Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30 %)

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

3-Mar-1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study followed standard test guidelines, however, no analysis of the test substance was performed in conjunction with this study.

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

yes

Remarks:

Minor deviation which was not believed to have affected the outcome of the study.

Principles of method if other than guideline:

Due to the volatility of the test substance, the 30 minute exposure time with aeration required by the guideline was modified to 5 minutes of vigorous stirring without aeration.

GLP compliance:

no

Remarks:

Study was performed in the spirit of the GLPs.

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

Water accomodated Fractions (WAFs) of the test substance were prepared in glass distilled water at a concentration of 1000 mg/l. A control WAF with glass distilled water only was also prepared. Test flasks were prepared by adding 16 ml of synthetic sewage, 284 ml of the WAF, and 200 ml of the prepared microbial inoculum into a 500 ml Erlenmeyer flask.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The inoculum used for this study was activated sludge obtained from a local sewage treatment plant (New Jersey, USA). The sludge was transferred to graduated cylinders and solids were washed three times with laboratory water. The final volume of the sludge was adjusted by concentrating the solids, to obtain an activated sludge with a total suspended solids (TSS) level of 3.77 g/l. Synthetic sewage was added to the sludge (50 ml/l) and the sludge was stored overnight with aeration and at a temperature of 10°C.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

5 min

Hardness:

no data

Test temperature:

17°C

pH:

no data

Dissolved oxygen:

8.42 mg/l at initiation, 1.64mg/l after 4 minutes.

Salinity:

freshwater

Nominal and measured concentrations:

1000 mg/l nominal
BPH Concentration = 250 nmol/mg Carbon (Bioavailable Petroleum Hydrocarbon)

Details on test conditions:

Due to the volatility of the test substance, the 30 minute exposure time with aeration required by the guideline was modified to 5 minutes of vigorous stirring without aeration. Lowering the inoculum temperature slowed down the respiration rate of the sludge avoiding dissolved oxygen depletion during the 5 minute exposure time and 10 minute measurement period. The reference and control flasks were treated in the same manner.

Immediately after preparation, the test flasks were stoppered and stirred vigorously for 5 minutes without aeration at room temperature. After the 5 minute exposure time, approximately 300 ml from the test flask was transferred into a 300 ml BOD bottle for dissolved oxygen measurement. The respiration rate, as determined by O2 concentration, was measured over a period of up to 10 minutes, or until DO level was approximately 2.5 mg O2/l, whichever came first. The test temperature of the solution in the BOD bottle was measured following the last DO reading.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

5 min

Dose descriptor:

EC0

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Results with reference substance (positive control):

For the study to be valid, results for the reference substance, 3,5-dichlorophenol, must be in the range of 5 to 30 mg/l. The reference substance EC50 was determined to be 7.4 mg/l.

Validity criteria fulfilled:

yes

Conclusions:

Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30%), did not inhibit microbial respiration in a sludge sample at a concentration of 1000 mg/l. Therefore, Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30%), is not expected to adversely affect microbial activity in a wastewater treatment plant.

Executive summary:

Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30%), did not inhibit microbial respiration in a sludge sample at a concentration of 1000 mg/l. Therefore, Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30%), is not expected to adversely affect microbial activity in a wastewater treatment plant.

Description of key information

There is data available for this substance, which is presented in the dossier.

Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30%) did not inhibit microbial respiration in a sludge sample at a concentration of 1000 mg/l.

Additional information

One study was available and input as an endpoint record. The study is summarised below.

The study from Shell (1995) examined the toxicity of the test susbtance Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30%) to activated sludge of a predominantly domestic sewage. Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30%), did not inhibit microbial respiration in a sludge sample at a concentration of 1000 mg/l. Therefore, Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, aromatics (2-30%), is not expected to adversely affect microbial activity in a wastewater treatment plant.