Coprostanol adsorption behavior in agricultural soil, riverbed sediment, and sand

Abstract

The occurrence of coprostanol in soil, surface, and groundwater has recently been reported in several studies. Coprostanol indicates the presence of feces from mammals. For this reason, it is important to establish adsorption behavior in different kinds of geologic media. To our knowledge, we present for the first-time adsorption behavior of coprostanol in soil, sediment, and sand and an estimation of its potential bioavailability, fate, and transport behavior. Adsorption experiments were conducted in agricultural soil, riverbed sediment, and sandy soil samples. The Henry model fitted experimental adsorption curves best for soil and sediment samples. Henry adsorption coefficients (KD) were 193.7 L kg−1 for soil, 120.8 L kg−1 for sediment, and 94.8 L kg−1 for sand, which suggests that the adsorption of coprostanol is different in soil (high absorption), sediment (medium), and sand (low). Further, results showed that the Freundlich model fits observed adsorption better as compared to the Langmuir model, indicating that the sorption process is of the multilayer type for the heterogenous surface of soil sample. The Langmuir model fitted best the adsorption in sediment, and sand. This supports the hypothesis that the process here is of a monolayer adsorption type. The mean maximum sorption capacity estimated by the Langmuir model was 345.1 µg g−1 for soil, 133.2 µg g−1 for sediment, and 80.9 µg g−1 for sand. The high adsorption capacity of coprostanol in soil is predominantly controlled by organic matter, high CEC, clay content, possible intermolecular H-bonding, and hydrophobic interaction. The organic carbon content normalized sorption coefficient (KOC) revealed that coprostanol is considered a sub-high adsorbed and slightly mobile compound that has leaching properties and can migrate to groundwater posing potential risks to the groundwater system.