Little Pro on 2019-11-13
In chronic or long-term ecotoxicological studies, various toxicity test endpoints can be obtained. In this article, we will give a brief introduction to the most commonly seen endpoints: EC10, NOEC, LOEC, MATC and explain how to use them in environmental risk assessment.
ECx is the effect concentration at which x% effect (mortality, inhibition of growth, reproduction, etc) is observed compared to the control group. It is usually obtained using an appropriate statistical method such as regression analysis. When x is 10, ECx becomes EC10.
A sufficient number of concentration (dose) groups are needed to calculate ECx since the precision of the estimated ECx depends more on the number and spacing of concentrations rather than on the sample size per concentration or dose group.
NOEC (No Observed Effect Concentration) is the highest tested concentration for which there are no statistical significant difference of effect (p<0.05) when compared to the control group in long-term ecotoxicity studies.
Since NOEC is highly dependent on dose group setting in ecotoxicity studies, some authorites prefer the use of ECx as chronic endpoints. The advantage of regression method for the estimation of ECx is that information from the whole concentration-effect relationship is taken into account and that confidence intervals can be calculated.
LOEC (Lowest Observed Effect Concentration) is the lowest concentration where an effect has been observed in chronic ecotoxicity studies. LOEC is not NOEC.
However, LOEC can be used to derive NOEC if the effect percentage of the LOEC is known.
MATC (maximal acceptable toxicant concentration) is a calculated value and it is the geometric mean of the NOEC and the LOEC. If in the test report only the MATC is presented, the MATC can be divided by √2 to derive a NOEC.
LOEC and MATC are primarily used to calculate NOEC as NOEC is more commonly used in environmental risk assessment. Both NOEC and EC10 can be used for aquatic environmental hazard classification (see picture below) or calculating chronic Predicted No Effect Concentration (PNEC).
When classifying a mixture containing multiple components, we will need to start using M-factor. M-factor is also important for determining whether a mixture belongs to marine pollutant or not.
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