Evaluation of the effect of the intrinsic chemical properties of pharmaceutically active compounds (PhACs) on sorption behaviour in soils and goethite

Gergely Jakab,Tibor Filep,Zoltán Szalai,Lili Szabó,Attila Csaba Kondor

doi:10.1016/j.ecoenv.2021.112120

Abstract

The role of the chemical properties of Pharmaceutically Active Compounds (PhACs) in their sorption behaviour and consequently in their fate and mobility is of major environmental interest, but a comprehensive evaluation is still lacking. The sorption of nine PhAC molecules with distinct physico-chemical properties on soils and goethite was described using linear, Freundlich and Langmuir models and the relationship between the chemical structures of the compounds and the parameters of the adsorption was evaluated using redundancy analysis (RDA). The latter showed that the sorption of the pharmaceuticals was determined by the intrinsic chemical characteristics of the molecules, as shown by the 35% value of constrained variability. For the hydrophobic estrogens, E1, E2 and EE2, the logD value and the number of hydrogen bond sites were found to be the main controlling factors for adsorption, indicating that hydrophobic interaction and hydrogen bonding are the dominant sorption mechanisms. The π energy of the molecules also proved a very important parameter, governing the retention of PhACs in soils, especially in the case of carbamazepine, oxazepam and lamotrigine. The main controlling factor for ionic compounds, such as diclofenac sodium, tramadol or lidocaine, is the fraction of PhACs present as charged species, revealing the importance of Coulomb forces. The results of this study will allow semi-quantitative predictions to be made on how the molecular structure governs the sorption of PhACs and which sorption mechanism could be involved.

Highlights

Nowadays, due to the growing volume of medicines administered to both humans and animals, there is an ever greater need for information about Pharmaceutically Active Compounds (PhACs)
A clear trend was noted for the sorption of PhACs on soils, with greater values for hydrophobic compounds, while the adsorption of diclofenac sodium (DIC) was very limited
The Langmuir model appeared to be more suitable for describing the sorption of PhAC molecules, in contrast to the findings of many authors, e.g. Wu and Bi (2019) and Al-Khazrajy and Boxall (2016), who reported a better fit for the Freundlich adsorption model

Summary

Introduction

Due to the growing volume of medicines administered to both humans and animals, there is an ever greater need for information about Pharmaceutically Active Compounds (PhACs). This class of com pounds includes substances that are widely used in agriculture, medi cine and biotechnology, such as antibiotics, drugs and hormones. It is estimated that around 60–80% of PhACs, which amounts to some 100,000 tons or more per year, are not absorbed by animals or humans but are released into the environment (Gobel et al, 2005) These com pounds may accumulate in soil and water (Caracciolo et al, 2015; He et al, 2018; Kolpin et al, 2002) and many of them induce serious problems, making them a potential risk to human health and aquatic ecosystems even in low concentrations (Gomes et al, 2017; Klatte et al, 2017). Wastewater treatment plants (WWTPs) are considered to be the main contributor to environmental pollution with PhACs, because these WWTPs are not designed to eliminate these molecules (Valdes et al, 2014)

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