Phosphoryl trichloride

Endpoint summary

Additional information

Aquatic toxicity data on three trophic levels are available either on phosporyl trichloride (POCl3), phosphorus trichloride (PCl3) or phosphorus pentachloride PCl5 (OECD SIDS, SIAM 19, Oct 2004). The data on PCl3 and PCl5 can be used to assess the toxicity of POCl3 since phosphorus trichloride hydrolyzes to hydrochloric acid and phosphonic acid. Phosphonic acid and phosphorus acid are tautomeric molecules. Phosphorus acid is slowly oxidized by oxygen (air) to phosphoric acid (Merck 2001). And phosphorus pentachloride reacts vigorously with water and hydrolyzes to hydrochloric acid and phosphoric acid in two stages (Greenwood and Earnshaw, 1988). Both substance yield to the same hydrolysis products like POCl3.

Short-term toxicity to fish (OECD SIDS, SIAM 19, Oct 2004)

PCl3 was tested in a static limit test according to the method proposal of the German Environmental Protection Ageny “Lethal effects on Brachydanio rerio” using zebrafish (Danio rerio, Bayer AG 1991). The pH was adjusted. No effects could be observed within 96 h and the LC0 was determined to be ≥ 1000 mg/L. This value equals a LC0 of ≥ 597 mg/l of (neutralized) phosphonic acid as the hydrolysis product.

Additional results on toxicity to fish are available using PCl3 and PCl5. However, all studies were conducted without adjustment of the pH. Therefore, the results should not be used in hazard assessment since the effects were solely caused by low pH.

Short-term toxicity to aquatic invertebrates (OECD SIDS, SIAM 19, Oct 2004)

POCl3 and PCl3 were tested in an acute toxicity test according to the European guideline 92/69/EEC, method C.2 (equivalent to OECD TG 202) using Daphnia magna. In the non-buffered test solution the pH decreased from pH 7.9 in the controls to pH 6.7 at 25 mg/l, pH 3.7 at 50 mg/l, and pH 3.0 at 100 mg/l, each at the start of the incubation. For a test period of 24 h, an EC0 of 25 mg/l, an EC50 of 35.4 mg/l, and an EC100 of 50 mg/l were obtained. The same effect concentrations were measured after a test period of 48 hours. In the buffered test solution (pH 7.9) no effect was observed at the highest tested concentration of POCl3 (nominal 100 mg/l), suggesting that the effects in the non-buffered solutions were solely due to the pH decrease (Bayer AG, 2003b). The same results were obtained with PCl3 (Bayer AG, 2003c).

Toxicity to aquatic algae (OECD SIDS, SIAM 19, Oct 2004)

POCl3 and PCl3 were tested in an acute toxicity test according to the European guideline 92/69/EEC, method C.3 (equivalent to OECD TG 201) using Desmodesmus subspicatus. Both substances were tested in buffered and non-buffered test solutions. In the non-buffered solution, the pH depended on the nominal POCl3 concentration was pH 8.2 in the controls and pH 2.9 at 100 mg (nominal concentration at the start of the incubation period). In the non-buffered solution, a 72 h-ErC50 of 32 mg/l and a 72 h-EbC50 of 28 mg/l was determined. The 72h-NOEC was 12.5 mg/l for both growth rate and biomass. In buffered solution no effect was observed at the highest POCl3 concentration tested (nominal 100 mg/l). Thus, it can be concluded that the effects found in this study are caused by pH effects (Bayer AG, 2003d). Similar results were obtained with PCl3 (Bayer AG, 2003e).

Toxicity to microorganisms (OECD SIDS, SIAM 19, Oct 2004)

An acute toxicity test was conducted according to ISO 8192 (Test for the Inhibition of Oxygen Consumption by Activated Sludge) using activated sludge. After 3 h incubation an EC50 of 9450 mg/l and an EC0 of 3520 mg/l were determined (Bayer AG, 1991).

In overall conclusion, phosphoryl trichloride and its hydrolysis products are with high probability acutely not harmful to aquatic organisms and the inhibition of the degradation activity of activated sludge is not anticipated when introduced in appropriate low concentrations.