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Environmental fate & pathways

Adsorption / desorption

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Description of key information

In accordance with Column 2 adaptation statement of REACH Annex VIII and IX, adsorption/desorption screening and further studies on adsorption/desorption, information requirements 9.3.1 and 9.3.3, may be omitted since the log Kow value for the substance is <3.0 and has low potential for adsorption (CSR section 1.3).  (Q)SAR-modelled KOC values for terephthalic acid range from 18.28 to 79.24 L/kg.  

Key value for chemical safety assessment

Additional information

(Q)SAR-modelled Koc values for terephthalic acid (obtained with the KOCWIN v2.00 model of the US EPA) range from 18.28 to 79.24 L/kg. Based on these values, terephthalic acid is classed as moderately mobile to mobile and is expected to have a low tendency to adsorb to soils and sediments. KOC may be influenced by and vary significantly in response to pH. Under alkaline conditions, terephthalic acid will rapidly be converted to salts whose KOC may be expected to be lower (mobility higher) than that of the free acid.

The low Koc values modelled for terephthalic acid also imply a low tendency to associate with sludge solids during the primary settlement and secondary biological stages of waste water treatment. The majority of the TPA load contained in a treatment plant influent load may therefore be expected partition to the aqueous phase and to be routed toward aerobic biological treatment. Since process effluents discharged to treatment facilities are typically neutalised to protect both the plant hardware (concrete and metalwork) from corrosion and the biological treatment process from pH-shock effects, TPA is likely to be discharged in the form of salts that are more highly water soluble and have a correspondingly lower Koc than the parent acid. Salts formed by the pre-treatment neutralisation step are likely to have an even lower tendency than that of free terephthalic acid to bind to sludge solids.