Sorption and transport of sulfamethazine in agricultural soils amended with invasive-plant-derived biochar

Highlights

• Retention and transport of sulfamethazine in soil was studied with biochar amendment.

• Invasive-plant-derived biochar produced at high temperature showed the highest SMZ sorption.

• Highest SMZ retention at pH 3 might be due to π–π electron donor–acceptor interaction.

• Biochar treatment achieved 85% SMZ retention in soil columns indicating low transport.

Abstract

Sulfonamides (SAs) are one of the most frequently used antibiotics in the veterinary industry, showing high mobility in soils. Objectives of this research were to determine the sorption, distribution coefficients and involvement of different ionic forms of sulfamethazine (SMZ), a representative SAs, and to evaluate the transport of SMZ in biochar treated soils. Biochars were produced from an invasive plant, burcucumber (Sicyos angulatus L.), under slow pyrolysis conditions at peak temperatures of 300 °C (biochar-300) and 700 °C (biochar-700), respectively. The abilities of the biochars to retain SMZ in loamy sand and sandy loam soils were examined under different pHs and SMZ loadings. Soil column experiments were performed with and without biochars addition. Results showed that biochar-700 had a high degree of SMZ retention, with resultant decreased pH in both soils. Modeled effective sorption coefficients (K_D,eff) values indicated that the observed high SMZ retention at pH 3 could be attributed to the π-π electron donor–acceptor interaction and electrostatic cation exchange, whereas at pH 5 and 7, cation exchange was the main mechanisms responsible. There was no temporal retardation of SMZ in biochar treated soil as compared to the untreated soil. However, biochar-700 treatment achieved up to 89% and 82% increase in the SMZ retention in sandy loam and loamy sand soils, respectively. The overall results demonstrated that burcucumber biochar produced at higher temperature was effective in reducing the mobility of SMZ in the studied soils.

Introduction

Pharmaceutical residues, which are recognized as emerging contaminants, are frequently detected in treated wastewater, surface water, and groundwater worldwide (Hu et al., 2010). Sulfonamides (SAs) are one of the most frequently used antibiotic classes in the veterinary industry (Kwon et al., 2011). They are reported to be the second most frequently used group of antibiotics in France, Germany, and the United Kingdom, accounting for 11–23% of the total veterinary antibiotic usage (Thiele-Bruhn, 2003), and in the U.S., SAs are the fourth largest group of antibacterials used (AHI, 2002). Hence, SAs may be detected in most environmental samples (Hu et al., 2010) as it has been ubiquitously found in the high ng/L (sometimes reaching 10,000 ng/L) range in discharges from Wastewater Treatment Plants (WWTP), and in the low ng/L (<100 ng/L) range in rivers and groundwater (Kim et al., 2011). Among different SAs in the veterinary industry, sulfamethazine (SMZ) is the most commonly used drug, and thus is frequently detected in the environment due to its high mobility and low sorptivity (Haller et al., 2002).

Sulfonamides (SAs) are characterized by relatively unreactive soil surface interactions, and hence, show a high mobility in soils (Kim et al., 2011, Kim et al., 2010b, Thiele-Bruhn, 2003). Recent studies have reported that the sorption of SMZ depends strongly on soil pH, organic matter content, clay content, cation exchange capacity and ionic strength (Gao and Pedersen, 2005, Haham et al., 2012, Kahle and Stamm, 2007, Thiele-Bruhn et al., 2004). The high polarity, low octanol–water distribution coefficients (K_ow), low chelating ability and high water solubility of SMZ, all contribute to its low affinity to soils (Thiele-Bruhn et al., 2004). Many studies have been conducted recently to determine the fate of SMZ in different soils (Kim et al., 2010a, Kurwadkar et al., 2007, Thiele-Bruhn et al., 2004). Because of low affinity of SMZ to soil mineral particles, it is important to find an effective soil amendment for the management of SMZ-contaminated soil and water.

Due to its heavy usage, it has been found in manure, effluent from wastewater treatment plants (WWTPs) as well as leachate from animal burial sites (Ok et al., 2011). Therefore, once released into the soil environment, SMZ may be leached into groundwater and flow with water (Ok et al., 2011). Sulfamethazine has been found in groundwater samples in many places, including Korea, Germany, China, Spain, Taiwan and the U.S., at concentrations up to 0.67 μg/L (Kim et al., 2011). The presence of SMZ such as other sulfonamides in the environment may lead to the development and spread of antibiotic resistant bacteria (Heuer et al., 2011). It may also result in increased phytotoxicity to plants, however, only a few studies have been conducted with this regard (Dolliver et al., 2007).

Biochar, which is derived from the thermal decomposition of carbon-rich biomass, is being widely used in agriculture as a soil amendment as it can effectively increase soil fertility and create a carbon sink to mitigate environmental pollution of many compounds which are associated with global warming (Awad et al., 2012). Biochar has been found to be an effective adsorbent for various contaminants. A number of investigations have revealed the potential of biochar as a low-cost adsorbent for the control of pollutant migration in soils, applicable to both organic and inorganic pollutants (Ahmad et al., 2012a, Tsang et al., 2007). However, among the different species of pollutants studied previously, only a few have focused on the removal of pharmaceuticals by soil, particularly using biochar under different pH values and pollutant loadings (Yao et al., 2012).

Since biochars can be produced from many kinds of feedstock, invasive plant species could be a potentially effective kind, and the collection and utilization of such materials have additional ecosystem benefits. Burcucumber (Sicyos angulatus L.) is a wide-spread invasive species in Korea, and it has been regarded as one of the most invasive species (Kil et al., 2006). This plant has harmful impacts on not only agriculture but also the natural ecosystems. Due to its severe threat to the country's rich biodiversity, the Korea Ministry of Environment has adopted a series of regulations for its control, and also called for contributions of the general public to eliminate the plant (Ahmad et al., 2014). In this light, our study intends to make use of the burcucumber biomass as a feedstock to produce biochars. The overarching objective of this work was to understand the adsorption and transport behavior of SMZ in biochar-amended and untreated soils attempting to reduce contaminant leaching from wastewater used for soil irrigation, manure applied soils or animal burial sites. The specific objectives were to: (1) determine the sorption and distribution coefficients of SMZ in the simulated biochar-amended soil environment; (2) determine the involvement of different ionic forms of SMZ in sorption; and (3) determine the effects of the texture of biochar-amended soil on transport of SMZ.