Bis(2-ethylhexyl) phthalate

Toxicity to microorganisms

Description of key information

From the reliable data avialable, no adverse effects are expected upon exposure of sewage sludge microorganisms to DEHP.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

2 007 mg/L

Additional information

In most of the available studies concentrations well above water solubility of DEHP have been tested.

Three relevant data are available for this endpoint.

- Diefenbach 1999 (key study, reliability category 2), studied inhibition of activated sludge respiration in a study performed according OECD 209 and compliant to GLP. DEHP was added without and with emulsifier (TWEEN 80) to activated sludge from the municipal treatment plant Marl-West, treating predominantly domestic sewage. As concentration of emulsifier is high and above OECD recommendation (400 mg/L instead of 100 mg/L), only data without emulsifier will be considered.

Nominal test concentrations (without emulsifier) were 92.8; 235.6; 556.2; 1039 and 2007 mg/L

No inhibition of activated sludge respiration was observed at the highest tested DEHP concentrations, 2007 mg/l (without emulsifier) and 1,000 mg/l (with TWEEN 80).

All validity criteria were fulfilled. Concentrations tested were well above water solubility but bioavailability of DEHP for bacteria requires prior adsorption of the substance on sludge. As up to the highest tested concentrations no inhibition was observed, we can expect that at environmental concentration no hazard will occur. Therefore this study is considered as reliable with restrictions and is used as key study in the present assessment.

NOEC = 2007 mg/L will be used in the PNEC derivation for Sewage Treatment Plant

This result is supported by 2 other studies:

- Jonsson et al 2003 (reliability category 2), in which authors tested the acute toxicity of DEHP (and other compounds) on the bacterium Vibrio fischeri according to the ISO 11348 -3 standard. They tested five to nineteen different concentrations (depending on compound) with a maximum of 0.003 mg/L, corresponding to the actual water solubility as reported by Staples et al., 1997. At the test conditions, EC10 (15min) and EC50 (15min) were above 0.003 mg/L estimated by a software using the non-linear regression method by considering reduction of luminescence as the endpoint.

- Perez et al. 1983, showed for a marine model ecosystem no effects at the highest DEHP concentrations tested: 0.059 mg/l during winter and 0.016 mg/l during summer conditions. However, it should be noted that the marine conditions might have affected the bioavailability of the substance.

As an overall conclusion, DEHP is considered as not harmful to aquatic microorganisms and is not expected to have hazardous effects on water treatment plants.