It's a good question, several times I've made it to colleagues. Nobody has been able to answer me.

There are pesticides as 2,4-D that are known to enhance the phytoplankton abundance at low concentration and to inhibit it at higher. So, it is necessary to use wide ranges.

Verónica Laura Lozano I am not clear why it is so in case of almost every pesticide?

If you will perform an experiment, you should do something like 0.01, 0.1, 1, 10, 100 and 1000 mg/L. It is interesting to use some concentrations that are used in another specie to compare. For example this is important if you work with monospecific experiment to see if there is different sensitivity. So, regard works that use the same pesticide and make a table to decide.

because for regulations you need to determine the concentration that causes 50% reduction in growth rate and biomass. Because the chemicals are not very active on algae, you must test at high concentrations, often up to the limit of solubility for the chemical. You can find the test methods on the OECD site. You are correct that the results often are not environmentally relevant, but are required before a product is approved for release into the environment.

Thank you John P Wright for your answer.But I am not clear how the data generated can be employed for ecological risk assessment when there is no correlation between the environmental concentration and concentration used in the experiment.

if the concentration that causes an effect is higher than the estimated concentration in the environment, then it is assumed there will no effects in the environment and therefore the product can be approved for use. The risk ssessment process is according to regulatory guidance documents. If the effect concentration is lower then the environmental concentration, then either further data refinements are done (more complex studies), or the product is not approved.

Thank you John P Wright for this nice explanation.I will be grateful if you can kindly provide me research article related to this so that I can enrich my knowledge.

The EFSA guidance document on aquatic organisms can be found here as an example: https://www.efsa.europa.eu/en/efsajournal/pub/3290

"Guidance on tiered risk assessment for plant protection products for aquatic organisms in edge-of-field surface waters".

The OECD test method for algae and cyanobacteria can be found here: https://www.oecd-ilibrary.org/environment/test-no-201-alga-growth-inhibition-test_9789264069923-en

note that under the methods it describes the use of range finding studies and the test concentrations at either 100 mg/L or the limit of solubility.

Thank you John P Wright .

Hi Prithu,

concentrations up to 100mg/L are often used in standard test on algae because those data are relevant for the classification of the substance according to Globally Harmonised System of the United Nations (GHS UN).

The substance will be classified:

- Category Acute 1 if 72h or 96h-EC50 =< 1 mg/L

- Category Acute 2 if 72h or 96h-EC50 >1 but =< 10 mg/L

- Category Acute 3 if 72h or 96h-EC50 >10 but =< 100 mg/L

The classification will impact the labelling, transport and release of the substance.

However, note that tested concentrations above the water solubility of the substance are not relevant.

Thank you Geneviève Deviller.Can you kindly provide me any research article related to this.It will be really helpful.

Dear Prithu,

it is not related to research but to regulation of chemicals. You'll find the GHS UN for the environment in the attached.

Thank you Geneviève Deviller.