4,4'-cyclohexylidenedi-o-cresol

Toxicity to aquatic algae and cyanobacteria

Description of key information

Under the conditions of this study, the 96 hour ErC50 was > 1165 µg/L. The 96 hour NOEC was 595 µg/L DMBPC when determined using the number of cells/mL or the average specific growth rate.

Key value for chemical safety assessment

EC50 for freshwater algae:

1 165 µg/L

EC10 or NOEC for freshwater algae:

595 µg/L

Additional information

The toxicity potential of the test material to freshwater algae was investigated in accordance with the standardised guideline EPA OPPTS 850.5400 under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

The definitive toxicity test was conducted at 24 ± 2°C with five concentrations of test substance, a control, and a solvent control (0.10 mL/L dimethylformamide). Nominal concentrations were 0 (control and solvent control), 75, 150, 300, 600 and 1200 µg/L. Each solution was subdivided into three clear glass 250 mL Erlenmeyer flasks. The flasks were inoculated with approximately 10 000 algal cells/mL and capped with inverted glass beakers. Test vessels were randomly arranged on a rotary shaker adjusted to approximately 100 rpm in an incubator. 

The number of algal cells/mL in each test vessel and the occurrence of relative size differences, unusual cell shapes, colours, flocculations, adherence of cells to test containers, or aggregation of cells was determined visually by means of direct microscopic examination with a haemocytometer at 24, 48, 72, and 96 hours. 

A 0.5 mL aliquot of test media from each test vessel where growth was maximally inhibited (1200 µg/L nominal DMBPC concentration) was combined in a 250 mL flask with 100 mL of fresh media to determine whether toxic effects were algicidal or algistatic. This culture was incubated under test conditions for 48 hours.

Insoluble material was not observed during the test.  The initial measured concentrations ranged from 97 to 108 % of the nominal concentrations and the final measured concentrations were 57 to 76 % of the nominal concentrations.

The algal population grew well, resulting in an average of 4 173 000 cells/mL in the control after 96 hours. No effects were noted during the test. The 0.5 mL aliquot that was incubated for a further 48 hours indicated that any toxic effect at this concentration was algistatic rather than algicidal.

Exposure of algae to DMBPC for 96 hours resulted in a median effective concentration (EC50) that was greater than 1165 µg/L (the highest tested concentration and reported water solubility limit) when calculated using the number of cells/mL or the average specific growth rate, and 1141 µg/L when calculated using the area under the growth curve. The 96 hour no observed effect concentration (NOEC) is 595 µg/L DMBPC when determined using the number of cells/mL or the average specific growth rate, and 161 µg/L when determined using the area under the growth curve.