Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Comparative toxicity of organic mixture attached to road deposited sediments: Inadequacy of conventionally using individual pollutants to assess comprehensive hazard effects Nian Hong a,b , An Liu a,b,* , Panfeng Zhu a , Yuting Zhan a,b , Mengting Yang a,b,** , Zhenxuan Zhang a,b , Bo Yang a,b , Yuntao Guan c a College of Chemistry and Environmental Engineering, Shenzhen University, 518060, Shenzhen, China b Shenzhen Key Laboratory of Environmental Chemistry and Ecological Remediation, 518060, Shenzhen, China c Guangdong Provincial Engineering Technology Research Centre for Urban Water Cycle and Water Environment Safety, Graduate School at Shenzhen, Tsinghua University, 518055, Shenzhen, China ARTICLE INFO Keywords: Road deposited sediments Stormwater quality Urban road Stormwater reuse ABSTRACT Organic pollutants attached on road deposited sediments (RDS) during dry days can be washed-off into stormwater runoff during rainfall events, undermining stormwater reuse safety. Previous research studies commonly utilized individual pollutant groups and their quantity to evaluate the hazard effect of pollutants attached to RDS in terms of stormwater reuse. Since many types of organic pollutants are present together rather than individually, conventional approaches might not permit a comprehensive understanding of how appro- priately the RDS polluted stormwater can be reused. This study undertook a toxicity test of organic pollutants attached to RDS using Chinese hamster ovary cells (CHO), testing a hypothesis that solely focusing on individual pollutant groups are not adequate to represent hazard effects of resulting stormwater and hence their adequacy for reuse. It is noted that comparative toxicity of RDS is not strongly related to total solids (commonly seen as the key carrier of pollutants) and chemical oxygen demand (COD, representing organic matters). Additionally, the comparison results of spatial distributions of toxicity (in this study) and individual pollutants in previous studies did not show a similar trend. These results imply that toxicity should be also used to indicate how stormwater can be safely reused while solely investigating individual pollutants can not adequately show a comprehensive hazard effect in terms of ensuring stormwater reuse safety. Based on study outcomes, a new assessment approach considering both pollutant and toxicity were proposed. This will assist on effective stormwater reuse and en- suring their reuse safety. 1. Introduction With the economic development and population expansion, an in- creasing number of cities have to be faced with water crisis. Stormwater reuse has been given an increasing attention to mitigate water resource shortage (Lau et al., 2017; Sa'd A et al., 2014; Wen et al., 2018). Road stormwater is important for reuse since there are large road areas in urban environments, producing a large quantity of stormwater runoff. However, many pollutants are deposited on urban surfaces during dry days due to traffic and surrounding anthropogenic activities and a number of pollutants are toxic. These pollutants are primarily attached to road deposited sediments (RDS). When rainfall events occur, along with RDS, these toxic pollutants can enter stormwater runoff, undermining stormwater reuse safety. Among toxic pollutants on urban surfaces, organic pollutants are common and previous researchers have found many organic pollutants in urban stormwater such as benzene series pollutants (BTEX) (Li et al., 2018; Liu et al., 2018; Yu et al., 2017), polycyclic aromatic hydro- carbons (PAHs) (DiBlasi et al., 2008; Hussain et al., 2015), total pet- roleum hydrocarbons (TPHs) (Al-Baldawi et al., 2015; Liu et al., 2019), pesticides (Rippy et al., 2017; Topaz et al., 2018) and pharmaceuticals and personal care products (PPCPs) (Boyd et al., 2004). The sources of these organic pollutants on urban roads primarily include traffic emission (Hong et al., 2018), incomplete combustion of fossil fuels (Khanal et al., 2018), by-products of combustion processes (Zhang et al., 2019), oils and lubricants leakage (Thorpe and Harrison, 2008), https://doi.org/10.1016/j.ecoenv.2019.05.025 Received 7 March 2019; Received in revised form 7 May 2019; Accepted 9 May 2019 * Corresponding author. College of Chemistry and Environmental Engineering, Shenzhen University, 518060 Shenzhen, China. ** Corresponding author. College of Chemistry and Environmental Engineering, Shenzhen University, 518060, Shenzhen, China E-mail addresses: liuan@szu.edu.cn (A. Liu), yangmt@szu.edu.cn (M. Yang). Ecotoxicology and Environmental Safety 180 (2019) 357–365 0147-6513/ © 2019 Elsevier Inc. All rights reserved. T