Tar, wood

Toxicity to aquatic algae and cyanobacteria

Description of key information

The following results for the test item Tar wood were determined:
Endpoint NOEC LOEC EC10 EC50 
Growth Rate 3.0 mg/L 15 mg/L 14 mg/L 17 mg/L 
AUC 3.0 mg/L 15 mg/L 13 mg/L 15 mg/L 
Yield 3.0 mg/L 15 mg/L 13 mg/L 15 mg/L 

Key value for chemical safety assessment

EC50 for freshwater algae:

17 mg/L

EC10 or NOEC for freshwater algae:

14 mg/L

Additional information

DISCUSSION AND CONCLUSION

The study was performed using six concentrations ranging from 0.32 to 100 mg/L. Incubation time (test systemDesmodesmus subspicatus) was 72 hours. The cell concentration of each replicate was determined by measuring the absorption of the solutions at 440 nm every 24 hours with a spectral photometer. The cell density of the cultures was calculated based on the correlation curve between the adsorption and the cell density of the cultures determined by microscope counts. Growth rate µ, area under the growth curve (AUC^[1]) and the yield^[2]were determined from the cell densities at the respective observation times. 

Significant inhibition of algal growth was observed at the following concentrations:

100 mg/L and 32 mg/L.

At the start and at the end of the test, the content of the test item in the test solutions was estimated using DOC analysis. Only in the three highest treatments, additional dissolved carbon was detectable, as in the lower treatments DOC values were in the same range as in the control. Because no inhibition could be observed in the lower concentrated treatments, this can be sta.ted as uncritical for evaluation. The recovery after 72 hours was in a range of 36 to 87 % of the start concentration. The measured concentrations lay between 49 % and 60 % of the nominal concentration at the beginning of the test and between 18 % and 52 % of the nominal concentration at the end of the test. Therefore, the determination of the results was based on the geometric mean of the measured concentrations in the three highest concentrated treatments.

In the highest concentrated treatment, photometric measurement was biased because of clouded colored test solution. Because no algal cells could be observed via microscopic observation, inhibition in this treatment was stated as 100 %.

The EC50s of potassium dichromate were determined in a separate reference test (GLP study no. 201308R301). For the estimation of the EC50s of the positive control, the fits showed sufficient statistical correspondence of the data with the dose-response-equation.

The values were within the normal range of the laboratory.

All validity criteria were met. 

No observations were made which might cause doubts concerning the validity of the study outcome.

The result of the test can be considered valid