Registration Dossier
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EC number: 272-745-1 | CAS number: 68910-55-4
Toxicity to aquatic algae and cyanobacteria
Administrative data
Link to relevant study record(s)
Description of key information
The 72-hour EC50 for the marine alga Skeletonema costatum was calculated in the original study report as 130.5 mg/L based on nominal Water Accommodated Fraction (WAF) concentrations. A re-analysis of the mean cell count data, reveals that the 17.8 mg/L concentration data are an outlier (i.e., mean cell counts at 24 h, 48 h, and 72 h are much lower at 17.8 mg/L than in both the next lower [10 mg/L] and next higher [31.6 mg/L] test concentrations). Therefore, a clear dose response relationship is not evident and a post-hoc analysis is warranted in accordance with OECD 201 guidance, ¶45, without the outlier data. Re-analysis of the data, results in an EC50 of 125.5 mg/L. In addition, organolignite's physical properties (i.e., low water solubility [54 µg/L] and dark brown/black color), suggest that the observed algal growth reduction is due to a physical effect and not a direct toxic effect.
Key value for chemical safety assessment
- EC50 for marine water algae:
- 125.5 mg/L
Additional information
The acute toxicity of the test substance, organolignite, to the marine alga, Skeletonema costatum, was determined using test method ISO 10253: 1998. Alga were exposed in static conditions for 72 hours to nominal water accommodated fractions (WAFs) containing concentrations of the test substance of 10.0, 17.8, 31.6, 56.2, 100.0, and 177.8 mg/L. The original study report calculated a 72 hour-EC50 of 130.5 mg/L, a LOEC of 17.8 mg/L, and a NOEC of 10 mg/L. A re-analysis of the mean cell count data from this study, reveals that the 17.8 mg/L data are an outlier (i.e., mean cell counts at 24 h, 48 h, and 72 h are much lower at 17.8 mg/L than in both the next lower [10 mg/L] and next higher [31.6 mg/L] test concentrations). Therefore, a clear dose response relationship is not evident and a post-hoc analysis is warranted in accordance with OECD 201 guidance, ¶45, without the outlier data. Re-analysis of the data, results in an EC50 of 125.5 mg/L, a LOEC of 177.8 mg/L, and a NOEC of 100 mg/L. In addition, organolignite is minimally soluble in water (54 µg/L), so the observed algal toxicity (at concentrations well above water solubility) are not expected to be due to direct toxicity, but a physical effect. Specifically, organolignite is a dark brown to black powder substance, which is expected to reduce the availability of photosynthetically active light and limit algal growth in a concentration-dependent manner.
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