Tetrakis(hydroxymethyl)phosphonium sulphate(2:1)

Toxicity to aquatic algae and cyanobacteria

Description of key information

OECD Guideline 201, GLP, key study, validity 1:
96h-ErC50 (Selenastrum capricornutum) = 0.492 mg/L (nominal, as main ingredient)
96h-NOECr (Selenastrum capricornutum) = 0.048 mg/L (nominal, as main ingredient)
ISO Guideline 10253, GLP, key study, validity 2:
72h-ErC50 (Skeletonema costatum) = 0.12 mg/L (nominal, as main ingredient)
72h-NOECr (Skeletonema costatum) = 0.075 mg/L (nominal, as main ingredient)
In conclusion, THPS is considered very toxic to aquatic algae.

Key value for chemical safety assessment

EC50 for freshwater algae:

0.492 mg/L

EC50 for marine water algae:

0.12 mg/L

EC10 or NOEC for freshwater algae:

0.048 mg/L

EC10 or NOEC for marine water algae:

0.075 mg/L

Additional information

Four studies are available to assess the toxicity of the active substance THPS to algae. These studies were performed on the THPS in solution in static conditions, with freshwater and marine species. The relevant results were expressed as main ingredient (100% active substance).

There is one study of reliability 1 on the freshwater species Selenastrum capricornutum (Jenkins, 1991d) and three studies of reliability 2 on the marine species Skeletonema costatum (Hushagen, 1994; Brakstad, 1994; Vryenhoef, 2004). All studies lead to similar NOEC and EC50 values.

The study of best reliability and lowest NOEC value has been defined as key study (Jenkins, 1991d), and the study of best reliability and lowest EC50 value has also been defined as key study (Hushagen, 1994).

Results are expressed in the table below (as main ingredient):

Test method	Species	Endpoint / Type of test	Exposure	Reliability	Flag	Results (ErC50 (95% CL), mg/L)	Results (ErC10 (95% CL) or NOECr, mg/L)	Reference
OECD Guideline 201	Selenastrum capricornutum (freshwater species)	Growth inhibition / acute and chronic	Static, 96h	1	KS	0.492 (0.408-0.630)	0.048	Jenkins, 1991d
ISO 10253	Skeletonema costatum (marine species)	Growth inhibition / acute and chronic	Static, 72h	2	KS	0.12 (0.075-0.24)	0.075	Hushagen, 1994
ISO 10253	Skeletonema costatum (marine species)	Growth inhibition / acute and chronic	Static, 72h	2	SS	0.266 (0.244-0.290)	0.044 (0.032-0.057)	Brakstad, 1994
ISO 10253	Skeletonema costatum (marine species)	Growth inhibition / acute and chronic	Static, 72h	2	SS	0.465	0.0469	Vryenhoef, 2004*

* This study is not owned by Solvay, the test report is available on the US EPA web site at EPA/OPPT/Toxic Substance Control Act Section 8(e), the test substance was not manufactured by Solvay,THPS main ingredient content is 75 %.

According to the key studies, THPS is considered very toxic to aquatic algae with an EC50 value based on growth rate at 0.12 mg/L on a marine algae species (Skeletonema costatum) and a NOEC value based on growth rate at 0.048 mg/L on a freshwater algae species (Selenastrum capricornutum).