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

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.

Polychlorinated biphenyls in Nepalese surface soils: Spatial distribution, air-soil exchange, and soil-air partitioning

Regardless of the ban on the polychlorinated biphenyls (PCBs) decade ago, significant measures of PCBs are still transmitted from essential sources in cities and are all inclusive ecological contaminants around the world. In this study, the concentrations of PCBs in soil, the air-soil exchange of PCBs, and the soil-air partitioning coefficient (K_SA) of PCBs were investigated in four noteworthy urban areas in Nepal. Overall, the concentrations of ∑₃₀PCBs ranged from 10 to 59.4ng/g dry weight; dw (mean 12.2ng/g ±11.2ng/g dw). The hexa-CBs (22-31%) was most dominant among several PCB-homologues, followed by tetra-CBs (20-29%), hepta-CBs (12-21%), penta-CBs (15-17%) and tri-CBs (9-19%). The sources of elevated level of PCBs discharge in Nepalese soil was identified as emission from transformer oil, lubricants, breaker oil, cutting oil and paints, and cable insulation. Slightly strong correlation of PCBs with TOC than BC demonstrated that amorphous organic matter (AOM) assumes a more critical part in holding of PCBs than BC in Nepalese soil. The fugacity fraction (ff) results indicated the soil being the source of PCB in air through volatilization and net transport from soil to air. The soil-air partitioning coefficient study suggests the absorption by soil organic matter control soil-air partitioning of PCBs. Slightly weak but positive correlation of measured Log K_SA with Log K_OA (R² = 0.483) and Log K_BC-A (R² = 0.438) suggests that both Log K_OA and Log K_BC-A can predict soil-air partitioning to lesser extent for PCBs.

Levels and Sources of Organochlorine Pesticides in Surface Sediment from Anhui Reach of Huaihe River, China

Twenty-two organochlorine pesticides (OCPs) were investigated in Anhui reach of Huaihe river, China. Seventeen out of 22 OCPs were detected by GC-MS. The mean concentrations of OCPs followed the order: HCHs > DDTs > HCB > chlordanes > endosulfans. Levels of total HCHs and total DDTs ranged from 2.54 to 13.91 ng g^-1 (mean = 7.52 ng g^-1) and 0.016 to 2.54 ng g^-1 (mean = 0.45 ng g^-1), respectively. The concentrations of DDTs were lower than those of HCHs. Compared with the other rivers in China, DDTs and HCHs were relatively lower or similar. Statistical analysis indicated that the OCPs concentration differences were not insignificant between upstream, midstream and downstream. The compound compositions suggested that historical usage of lindane and fresh DDT were the main sources. The regression analysis indicated that TOC has influence on the levels of HCHs and little influence on the levels of DDTs in the sediments.

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.