In water-scarce areas, diluted wastewater has been used for agricultural purposes for centuries (WWAP, 2017). In recent decades, advanced technologies have become available for treating wastewater (WWAP, 2017) so that, it is used increasingly as an agricultural irrigation water source (Calderón-Preciado et al., 2011; Chen et al., 2011; Hyland et al., 2015; Nason et al., 2019; Wu, Conkle, & Gan, 2012; Wu et al., 2014).
Wastewater treated for reuse is referred to as reclaimed water. A typical wastewater treatment process for reclamation includes:
- primary treatment to remove large objects and particles;
- secondary treatment to remove biochemical oxygen demand; and
- tertiary treatment consisting of sand filtration; and disinfection.
Truckee Meadows Wastewater Reclamation Facility (TMWRF) in Reno, Nevada, uses stringent nitrogen and phosphorus removal in addition to these treatment processes. Once the water has passed through the treatment plant, it is “reclaimed.” Some TMWRF reclaimed water is used to irrigate local golf courses and the University of Nevada, Reno Experiment Station’s Main Station Field Laboratory (MSFL). The remainder is released to the Truckee River to be used again elsewhere in the basin. Other wastewater treatment facilities in the U.S. similarly release reclaimed water to rivers and lakes or inject it into groundwater aquifers for storage and future reuse.
Various pollutants have been detected at trace concentrations in reclaimed water, including pharmaceuticals and personal care products (PPCP) (Chen et al., 2011; Dodgen et al., 2015; Goldstein, Shenker, & Chefetz, 2014; Guo & Krasner, 2009; Pan Liu, & Yin, 2016; Wu et al., 2014). Trace concentrations of pharmaceuticals are present because they are incompletely metabolized by humans and not entirely removed by wastewater treatment processes (Awfa et al., 2018; Pan et al., 2016). When reclaimed water is used for irrigation, soil and crops are exposed to PPCPs (Dodgen et al., 2015; Goldstein et al., 2014; Kinney et al., 2006; Wu et al., 2012; Wu et al., 2013; Wu et al., 2014). Thus, reclaimed water is a potential source of PPCPs in plants and soil when used for irrigation. Examples of pharmaceuticals found in trace amounts in reclaimed water include antibiotics, anticonvulsants and analgesic pain relievers. Personal care products found in reclaimed water include soaps, shampoos, cosmetics and insect repellents.
The presence of PPCPs in reclaimed wastewater and their translocation and accumulation in(to) irrigated crops may pose a phyto-toxicological risk (Herklotz et al., 2010), leading to decreased yields (Poustie et al., 2020), exposure to humans and livestock, or increased the proliferation of antibiotic resistance (Boxall et al., 2006). Human health risks associated with dietary intake of individual PPCPs present in reclaimed water-irrigated produce have been studied extensively and are estimated to be low (Carter et al., 2014; Wu et al., 2013). These studies compare acceptable daily intake (ADI) to consumptive exposure to determine if exposure may impact human health. However, data sources for such risk assessments typically are limited to samples from produce:
- cultivated in hydroponic environments (Calderón-Preciado et al., 2011; Herklotz et al., 2010; Hyland et al., 2015; Nason et al., 2019);
- grown under well-controlled greenhouse conditions (Carter et al., 2014; González-Naranjo, Boltes, & Biel-Maesto, 2013; Revitt, Balogh, & Jones, 2015); and/or
- experimentally exposed to a single PPCP at a time (Chen et al., 2011; Grossberger et al., 2014; Kinney et al., 2006).
While results from such highly controlled experimental environments are useful, they do not represent the actual conditions of landscape-scale irrigated agriculture using reclaimed water. Little landscape-scale data exist because of the difficulty in conducting large field experiments where plants and soils are simultaneously exposed to multiple PPCPs from irrigation with reclaimed water. Eleven compounds were selected to represent diverse physicochemical, environmental transport, degradation and occurrence in reclaimed water. The objectives of this research were to:
- determine the concentrations of various PPCPs in reclaimed water;
- determine PPCP concentrations in soil, soil pore water, and the shoots and leaves of alfalfa irrigated with reclaimed water for a period greater than 10 years; and
- determine the fate via mass balance of applied PPCPs that were present in soil up to 60 cm deep, and in the alfalfa shoots and leaves.
For research methods, results, summary, and references use the link below to open the complete special report.