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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

One freshwater green alga study using Pseudokirchneriella subcapitata.  Three studies were conducted: in two of these studies the algal media was amended with either 10 or 20 mg humic acid/L.  The values from the study using 20 mg/L humic acid were more sensitive than the values from the 10 mg/L study and are the ones presented.  

Key value for chemical safety assessment

EC50 for freshwater algae:
4.94 mg/L
EC10 or NOEC for freshwater algae:
1.3 mg/L

Additional information

The purpose of this study was to assess the effects of Paraformaldehyde, oligomeric reaction products with 4-tert-butylphenol, m-phenylenebis(methylamine), refered to as Mannich Base PTBP-MXDA, to the freshwater green alga, Pseudokirchneriella subcapitata, over a 72-hour static exposure period. These data were used to determine EL50 values for 72-hour cell density, 0-72-hour cell yield, and average specific growth rate from 0 to 72 hours. Mannich Base PTBP-MXDA has low aqueous solubility and therefore test solutions were prepared from a water accomodated fraction (WAF). Mannich Base PTBP-MXDA possesses cationic properties and was, therefore, tested in line with the OECD (2000) recommendation for testing cationic properties for the mitigating effect of 0, 10, and 20 mg/L humic acid. The results of the test are as follows:

Without Humic Acid: 72 hour cell density EL50 = 0.111 mg Mannich Base PTBP-MXDA/L; NOELR = 0.010 mg/L; 0 -72 -hour cell yield EyL50 = 0.111 mg Mannich Base PTBP-MXDA/L; NOELR = 0.010 mg/L; 0 -72 hour growth inhibition ErL50 = 0.179 mg Mannich Base PTBPMXDA/ L; NOELR = 0.010 mg/L.

With 10 mg Humic Acid/L: 72 hour cell density EL50 = 13.6 mg Mannich Base PTBP-MXDA/L; NOELR = 8.0 mg/L 0-72-hour cell yield EyL50 = 13.5 mg Mannich Base PTBP-MXDA/L; NOELR = 8.0 mg/L; 0-72 hour growth inhibition ErL50 >20 mg Mannich Base PTBP-MXDA/LNOELR = 8.0 mg/L.

With 20 mg Humic Acid/L: 72 hour cell density EL50 = 3.04 mg Mannich Base PTBP-MXDA/L; NOELR = 1.3 mg/L; 0-72-hour cell yield EyL50 = 3.09 mg Mannich Base PTBP-MXDA/L; NOELR = 1.3 mg/L; 0-72 hour growth inhibition ErL50 = 4.94 mg Mannich Base PTBP-MXDA/L; NOELR = 1.3 mg/L.

Thus, the addition of humic acid reduced the toxicity of Mannich Base PTBP-MXDA for each of the endpoints examined. The endpoints reported as the overall endpoints, and those used to derive the PNEC values will be from the study using 20 mg/L humic acid because they are the most conservative, while being the most environmentally relevant.