A. L. Ramanathan

Tracing the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain, India: a source identification perspective

Arsenic contamination in groundwater is of increasing concern because of its high toxicity and widespread occurrence. This study is an effort to trace the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain of India through major ion chemistry, arsenic speciation, sediment grain-size analyses, and multivariate statistical techniques. The study focuses on the distinction between the contributions of natural weathering and anthropogenic inputs of arsenic with its spatial distribution and seasonal variations in the plain of the state Bihar of India. Thirty-six groundwater and one sediment core samples were collected in the pre-monsoon and post-monsoon seasons. Various graphical plots and statistical analysis were carried out using chemical data to enable hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies, and factors controlling groundwater quality. Results suggest that the groundwater is characterized by slightly alkaline pH with moderate to strong reducing nature. The general trend of various ions was found to be Ca2+xa0>xa0Na+xa0>xa0Mg2+xa0>xa0K+xa0>xa0NH4+; and HCO3−xa0>xa0Cl−xa0>xa0SO42−xa0>xa0NO3−xa0>xa0PO43−xa0>xa0F− in both seasons. Spatial and temporal variations showed a slightly higher arsenic concentration in the pre-monsoon period (118xa0μg/L) than in the post-monsoon period (114xa0μg/L). Results of correlation analyses indicate that arsenic contamination is strongly associated with high concentrations of Fe, PO43−, and NH4+ but relatively low Mn concentrations. Further, the enrichment of arsenic is more prevalent in the proximity of the Ganges River, indicating that fluvial input is the main source of arsenic. Grain size analyses of sediment core samples revealed clay (fine-grained) strata between 4.5 and 7.5xa0m deep that govern the vertical distribution of arsenic. The weathering of carbonate and silicate minerals along with surface-groundwater interactions, ion exchange, and anthropogenic activities seem to be the processes governing groundwater contamination, including with arsenic. Although the percentage of wells exceeding the permissible limit (50xa0μg/L) was less (47%) than that reported in Bangladesh and West Bengal, the percentage contribution of toxic As(III) to total arsenic concentration is quite high (66%). This study is vital considering that groundwater is the exclusive source of drinking water in the region and not only makes situation alarming but also calls for immediate attention.

Transport and distribution of heavy metals in Cauvery river

Heavy metal transport in Cauvery river chiefly takes place in the particulate form. Tributaries Hemevathi and Kabini draining highly mineralized areas contribute significantly to the heavy metal load of the Cauvery river. Particulate metal transport is influenced by the presence of major dams built across the river. Factor analysis of the elemental data identifies two major group of heavy metals, (a) Fe, Mn, Cr, V and Ti and (b) Cu, Pb and Zn in the suspended sediments of Cauvery river. Heavy metals in surface sediments show wide variations in their concentrations due to the non-uniform grain size distribution of the sediments. The elements Fe, Mn, Pb, Cu, Zn, Ni, Co and As are dominantly present in the <20 μm fraction of the river sediments. Speciation studies show that Fe-Mn oxide phase held the largest share of heavy metals in the sediments. The depth variation of heavy metals in the core sediments suggest their similar mobility during diagenesis. Geoaccumulation indices calculated suggest that Cd, Zn, Cr, Pb, Cu and Ni are enriched in sediments several times over background values.

Quantification and distribution of heavy metals from small-scale industrial areas of Kanpur city, India

Kanpur city has large number of small-scale industries (SSIs), primarily comprising of textile and leather industries. This study inventorises the presence of heavy metals in the samples collected from Panki and Jajmau Industrial Areas of Kanpur city. The bulk concentration of heavy metals found in solid waste samples was Fe as 1885 and 2340 mg/kg, Mn 173 and 445 mg/kg, Zn 233 and 132 mg/kg, Cu 20 and 28 mg/kg, Cd 1.4 and 1.1mg/kg, Ni 26 and 397 mg/kg, Pb 107 and 19 mg/kg, Cr 1323 and 734 mg/kg, respectively. Heavy metal concentration was also found to be high in soil and road dust samples viz. Ni and Pb were in higher concentration in few samples, whereas Cr was found in higher concentration in all samples than the recommended values of USEPA and specifications for compost quality contained in the Indian Municipal Solid Wastes (Management and Handling) Rules, 2000. The heavy metal pollution so detected is indicative of contamination in ground and surface water and food chain. This raises concerns pertaining to adverse consequences to environment and human health.

Geochemistry of the Cauvery Estuary, East Coast of India

Major ion chemistry of water and elemental geochemistry of suspended and surficial sediments collected from the Cauvery Estuary were studied to understand the geochemical processes in this tropical estuarine system. Specific conductance (EC), total dissolved solids (TDS), and total suspended matter (TSM) increased conservatively with increasing chlorinity. In general, SO42−, Na, K, Ca, and Mg showed an increasing trend while H4SiO4 and PO43− showed a decreasing trend toward the sea. Additional removal mechanisms operating for these ions in the Cauvery Estuary have been identified based on observed concentrations. Factor analysis pointed out the sources contributing to the observed trends in estuarine water chemistry. POC and PON decreased toward the high chlorinity zone. TSM in the Cauvery Estuary were mostly of inorganic nature. Stable carbon isotope values showed that the carbon was equally of marine and terrestrial origin and helped to delineate the contribution of river water and seawater. The ϕ mean size (a logarithmic grain size scale commonly used by sedimentologists) indicated that the surficial sediments were primarily comprised of coarse and silt, whereas suspended sediments were principally silt and clay. Suspended sediments were enriched in clays compared to surficial sediments. Quartz and feldspar were abundant among detritals while chlorite, kaolinite, and montmorillonite were dominant among clays. Silicon was the most abundant element in the sediments followed by Al, Ca, Na, K, Fe, Mn, and P. Heavy metals were enriched in the suspended sediments compared to the surficial bottom sediments as follows: Fe = 3.5, Mn = 7.4, Pb = 1.1, Zn = 15.2, Cu = 7.4, and Cr = 4.0. The levels of Cd, Cr, Zn, and Fe increased up the middle reaches and then decreased toward the sea due to urban effluent and fertilizer input. Size fractionation studies indicated that the metal concentration in the finer fraction was 50% higher by mass than the coarse silt and fine silt fractions. Chemical fractionation studies showed that the abundance of metals were in the order of residual > organic/sulfide > carbonate > Fe/Mn oxide > exchangeable fractions.

Chemical fractionation and translocation of heavy metals in Canna indica L. grown on industrial waste amended soil

A pot experiment was carried out to assess the effect of different amendments of industrial sludge on the growth of Canna indica L. as well as the translocation potential of heavy metals of this plant. The accumulation of metals (Cr, Fe, Cd, Cu, Ni, Zn, Mn and Pb) in different parts of C. indica L. grown on industrial sludge-amended soil increased with time and increasing doses of sludge amendments. Sequential extraction method was followed to estimate the different fractions of heavy metals in sludge-amended soils collected from different periods of this study. The results showed that Mn, Zn, Cd, Cr and Pb were mostly associated with Fe-Mn oxide fraction in all amendments, whereas, Ni was mostly found in residual (RES) fraction. Cu and Fe were found to be higher in organically bounded form (OM) and RES fraction. The metal concentration in C. indica L. after 90 days of experiment started, was in the order of Fe>Cr>Mn>Zn>Ni>Cu>Cd>Pb and the metal translocation was found lesser in shoot. With the increasing percentage of sludge amendments in soil the metal concentrations increased in different parts of plants. Overall, the plant C. indica L. was found to be well adapted in industrial sludge amendments and it may be recommended that this plant was found suitable for phytoremediation of most of the studied metals.

Sediment transport in the Cauvery River basin: sediment characteristics and controlling factors

Abstract During the monsoon period, 75% of the annual rainfall, 73% of the annual water discharge and 85% of the annual sediment transport takes place in the Cauvery River. Basin geology and river water discharge are the major natural factors controlling the sediment transport. Sediment transport in the Cauvery River is greatly influenced by the presence of two major dams built across the river. An examination of the particle-size distribution of the suspended sediments shows that the less than 20 μm fraction accounts for nearly 60% of the total sediment transported by the river. At dam sites, coarse sediments are selectively removed from the suspended load. The suspended mineralogy is dominated by quartz and feldspar, followed by clay minerals and carbonates. Clay minerals average about 30% and are dominated by the montmorillonite type. The results of our study also demonstrate the importance of such sediment characteristics as particle size and mineralogy in controlling the trace metal distribution in sediments.

Nature and transport of solute load in the cauvery river basin, India

Abstract The nature of solute transport in the Cauvery river was studied during a 5 year period (1985–1989). On the basis of our analytical results, the discharge weighted average chemical composition of the Cauvery river has been computed and compared with major rivers of India and the world. The chemical composition of Cauvery river water is dominated by Na and HCO 3 . The river water chemistry strongly reflects the dominance of continental weathering and impact by atmospheric precipitation. The river water composition is increasingly dominated by Na and Cl in the downstream region of the river, indicating the influence of airborne salts with oceanic affinities. The observed chemical data of the Cauvery river water was used to predict the mineral assemblages in the carbonate and alumino-silicate system and compared with observed mineralogical composition of suspended sediments. Over 90% of the material transported in the Cauvery river is transported in dissolved form. The total dissolved material transported from the Cauvery to the Bay of Bengal accounts for 14% of the annual flux of dissolved load from Indian rivers to the neighboring seas.

Study on the hydrogeochemical characteristics in groundwater, post- and pre-tsunami scenario,from Portnova to Pumpuhar, southeast coast of India

Natural hazards cause great damage to humankind and the surrounding ecosystem. They can cast certain indelible changes on the natural system. One such tsunami event occurred on 26 December 2004 and caused serious damage to the environment, including deterioration of groundwater quality. This study addresses the groundwater quality variation before and after the tsunami from Pumpuhar to Portnova in Tamil Nadu coast using geochemical methods. As a part of a separate Ph.D. study on the salinity of groundwater from Pondicherry to Velankanni, water quality of this region was studied with the collection of samples during November 2004, which indicated that shallow aquifers were not contaminated by sea water in certain locations. These locations were targeted for post-tsunami sample collection during the months of January, March and August 2005 from shallow aquifers. Significant physical mixing (confirmed with mixing models) within the aquifer occurred during January 2005, followed by precipitation of salts in March and complete leaching and dissolution of these salts in the post-monsoon season of August. As a result, maximum impact of tsunami water was observed in August after the onset of monsoon. Tsunami water inundated inland water bodies and topographic lows where it remained stagnant, especially in the near-shore regions. Maximum tsunami inundation occurred along the fluvial distributary channels, and it was accelerated by topography to a certain extent where the southern part of the study area has a gentler bathymetry than the north.

Characterization of phosphorus fractions in the sediments of a tropical intertidal mangrove ecosystem

Solid phases of phosphorus fractions in the surface and core sediments were studied to understand the biogeochemical cycling and bioavailability of phosphorus in the Pichavaram intertidal mangrove sediments of India. Total P in surface and core sediments ranged between 451–552 and 459–736xa0μgxa0g−1 respectively and Fe bound P was the dominant fraction. Low levels of Fe bound P in the mangrove zone than the two estuarine zones may be because of high salinity inhibition of phosphate adsorption onto the Fe-oxides/hydroxides. Post-depositional reorganization of P was observed in surface sediments, converting organic P and Fe bound P into the authigenic P. High levels of organic P in the mangrove zone is primarily due to intensive cycling and degradation of organic matter and adsorption of phosphate on the organic molecules. The burial rates and regeneration efficiency of P in the intertidal mangrove ecosystem ranged from 5.41 to 7.27xa0μmol P cm−2xa0year−1 and 0.122 to 0.233xa0μmol P cm−2 year−1, respectively. High burial efficiency (≈99%) of P proves the earlier observation of limiting nature of P for the biological productivity. Further, bioavailable P (exchangeable Pxa0+xa0Fe bound Pxa0+xa0organic P) constituted a considerable proportion of sedimentary P pool of which an average accounted for 55 and 50% in surface and core sediments respectively. The results indicate that significant amount of P is locked in sediments in the form of authigenic P and detrital P which makes P as a limiting nutrient for the biological productivity.

Sediment and heavy metal accumulation in the Cauvery basin

Eleven cores were collected from the Cauvery basin. Radiometric dates were used to determine modern sediment accumulation rates. Sediment accumulation rates ranged from 0.4 to 4 mm yr−. Heavy metal concentration decreases with the increase of depth. The heavy metal concentrations at certain depths are attributed to the irregular input of metals and their remobilization. Heavy metal accumulations have been computed using sediment accumulation rates, and accumulation rates show an additional anthropogenic input of metals and sediments in the recent past. Factor analysis and correlation analysis show the diverse source and accumulation mechanism influencing the metal distribution in the basin.