How Pharmaceutical Residues Occur, Behave, and Affect the Soil Environment

Abstract

Many pharmaceuticals (PhMs), compounds for the treatment or prevention of diseases in humans and animals, have been identified as pollutants of emerging concern (PECs) due to their wide environmental distribution and potential adverse impact on nontarget organisms and populations. They are often found at significant levels in soils due to the continuous release of effluent and sludge from wastewater treatment plants (WWTPs), the release of which occurs much faster than the removal of PhMs. Although they are generally present at low environmental concentrations, conventional wastewater treatment cannot successfully remove PhMs from influent streams or biosolids. In addition, the soil application of animal manure can result in the pollution of soil, surface water, and groundwater with PhMs through surface runoff and leaching. In arid and semiarid regions, irrigation with reclaimed wastewater and the soil application of biosolids are usual agricultural practices, resulting in the distribution of a wide number of PhMs in agricultural soils. The ability to accurately study the fate of PhMs in soils is critical for careful risk evaluation associated with wastewater reuse or biosolid return to the environment. The behavior and fate of PhMs in soils are determined by a number of processes, including adsorption/desorption (accumulation) to soil colloids, biotic (biodegradation) and abiotic (chemical and photochemical degradation) degradation, and transfer (movement) through the soil profile. The sorption/desorption of PhMs in soils is the main determinant of the amount of organic chemicals taken up by plant roots. The magnitude of this process depends on several factors, such as crop type, the physicochemical properties of the compound, environmental properties, and soil-plant characteristics. PhMs are assumed to be readily bioavailable in soil solutions for uptake by plants, and such solutions act as carriers to transport PhMs into plants. Determining microbial responses under exposure conditions can assist in elucidating the impact of PhMs on soil microbial activity and community size. For all of the above reasons, soil remediation is critical when soil pollutants threaten the environment.

Keywords: emerging pollutants; pharmaceuticals; plant uptake; soil behavior; soil remediation.

Figure 1

Worldwide pharmaceutical market sales (2001–2023). Red points are values (billion USD per year) and blue line is regression line.

Figure 2

Main sources of VPhMs and HPhMs in the environment.

Figure 3

Environmental compartmentalization of PhMs.

Figure 4

Schematic drawing of the behavior and fate of PhMs in soil.

Figure 5

Processes involved in the fate of PhMs in soil.

Figure 6

Possible direct photolysis chemical events (PX: Pharmaceutical; (PX)^•: Excited state; P⁺, P⁻, X⁺, X⁻: Ionizated forms).

Figure 7

Diagram showing the biodegradation of PhMs in soil.

Figure 8

Scheme showing main plant uptake pathways.

Figure 9

Soil remediation techniques depending on the strategy used, the location of the process, and the type of treatment.