The performance of buffer zones for removing pesticides from runoff water varies greatly according to landscape settings, hydraulic regime, and system design. Evaluating the performance of buffers for a range of pesticides and environmental conditions can be very expensive. Recent studies suggested that the fluorescent dyes uranine and sulforhodamine B could be used as cost-effective surrogates of herbicides to evaluate buffer performance. However, while transformation mechanisms in buffers have been extensively documented, sorption processes of both dyes have rarely been investigated. In this study, we measured the adsorption, desorption, and kinetic sorption coefficients of uranine and sulforhodamine B for a diverse range of buffer zone materials (soils, litters, plants) and compared the adsorption coefficients (Kd) to those of selected herbicides. We also compared the global sorption capacity of 6 ditches, characterized by varying proportions of the aforementioned materials, between both dyes and a set of four herbicides using the sorption-induced pesticide retention indicator (SPRI). We found that both the individual Kd of uranine for the diverse buffer materials and the global sorption capacity of the ditches are equivalent to those of the herbicides diuron, isoproturon, and metolachlor. The Kd of sulforhodamine B on plants and soils are equivalent to those of glyphosate, and the global sorption capacities of the ditches are equivalent for both molecules. Hence, we demonstrate for the first time that uranine can be used as a proxy of moderately hydrophobic herbicides to evaluate the performance of buffer systems, whereas sulforhodamine B can serve as a proxy for more strongly sorbing herbicides.

Rapid urbanization of the Philippines, especially of Metro Manila area, has caused serious water pollution. Main causes of this are categorized into industrial wastewater and domestic wastewater, discharged without sufficient treatment. As for industrial wastewater, it is essential to put strict regulations on effluent standards, and for municipalities to keep a regular check to ensure these regulations are observed. Philippine government has been working on the improvement of the legislation and control of industrial wastewater until now. However, from now on, it is vital to put more efforts in getting domestic wastewater treated properly. It is indeed crucial to put the existing sewerage construction plans into practice, but generally, sewerage systems require; 1) long construction period, 2) effective funding, 3) high-density construction, and 4) human resources to run the systems effectively. Meanwhile, on-site waste water treatment tanks, or what we called purifiers, can play an important role in controlling the pollution of water environment, and they will serve to complement the sewerage system even after the completion of construction. Small-scale on-site wastewater treatment tanks, or small-scale purifiers, developed and used in Japan especially in developing countries, not only in the scope of environmental conservation but also from the viewpoint of utilizing the economic resources in the private sector