RESEARCH ARTICLE Biochemical responses of a freshwater fish Cirrhinus mrigala exposed to tris(2-chloroethyl) phosphate (TCEP) Jesudass Sutha 1 & Pottanthara Ashokan Anila 1 & Sathisaran Umamaheswari 1 & Mathan Ramesh 1 & Arul Narayanasamy 2 & Rama-Krishnan Poopal 3 & Zongming Ren 3 Received: 2 March 2020 /Accepted: 29 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Freshwater fish Cirrhinus mrigala were exposed to tris(2-chloroethyl) phosphate (TCEP) with three different concentrations (0.04, 0.2, and 1 mg/L) for a period of 21 days. During the study period, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels were significantly (p < 0.05) inhibited. The superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and lipid peroxidation (LPO) levels were increased significantly (p < 0.05) in gills, liver, and kidney tissues, whereas glutathione (GSH) and glutathione peroxidase (GPx) (except liver tissue) activities were inhibited when compared to the control group. Likewise, exposure to TCEP significantly (p < 0.05) altered the biochemical (glucose and protein) and electrolyte (sodium, potassium, and chloride) levels of fish. Light microscopic studies exhibited series of histopathological anomalies in the gills, liver, and kidney tissues. The present study reveals that TCEP at tested concentrations causes adverse effects on fish and the studied biomarkers could be used for monitoring the ecotoxicity of organophosphate esters (OPEs). Keywords Organophosphate esters . Thyroid hormones . Oxidative stress . Ionic compounds . Histopathology . Fish Introduction Flame retardants (FRs) are organic chemicals that are used extensively in many polymer-based industrial and house-hold goods to prevent the chances of explosion or to avoid damage of materials during fire accident. The usage of FRs is increasing every year (Mags- Novel; News and Events 2015). The major concern is that FRs do not bind with the polymers; hence, the possibility of leaching into their environment is higher. FRs have been detected in environment including human body fluids up to micrograms or even more; unfortunately, these chemicals have potential to cause toxicological impacts on liv- ing organism even at low level (Morgan et al. 2019). Different groups of FRs such as bromine, chlorine, phosphorus, nitrogen, boron, and metallic hydroxide-based organic compounds have been utilized so far. Some of the FRs are listed as persistent organic pollutants and banned for using further (Sugeng et al. 2017; Hao et al. 2018; Hou et al. 2019). Organophosphate flame retardants (OPFRs) with logKow ranges from 1.44 to 9.49 and logKoc from 2.21 to 6.87 have been used as substitute for toxic FRs and additives in combustible products up to 15% (Cristale et al. 2016; Wolschke et al. 2018; Chokwe and Okonkwo 2019). During manufacturing, these OPFRs might leach and reach the environment. The persistence nature of their chlorine atoms in the environment could be a contributor for the formation of various hazardous polychlorinated com- pounds such as dibenzo-p-dioxins, dibenzofurans, and dioxin- like polychlorinated biphenyls, hexa- and penta-chloroben- zene, and penta-chlorophenol (Matsukami et al. 2014). Among OPFRs, tris(2-chloroethyl) phosphate (TCEP) is a high production volume chemical, which is extensively used in many polymeric materials such as adhesives, polyvinyl chlo- ride, textiles, baby products, plastics, electric and electronic products, and building materials up to 30% (Liu et al. 2016; Responsible Editor: Philippe Garrigues * Mathan Ramesh mathanramesh@yahoo.com * Zongming Ren zmren@sdnu.edu.cn 1 Unit of Toxicology, Department of Zoology, School of Life Sciences, Bharathiar University, Coimbatore 641046, India 2 Disease Proteiomics Laboratory, Department of Zoology, School of Life Sciences, Bharathiar University, Coimbatore 641046, India 3 Institute of Environment and Ecology, Shandong Normal University, Jinan, People’s Republic of China Environmental Science and Pollution Research https://doi.org/10.1007/s11356-020-09527-0