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The toxicity of HCA to various aquatic organisms has been examined.

For algae, it was not possible to maintain hexyl cinnamic aldehyde at the solubility limit of the substance in a 72 hour study as it photodegraded and hydrolysed (and perhaps biotically degraded) under the conditions of the study. For this reason, the EC50 cannot be calculated at the maximum attainable concentration which was attainable in the study.

For daphnids an acute study was originally considered invalid due to the use of solvents in a flow-through study which led to effects above the water solubility of the test substance as defined in an OECD 105 study. However, futher to the performance of a new solubility study in both ultra-pure water and daphnid medium, it was found that the original water solubility study erroneously provided results around 0.3 mg/L. The true water solubility in mineral medium is around 1.5 mg/L and therefore the toxicity observed in the daphnid study is below the solubility limit. substance losses by protecting the test solutions from light during the study, keeping them under closed conditions and using a semi-static technique. No significant effects (5% immobilisation) were observed up to a WSF loading of 1 mg/L, significantly higher than the maximum water solubility limit for hexyl cinnamic aldehyde. Effects were observed at the higher WSF concentrations but these are considered of no significance as they were hundreds of times higher than the solubility limit and almost certainly contained micro-droplets of test substance.

For fish in acute, no effects were observed up to the aqueous solubility limit of the substance. Any mortality or effects observed were therefore due to physical effects due to the solvent artificially maintaining the test substance in an emulsion that was stable under the conditions of the study (flow-through conditions) but not possible to maintain under environmental conditions.

For chronic effects, a chronic study was performed on daphnid according to international guidelines but with the use of solvent. It appears that there were no statistically significant treatment-related effects on survival, reproduction or growth at concentrations up to 63 µg a.i./L. Growth, measured as length and dry weight, and reproduction were the most sensitive biological endpoints measured in this study. Daphnids exposed to the test substance at a concentration of 157 µg a.i./L had statistically significant reductions in growth and reproduction in comparison to the pooled control. Consequently, the 21-day EC10 value for adult immobility was 107 µg a.i./L and the 21-day EC10 value for reproduction was 69 µg a.i./L. 

In the algae study the NOEC is based on the measured concentration of 0.065 mg/L which relates to the maximum attainable concentration which was tested in the study for this species (i.e. not a true NOEC).

Under normal circumstances a chronic fish study could also be requested, however for several reasons this study is considered unjustified. Firstly, due to the abiotic (and perhaps biotic) degradation properties of the substance and its high potential for adsorption, the long-term fish study would be technically difficult to perform. Secondly, as this substance is expected to adsorb to organic matter and sediment and would be expected to degrade rapidly it would not be expected to be present at concentrations that could cause toxicity in the pelagic compartment.

Based on biodegradation studies, micro-organisms are not considered sensitive to the test substance.

In conclusion, for acute data, toxicity was observed belfor one species, daphnids, at 0.247 mg/L (meaused concentration). Other studies in which toxicity was found either found effects at or above the water solubility limit of hexyl cinnamic aldehyde or no effects at the highest concentration attainable over the study period.

For chronic data in the pelagic compartment, a chronic NOEC was determned for Daphnia magna at a concentration of 63 µg/L.