The amounts of wastewaters produced around the world are vast. For example, in Finland approximately 100 000 cubic meters of urban wastewater effluents per inhabitant are discharged each year. A recent study in Finland confirmed that Finnish wastewater treatment plants are efficient in removing components that might cause acute effects in whole organisms. However, indications of estrogenic and genotoxic potential were detected in effluents discharged from these treatment plants. Thus, treated wastewater effluents still may cause harmful effects on the environment.