

The degradation of the test item in the static test was found to be 99 % after 28 days. The degradation within the 10-day-window, which started at day 2, was 102 %. Therefore, the test item can be considered as readily biodegradable according to OECD criteria.

The degradation of the reference substance sodium benzoate had reached 104 % within the first 14 days. The difference of extremes of replicate values of the removal of the test item at the end of the test and at the end of the 10-d window is less than 20 %. Therefore, the test can be considered as valid.

No inhibitory effects of the test item were observed (more than 35 % degradation occurred within 14 days) in the toxicity control.

No significant abiotic degradation or adsorption occurred within the test duration.

Due to the results, the test item can be identified as readily biodegradable under the chosen test conditions.

Description of key information

The substance is readily biodegradable (according to OECD criteria)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

The biodegradability of the test item under aerobic conditions was investigated in 3 tests on ready biodegradability according to the OECD guidelines 301 A (Fraunhofer IME, 2011) 301 C (MITI, 1989) and 301 D (Gericke & Gode, 1990). In addition, one study anaerobic conditions is available (Eiroa et al., 2016)

In the DOC Die-Away Test (OECD 301 A), conducted in compliance with the principles of Good Laboratory Practice (GLP) and therefore selected as key-study, the degradation of the test item (30 - 55 % W/W aqueous solution) was found to be 99 % after 28 days. The degradation within the 10-day-window, which started at day 2, was 102 %. No inhibitory effects of the test item were observed (more than 35 % degradation occurred within 14 days) in the toxicity control (Frauenhofer IME, 2011).

In the MITI-I-Test (OECD 301 C) degradation after 14 days was found to be 91% of BOD/ThOD and 97% of TOC. The test was performed with paraformaldehyde, a low molecular weight polymer of formaldehyde. In water paraformaldehyde is hydrolyzed leading to formaldehyde, therefore the data can be used to support the key data on biodegradation of the test item.  Although the test substance concentration indicates that toxic effects can not be excluded (Klecka, 1985 the degradation was nearly complete. In a Closed-Bottle-Test (OECD 301 D), the substance degraded to 90% of ThOD after 28 days. No data are reported referring to the 10-days window criteria. (MITI, 1989)

 In the Closed-Bottle Test (OECD 301 D) the biodegradability of the test item was found to be 90% ThOD within 28 days. Information on the 14-day window criterion was not given. Therefore, the test item was proved to be at least “readily biodegradable but failing the 10-d window” according to EU Technical Guidance Document. (Gerike, 1990). No details about the test performance are given. Nevertheless, the data are adequate to support the key study.

 

 

Overall, due to the results of the available tests according to OECD 301 A, C and D the test item can be identified as readily biodegradable under enviromental conditions. This is in agreement with the OECD evaluation (OECD, 2004).

Mechanism of biodegradation: The mechanism of formaldehyde degradation by Pseudomonas putida is initiated by a dismutation reaction, yielding formic acid and methanol as products. Degradation of the products began after exhaustion of formaldehyde in the medium. (Adroer, 1990)

 

The anaerobic degradation of the test item was studied in a non-guideline batch test (Eiroa et al., 2006). Sludge from the anoxic chamber of the full-scale wastewater treatment plant of a resin-producing factory was used as inoculum. An initial formaldehyde concentration of 1360 mg/L was applied. The test item concentration decreased rapidly in the test medium, after 4 days the test substance was completely biodegraded. Simultaneously to the test item removal, methanol and formic acid were formed as intermediate products. Degradation of both metabolites began after the exhaustion of the test item in the medium. In conclusion the test item is rapidly removed in anaerobic digester sludge based on these results.