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Environmental fate & pathways

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The fate and behaviour of a chemical is largely governed by its inherent physico-chemical properties, As vapour pressure, water solubility, partition coefficient (HPLC method.

The sorption or binding behaviour of chemicals to sediment is determined by certain properties. Especially substances with high Log Kow or Log Koc values adsorb to the organic fraction of the sediment and soil.

In general substances with a Koc <500-1000 L/kg are not likely sorbed to sediments (SETAC 1993).

According to this, a log Koc or log Kow of >=3 is used as trigger value for sediment effect assessment although other concentration or combinations of triggers might be important as well (e.g. binding to sediment particles) that is not Kow/Koc driven, but where for instance the distribution coefficient Kd is important, persistence in the sediment compartment. Substances with a high potential to adsorb onto sediment (e.g. log Kow >5 or Log Koc >3) require sediment assessment even at tonnages below 1000 t/y.

Substances with tonnages below 1000 t/y and a not having a high potential for adsorption (e.g.log Kow <5 or log Koc <3)do not normally need a sediment risk assessment.

The same triggers as for parent compounds (e.g. log Koc >3) can be applied to degradation products.

If it is foreseeable that degradation products accumulate in the sediment or soil compartment, testing of degradation products might be necessary. Results from biodegradability test on similar substance indicates non biodegradability in water.

The substance under evaluation is not readily biodegradable, therefore no degradation products are expected in water compartment, and their accumulation in sediments and soil.

 

Acid Brown 373 is a very complex UVCB substance, therefore the Koc has been calculated starting from the three more-representative molecular formula.

The estimated values for the three substance are higher than 3

Chemical structure 1: Log Koc (estimation MCI method) = 5.36 Log Koc (estimation Kow method) = 2.11

Chemical structure 2: Log Koc (estimation MCI method) = 7.25 Log Koc (estimation Kow method) = 2.50

Chemical structure 3: Log Koc (estimation MCI method) = 8.4 Log Koc (estimation Kow method) = 5.14

and this could suggest a potential adsorption property on sediment and soil compartments.

However they are estimated value, while is available an experimental Kow that can be evaluated, being compared to the >=3 trigger value. The Log Pow experimental, based on the OECD Guideline 117 was stated at < 0.3

Furthermore, the substance has a high solubility ( 37.98 ± 2.89 g/L).

All compounds with a log Kow of less than 1.0 are assigned an estimated log BCF of 0.5 (3.166 L/Kg) (same as in BCFWIN). The substance can be considered non bioaccumulative.

As conclusion, it can be assumed that the substance has not a potential adsorption property on sediment and soil compartments.