Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Examining the role of total organic carbon and black carbon in the fate of legacy persistent organic pollutants (POPs) in indoor dust from Nepal: Implication on human health Ishwar Chandra Yadav a,b,* , Ningombam Linthoingambi Devi c , Jun Li a , Gan Zhang a a State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, PR China b Department of International Environmental and Agricultural Science (IEAS), Tokyo University of Agriculture and Technology (TUAT) 3-5-8, Saiwai-Cho, Fuchu-Shi, Tokyo, 1838509, Japan c Centre for Environmental Sciences, Central University of South Bihar, SH-7, Gaya-Panchanpur, Post-Fatehpur, P.S-Tekari, District-Gaya, 824236, Bihar, India ARTICLE INFO Keywords: Urban area Nepal Dust ingestion Dermal absorption Technical DDT Lindane ABSTRACT Despite the fact that the consumption and import of legacy persistent organic pollutants (POPs) have been stopped in Nepal since 2001, they are still of worry for human prosperity and the environment because of their persistence behavior and constant release from sources that are presently being used. The essential objective of this study was to assess the concentration and spatial distribution of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in residential dust from Nepal keeping in mind the end goal to evaluate the importance of total organic carbon (TOC) and black carbon (BC) in the fate of legacy POPs. Additionally, health risk exposure via dust ingestion and dermal absorption was estimated to evaluate the significance of dust media for human exposure. Results demonstrated that ∑OCPs in dust was 37 times greater than ∑PCBs. DDT was mostly dominated in the dust, and contributed 90% of the ∑OCPs, while hexa-CBs predominated among PCBs and represented 34% of ∑PCBs. Birgunj and Biratnagar had a relatively higher level of ∑OCPs and ∑PCBs than those of Kathmandu and Pokhara. TOC and BC showed a poor connection with OCPs, recommending little or no role. However, PCB in the dust, especially low congeners was strongly linked with TOC but not BC indicating the significant role of TOC. The daily risk exposure estimation indicated dermal absorption through dust as the principal means of OCPs/PCBs intake to both adult and children population. These estimated exposures were 2–4 orders of magnitude inferior to their corresponding reference dose showing insignificant risk. 1. Introduction Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are ubiquitous and persistent semi-volatile organic compounds (SVOCs) that were largely applied all over the world (Rogi, 2008). DDT and PCBs were utilized extensively worldwide, with global production of about one million metric tons individually (Breivik et al., 2004; Li and Macdonald, 2005). OCPs, such as dichlorodiphenyltrichloroethane (DDT) were utilized to control insects on agricultural crops and insect- (bug) bites. Likewise, different proportions of PCBs were incorporated in electrical and electronic materials, heat transfer, and hydraulic ma- chines. Both OCP and PCBs are extremely bioavailable, readily bio-ac- cumulate and can be biomagnified to a high degree in food chains (ATSDR, 2004). They can antagonistically influence human well-being and other living organisms, by damaging the nervous system, reproductive and developmental disorders, and cancers. The higher concentrations of OCPs and PCBs in different ecological compartment have become global issues because of their long-range atmospheric transport (LRAT) from the source region to farther away from the source region (Harner et al., 2004; Motelay-Massei, 2005). Due to their severe health impact, OCP and PCBs were regulated and restricted in many developed countries in late 1970 (Rogi, 2008). Nonetheless, de- spite limitation on consumption and production of legacy SVOCs, these compounds are still amongst the most pervasive environmental pollu- tants and are all around distinguished on the earth, comprising re- sidential dust. The potential source region for some of the banned le- gacy POPs has received much attention in many under-developed countries, especially in subtropical and tropical regions after the adoption of Stockholm Convention on POPs (SCPOPs) (Zhang et al., 2010). The SCPOPs obliged the party country to identify and monitor https://doi.org/10.1016/j.ecoenv.2019.03.048 Received 9 November 2018; Received in revised form 6 March 2019; Accepted 12 March 2019 * Corresponding author. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, PR China. E-mail address: icyadav.bhu@gmail.com (I. Chandra Yadav). Ecotoxicology and Environmental Safety 175 (2019) 225–235 0147-6513/ © 2019 Elsevier Inc. All rights reserved. T