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Toxicity to microorganisms

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toxicity to microorganisms
Type of information:
experimental study
Adequacy of study:
weight of evidence
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Ciliated protozoan populations were tested in spiked activated sludge mixed liquor, which is relevant for the effects assessment of STPs. Lead concentrations were measured, and relevant endpoint/end parameter are reported. followed methodology is well described
no guideline followed
other: method described in the publication
Principles of method if other than guideline:
Ciliated protozoa populations are exposed for 24 to lead chloride, using activated sludge mixed liquor (containing bacteria as food source) as test medium
GLP compliance:
not specified
Analytical monitoring:
Details on sampling:
50 mL of activated sludge mixed liquor was filtered (0.45 ug/L)
Details on test solutions:
250 mL sample of activated sludge mixed liquor
Test organisms (species):
other: Aspidisca lynceus
Details on inoculum:
Protozoan community living in the activated sludge mixed liquor collected from the aeration basin of the sewage treatment plant in Roncocesi, Reggio Emilia (Italy), treating urban and industrial waste.
The whole sludge microbial community, maintained into the original microbiota, was tested; tests are therefore more similar to field tests than to lab tests.
Test type:
Water media type:
Limit test:
Total exposure duration:
24 h
no data
Test temperature:
20 +/- 2 °C
7.6 +/- 0.2
Dissolved oxygen:
continuous aeration
no data
Nominal and measured concentrations:
nominal: 150, 200, 300, 400, 500 mg/L
measured after 24h in activated sludge: 1.50, 1.98, 2.79, 3.09, 6.98 mg/L
Details on test conditions:
- Test vessel: 500 mL glass flask containing 250 mL activated sludge mixed liquor
- Control: sample of untreated activated sludge mixed liquor

- No additional feeding during the test; normal bacterial population present in the test medium

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : number of surviving organisms was determined by microscopic observations at 100 x magnification.
Non-motile cells on the surface of the flock were regarded as dead
For each concentration the estimate of protozoan numbers was based on enumerations from sub-samples.
For each concentration two subsamples (replicates) were counted

24 h
Dose descriptor:
other: LC50
Effect conc.:
3.78 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
Basis for effect:
other: mortality
Remarks on result:
other: 95% CL: 3.07 - 5.08
Details on results:
no additional remarks
Reported statistics and error estimates:
LC50s were determined using a probit analysis computer (Finney, 1978)
Validity criteria fulfilled:
not specified
The test method is well described, and a LC50 was determined for this test species. Values are based on measured Pb-levels. Due to the followed test method, the results are more field data than lab data.

Description of key information

Values are based on data for lead. Data stems from toxicity tests with bacterial and protozoan species in STP.

Key value for chemical safety assessment

EC50 for microorganisms:
1 mg/L

Additional information