Nitrated- and oxygenated-polycyclic aromatic hydrocarbon in urban soil from Nepal: Source assessment, air-soil exchange, and soil-air partitioning.

In contrast to more frequently investigated priority pollutants, such as polycyclic aromatic hydrocarbons (PAHs), only little is known about the fate and distribution of nitrated- and oxygenated-PAHs (NPAHs and OPAHs) in urban soils, particularly in Indian sub-continent. Moreover, experimental data on air-soil exchange and soil-air partitioning are also lacking, which is critical in assessing the partitioning, fugacity coefficient, and secondary emission of PAH-derivatives. Hence, this article provides an insight into the fate, sources, air-soil exchange, and soil-air partitioning of PAH-derivatives on a molecular basis. Prospective health risk due to their exposure has also been discussed. The result showed that PAH-derivatives had significantly polluted all four Nepalese cities. Æ©15NPAHs and Æ©2OPAHs in soil were 4 and 20 times lower than their parent-PAHs, and ranged 396-2530 ng/g (median 458 ng/g) and 91.9-199 ng/g (median 94.9 ng/g), respectively. Æ©15NPAHs was higher than a few global studies, while Æ©2OPAHs was lower than some of the less urbanized/remote areas worldwide. The 6-Nitobenzo[a]pyrene (6-NBaP) was most abundant in soil, and accounted for 10-12% of Æ©15NPAHs, while Benzanthrone (BZONE) exceeded among OPAHs, and represented 71-76% of Æ©2OPAHs, respectively. Source identification study indicated that direct emissions from domestic/residential cooking and heating and secondary formations are the essential sources of derivative chemicals in soil. Fugacity fraction ratio (fratio) indicated volatilization from the soil. The soil-air partitioning study showed sorption by soil organic matter/black carbon has little role in soil-air partitioning of PAH-derivatives in Nepal's urban soil. The toxicity equivalency quotients (TEQs) of NPAHs (314 ± 102 ng/g) was estimated slightly higher than their parent-PAHs (294 ± 121 ng/g) suggesting a relatively higher risk of soil toxicity in Nepal.

Spatial distribution, source analysis, and health risk assessment of heavy metals contamination in house dust and surface soil from four major cities of Nepal.

Raising population, deteriorating environmental conditions and limiting natural resources to handle the key environmental health problems have critically affected human health and the environment. Policy makers and planners in Nepal are more concerned today than at any other time in the past about the deterioration of the environmental condition. Therefore, understanding the connection between pollution and human wellbeing is fundamental endeavors to control pollution exposures and secure human wellbeing. This ability is especially critical for countries like Nepal where the issues of environmental pollution have customarily taken a second place to request for economic development. In this study, spatial distribution and sources of 12 heavy metals (HMs) were investigated in surface soils (n = 24) and house dust (n = 24) from four major urban areas of Nepal in order to mark the pollution level. Additionally, a health risk was estimated to establish the link between HMs pollution and human health. Results showed that the median concentration of Ag, Cd, Co, Cr, Cu, Ni, Pb, Sb, Mn and Zn in soil and dust were 2-13 times greater than the background value. The As, Zn, Cu, Cd, and Pb showed a relatively higher spatial variability in soil and dust. Zn was the most abundant metal measured in dust and soil and accounted for 59% and 55% of ∑7HMs, respectively. The HMs in soil and dust were poorly correlated with total organic carbon (TOC) and black carbon (BC), suggesting little or no influence on HMs contamination. Source analysis study indicated the distribution of Cr, Ni, Sb, Ag, Pb, Cu, and Zn in soil and dust are mainly affected by anthropogenic sources, particularly traffic emissions, industrial source, and domestic households materials, while Co, Fe, As, Mn and Cd were from natural sources. The estimated carcinogenic risk (CR) of HMs in soil and dust exceeded the acceptable level of human exposure, recommending significant CR to the local population.

Measurement of legacy and emerging flame retardants in indoor dust from a rural village (Kopawa) in Nepal: Implication for source apportionment and health risk assessment.

Under the Stockholm Convention, signatory countries are obliged to direct source inventories, find current sources, and provide ecological monitoring evidence to guarantee that the encompassing levels of persistent organic pollutants (POPs) are declining. However, such monitoring of different types of POPs are to a great degree constrained in most developing countries including Nepal and are primarily confined to suspected source area/ densely populated regions. In this study, 9 polybrominated diphenyl ethers (PBDEs), 2 dechlorane plus (DPs), 6 novel brominated flame retardants (NBFRs) and 8 organophosphate ester flame retardants (OPFRs) were investigated in indoor dust from a rural area (Kopawa) in Nepal in order to evaluate their occurrence/level, profile, spatial distribution and their sources. Additionally, health risk exposure was estimated to anticipate the possible health risk to the local population. The results showed that OPFRs was the most abundant FR measured in the dust. The concentration of ∑8OPFRs was about 2, 3 and 4 orders of magnitude higher than the ∑6NBFRs, ∑9PBDEs, and ∑2DPs, respectively. Tris (methylphenyl) phosphate (TMPP) and Tris (2-ethylhexyl) phosphate (TEHP) were the most abundant OPFRs analyzed in the dust; while decabromodiphenyl ethane (DBDPE) exceeded among NBFRs. Likewise, 2,2',3,3',4,4',5,5',6,6'-decabromodiphenylether (BDE-209) was the most identified chemical among PBDEs. The total organic carbon (TOC) content in dust was significantly and positively connected with octa-BDEs (Rho = 0.615, p < 0.01), BTBPE (Rho = 0.733, p < 0.01), TPHP (Rho = 0.621, p < 0.01), TEHP (Rho = 0.560, p < 0.01) and TMPPs (Rho = 0.550, p < 0.01), while black carbon (BC) was either weakly related or not related, suggesting little or no impact of BC in the distribution of FRs. Principal component analysis indicated the contribution from commercial penta-, octa- and deca-BDEs formulation, the adhesive substance, food packaging and paints, and degradation of BDE-209 as the essential sources of FRs. Health risk exposure estimates showed that dermal absorption via dust as the primary route of FRs intake. The estimated daily exposure of PBDEs, NBFRs and OPFRs were 2-10 orders of magnitude lower than their corresponding reference dose (RfD), suggesting insignificant risk. However, other routes such as inhalation and dietary intake might still be significant in the case of Kopawa which should be tested in future.

Polychlorinated Biphenyls in Surface Soil from North-East India: Implication for Sources Apportionment and Health-Risk Assessment.

Although India never manufactured polychlorinated biphenyls (PCBs), evidence suggests the prevalence of PCBs in multi-environmental matrices. Despite the high level of PCBs that has been detailed in the major urban areas of India, little is known about the fate and sources of PCBs in Northeast India (NEI). This motivated us to investigate the contamination level and sources of PCBs in the surface soil. In this study, the environmental concentration and sources of 25 PCBs were investigated in surface soil (n = 60) from three states of NEI (lower Assam, Manipur, and Tripura). Additionally, the relationship between soil organic carbon (SOC) and PCBs was studied to investigate the role of SOC in the distribution of PCBs. Overall, the concentration of ∑25PCBs ranged from 2950 to 16,700 pg/g dw (median 7080 pg/g dw), 3580-21,100 pg/g dw (median 11,500 pg/g dw), and 2040-11,000 pg/g dw (median 4270 pg/g dw) in Assam, Manipur, and Tripura, respectively. Low-chlorinated PCBs were more prevalent than highly chlorinated PCBs. PCB-49 was identified as the most abundant in soil, followed by PCB-52, and accounted for 13% and 12.9% of ∑25PCBs, respectively. With respect to land use categories, high ∑25PCBs were related to grassland areas and proximity to the roadside soil. The principal component analysis indicated emissions from technical PCB mixtures, combustion of municipal wastes/residential wood, incineration of hospital wastes, and e-waste recycling/disposal sites are the real sources of PCBs. Marginally, a moderate-to-weak correlation of SOC with ∑25PCBs (R2 = 0.144, p < 0.05) and their homologs (R2 = 0.280-0.365, p < 0.05) indicated the little role of SOC in the dispersion of PCBs. The estimated toxic equivalency of dioxin-like PCBs suggested that PCB-126 is the most toxic contaminant to endanger the human population.

Chemometric evaluation of heavy metal pollutions in Patna region of the Ganges alluvial plain, India: implication for source apportionment and health risk assessment.

While metal pollution and distribution in soil are well documented for many countries, the situation is more serious in developing countries because of the rapid increase in industrialization and urbanization during last decades. Although it is well documented in developed countries, data about substantial metal pollution in Indian soil, especially in eastern Ganges alluvial plain (GAP), are limited. In this study, eight different blocks of Patna district located in eastern GAP were selected to investigate the contamination, accumulation, and sources of metals in surface soil considering different land use types. Additionally, human health risk assessment was estimated to mark the potential carcinogenic and non-carcinogenic effect of metals in soil. The concentration of all metals (except Pb) in soil was below the Indian standard limit of the potential toxic element for agricultural soil. Pb was the most abundant in soil, followed by Zn and Cu, and accounted for 52, 33 and 8% of the total metal. In terms of land use types, roadside soil detected higher concentrations of all metals, followed by park/grassland soil. Principal component analysis results indicated traffic pollution and industrial emissions are the major sources of heavy metals in soil. This was further confirmed by strong inter-correlation of heavy metals (Cd, Cr, Ni, Cu and Pb). Human health risk assessment results indicated ingestion via soil as the primary pathway of heavy metal exposure to both adults and children population. The estimated hazard index was highest for Pb, suggesting significant non-carcinogenic effect to both adults and children population. The children were more prone to the non-carcinogenic effect of Pb than adults. However, relatively low cancer risk value estimated for all metals suggested non-significant carcinogenic risk in the soil.

Altitudinal and spatial variations of polycyclic aromatic hydrocarbons in Nepal: Implications on source apportionment and risk assessment.

Although several global/regional studies have detailed the high level of polycyclic aromatic hydrocarbons in urban areas worldwide, unfortunately, Nepal has never been part of any global/regional regular monitoring plan. Despite few sporadic studies exist, the systematic monitoring and integrated concentration of PAHs in urban region of Nepal are lacking. In this study, the concentrations, sources, and health risk assessment of 16 PAHs in air (n = 34) were investigated in suspected source areas/more densely populated regions of Nepal. Four potential source areas in Nepal were focused as it was conjectured that urban centers in plain areas (Birgunj and Biratnagar) would possibly be more influenced by PAHs as a result of intense biomass/crop residue burning than those in hilly areas (Kathmandu and Pokhara). The overall concentrations of ∑16PAHs ranged from 4.3 to 131 ng/m3 (median 33.3 ng/m3). ∑16PAH concentrations in plain areas were two folds higher than those in hilly areas. PHE was the most abundant followed by FLUA, PYR, and NAP, which accounted for 36%, 15%, 12%, and 9% of ∑16PAHs, respectively. Principal component analysis confirmed that PAHs in highly urbanized areas (Kathmandu and Pokhara) were related to diesel exhausts and coal combustion, while PAHs in less urbanized regions (Birgunj and Biratnagar) originated from biomass and domestic wood combustions. Furthermore, in the urban areas of Nepal, vehicular emission could also influence atmospheric PAHs. The lifetime cancer risk per million populations due to PAH exposures was estimated to be higher for plain areas than that for hilly areas, suggesting a relatively greater risk of cancer in people living in plain areas.

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 ∑8OPE 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 ∑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 ∑8OPEs especially TMPP and TPHP suggested significant potential adverse risk for aquatic organisms.

Organophosphate ester flame retardants in Nepalese soil: Spatial distribution, source apportionment and air-soil exchange assessment.

Despite soil being the major terrestrial environmental reservoir and one of the significant sinks for many hydrophobic organic compounds including organophosphate ester flame retardants (OPFRs), limited information is available about concentration and fate of OPFRs contamination in urban soil in general and especially in case of Nepal. This study investigates the environmental concentration, spatial distribution and source apportionment of eight OPFRs in surface soil (n = 28) from four major cities of Nepal with special interest on air-soil exchange. Overall, significantly high concentrations of ∑8OPFR were measured in soil ranging from 25-27,900 ng/g dw (median 248 ng/g dw). In terms of compositional pattern, tris(methyl phenyl) phosphate (TMPP) was the most abundant phosphorus chemical in soil, followed by tris(2-chloroisopropyl) phosphate (TCIPP), and accounted for 35-49% and 8-25% of ∑8OPFRs, respectively. The high level of these OPFRs was attributed to local sources as opposed to transboundary influence from remote areas. A Spearman's rank correlation analysis exhibited weak correlation of ∑8OPFRs with TOC (Rho = 0.117, p < 0.05) and BC (Rho = 0.007, p < 0.05), suggesting little or no influence of TOC and BC on the concentration of ∑8OPFRs. The fugacity fraction (ff) results indicated a strong influence of soil contamination on atmospheric level of OPFRs via volatilization.

Possible emissions of POPs in plain and hilly areas of Nepal: Implications for source apportionment and health risk assessment.

Ambient air is a core media chosen for monitoring under the Stockholm Convention on POPs. While extensive monitoring of POPs in ambient air has been carried out in some parts of the globe, there are still regions with very limited information available, such as some developing countries as Nepal. This study therefore aims to target the occurrence of selected POPs in Nepal in suspected source areas/more densely populated regions. Four potential source regions in Nepal were furthermore targeted as it was hypothesized that urban areas at lower altitudes (Birgunj and Biratnagar located at approximately 86 and 80 m.a.s.l.) would be potentially more affected by OCPs because of more intensive agricultural activities in comparison to urban areas at higher altitudes (Kathmandu, Pokhara located 1400 and 1135 m.a.s.l). As some of these areas could also be impacted by LRAT, air mass back trajectories during the sampling period were additionally evaluated using HYSPLIT. The concentrations of overall POPs were twice as high in plain areas in comparison to hilly areas. DDTs and HCHs were most frequently detected in the air samples. The high p,p'-DDT/(pp'-DDE + pp'-DDD) ratio as well as the low o,p'-DDT/p,p'-DDT ratio observed in this study was inferred as continuing use of technical DDT. High levels of ∑26PCBs were linked to proximity to highly urbanized and industrial areas, indicating the potential source of PCBs. The measured concentrations of legacy POPs in air from this study is assumed to represent a negligible health risk through inhalation of ambient air, however, other modes of human exposure could still be relevant in Nepal. The air mass backward trajectory analysis revealed that most of the air masses sampled originated from India and the Bay of Bengal.

Occurrence, profile and spatial distribution of organochlorines pesticides in soil of Nepal: Implication for source apportionment and health risk assessment.

Nepal is a landlocked country located between world's two most populous countries-India and China where high level of organochlorines pesticides has been reported from multi-environmental matrices. In this study, we investigated the occurrence, distributions and profile of selected OCP chemicals in surface soil samples (N=72) from four major cities of Nepal. Overall, the sum of total OCPs in soil ranged from 20 to 250ng/g with Biratnagar being the most polluted site in Nepal. DDTs and endosulfans were the most abundant OCP chemicals in soil samples. The concentration of DDTs ranged from 8 to 230ng/g, 8-56ng/g, 8-63ng/g, and 8-27ng/g in surface soil, while endosulfans were in the range of 2.9-3.3ng/g, 2.8-8.7ng/g, 2.8-3.4ng/g, 2.8-3.2ng/g in Biratnagar, Kathmandu, Pokhara and Birgunj, respectively. The isomeric ratio of DDT and their metabolites suggested the ongoing usages of technical DDT as well as dicofol in this region. Lower ratio of α/ß-endosulfan indicated past application of endosulfans in Nepal. HCHs were less detected OCPs in soil sample accounting only 4-9% of ∑OCPs. The isomeric ratio of α-/γ-HCH indicated that the HCHs may be originated from mixed source of technical HCH as well as lindane use. Scattered plot of TOC and BC showed they were weakly and positively related with concentration of OCPs in soil. Health risk assessment modeling study of OCPs in soil suggested moderate cancer risk with ingestion being the most potential pathway of OCPs exposure.

Environmental carcinogenic polycyclic aromatic hydrocarbons in soil from Himalayas, India: Implications for spatial distribution, sources apportionment and risk assessment.

The Indian Himalayan Region (IHR) is one of the important mountain ecosystems among the global mountain system which support wide variety of flora, fauna, human communities and cultural diversities. Surface soil samples (n = 69) collected from IHR were analysed for 16 priority polycyclic aromatic hydrocarbons (PAH) listed by USEPA. The ∑16PAH concentration in surface soil ranged from 15.3 to 4762 ngg(-1) (mean 458 ngg(-1)). The sum total of low molecular weight PAH (∑LMW-PAHs) (mean 74.0 ngg(-1)) were relatively lower than the high molecular weight PAH (∑HMW-PAHs) (mean 384 ngg(-1)). The concentration of eight carcinogenic PAHs (BaA, CHR, BbF, BkF, BaP, DahA, IcdP, BghiP) were detected high in mountain soil from IHR and ranged from 0.73 to 2729 ngg(-1) (mean 272 ngg(-1)). Based on spatial distribution map, high concentration of HMW- and LMW-PAHs were detected at GS1 site in Guwahati (615 and 4071 ngg(-1)), and lowest concentration of HMW-PAHs were found at IS6 in Itanagar (5.80 ngg(-1)) and LMW-PAHs at DS2 (17.3 ngg(-1)) in Dibrugarh. Total organic carbon (TOC) in mountain soil was poorly connected with ∑PAHs (r(2) = 0.072) and Car-PAHs (r(2) = 0.048), suggesting the little role of TOC in adsorption of PAHs. Isomeric ratio of PAHs showed the source of PAH contamination in IHR is mixed of petrogenic and pyrogenic origin and was affirmed by PAHs composition profile. These source apportionment results were further confirmed by principal component analysis (PCA). Eco-toxicological analysis showed the calculated TEQ for most carcinogenic PAH were 2-4 times more than the Dutch allowed limit, while TEQ of BaP was 25 times high, suggesting increasing trend of carcinogenicity of surface soil.

Spatial distribution, source apportionment and ecological risk assessment of residual organochlorine pesticides (OCPs) in the Himalayas.

The Indian Himalayan Region (IHR) is one of the important mountain ecosystems among the global mountain system which support wide variety of flora, fauna, human communities and cultural diversities. Surface soil samples collected from IHR were analysed for 23 organochlorine pesticides (OCPs). The concentration of ∑OCPs ranged from 0.28 to 2143.96 ng/g (mean 221.54 ng/g) and was mostly dominated by DDTs. The concentration of ∑DDTs ranged from 0.28 to 2126.94 ng/g (mean 216.65 ng/g). Other OCPs such as HCHs, endosulfan and heptachlor, Aldrin and dieldrin were detected in lower concentration in IHR. Their concentrations in soil samples ranged from ND to 2.79 ng/g for HCHs, ND to 2.83 ng/g for endosulfans, NDto 1.46 ng/g for heptachlor, ND to 2.12 ng/g for Aldrin and ND to 1.81 ng/g for dieldrin. Spatial distribution of OCPs suggested prevalence of DDTs and HCHs at Guwahati and Itanagar, respectively. The close relationship between total organic carbon (TOC) and part of OCP compounds (especially α- and γ-HCH) indicated the important role of TOC in accumulation, binding and persistence of OCP in soil. Diagnostic ratio of DDT metabolites and HCH isomers showed DDT contamination is due to recent application of technical DDT and dicofol, and HCH contamination was due to mixture of technical HCH and lindane source. This was further confirmed by principal component analysis. Ecological risk analysis of OCP residues in soil samples concluded the moderate to severe contamination of soil.