Journal of Hazardous Materials 402 (2021) 123778 Available online 25 August 2020 0304-3894/© 2020 Elsevier B.V. All rights reserved. Polystyrene nanoplastic induces oxidative stress, immune defense, and glycometabolism change in Daphnia pulex: Application of transcriptome profling in risk assessment of nanoplastics Zhiquan Liu a, b , Yiming Li a , Edgar P´ erez b , Qichen Jiang c , Qiang Chen a , Yang Jiao a , Yinying Huang a , Ying Yang c , Yunlong Zhao a, * a State Key Laboratory of Estuarine and Coastal Research, School of Life Sciences, East China Normal University, Shanghai, 200241, China b Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN, 47907, United States c Freshwater Fisheries Research Institute of Jiangsu Province, Nanjing, 210017, China A R T I C L E INFO Editor: R. Debora Keywords: Nanoplastic Transcriptome Environmental contaminant Daphnia Oxidative stress ABSTRACT Aquatic environments are generally contaminated with nanoplastic material. As a result, molecular mechanisms for sensitive species like Daphnia are needed, given that mechanistic nanoplastic toxicity is largely unknown. Here, global transcriptome sequencing (RNA-Seq) was performed on D. pulex neonates to quantitatively measure the expression level of transcripts. A total of 208 differentially expressed genes (DEGs) were detected in response to nanoplastic exposure for 96 h, with 107 being up-regulated and 101 down-regulated. The gene functions and pathways for oxidative stress, immune defense, and glycometabolism were identifed. In this study, D. pulex neonates provide some molecular insights into nanoplastic toxicity. However, more studies on DEGs are needed to better understand the underlying mechanisms that result as a response to nanoplastic toxicity in aquatic organisms. 1. Introduction In the 1970s, plastic litter was frst observed in the aquatic envi- ronment (Carpenter and Smith, 1972; Colton et al., 1974). Through the long-term infuence of weathering, ultraviolet radiation (UV), and other environmental factors, plastic litter in the environment can be degraded into nanoscale and microscale particles (Galloway et al., 2017). Micro- plastics are defned as those particles which are between 1 μm to 5 mm in size, whereas nanoplastics are those which are smaller than 1 μm or 100 nm (Hartmann et al., 2019; Koelmans et al., 2019; Thompson et al., 2004). While microplastics research has been extensive in both fresh- water and marine environments, nanoplastics research is still in its in- fancy, but has been detected in several environmental compartments (sediment, surface water, marine, and freshwater), including remote areas with sparse human activity, like the arctic and deep sea (Chae and An, 2017; Mattsson et al., 2018). However, a major challenge in nano- plastics research is that its detection methods are still developing. Nanoplastics can be released directly into the environment via in- dustrial releases, products containing nanoplastic materials (e.g. drug delivery systems and waterproof coatings), or through the degradation of larger plastic waste (Shen et al., 2019). Since nanoplastics are ubiq- uitous in the environment; human, organism, and ecosystem health concerns are becoming more relevant (Lehner et al., 2019). A signifcant volume of research has been invested in understanding nanoplastic toxicity on marine organisms; however, the same is not true for freshwater organisms (Eerkes-Medrano et al., 2015; Strungaru et al., 2019). To date, only a few studies have explored the effects of nano- plastic on freshwater alga, fsh, and zooplankton (Besseling et al., 2014; Li et al., 2020; Zhang et al., 2020a). Because nanoplastics are frequently detected in freshwater environments, it is considered to be a source, and a major transport pathway for plastics present in oceanwater (Dris et al., 2015; Wagner and Reemtsma, 2019). Consequently, more research is needed to determine the effects of nanoplastics on freshwater organisms. To address this gap, an abundant freshwater Cladoceran (Daphnia) was used as our model organism. Other researchers have demonstrated that Daphnia is a reliable model organism to study the effects of nano- plastics because it offers many unique advantages (Liu et al., 2020a, 2019; Wu et al., 2019; Zhang et al., 2020b). A few of these advantages include: fast generation time, non-selective flter feeder, widely distributed in the environment, primary consumer in aquatic food webs, * Corresponding author at: East China Normal University, 500 Dongchuan Road, Shanghai, 200241, China. E-mail addresses: liuzhiquan1024@163.com (Z. Liu), ylzhao426@163.com (Y. Zhao). Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat https://doi.org/10.1016/j.jhazmat.2020.123778 Received 1 June 2020; Received in revised form 16 August 2020; Accepted 18 August 2020