Abstract
A study was conducted on the sorption of 17α-ethynylestradiol (EE2) on five soils formed under different redox conditions: an Arenosol (A_20) with fully aerobic conditions, two Gleysol samples (G_20 and G_40) with suboxic and anoxic conditions and two Histosols (H_20 and H_80) with mostly anoxic conditions. The soils were characterized on the basis of total organic carbon (TOC), specific surface area (SSA) and the Fourier transform infrared spectra of the humic acid and humin fractions (the soil remaining after alkali extraction) of the soil. The maximum adsorption capacity of the soils (Qmax) ranged from 10.7 to 83.6 mg/g in the order G_20 > H_20 > G_40 > A_20 > H_80, which reflected the organic matter content of the soils. The sorption isotherms were found to be nonlinear for all the soil samples, with Freundlich n values of 0.45–0.68. The strong nonlinearity found in the adsorption of the H_80 samples could be attributed to their high hard carbon content, which was confirmed by the high aromaticity of the humin fraction. The maximum sorption capacity (Qmax) of the soils did not increase indefinitely as the organic carbon content of the soils rose. There could be two reasons for this: (i) the large amount of organic matter may reduce the number of binding sites on the surface, and (ii) the decrease in SSA with increasing soil OC content may limit the ability to adsorb EE2 molecules. In anaerobic soil samples, where organic matter accumulation is pronounced, the amount of aromatic and phenolic compounds was higher than in better aerated soil profiles. Strong correlations were found between the amount of aromatic and phenolic compounds in the organic matter and the adsorption of EE2 molecules, indicating that π-π interaction and H-bonding are the dominant sorption mechanisms.
Highlights
The fate and transport of endocrine-disrupting chemicals (EDCs), such as estrogens, in the soil-water system are a growing concern, because these bioactive compounds have been widely detected in wastewater, reclaimed water and rivers (Khanal et al, 2006; Citulski and Farahbakhsh, 2010; Song et al, 2018)
The H_80 sample was formed under absolutely anoxic conditions, its organic matter content was very low (0.25%). This could be explained by the fact that this layer was formed under the root zone, excluding organic matter accumulation
This study investigated the adsorption of EE2 on soils with organic matter in different decomposition stages and with different quality based on redox status
Summary
The fate and transport of endocrine-disrupting chemicals (EDCs), such as estrogens, in the soil-water system are a growing concern, because these bioactive compounds have been widely detected in wastewater, reclaimed water and rivers (Khanal et al, 2006; Citulski and Farahbakhsh, 2010; Song et al, 2018). In a study on Spanish groundwater samples (Jurado et al, 2019) for the emerging organic contaminants (EOCs), including several EDCs molecules, showed that the most of these substances are usually detected at low ng/L concentration range in the groundwater bodies. They are reported at concentrations >100 ng/L, it is required to set up threshold quality values, because groundwater is a valuable water resource worldwide. The current, three-step cleaning technologies are not able to fully eliminate these hormones from the wastewater (Kim et al, 2015)
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