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Environmental fate & pathways

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Isomerization of CAS 16090-02-1 in sewage was found to be very fast. A simple model was used to simulate the partitioning of the substance under the influence of sunlight. ln solutions with low particle content, the ratio is dominated by the photochemically favoured (Z)-isomer. With increasing particle content, the more strongly adsorbing (E)-isomer is favoured and becomes the dominant species. Very good agreement between model calculation and field data is obtained for primary and secondary effluent. Primary sludge is settled before isomerization can take place .

From field data the following conclusions concerning the behaviour and fate of the substance in a mechanical sewage treatment plant can be drawn:

(I) elimination ot TS from wastewater occurs during both mechanical and biological treatment.

(II) overall removal rate of 98 % was observed.

(III) elimination is due to adsorption to primary and activated sewage sludge and the observed elimination, rate is consistent with the individual sorption behaviour of the TS as investigated in laboratory experiments.

(IV) no evidence for biodegradation of TS was found during the (aerobic) biological treatment of wastewater with activated sludge and during anaerobic-mesophilic digestion of raw sewage sludge.

(V) the TS removed during wastewater treatment is thus quantitatively recovered in anaerobically digested, sewage sludge.

Assuming biodegradation processes are not significant, the only elimination processes are adsorption and photodegradation.

The adsorption properties of the substance should consist of a high affinity to organic solids. Additionally, this high affinity to organic solids will lead to a high extent of elimination in the sewage treatment plants, due to adsorption onto the sewage sludge. A disadvantage of this high affinity may be that the TS rapidly adsorbs on suspended solids in natural surface waters.

Monitoring data about the STPs efficacy are available and the results on the investigation about the efficacy of the STPs confirm that the substance can be removed in appreciable percentage.