Fate, transport and ecological risk of antibiotics from pig farms along the bang pakong River, Thailand

https://doi.org/10.1016/j.agee.2020.107123Get rights and content

Highlights

  • Removal processes of veterinary antibiotics during transport into the river were investigated and modeled.

  • Random forest (RF) model showed the best fit to the dynamics of actual antibiotic concentrations.

  • Physicochemical properties of antibiotics determined their fate and transport.

  • RF can describe from farm to river the ecological risks of antibiotics.

Abstract

This study was conducted to investigate the impact of different seasons (dry and rainy seasons) in 2018 on the fate, transport, and ecological risk of antibiotics drained from pig farms along the Bang Pakong River, Thailand. Twenty-one residual antibiotics were detected in pig farm effluents, drainages, and the river in both seasons. Amoxicillin, tetracycline, chlortetracycline, and tiamulin were found dominantly in the pig farm effluents, showing high detection frequencies of 83–100 % in the total number of the effluent samples. Maximum concentrations of these four dominant antibiotics in the drainage and the river were 0.12–5.20 μg L−1 in the dry season and 0.12–16.1 μg L−1 in the rainy season. Tetracycline (15.1 μg L−1) and chlortetracycline (16.1 μg L−1) were found at the highest concentrations in the rainy season. The multiple linear regression and random forest analyses between residual antibiotics in the farm effluents and the river in both seasons were performed to model dilution and removal processes of the antibiotics. The antibiotic removal processes were determined by their partition coefficients, solubility, biodegradability, and volatility. Compared to multiple linear regression, random forest models better identified the removal processes of pig farm antibiotics drained into the river. The risk quotient (RQ) of tiamulin determined based on its actual concentration in the river (0.0016 and 0.0017 in dry and rainy seasons) and its modeled concentration in river as predicted by random forest model (0.0029 and 0.001 in dry and rainy seasons) presented its potential ecological risk to fish, daphnia and green algae.

Introduction

Antimicrobial drugs are widely used in pig farm production to keep animal health and to increase productivity (Economou and Gousia, 2015). Common antibiotic uses in the pig farm were in classes of β-lactam, tetracyclines, sulfonamides, lincosamides, macrolides, and quinolones (Arnold et al., 2004; Trauffler et al., 2014; Lekagul et al., 2019b). Those classes are given to pigs by injection in addition to food or water. But, the consumption pattern of those antibiotics are varied across regions and countries worldwide (Lekagul et al., 2019b). When the antibiotic adsorption is poor in the animal gut, approximately 30 %–90 % of residual antibiotics are estimated to excrete to the environment via manure and wastewater (Kuppusamy et al., 2018; Manyi-Loh et al., 2018). According to the reports from Wei et al. (2011); Ben et al. (2013); Zhi et al. (2018), the highest residual concentration of pig fam antibiotic in wastewater was tetracyclines (3.7–1000 μ L−1) following by sulfonamides (0.01–400 μ L−1), quinolones (0.011–32 μ L−1), β-lactam (0.24–30 μ L−1), aminoglycosides (1.4–14.6 μ L−1), macrolides (0.02–1.2 μ L−1) and tiamulin (1.1 μ L−1). Those residual antibiotics could then enter stream or river via runoff or direct effluent discharge from the pig farm (Sarmah et al., 2006). However, residual antibiotic concentration over 450 μg L−1 in surface water may be not deemed harmful to human, but bioassay revealed that some antibiotic at a concentration below 10 μg L−1 in surface water was found to affect microbes (Danner et al., 2019). Zhang et al. (2012) and Jiang et al. (2014) reported that residual concentration of tetracyclines, sulfonamides, and quinolones was detected at 1.1–360 μg L−1 in a river, which exhibited relatively high ecological risks to aquatic organisms. Additionally, the residual antibiotic in surface water, even low concentration, could also exert selective pressure to the bacterial population to acquire antibiotic-resistant (Kümmerer, 2009a, 2009b; Gullberg et al., 2011), which is more harmful to human and animal since river water is widely used as a source of drinking water, irrigation and recreational purposes (Xi et al., 2009; Liu et al., 2018).

Pig farms in Thailand were developed in the 1960s when the first commercial pig feeds were imported from the United Kingdom and the United States (Thanapongtharm et al., 2016). Once the small farms were developed to medium and large farms, the introduction of modern technologies and farm management strategies were subsequently proposed. Antimicrobial drug use for treating pig infections and growth promoter were also considered at that period. However, pig farms in Thailand were remarkably developed for almost 40 years, the management of the wastewater treatment is still limited. Most pig farms in Thailand widely use lagoons in series as a common wastewater treatment process, which given the maximum COD removal of 59 %, and the remaining concentration of NH3+ was found to be higher than 70 mg L−1 (Zhang et al., 2013). Also by using longer hydraulic retention times (HRT) of 6–8 days, lagoon treatment could only degrade 40 %–50 % of lincomycin and tetracycline, whereas remaining concentrations were stable thereafter (Kuchta and Cessna, 2009; Kühne et al., 2000). Previous research has revealed a significant contribution of pollution load from pig farming in the central region of Thailand specifically from the discharge of raw pig wastes in small farms and overflow of effluents from large-farm liquid treatment systems (Schaffner et al., 2010). However, a study on antibiotic contamination especially from pig farming and its consequence in natural ecosystems is still very limited in Thailand.

When veterinary antibiotics reach river water from the pig farm and other sources, their removal processes during such transportation along the river are dependent on dilution and their physicochemical properties (Hoa et al., 2011; Li et al., 2016; Selvam et al., 2017). The disappearance rate of antibiotics via dilution was significantly associated with seasonal variation such as dry and rainy seasons due to different dilution factors (Lei et al., 2019) and transport of antibiotics along the river (Diwan et al., 2018). Nevertheless, all-important physicochemical properties that significantly affect the removal processes of antibiotics along the flowing stream have not been well understood. A report by Yan et al. (2013) could only clarify that molecular weight and organic-water partition coefficient of antibiotics affect the adsorption affinity with suspended particles in the river, whereas Chen et al. (2018a, 2018b) showed that the removal processes of antibiotics in river mainly determined by only their partition coefficients and degradation haft life. But, other possible factors such as solubility in water (Y. Chen et al., 2018a, 2018b) and volatility (Daghrir and Drogui, 2013) did not mention together with the above studies. Likewise, the effective statistical methods i.e., multiple linear regression (MLR) and random forest (RF) models (Grégoire, 2015; Biau and Scornet, 2016), which can make more clear evidence on the relationship between one response variable and two or more explanatory variables are rarely used in the study of fate and transport of antibiotics. Meanwhile, ecological risk of antibiotics to aquatic organisms in the river, classified by Risk Quotient (RQ) value i.e., low risk (0.01 < RQ < 0.1), medium risk (0.1 < RQ < 1) and high risk (RQ > 1), were commonly determined based on actual antibiotics levels in the rivers and the predicted no-effect concentration (Hoa et al., 2011; Zhang et al., 2015; Zhou et al., 2016), but there was no approach towards a quantitative model and the prediction of ecological risk of antibiotics based on their actual concentration in pig farm effluent.

Since it is currently not possible to quantitatively describe removal processes and ecological risk of antibiotics via modeling processes, we aimed to study the impact of seasonal variation on the fate, transport and ecological risk of pig farm antibiotics drained along the Bang Pakong River, Thailand. MLR and RF models were applied to residual antibiotics from the pig farm effluents and river in both seasons to model the dilution and their physicochemical properties, which possibly affect removal processes, fate and transport of antibiotics in the river. Subsequently, the established models were further applied to describe the ecological risks of antibiotics from pig farm effluent to aquatic organisms including fish, daphnia, and green algae.

Section snippets

Study area and sample collection

The investigation was conducted at Chachoengsao Province, which is in eastern Thailand and known as one of the intensive pig production areas. A source of water consumed in most pig farms is commonly the Bang Pakong River. Total number of pig farms in the area was approximately 500 and they are classified into three categories: small farm (<500 heads), medium farm (500–1000 heads), and large farm (>10,000 heads). Commonly, small and medium farms are located close to Bang Pakong River whereas

Water quality of the effluent, the drainages and the river

Regarding effluents from pig farms, pH was in neutral (7.2–8.0) while EC ranged from 1184 μS cm−1 to 4100 μS cm−1 (Table A.2). COD was 102–691 mg L−1 at the small farms, 187–730 mg L−1 at the medium farms, and 23–326 mg L−1 at the large farms while NH3-N was 71–186 mg L−1, 2–79 mg L−1, and 5–109 mg L−1, respectively. Higher concentrations of COD were mostly detected at Farm F1, F4, and F6 where the number of lagoons ranges only from two to three per farm. Furthermore, the highest COD was found

Conclusion

We investigated the fate, transport, and ecological risk of antibiotics along the Bang Pakong River and found that residual antibiotics in the river are discharged from pig farms especially in the rainy season. In this target area, TCs (TE and CTC) and TIA were dominant antibiotics in the pig farm effluent and were determined as major antibiotics in the drainages and the river. Those antibiotics presented a low ecological risk to aquatic organisms in the drainages. Also, the removal processes

Declaration of Competing Interest

The authors also declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors are grateful to Kurita Water and Environment Foundation (KWEF), Japan for funding this research under the 20th anniversary KWEF commemorative research project. The study was also carried out under the scheme of collaborative research (CR), the Ph.D. Sandwich Program of AUN/SEED-Net, which is supported by the Japan International Cooperation Agency (JICA) as well as the Global Partnership program supported by Thailand Science Research and Innovation (TSRI).

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