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Environmental fate & pathways

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Formaldehyde occurs naturally in the environment and is the product of many natural processes (e. g. biomass combustion such as forest and brush fires).

After release into the environment, formaldehyde will partition to both the air and water phases . Formaldehyde is a highly reactive compound which undergoes rapid photodegradation in the atmosphere. Therefore, transportation over large distances is not deemed to be of great importance. Reaction with the hydroxyl radical is considered to be the most important photooxidation process. Factors influencing the atmospheric lifetime of formaldehyde, such as time of day, intensity of sunlight, temperature, etc., are mainly those affecting the availability of hydroxyl and nitrate radicals. The atmospheric half-life of formaldehyde, based on hydroxyl radical reaction rate constants, is calculated to be between 7.1 and 71.3 hours. Products that can be formed from hydroxyl radical reaction include water (H2O), formic acid (HCOOH), carbon monoxide (CO) and the hydroperoxyl/ formaldehyde adduct (HCO3).

Formaldehyde is water soluble and highly reactive in natural aquatic environments. Formaldehyde exhibits no potential for hydrolysis, due to the absence of hydrolyzable groups. In water, formaldehyde undergoes essentially complete hydration to yield the gem-diol, methylene glycol. Equilibrium almost totally favours the glycol; less than 0.04% by weight of unhydrated formaldehyde is found in highly concentrated solutions.

Besides abiotic degradation, biotic degradation represents a relevant major sink for formaldehyde in water and soil. The substance is readily biodegradable according to OECD criteria and is rapidly mineralized under aerobic and anaerobic conditions.

Due to the low log Kow (0.35), accumulation in organisms is not to be expected. Furthermore, the substance is not expected to adsorb to a high degree to suspended solids and sediment (log Koc = 1.2). When exposed to water the substance will not evaporate into air (Henry's Law constant < 1 Pa m3/mol). Using simple environmental models based on fugacity, the main target for environmental distribution will be water (Mackay Level I calculation; BASF SE, 2008).