usually in my plant we are doing em monitoring by settle plate method by using scda plates, is it necessary to add polysorbate and glecerol to that exposed scda plates?
Yes it is necessary because polysorbate 80 neutralize the phenolic disinfectants,hexachlorophene,formalin and with lecithin alcohol.
Glycerol help in retention of moisture and serves as carbon source.
In my opinion, for active and passive air plates its not mandatory. For contact plates yes its mandatory.