Organophosphate flame retardants (OPFRs) were widely used in plastics, textiles, electronic equipment, furniture, as well as construction (Stevens et al., 2006). Especially in industrial process, OPFRs are usually applied as antifoaming agents, and as flame retardants or plasticizers in consumer goods (Van der Veen and de Boer, 2012; Wei et al., 2015). OPFRs are generally classified into alkyl-OPFRs, aryl-OPFRs, chlorinated OPFRs, bromine OPFRs and other organophosphate esters. Because of the ban and restriction of partial bromine flame retardants in Stockholm Convention and RoHS of the European Union, chlorinated OPFRs such as tris(chloropropyl) phosphate (TCPP), tris(2-chloroethyl) phosphate (TCEP) and tris(dichloropropyl) phosphate (TDCPP) are widely used all over the world. Triphenyl phosphate (TPP) are widely used for computer screens and TV sets, and tis(2-butoxyethyl) phosphate (TBEP) is for floor polishes (Marklund et al., 2003).
Research shows the roles played by OPFRs are through physical mixture but not the chemical bond (Kemmlein et al., 2003; Kim and Kannan, 2018), thus the OPFRs may easily diffused into the environment through volatilization, abrasion and dissolution (Pang et al., 2016; Reemtsma et al., 2008). OPFRs may release from furniture, plastics, vehicle or industrial process into air, then afflux into surface water through wet deposition. OPFRs may directly discharged into municipal drainage network, and let it into surface water followed by STPs treatment. Several researches had shown that the ratio for mass loadings of TPP, TCPP, TDCPP and tri-n-butyl phosphate (TNBP) in STPs influent to the production was about 1.3–2.8% (Kim et al., 2017; Marklund et al., 2005; Schreder and La Guardia, 2014). As we surveyed and reported in other studies (Kim, et al., 2017), OPFRs cannot be treated in STPs and would finally transport into the potable water. Researches had reported the occurrence and distribution of OPFRs in air, water and STPs. The emission rate of OPFRs from building materials and electronic equipment could be up to 339 µg/m2/h (Takigami et al., 2009). Möller et al. (2012) detected OPFRs in the atmosphere of the Arctic and Antarctic, demonstrating for the first time the long-range migration capability of OPFRs worldwide. A survey of the water quality of sewage treatment plants (STPs) in European countries showed that TCPP and TCEP could be detected in the effluent of most STPs at a concentration of several hundred ng/L (Loos et al., 2013).
The high population density in cities has led to massive usage and discharge of OPFRs, making them widely disseminated in aquatic environments, such as drinking water, surface water, groundwater and municipal STPs (Reemtsma, et al., 2008; Shi et al., 2016). Studies have found that OPFRs exposed to the aquatic environments can enter the human body through food contamination, bioaccumulation, direct contact or ingestion, resulting in their detection in human hair, nails, urine and breast milk (Sundkvist et al., 2010; Liu et al., 2015; Zhang et al., 2016; He et al., 2018). Therefore, OPFRs pose a potential threat to human health and water environmental safety. As the capital of China, Beijing is the center of national political, economic, and cultural development, with a population of 21.73 million, and the population density (1324 people/km2) ranks second among all cities (Ma et al., 2017a), thus it is conceivable that OPFRs would be used and consumed in significant quantities in this city (Shi et al., 2016). However, the current research on the occurrence and risk of OPFRs is still limited, especially lacking of comprehensive data on OPFRs exposure in different water bodies of high population density cities, such as Beijing.
Based above, we studied the distribution of six kinds of flame retardants such as TPP, tricresyl phosphate (TCP), TCPP, TCEP, TDCPP and tris(2,3-dibromopropyl) phosphate (TDBP) in typical urban water (surface river, underground water, sewage treatment plants (STPs)) of Beijing, China. Finally, environmental risk of OPFRs in water was evaluated to explore the impact of these chemicals on aquatic organisms. These results will help to understand the pollution levels and environmental risks of OPFRs in typical urban water bodies of modern metropolis, and provide data support for the establishment of OPFRs regulatory standards.