Concentration and spatial distribution of organophosphate esters in the soil-sediment profile of Kathmandu Valley, Nepal: Implication for risk assessment

Despite the fact that soil and sediments, which act as a sink or potential source of organic pollutants, have been polluted with organophosphate esters (OPEs) around the globe, extremely constrained data is accessible on environmental concentration and fate of OPEs in solid matrices in whole of the South Asia particularly if there should be an occurrence in Nepal. In this study, surface soil (N = 19) and sediments samples (N= 20) were analyzed for eight different OPE in Kathmandu Valley during October 2014. The concentration of Sigma 8OPE measured in sediments samples was 12 times higher than soil and ranged 983-7460 ng/g dw (median 2210 ng/g dw) and 6527,500 ng/g dw (186 ng/g dw), respectively. TMPP was most abundant in soil followed by TCIPP, TEHP and EHDPHP and ranged 17-25,300 ng/g dw (41.3 ng/g dw), 11.2-911 ng/g dw (31.7 ng/g dw), 8.52-858 ng/g dw (26.1 ng/g dw) and 10.2-114 ng/g dw(25.6 ng/g dw), respectively. TEHP was most prevalent in sediments followed by TMPP and EHDPHP and were in the range of 657-3020 ng/g dw(median 1140 ng/g dw), 267-2630 ng/g dw (median 815 g/g dw), 34-418 ng/g (median 131 ng/g dw), respectively. The sources of the high level of OPEs in soil was related to the end point use of consumer materials, traffic emission, and close proximity to commercial and industrial areas; while domestic sewage discharges and effluents from carpet industry were identified as the possible entry of OPE in sediments. Total organic carbon (TOC) and black carbon (BC) content in soil were moderately and positively correlated with Sigma 8OPE indicating more or less influence of soil organic carbon. The health risk assessment suggested dermal absorption of OPEs via soil is the primary pathway of human exposure to the general population. The significantly high-risk quotient (RQ) estimated for Sigma 8OPEs especially TMPP and TPHP suggested significant potential adverse risk for aquatic organisms. (C) 2017 Elsevier B.V. All rights reserved.