Occurrence and risks of antibiotics in the Laizhou Bay, China: Impacts of river discharge Ruijie Zhang a,b , Gan Zhang a,b,n , Qian Zheng a , Jianhui Tang b , Yingjun Chen b , Weihai Xu c , Yongde Zou d , Xiaoxiang Chen d a State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China b Key Laboratory of Coastal Environmental Process, CAS, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China c South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China d Nanhai Entry-Exit Inspection and Quarantine, Foshan 528200, China article info Article history: Received 2 December 2011 Received in revised form 3 March 2012 Accepted 6 March 2012 Available online 22 March 2012 Keywords: Antibiotics Laizhou Bay Bohai Sea River discharge Risk assessment abstract The presence of thirteen antibiotics categorized into four different groups (fluoroquinolones, macro- lides, sulfonamides and trimethoprim) was investigated in the rivers discharging to the Laizhou Bay and the seawater of the bay, and the impacts of river discharge on the marine environment were assessed. The results revealed that the same antibiotics predominated in both the river water and the seawater. Additionally, the detected antibiotics in the river water were generally higher than those in the inner bay and in the open bay, reflecting the importance of the riverine inputs as a source of antibiotics. Risk assessment based on the calculated risk quotients (RQ) showed that enoxacin, ciprofloxacin, and sulfamethoxazole in the two aquatic environments both posed high ecological risks (RQ 41) to the most sensitive aquatic organisms Vibrio fischeri, Microcystis aeruginosa and Synecho- coccus leopoliensis, respectively. & 2012 Elsevier Inc. All rights reserved. 1. Introduction The residues of antibiotics are widely present in aquatic environments when they are used extensively in human and veterinary medicine and in aquaculture (Kummerer, 2009). These antibiotics can cause ecological harm in organisms and promote antibiotic resistance genes (ARGs), a newly emerging contami- nant, in bacterial populations (Eguchi et al., 2004; Kummerer, 2004). Past studies have focused on antibiotics in the terrestrial aquatic environment, such as sewage treatment plants (STPs), rivers and groundwater (Kummerer, 2009). However, it is well known that the ocean is an important sink of many terrestrial contaminants. Many of these contaminants (particularly hydro- philic compounds) are poured into marine environment by riverine inputs (Duan et al., 2008; Guan et al., 2009a,b; Kaly, 2004). Therefore, a few researchers have begun to study anti- biotics in the marine environment (Martinez Bueno et al., 2009; Jia et al., 2011; Minh et al., 2009; Wille et al., 2010; Xu et al., 2007; Zou et al., 2011) and have found that riverine inputs, STP effluents and mariculture are the main sources of antibiotics in the marine environment (Holmstrom et al., 2003; Jia et al., 2011; Minh et al., 2009; Zou et al., 2011). Among these scarce studies, only a few have involved quantificational assessment of impacts of land-source inputs (riverine inputs or STP effluents) on the marine environment by flux (Minh et al., 2009; Zou et al., 2011), the dilution factor (Minh et al., 2009) or principal component analysis followed by multiple linear regression (PCA–MLR) (Jia et al., 2011). But to our knowledge, limited studies assessed the ecological risks of antibiotics in the marine environment by now (Backhaus et al., 2000). Laizhou Bay, a typically semi-enclosed inner sea, is one of the three main bays of the Bohai Sea, North China, making up 10 percent of the total area. The bay is an important production base of fishery in China, with developed aquaculture and fishing industry providing large amounts of aquatic products to humans. Industrial and urban developments have been booming around the bay in recent years. This area is part of Bohai Economic Circle—an important economic zone in China. Besides the dense industries and population, there is developed animal husbandry and aquaculture in the area. Therefore, large amounts of indus- trial wastewaters, domestic sewage and wastewater from animal raising industries are produced and poured into the aquatic environment. In addition, there are more than 23 continental rivers (including the Yellow River—the second largest river in China) with a length of more than 10 km flowing into the Laizhou Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety 0147-6513/$ - see front matter & 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.ecoenv.2012.03.002 n Corresponding author. Postal address: No. 511 Kehua Street, Tianhe District, Guangzhou, Guangdong Province, China. Fax: þ86 20 8529 0317. E-mail address: zhanggan@gig.ac.cn (G. Zhang). Ecotoxicology and Environmental Safety 80 (2012) 208–215