Zinc dilactate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Read-across from lactic acid, representing the lactate ion of the assessed substance.

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Municipal sewage treatment plant: 'Waterschap de Maaskant', 's-Hertogenbosch, the Netherlands, receiving predominantly domestic sewage.
The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105 °C to determine the amount of suspended solids (4.3 g/I of sludge, as used for the test). The pH was 7.8 on the day of sampling and 7.5 on the day of testing. The batch of sludge was used one day after collection; therefore 50 ml of synthetic sewage feed was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

18-18.6 °C

pH:

7.9

Dissolved oxygen:

7.7-7.8 mg/L

Nominal and measured concentrations:

100 mg/L test material nominal (88 mg/L active substance nominal).

Details on test conditions:

Type: other: Activated sludge respiration inhibition test
TEST SYSTEM
- Test vessel: All glass, approximately 300 ml oxygen bottles and 1 litre test bottles.

TEST MEDIUM / WATER PARAMETERS
Adjusted ISO medium, formulated using RO-water (tap-water purified by reverse osmosis; GEON Waterbehandeling, Berkel-Enschot, The Netherlands) with the following composition:
CaCI2.2H2O 211.5 mg/I
MgSO4.7H2O 88.8 mg/I
NaHCO3 46.7 mg/I
KCl 4.2 mg/I

SYNTHETIC SEWAGE FEED
16 g peptone 11 g meat extract
3 g urea
0.7 g NaCI
0.4 g CaCI2.2H2O
0.2 g MgS04.7H2O
2.8 g K2HP04
Dissolved in Milli-Q water, made up to 1 litre and filtered.
The pH was adjusted from 6.8 to 7.0 with 1 M NaOH (Merck, Darmstadt, Germany).

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Oxygen consumption

TEST CONCENTRATIONS
Limit test

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 88.2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: corrected for lactic acid content of the test material (88.2 %)

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 88.2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: corrected for lactic acid content of the test material (88.2 %)

Results with reference substance (positive control):

- Results with reference substance valid? Yes
- Relevant effect levels: EC50 = 5.9 mg/L

Validity criteria fulfilled:

yes

Conclusions:

Lactic acid does not inhibit activated sludge respiration at concentrations up to 88.2 mg/L (corrected for lactic acid content of the test material). Inhibition was -1.1 % (i.e. slight stimulation).

Executive summary:

The influence of L-(+)-lactic acid on the respiration rate of activated sludge was investigated after a contact time of 3 hours.

The study procedure was based on OECD guideline 209 (adopted April 4, 1984), EEC Directive 67/548 amended November 18, 1987 (87/302), Part C, Publication No. L133, adopted May 30, 1988 and ISO Standard 8192 (1986).

The batch of the test material was a clear and colourless liquid (88.2 % aqueous solution of lactic acid) that could easily be mixed with water. A stock solution of 500 mg/L was prepared by adding 126.0 mg test substance to 250 ml of Milli-RO water. A stirring period of 30 minutes was used to accelerate dissolution and to ensure homogeneity. Volumes of the stock solution corresponding to the test concentration were then added to the test media. A concentration of 100 mg/L of the test material was tested in duplicate. Optimal contact between the test substance and test medium was ensured applying continuous aeration and stirring.

No significant inhibition of the respiration rate of the sludge was recorded at 100 mg test material per litre. The duplicate measurement confirmed the result of the first measurement. Therefore no further testing was needed.

Since all criteria for acceptability of the test were met, this study was considered to be valid.

In conclusion, under the conditions of this present test, L-(+)-lactic acid was not toxic to waste water (activated sludge) bacteria at a concentration of 88.3 mg/L (corrected for lactic acid content of the test material).

Reference 2

Endpoint:

toxicity to microorganisms

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: study not according to standard protocol but good quality and considered relevant for microbial ecotoxicity. Culture medium, test water conditions well described and relevant for the PNEC STP.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Lab-designed batch growth system for measurement of inhibition kinetics of activated sludge process.

GLP compliance:

not specified

Analytical monitoring:

yes

Vehicle:

no

Test organisms (species):

activated sludge

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 d

Test temperature:

25°C

pH:

7+/-0.2

Nominal and measured concentrations:

nominal doses: 1,5,10,20 mg Zn/l

Details on test conditions:

the sludge was shock-dosed with the nominal zinc concnetrations indicated above. Mixed liquor suspended solids measurements were done every 2 hrs.

Reference substance (positive control):

no

Duration:

3 d

Dose descriptor:

NOEC

Effect conc.:

5 mg/L

Nominal / measured:

nominal

Conc. based on:

not specified

Basis for effect:

growth inhibition

Validity criteria fulfilled:

yes

Conclusions:

Test not done according to standard protocol, but of good quality and considered useful for supporting the PNEC for STP.

Executive summary:

Study into the effect of zinc on activated sludge growth kinetics by following the rate of change of biomass production in batch growth experiments. NOEC of 5 mg Zn/l was derived.

Reference 3

Endpoint:

toxicity to microorganisms

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: study not according to standard protocol but good quality and considered relevant for the setting of the PNEC-STP. Culture medium, test water conditions well described and relevant.

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Version / remarks:

for the respiration measurements

Qualifier:

equivalent or similar to guideline

Guideline:

other: Swedish EPA report Nr 4424 (1995) for the inhibition of nitrification

GLP compliance:

not specified

Analytical monitoring:

no

Details on sampling:

metal stock solutions were checked for correct metal concentration.

Vehicle:

no

Test organisms (species):

activated sludge

Details on inoculum:

Activated sludge samples for nitrification inhibition and respirometry bioassays were collected from the aeration tank of the Urduliz waste water treatment works (Biskaia, Spain) ("model B").

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20°C

Nominal and measured concentrations:

not indicated

Details on test conditions:

Tests were carried out in 1 L test bottles, containing 0.5 l test solution. Bottles were sealed and the sludge was monitored for 3 hrs by an electrolytic respirometer. Oxygen consumption was measured every 5 minutes for 3 hrs.

Duration:

3 h

Dose descriptor:

IC50

Effect conc.:

> 10 mg/L

Nominal / measured:

nominal

Conc. based on:

not specified

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

IC50

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

not specified

Basis for effect:

inhibition of nitrification rate

Details on results:

The following other parameters were also measured but considered of less relevancy for REACH: Vibrio fischeri toxicity test, ATP bioluminescence test (very insenssitive to zinc), enzyme inhibition .

Reported statistics and error estimates:

Error bars are graphically reported, are very small (number of tests respiration: 11; for nitrification inhibition: 10)

Validity criteria fulfilled:

yes

Conclusions:

Tests done according to standard protocol. Good quality and considered relevant for settting the PNEC STP.

Executive summary:

Five rapid direct toxicity assessment methods were used in 3 EU member states. Nitrification inhibition and respiration were measured as REACH-relevant endpoints. The IC50 for respiration was graphically derived as > 10mg Zn/l, the IC50 for nitrification inhibition was 10mg Zn/l.

Reference 4

Endpoint:

activated sludge respiration inhibition testing

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

study not according to standard protocol but good quality and considered useful for setting the reference value for acute aquatic ecotoxicity. Study used for that purpose in the EU risk assessment process on zinc (ECB 2008). Culture medium, test water conditions well described and according to the conditions set out in OECD 209.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

not specified

Analytical monitoring:

not specified

Vehicle:

no

Details on test solutions:

test is performed by adding activated sewage sludge to a series of vessels with synthetic sewage medium

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Inoculate originated from a predominantly domestic sewage treatment plant (Rungsted municipal sewage treatment plant , DK). The concentration of sludge in the final test mixture was 1.5g/l of suspended solid.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

pH:

7.5

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

5.2 mg/L

Nominal / measured:

not specified

Conc. based on:

not specified

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Validity criteria fulfilled:

yes

Conclusions:

Tests done under conditions similar to standard protocol. Good quality and used in the EU risk assessment for setting the PNEC for STP.

Executive summary:

Study compares the effect of different substances , e.g. zinc on different microbiological parameters. The EC50 for sludge respiration inhibition was used in the risk assessment for setting the PNEC for STP. Result: see "results " section.

Description of key information

100 mg/L lactic acid (nominal formulation, nominal active is 88 mg/L) is not inhibiting to activated sludge; the EC₅₀ for zinc sulphate is 5.2 mg/L, corresponding to 7.84 mg/L zinc lactate.

Key value for chemical safety assessment

EC50 for microorganisms:

7.84 mg/L

Additional information

Aquatic toxicity of zinc lactate can be understood in terms of the aquatic toxicity of lactic acid and zinc(II).