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 ∑8 OPE measured in sediments samples was 12 times higher than soil and ranged 983-7460ng/g dw (median 2210ng/g dw) and 65-27,500ng/g dw (186ng/g dw), respectively. TMPP was most abundant in soil followed by TCIPP, TEHP and EHDPHP and ranged 17-25,300ng/g dw (41.3ng/g dw), 11.2-911ng/g dw (31.7ng/g dw), 8.52-858ng/g dw (26.1ng/g dw) and 10.2-114ng/g dw (25.6ng/g dw), respectively. TEHP was most prevalent in sediments followed by TMPP and EHDPHP and were in the range of 657-3020ng/g dw (median 1140ng/g dw), 267-2630ng/g dw (median 815g/g dw), 34-418ng/g (median 131ng/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 ∑8 OPE 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 ∑8 OPEs especially TMPP and TPHP suggested significant potential adverse risk for aquatic organisms.