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Environmental fate & pathways

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Description of key information

Phototransformation of the test substance was calculated using generally accepted method EPI suite AOPWIN. The following results were obtained: PHOTOCHEMICAL REACTION WITH OH RADICALS  Concentration of OH radicals: 500000  Degradation rate constant: 0.0000000000083217 cm³/molecule-sec  Temperature for which rate constant was calculated: 25 °C  Calculated t 1/2 is based on a 24 h day.  The halflife of ethylene glycol in air is estimated to DT50 = 46.3 h. Hydrolysis of the test substance was studied using 13C-NMR techniques andspectrophotometric analysis. The degree of hydrolysis was measured by detection of formaldehyde. During the reaction time, increasing amounts of formaldehyde were observed. At all pH values, the content of formaldehyde reached a plateau, an equilibrium between the reactants was observed. The studies demonstrate the rapid hydrolysis. At large dilutions which are expected under environmental conditions (in wastewaters or surface waters) as well as in human body fluids, the test substance is expected to hydrolyse completely to formaldehyde and ethylene glycol.

Additional information

Information on formaldehyde

Hydrolysis and phototransformation in water

Hydrolysis of formaldehyde can be excluded because of the absence of a hydrolysable group in the molecule. Therefore, a test on hydrolysis in water is scientifically unjustified. There are no tests on photolysis of formaldehyde in aqueous solutions available which would allow deriving a reaction rate for surface waters. In aqueous solutions formaldehyde hydrate is formed which has no chromophore that is capable of absorbing sunlight and thus should not decompose by direct photolysis. The reaction of formaldehyde with OH-radicals (indirect photolysis) was studied in cloud water. However, because of the different composition of aerosols compared to surface waters the reaction rate obtained for aerosol cannot be adopted for the oxidation in surface waters. Because of the ready biodegradability, photolysis in surface waters is expected to be of minor importance. In conclusion, a test on phototransformation in water would not improve the database for the hazard assessment and is therefore scientifically unjustified. In aqueous solutions, formaldehyde forms the hydrate CH2(OH)2. Monomeric, physically dissolved formaldehyde is only present in low concentrations of up to 0.1 wt %. The polymerization equilibrium HOCH2OH + n CH2ODHO(CH2O)n+1−H is catalyzed by acids and is shifted toward the right at lower temperature and/or higher formaldehyde concentrations, and toward the left if the system is heated and/or diluted. At environmental relevant concentrations, formaldehyde is expected to exist predominantly as hydrate. Paraformaldehyde dissolves slowly in cold water, but readily in warm water where it undergoes hydrolysis and depolymerization to give a formaldehyde solution (Ullmann 2005).

 

Phototransformation in air

In the gas phase, formaldehyde is rapidly degraded in air via reaction with OH radicals; degradation by nitrate and ozone is negligible. The decomposition by direct photolysis is 1.5 times higher than by OH radicals. The main transformation products are hydrogen and carbon monoxide. In cloud water, formaldehyde hydrate reacts with OH-radicals (indirect photolysis) to form formic acid (Chameides and Davies 1983). Based on the half-life constants of formaldehyde, accumulation in the atmosphere is not to be expected. Furthermore, the Henry's law constant is relatively low. Therefore, formaldehyde is not expected to volatilise to air from water surfaces in significant quantities and the amount which reaches the air compartment will be washed out by rain.