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Environmental fate & pathways

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Based on the physico-chemical properties of thioglycolic acid and salts (high solubility and low Log P), it is considered that these substances are not expected to adsorb to suspended solids, sediments and soils and are mobile in soil. The potential for bioaccumulation in aquatic or terrestrial species is also considered as negligible.

Usually modeling approach is proposed to roughly estimate possible transport between environmental compartments. This approach cannot necessarily be followed for all categories of substances. Ionizable substances like thioglycolic acid and salts for instance do not fit in relevancy criteria of the common models used. It is important to have information on pH-dependence and one cannot ignore influence of the mineral matrix.

Nevertheless some physico-chemical properties can be used for addressing some points related to substances compartimentation. With a Henry's Law constant of 1.45 x 10-6atm-m3/mole, thioglycolic acid is expected to be essentially non-volatile from water or moist surfaces (Lyman et al., 1990). Thioglycolic acid is also not expected to volatilize from dry soil surfaces based upon an experimental vapor pressure of 16 Pa (Tremain, 2007).

Behavioural information available demonstrate the velocity of oxidaton of thioglycolic acid in oxygen saturated tap water which has been demonstrated to be very high (Smolin and Fölsing, 2009). That means that thioglycolic acid is not stable in some environmental conditions. This information about abiotic degradation of thioglycolic acid is also supported by biotic degradation data.

For the evaluation of the biodegradability of thioglycolic acid, ready biodegradation and inherently biodegradation test results have been considered but also results obtained with diammonium dithiodiglycolate as main oxidation product of thioglycolic acid.

Considering the overall information available for thioglycolic acid and its main oxidation product, the dithiodiglycolic acid, it can be considered that thioglycolic acid and its salts are ready biodegradable and do not raise concern in terms of persistency. Thioglycolic acid and salts are readilly biodegradable, are easilly oxidized and therefore hydrolysis test is not required and this endpoint is waived.