Dear Ishaq, the use of assessment factor (AF) method or Species Sensitivity Distribution (SSD) method is depending on the availability of relevant and reliable toxicological data. Most of the time the AF method is use because the number of available data is scarce but in any case a minimum dataset is necessary to perform environmental risk assessment. You can have a look to the ECHA guidance Chapter R.10: Characterisation of dose [concentration]-response for environment for more details. Hoping it helps.
Thanks for your kind reply. I would like to get some more detailed information, Can you inbox me your email address or send me an email [email protected]