Sources of polycyclic aromatic hydrocarbons in sediments of the Bharalu River, a tributary of the River Brahmaputra in Guwahati, India Karishma Hussain a , S. Balachandran b , Raza Rafiqul Hoque a,n a Department of Environmental Science, Tezpur University, Tezpur 784028, India b Department of Environmental Studies, Vishva-Bharati, Shantiniketan 731235, India article info Article history: Received 18 February 2015 Received in revised form 5 July 2015 Accepted 6 July 2015 Keywords: PAHs Hazard risk Bank sediment Sources identification abstract Analysis of riverine sediments offers important information regarding anthropogenic activities in the adjacent watershed. In this study, we provide polycyclic aromatic hydrocarbon (PAH) levels, their pos- sible sources and potential hazards in the Bharalu tributary of the Brahmaputra River flowing through Guwahati city in India. The USEPA's 16 priority PAHs were determined in river bank sediments during two distinct seasons viz. pre- and post-monsoon. The ∑PAHs concentrations varied between 338 and 23,100 ng g 1 during post-monsoon and between 609 and 8620 ng g 1 during pre-monsoon. Mean benzo(a)pyrene (BaP) levels were between 17.8 712 and 21.9 727 ng g 1 during post- and pre-monsoon seasons respectively. Spatial variations were observed. Interestingly, bank sediment samples from the sites near the confluence of the Bharalu River with the Brahmaputra River were found to have maximum concentrations of PAHs during post-monsoon season. The profile of the PAHs was dominated by 3-, 4- and 6-ring compounds. We estimated hazards of PAHs as RQ ∑PAHs , which showed seasonal variation: 3 times higher during post-monsoon than pre-monsoon. 3-and 4-ring PAHs were the major PAHs of concern. The Bharalu River sediment was found to pose medium to high hazards to ecosystem. The individual PAHs including Acy, Phen and Pyr were observed with RQ(MPCs) value 41 indicating severe hazards during post-monsoon and pre-monsoon season. A very high percentage of coefficient of varia- tion (CV) for PAHs during post-monsoon also revealed great variation in hazards and sources in this season. The diagnostic ratios indicated both petrogenic and pyrogenic origin of the PAHs. The pyrogenic contributions were mainly attributed to emissions from diesel, gasoline and wood combustion which are mainly from anthropogenic sources. & 2015 Elsevier Inc. All rights reserved. 1. Introduction Polycyclic Aromatic Hydrocarbons (PAHs) make a unique class of ubiquitous and persistent organic pollutants in the environ- ment, which come from anthropogenic sources like combustion engines, residential heating, industrial activities and biomass burning (White, 1986). Due to their carcinogenic, mutagenic and genotoxic effects PAHs have attracted considerable attention in the recent times around the world. Due to high toxicity, stability and high lipophilic nature, PAHs can move through food chains, and human being could be the final destination (IARC, 1983; Okay et al., 2000; Vagi et al., 2005). The United States Environmental Protection Agency (USEPA) prioritised a group of 16 PAHs, of which Benzo[a]anthracene (BaA), Benzo[a]pyrene (BaP), Benzo[b] fluoranthene (BbF), Benzo[k]fluoranthene (BkF), Chrysene (Chry), Dibenzo[a,h]anthracene (DBA) and Indeno[1,2,3-c,d]pyrene (IP) have been regarded as probable carcinogens (USEPA, 2002). More so, BaP is termed as index or gold standard of the whole group of PAHs due to its high carcinogenic potency. The PAHs are transported to aquatic environments through various routes like atmospheric fall out, runoff from land and pa- vements, wastewater discharge, oil leakage and storm water. Upon entering an aquatic system, PAHs preferably tend to settle or partition onto non-aqueous phase such as sediment due to their hydrophobicity and high octanol/water partition coefficients. Such adsorption to solid particles makes them less susceptible to de- gradation through photochemical and biological oxidation, which is why PAHs tend to persist for longer period in the environment. Therefore, there is a tendency in the PAHs to accumulate in high concentrations, high molecular weight PAHs (HMW-PAHs) in particular, especially when sediment is in anaerobic environment (Guzzella, Depaolis, 1994). Sediment thus acts as pollutant a trap which, with time, magnifies to higher degree of toxic load, and can Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety http://dx.doi.org/10.1016/j.ecoenv.2015.07.008 0147-6513/& 2015 Elsevier Inc. All rights reserved. n Corresponding author. E-mail address: rrh@tezu.ernet.in (R. Rafiqul Hoque). Ecotoxicology and Environmental Safety 122 (2015) 61–67