Multimedia environmental fate and transport model of dichlorodiphenyltrichloethane at Sayong River watershed based on fugacity approach

Abstract

Dichlorodiphenyltrichloroethane (DDT) is one of the most concerning compounds in the group of persistent organic pollutants (POPs) due to its persistence and harmfulness on environment. This thesis details the development of a multimedia environmental fate and transport model to assess the distribution and transfer processes of DDT in air, soil, water and sediment in the Sayong River watershed. Geographical Informational System (GIS) was employed to divide the watershed into up, mid and down-streams. The levels of DDT in the air, soil, water and sediment in the Sayong River watershed were monitored the period of between November 2014 and May 2015. Samples were collected and extracted through Solid Phase Extraction (SPE) and ultrasonication. Extracted samples were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). For the development of model, the compartments and tranfer processes were setup along with the steady state and chemical equilibrium assumptions. Fugacity concept was used to formulate the distribution mechanism processes. Input parameters, consisting of chemical emission data, environmental properties and physical-chemical properties, were selected as secondary data. Microsoft Excel-Visual Basic Application (VBA) was used to encode the calculation. The total concentrations of DDT were observed to be in the range of 5.25-53.53 µg/g for soil, 0.22-37.88 µg/g for sediment and 0-0.38 µg/g for air. Meanwhile, there was no DDT found in the water samples. In addition, the model predicted reasonably accurate concentrations within an order of magnitude (0.01-0.25) in log unit. The advection outflow in air was determined to be the most important process of DDT in this model with the rate range of 0.12-0.26 mol/h. From the sensitivity analysis, the vapour pressure (Ps) and organic carbon - water partition coefficient (KOC) were concluded to be the most influential parameters where the Sensitivity Coefficient (SC) being higher than 0.5. This model is important as it can provide an efficient and cost effective measure to assess the fate and movement of DDT in the Sayong River watershed.