Abstract
Pharmaceuticals and personal care products (PPCPs) have drawn increasing concern of environmental health as they are continuously released into the environment. This study examined the effects of birnessite (δ-MnO2) on the transport and retention of five PPCPs in porous media under steady saturated flow conditions. Considering that natural birnessite occurs as discrete particles and small nodules, birnessite-coated sand was used to mimic the natural regime of birnessite in the environment. Batch isotherm experiments were conducted using uncoated and birnessite-coated sand; results showed that the difference in the affinity of the five PPCPs was correlated to their polarity characteristics. Column experiments were conducted by mixing 0, 10, and 20% birnessite-coated sands with the uncoated sands. These three percentages are equivalent to three contents of manganese (Mn) in the experimental columns (0, 55, and 109 μg Mn g−1 sand). Results suggested that polar compounds (such as bisphenol-A, tetracycline, and ciprofloxacin) had a higher affinity to birnessite-coated sands than the weak polar compounds (such as ibuprofen and carbamazepine) because the polarity was favorable to electrostatic attraction and oxidative reaction. Overall, birnessite decreased the mobility of polar PPCPs but exerted no significant effect on the mobility of weak polar PPCPs under continuous flow conditions. The polarity-based correlation extended traditional electrostatic theory while well interpreting the complicated effects of birnessite on the adsorption and transport of PPCPs, especially neutral or non-dissociated compounds like carbamazepine.
Highlights
Global economic and population growth drives high production and usage volumes of pharmaceuticals and personal care products (PPCPs)
The results showed that strong polar Pharmaceuticals and personal care products (PPCPs) have a relatively higher affinity to the birnessite-coated sand than to the uncoated sand
These results are consistent with those in the studies by Figueroa and MacKay (2005), Leal et al (2013), and Xing et al (2016), who demonstrated that specific adsorption mechanisms of tetracycline and ciprofloxacin include electrostatic attraction and surface complexation
Summary
Global economic and population growth drives high production and usage volumes of pharmaceuticals and personal care products (PPCPs). Fick et al (2009) reported that ciprofloxacin concentrations were as high as 6.5 mg L−1 in the effluent of a wastewater treatment plant. Some PPCPs can pass through soil layers and transport into groundwater (Qin et al, 2015; Lee et al, 2019). Xu et al (2009) found that triclosan, ibuprofen, and carbamazepine have the potential to move into deep soil profile and groundwater. Lyu et al (2019) used the Hydrus-1D model to simulate the leaching potential of PPCPs after long-term irrigation with reclaimed water and reported that many PPCPs occurred in the shallow groundwater after a decade of the irrigation. Turner et al (2019) found that PPCPs with high mobility such as carbamazepine, ibuprofen, caffeine, and DEET could be detected in groundwater in concentrations up to 2.35 μg L−1. Understanding transport behaviors of different PPCPs in soils is important for the accurate assessment of groundwater risk
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