Insights into the distribution, partitioning and influencing factors of antibiotics concentration and ecological risk in typical bays of the East China Sea

Highlights

• Introduced P-PC and K_d to predict the migration trend of antibiotics.

• Water quality has greater impact on antibiotic partitioning than sediment properties.

• Antibiotics in sediments were more chronically toxic to Daphnia than those in water.

• Antibiotic properties drove their risk partitioning between water and sediments.

Abstract

In order to obtain in-depth insight of the behavioral fate and ecological risks of antibiotics in coastal environment, this study investigated the distribution, partitioning and primary influencing factors of antibiotics in water and sediment in the East China Sea. After quantification of 77 target antibiotics in 6 categories, ten antibiotics were detected simultaneously with a detection frequency >50.0% in water and sediment; the concentrations of these ten antibiotics were 0.1–1508.0 ng L⁻¹ and 0.01–9.4 ng g⁻¹ in water and dry sediment, respectively. Sulfadiazine and Azithromycin (Pseudo partitioning coefficient were 28–3814 L kg⁻¹ and 21–2405 L kg⁻¹, respectively.) had the largest partitioning coefficient between sediment and water. In addition, pseudo partitioning coefficient of Sulfadiazine and Clindamycin were higher than the values of corresponding equilibrium partitioning constant (K_d), which would likely cause them to re-release from sediment to water. Compared to the physiochemical properties of the sediment, water quality has a greater impact on antibiotic partitioning. We found that the partitioning of antibiotics was significantly positively correlated with salinity, suspended solids, pH, NH₄⁺-N and Zn; and negatively correlated with temperature, dissolved oxygen, PO₄³⁻, chemical oxygen demand, NO₃⁻-N, oil, Cu and Cd. The ecological risks of antibiotics in water and sediment were also evaluated for revealing their relationship with the concentration partitioning of antibiotics. Results showed that the target antibiotics mainly pose ecological risks to Daphnia with low and median chronic toxicity risk rather than fish and green algae. The antibiotics in sediment were more chronically toxic to Daphnia than that in water. The risk quotient ratio of sediment and water (RQ_s/RQ_w) ranged from 0 to 1154.0, which were exactly opposite of the values of organic carbon normalized partition coefficient (K_oc), suggesting that the physical properties of antibiotics drove the ecological risk allocation of antibiotics in sediment and water.

Introduction

With the increasing production and consumption, antibiotics have attracted much attention as an emerging pollutant in the environment. Antibiotics were widely detected in a variety of media, such as soils (Yi et al., 2019), rivers (Li et al., 2018a), seas (Li et al., 2018b) and so on. While existing literature primarily focused on the analysis of water samples, only a few studies have been conducted on sediment samples, and research on the partitioning behaviors of antibiotics between the surface water and sediment is therefore remained limited (Zhao et al., 2016). Nevertheless, it has been proven that the sediment was a vital sink and potential source for quinolones (QNs) and tetracyclines (TCs) basing on mass balance in Taihu Lake, China (Zhou et al., 2016). In addition, the adsorption of antibiotics by sediment was proven to be an important attenuation way for TCs and macrolides (MLs) (Sassman and Lee, 2005; Li and Zhang, 2010; Luo et al., 2011). Although the transfer of antibiotics from water into sediment has a short-term buffering effect on the pollution and ecological risks of the water, it can still aggravate antibiotic pollution and ecological risks in the long run. This is because after the antibiotic entered the sediment from water, the concentration of the antibiotic in the water decreased, but its degradation process in the sediment was hindered, thereby increasing its persistence (Zhou and Broodbank, 2014; Chen and Zhou, 2014). However, the antibiotics in the sediment will desorb into the water when the environment changes (Kim and Carlson, 2007; Kümmerer K., 2009). Therefore, a deeper understanding of the partitioning behaviors of antibiotics between the surface water and sediment will provide an insight into the long-term occurrence of the antibiotics (Zhou and Broodbank, 2014), as well as help us better assess their potential risks to the environment and human beings.

Determining the partitioning between sediment and water is a crucial process for assessing the environmental fate and risks of antibiotics. Due to the dynamic process of sediment-water interaction and the varying nature of sediment, the partitioning of antibiotics between surface sediment and water is variable (Zhou and Broodbank, 2014). Hence, the pseudo partitioning coefficient (P-PC) and equilibrium partitioning constant (K_d) were introduced, reflecting the partitioning coefficient of antibiotics in sediment-water in the natural dynamic and equilibrium environment, respectively. The P-PC values are highly valuable to assess partitioning between water and marine sediment under natural conditions (Siedlewicz et al., 2018). In the intertidal zone of the Bohai Bay, the P-PC values of TCs and QNs were 523–787 L kg⁻¹ and 293–951 L kg⁻¹, respectively, which were larger than that of SAs (10–97 L kg⁻¹) (Cheng et al., 2016). It was also indicated that QNs were prone to accumulation in the sediment with P-PC ranged from 4493 to 47093 L kg⁻¹, and the pseudo-partitioning coefficient of TCs ranged from 277 to 1880 L kg⁻¹ followed in a shallower large lake called Baiyangdian (Cheng et al., 2014). Furthermore, trimethoprim (TMP) and sulfamethoxazole (SMX) belonging to SAs were reported to have lower P–PCs than values reported for QNs and TCs in the South China Sea (Chen et al., 2015).

Different types of antibiotics have various behavioral characteristics (hydrolysis, photolysis, biodegradation, adsorption, etc.) in water and sediment, which is depending on their physicochemical properties and the external conditions. Research has pointed out that SAs exhibited high solubility and chemical stability in water and MLs tended to be hydrolyzed or adsorbed to soil and sediment (Huang et al., 2001). Roxithromycin (RTM), belonging to MLs, was reported having a large distribution coefficient between sediment and water due to its strong hydrophobicity and large molecular size (Chen and Zhou, 2014). It is reported that QNs were susceptible to photodegrade (Jiao et al., 2008), but they were easily adsorbed in sediment, which could be attributed to more ionic functional groups in their molecules (Zhang et al., 2007; Luo et al., 2011). Moreover, it has been described that the carboxyl in molecules significantly contributed to the adsorption capacity of QNs (Zhang and Dong, 2007). TCs had a high affinity for soil organic matter through cation bridging and cation exchange (Figueroa et al., 2004). Additionally, water and sediment properties played an essential role in distributing antibiotics (Zhou et al., 2011). It was known that properties like particle-size fractions, cation exchange capability (CEC) and metal ions content could substantially affect the partitioning behaviors of norfloxacin (NFX) and erythromycin (ETM) between the surface water and sediment (Zhao et al., 2016). Total organic carbon (TOC) of the sediment has been pointed to play a key role in the sorption processes of organic pollutants (Hou et al., 2010; Cheng et al., 2014). In reality, the partitioning behaviors of antibiotics are rather complex affected by more environmental factors. However, in contrast to antibiotics in surface water, the concentrations of antibiotics in sediment were less influenced by short-term environmental changes between seasons (Zhao et al., 2016).

To the best of our knowledge, little information was found on the partitioning of antibiotics and their ecological risks in seawater and sediment. This study explored the fate and risks of antibiotics in the East China Sea (ECS). ECS is one of China's four seas, and the coastal area of ECS is one of the most developed regions in China. With the rapid economic development and industrialization, this region has become one of the most affected areas by the significantly increased consumption of antibiotics (Zhang et al., 2015). Our previous study proved that 43 and 25 antibiotics were detected with total concentrations of 30.8–2106.1 ng L⁻¹ and 2.2–99.9 ng g⁻¹ in coastal water and sediment of ECS, respectively (Li et al., 2020). However, compared with the other three large sea areas in China, the antibiotic research on the ECS is still far behind (Chen et al., 2015; Li et al., 2018b).

In this study, 13 sites were selected for collecting seawater and sediment samples in three bays of ECS, and 77 antibiotics were analyzed. The primary objectives of this study were to (1) investigate the distribution, partitioning, influencing factors of antibiotics, as well as forecasting the partitioning trend of the target antibiotics in coastal water and sediment; (2) evaluate the ecological risks of antibiotics, and examine the distribution and partitioning of ecological risks of antibiotics in water and sediment; (3) explore the relationship between antibiotic concentration partitioning and ecological risk partitioning, and identify the key factors affecting the ecological risk allocation of sediment-water antibiotics.