Title: Comparison of equilibrium and non-equilibrium distribution coefficients for the human drug carbamazepine Authors
|Watson, Jack -|
|Nelson, Shad -|
Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 20, 2013
Publication Date: N/A
Interpretive Summary: The reuse of sewage effluent for irrigation is an effective way to increase water supplies in the desert southwest. Contaminants such as human drugs, found in treated effluent, have been identified as a potential problem for use of this water for irrigation. Batch equilibrium soil sorption (KD), defined as the mass of compound sorbed to soil at a specific solution phase concentration, is commonly used to determine the mobility of organic compounds in soil. However, water containing the human drug carbamazepine is usually flowing through soil. A comparison between KD from a flow through system and a batch equilibrium system were compared. The KD from the flowing system was found to be greater than from batch adsorption. The flowing system also resulted in increased flow rates and repeated solute pulses having progressively lower KD's. This indicates that the risk of carbamazepine leaching increases with increased water velocity and multiple applications.
Technical Abstract: The distribution coefficient (KD) for the human drug carbamazepine was measured using a non-equilibrium technique. Repacked soil columns were prepared using an Airport silt loam (Typic Natrustalf) with an average organic matter content of 2.45%. Carbamazepine solutions were then leached through the columns at 0.5 1.0 and 1.5 mL min-1 representing average linear flux rates of 1.8, 3.5 and 5.3 cm hr-1 respectively. Each flow rate was replicated three times and three carbamazepine pulses were applied to each column resulting in a total of 9 columns with 27 total carbamazepine pulses. Breakthrough curves were used to determine KD using the parameter fitting software CXTFIT. Results indicate that as flow rate decreased from 1.5 to 0.5 mL min-1, KD increased an average of 21%. Additionally, KD determined by column leaching (14.7 – 22.7 L kg-1) was greater than KD determined by batch equilibrium (12.6 L kg-1). Based on these KD’s carbamazepine would be characterized as non-mobile in the soil investigated. However, repeated carbamazepine applications resulted in an average 22% decrease in KD between the first and third applications. Decreasing KD is attributed to differences in sorption site kinetics and carbamazepine residence time within the column. This would indicate that the repeated use of reclaimed waste water at high application rates for long-term irrigation has the potential to lead to greater transport of carbamazepine than KD would predict.