TOXSWA calculates exposure concentrations of plant protection products in water and in sediment and is
used in risk assessment studies of aquatic organisms. Replacement of the TOXSWA 1.2 software by the more
recent FOCUS_TOXSWA software for use with the NL standard scenarios was investigated. The impact of the
replacement on the calculated exposure concentrations of parent compounds and of metabolites was
determined. For parent substances the calculated exposure concentrations of the two TOXSWA versions were
equivalent. Due to a different way to simulate metabolites, the differences in exposure concentrations
calculated by the two versions can be large. For the simulation of metabolite substances two approaches are
given to handle situations where the formation fraction is not known.