Tetrakis(hydroxymethyl)phosphonium chloride, oligomeric reaction products with urea

Toxicity to aquatic algae and cyanobacteria

Description of key information

Desmodesmus subspicatus (freshwater):  72h-EC50 = 0.23 mg/L (growth) for THPC-urea (a.i.)
The read across substance THPS shows a comparable  acute toxicity for algae: 
Selenastrum capricornutum (Pseudokircherella subcapitata) (freshwater): EC 50 = 0.652 mg/l (growth); EC 50 = 0.204 mg/l (biomass); 
NOEC = 0.063 mg/l (growth and biomass)
Skeletonema costatum (marine): EC 50 = 0.16 mg/l

Key value for chemical safety assessment

EC50 for freshwater algae:

0.23 mg/L

EC50 for marine water algae:

0.16 mg/L

EC10 or NOEC for freshwater algae:

0.067 mg/L

Additional information

The technical product "Tetrakis(hydroxymethyl)phosphonium chloride, oligomeric reaction products with urea" (THPC-urea) is a condensate of THPC and urea. The functional group of the THPC is the OH group. The functional group of the urea is the amino group NH2. The condensation of THPC and urea does not change both functional groups.

The first read across approach between THPC and THPS is considered applicable, as the organic phosphonium cation, which is the responsible part for the toxicological effects, is the same for both salts. The different anions (chlorid and sulfat) have no great influence on the solubility (both very high), the vapour pressure (both extrem low), and the log Kow (both extrem low and negativ).

The second read-across approach between THPC and THPC-urea is based on the fact, that THPC is an impurity of the technical product THPC-urea. THPC is more reactive and more toxic than THPC-urea. A worst case scenario is created assuming that THPC-urea is completely reactive like THPC.

Furthermore, the oxidative degradation of THPC-urea, THPS and THPC results in the same main metabolite THPO, which is far less toxic than THPC-urea, THPS and THPC.