Synthetic molluscicides are active at dilutions of 1 ppm (parts per million), with highly active ones being active at 1-2 powers of ten lower, related to the water immediately around the target organisms at contact times of 8-12 hours. At the borders of lakes, concentrations several times higher are necessary to guarantee effectivity during the contact time, because of dilution by the volume of the lake. Fish escape excessive concentrations and return after the dilution of the molluscicide. To prevent permanent contamination of the waters by parasite eggs in faeces, additional measures, such as the construction of latrines and teaching programmes are indispensable (see below). The removal of plants from irrigation systems increases water flow and the resulting losses of water and chemicals become problematic. After reduction of the transmission rate (see below) and the disappearance of the chemical, biological methods can be used for the stabilisation of the situation.
Major projects carried out in the St. Lucia / Caribian region, at El Fayum and in the Nile Delta region / Egypt and Blue Nile / Sudan provide a large database on the most relevant epidemiological questions (see the present website "Großprojekte").