Modelling pharmaceutical concentration in the soil profile using hydrus 1d

Authors: Gillis, D, S Prasher, G Price
Description: Pharmaceuticals are an emerging class of environmental contaminants that are receiving increased attention, although their environmental fate is for the most part unknown, especially in the vadose zone. HYDRUS-1D, a model of water and solute transport in the vadose zone, was used to describe the leaching of diazepam and iopromide. Data from a soil column study was extracted from the literature that reported concentration of these two compounds at increments of 5 cm depth, along with artificial rainfall rate and total leachate collected. Values for the organic carbon-water distribution coefficient were obtained from external sources. The inverse solution was used to obtain optimized parameter estimates for ?, DL, and DW. Predicted diazepam concentration was most sensitive to DL, a non-measurable parameter, while the least sensitive parameter was DW. There was good agreement between observed and predicted diazepam concentration and a low mass balance error. The pattern of iopromide distribution was not described well by HYDRUS-1D, and there was a large error in the final mass of solute (157% recovery). It was assumed that the poor fit was from the difference between the pKa of iopromide (9.9) and the pH of the soil (5.8), since iopromide contains many ionisable groups. This may have led to reduced sorption and higher water solubility. Decreasing the KD led to a pattern of iopromide transport that more closely resembled the observed values, but increased the solute mass balance error. The reason for the mass error for iopromide is not known.
Keywords: hydrus 1d, solute transport, soil hydrologic modelling, pharmaceuticals
Technical field: technical_fields_app7
Session name: Soil and water
Date: 2012
Identifier: CSBE12051
Coverage: Canada

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