DEVELOPMENT OF FATE AND TRANSPORT MODELS FOR MICROPOLLUTANTS IN NATURAL SURFACE WATERS

Abstract

This study developed a multimedia model coupled with a hydrological model (i.e., Soil and Water Assessment Tool (SWAT) for micropollutants, specifically polycyclic aromatic hydrocarbons (PAHs) and pesticides (malathion). PAHs are potentially carcinogenic substances that are persistent in the environment while pesticide contamination in soil and water also has negative effects on the diversity of the flora and fauna of local areas, hence; the concern for these micropollutants has been increasing over the years. Monitoring and modeling efforts of these micropollutants have been performed for several years to determine their possible sources and understand their movement in different media. Suitable methods have been investigated in order to accurately monitor them in the environment. However, it is expensive and laborious to conduct intensive monitoring activities. Taehwa River (TR) basin, South Korea and Pagsanjan-Lumban (PL) watershed, Philippines were the study areas for PAHs and pesticides, respectively. The hydrologic module of the SWAT was calibrated, and further used to simulate the fate and transport of micropollutants in the soil and waterbody. The model demonstrated that the temporal or seasonal variation of PAHs in soil and waterbody can be well reproduced. Meanwhile, the spatial distribution of PAHs showed that urban areas in TR watershed have the highest PAH loadings compared to rural areas. Temporal patterns of malathion from the SWAT and micropollutant models were also compared. Sensitivity analyses of the PAH soil and PAH water parameters were also able to determine the critical processes in TR watershed: degradation, deposition, volatilization, and washoff mechanism. For malathion, the sensitivity analyses revealed that application efficiency and settling velocity were the most sensitive parameters for the SWAT and micropollutant models, respectively. Sediment-related parameters, especially the degradation, were also significant to both models. We expect that this model will be able to aid the stakeholders in: regulating PAH concentrations emitted by various sources; managing pesticide usage in agricultural watersheds; and applying the model to other Persistent Organic Pollutants (POPs). Results from this study will also be able to aid the government and private environmental sectors to have an in-depth understanding in managing the contamination of micropollutants.