Raza Rafiqul Hoque

Seasonal attributes of urban soil PAHs of the Brahmaputra Valley.

Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous organic pollutants, which are both toxic and carcinogenic. In the present study seasonally collected composite soil samples of Guwahati city of the Brahmaputra Valley were analysed for of PAHs by HPLC column. Black carbon (BC) and organic carbon (OC) of soil samples were analysed by thermochemical oxidation method in a TOC analyzer. Mean concentrations of ∑PAHs (USEPA 16) were found to be 5570168±7003, 9052±1292 and 19294±17827 ng g(-1) during monsoon, pre- and post-monsoon seasons, respectively. Two- and 4-ring PAHs dominated and the 2-ring PAHs were particularly abundant during post-monsoon period. The carcinogenic potentials of PAHs were calculated as BaP equivalents, which was found to be maximum (1167.064 ng Ba Pq g(-1)) at industrial site. Diagnostic ratios of marker species indicated for pyrogenic origins of PAHs. Sources were indentified and contribution of individual sources was quantified by multivariate hyphenated model - Principal Component Analysis-Multiple Linear Regression (PCA-MLR). Mobile sources like the vehicular traffic were found to have contributed ∼63% to the PAHs load. The correlations of individual PAHs with BC or OC showed seasonal variations. High dependencies of PAHs on BC/OC ratios were found indicating that BC could be interfering with the association of PAHs and OC. However, such relationships showed seasonal bias and high positive dependencies were found during pre-monsoon period only. Strong relationships were found between PAHs and BC/OC during monsoon and post-monsoon seasons.

Bioavailability and health risk of some potentially toxic elements (Cd, Cu, Pb and Zn) in street dust of Asansol, India

Street dust samples were collected from five different types of land use patterns (busy traffic zone, urban residential area, national highways, industrial area and sensitive area) in a medium sized industrial city Asansol, India. The samples were fractionated into ≤53µm and analyzed for potential toxic elements (PTEs) viz. Zn, Cd, Pb and Cu. The mean total concentration of Zn, Cd, Pb and Cu in the urban street dust samples were 192, 0.75, 110 and 132mgkg-1 respectively. Chemical speciation was performed for PTEs to evaluate the bio-available fractions. Cu was mostly associated with organic matter phase while Zn, Pb and Cd with residual phase. Mean mobility factor (MF) for heavy metals in Asansol was Zn (54.6%)>Pb (49.1%)>Cu (25.3%)>Cd (22.7%). Geo-chemical indices such as Enrichment Factor (EF), geo-accumulation index (Igeo) and contamination Factor (CF) were in the order of Pb>Cd>Zn>Cu. Cluster analysis was done to understand the similarities among the sites. The risks of all metals was calculated with mobile fraction, which indicated actual risk due to PTEs was less (HI<1).

Sources of polycyclic aromatic hydrocarbons in sediments of the Bharalu River, a tributary of the River Brahmaputra in Guwahati, India.

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 possible sources and potential hazards in the Bharalu tributary of the Brahmaputra River flowing through Guwahati city in India. The USEPAs 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 ± 12 and 21.9 ± 27 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 >1 indicating severe hazards during post-monsoon and pre-monsoon season. A very high percentage of coefficient of variation (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.

Source and seasonal variation in the major ion chemistry of two eastern Himalayan high altitude lakes, India

A chemical survey of two high-altitudes lakes, i.e., Tsokyo Tso and Sella, was conducted during pre-monsoon (May) and post-monsoon (November) 2011. Lake water is found to be pure with very low EC values even lesser than rainwater. This shows where lake water receives most of its contribution. A comprehensive and systematic study on the seasonal pattern of major ions (Cl−, PO43−, HCO3−, NO3−, SO42−, Na+, K+, Ca2+, Mg2+, and SiO2) was carried out to understand the geochemical processes controlling water quality. There was marked seasonal variation observed for almost all ions. Factor analysis identifies geochemical controls, snow melting, and evaporative enrichment as main controlling factor. The partial pressure of CO2 (pCO2) value has increased in the post-monsoon probably due to higher atmospheric CO2 during winter. Overall, factor analysis identified processes like geochemical control, snowmelt water input, and evaporative enrichment in the pre-monsoon, atmospheric input and dilution of ions due to rainfall, microbial activities, and accumulation of weathered material lake system in the post-monsoon as governing processes switching among themselves in different seasons. HYSPILT back trajectory model was used to trace the source of long-range transport of pollutant. Results show for both the lakes that air arriving to the vicinity of the lake has an origin from the southeast direction during pre-monsoon and the mid-Gangetic plain during post-monsoon season, respectively. The results show that both the studied lakes have significant impacts of long-range transport of air pollutants rather than local interferences. Long-term monitoring of the fluctuation in key parameters can further verify the findings of this study.

Distribution and solid-phase speciation of toxic heavy metals of bed sediments of Bharali tributary of Brahmaputra River

Heavy metal (Fe, Mn, Zn, Cu, Ni, Pb, and Cd) concentrations and their chemical speciations were investigated for the first time in bed sediments of Bharali River, a major tributary of the Brahmaputra River of the Eastern Himalayas. Levels of Fe, Mn, Pb, and Cd in the bed sediments were much below the average Indian rivers; however, Cu and Zn exhibit levels on the higher side. Enrichment factors (EF) of all metals was greater than 1 and a higher trend of EF was seen in the abandoned channel for most metals. Pb showed maximum EF of 32 at site near an urban center. The geoaccumulation indices indicate that Bharali river is moderately polluted. The metals speciations, done by a sequential extraction regime, show that Cd, Cu, and Pb exhibit considerable presence in the exchangeable and carbonate fraction, thereby showing higher mobility and bioavailability. On the other hand, Ni, Mn, and Fe exhibit greater presence in the residual fraction and Zn was dominant in the Fe–Mn oxide phase. Inter-species correlations at three sites did not show similar trends for metal pairs indicating potential variations in the contributing sources.

Source contributions of Polycyclic Aromatic Hydrocarbons in soils around oilfield in the Brahmaputra Valley.

Surface soils from Borholla oilfield in the upper Brahmaputra Valley in India were studied for the USEPAs 16 priority Polycyclic Aromatic Hydrocarbons (PAHs). Analysis of PAHs was carried out by high performance liquid chromatography (HPLC) system equipped with an UV detector. Seasonality in PAHs concentrations was evident and the concentrations were found to be greater in post-monsoon season. There has been a dominance of low molecular weight PAHs (80-90% of total PAHs) indicating recent deposition from combustion sources. The concentration profiles appeared in the decreasing order of 3-ring >2-ring >4-ring >5-ring >6 ring PAHs. The sources of PAHs were identified using isomer pair ratios and Principal Component Analysis-Multiple Linear Regression (PCA-MLR) and Positive Matrix Factorisation (PMF). The ratios of diagnostic pairs indicated for both pyrogenic and petrogenic input of PAHs. The PCA-MLR modelling revealed that the <16% of contribution came from petrogenic origin and the rest 85% was found to be from pyrogenic sources. The PMF model also shown that <19% of PAHs source were petrogenic origin whereas rest from pyrogenic origin. The correlations of black carbon (BC) with PAHs also supported the pyrogenic contribution. The analysis of air mass back trajectories revealed that there has been contribution of both local and distant sources, through long range transport of pollutants, which were deposited to the site.

Spatial and Seasonal Variations of Water Soluble Ions in PM10 of Mid-Brahmaputra Plain of Assam Valley

A year-long study on water soluble ionic constituents of PM10 was conducted at mid-Brahmaputra plain during 2012-2013. Water soluble ions associated with PM10 viz. SO4 2-, NO3 -, Cl-, F-, NH4 +, K+, Ca2+, Na+ and Mg2+ were analyzed using Ion chromatograph (Metrohm 882 Compact IC Professional) for three representative sites. Marked differences were observed regarding PM10 loading and concentrations of major ions in three different sites, with maximum PM10 (71.1±56 μg/m 3) at urban site. Among anions, dominance of SO4 2and Clwere observed and Na+, NH4 + and K+ were found to be predominant cations. An explicit seasonal variation of ionic constituents was observed during the study period with maximum abundance of ions during winter season, and SO4 2was the most abundant ion during all the seasons. Pre-monsoon season showed influence of crustal input with high mass concentrations of Ca2+ and Na+ in PM10.The equivalent ion balance reveals the fact that except winter season, all other seasons experienced alkaline nature of particulates in the atmosphere. Influence of anthropogenic activities to the ionic constitutions of PM10 was revealed by calculating ionic ratios and enrichment factor. HYSPLIT trajectory analysis showed influence of long-range transport of pollutants to this region.