We have studied the effectiveness of surface tension on surfactants risk assessment. γ
tox was defined as surface tension at a point where acute aquatic toxicity of a surfactant emerges.
Oryzias latipes,
Daphnia magna, and
Podocopida were used for acute aquatic toxicity test of 7 surfactants and 3 detergents. γ
tox values were plotted on surface tension curves, and the effect of water hardness on toxicity and surface tension were examined. Results showed that γ
tox varies greatly by kind of surfactant or detergent. Therefore, aquatic toxicity cannot only be explained by surface tension. The change of aquatic toxicity with varying water hardness, however, could be explained by the change of surface tension. Aquatic toxicity of LAS (Linear Alkylbenzene Sulphonate) increased and aquatic toxicity of SOAP decreased with an increase of water hardness, but both γ
tox, values were constant. Aquatic toxicity was decreased by an addition of mud soil as adsorbent into surfactant solution. The toxicity change can be explained by the surface tension since γ
tox value of solution with and without mud soil were equal. These results showed that the change of aquatic toxicity of a surfactant caused by water property, such as water hardness, could be explained by the change of surface tension.
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