METAL SPECIATION IN THE YAMUNA RIVER WATER AND SEDIMENTS

Abstract

The pollution of riverine system by heavy metals has attracted a lot of attention of the scientific community. Metals gain access to aquatic environment by natural processes viz., weathering of soils and rocks, volcanic eruptions and from a variety of human activities. These metals may be present in diverse forms. Moreover, the forms may change with the existing physico-chemical environment. Since each form may have different bioavailability and toxicity, the environmentalists are rightly concerned about the exact forms of metal present in the aquatic environment. The measurement of total metal may not be able to provide information about the exact dimension of pollution and thus the metal speciation assumes great importance. The Yamuna is one of the major rivers of the country and traverses a distance of 1,376 km from its source in Himalayas to its confluence with river Ganga at Allahabad. The catchment of river extends to Uttar Pradesh, Himachal Pradesh, Haryana, Rajasthan and Madhya Pradesh and the entire union territory of Delhi. In addition to the traditional and religious bearings associated, the waters of Yamuna are being used for irrigation, domestic and industrial purposes. During the past forty years there has been a rapid industrial development in the Yamuna basin. A number of towns and cities in this area have very little or no waste treatment and disposal facilities. Most of the domestic and industrial waste thus gains access into the river. As a result some pockets of the river are believed to be VI intensely polluted and serve as reservoirs of variety of organics and inorganics. Some of the tributaries which meet Yamuna at different points also transfer some of their pollutional load to it. Inspite of the significance of Yamuna for a large population of the Northern region of India, no systematic metal speciation studies of its water and sediments had been carried out. Moreover, the available data on the spatial and temporal variations of different water quality parameters was not adequate. In this light, a study was conducted on the river Yamuna during 1988-89 by collecting water and bed sediment samples at seven selected sites from Dakpathar to Agra in three different seasons of the year i.e., postmonsoon (Sept.- Oct. '88), winter (Dec. '88 - Jan. '89) and summer (May - June '89). The selection of the sampling stations was based on the consideration of maximum representativeness and approachabi1ity. For convenience and clarity of presentation, the subject matter of the thesis has been divided into following six chapters: I. General Introduction II. System Under Study III. Materials and Methods IV. Physico-chemical Characteristics of the Yamuna Water V. Speciation of Cu, Zn, Cd and Pb of the Yamuna Water VI. Characterisation and Metal Speciation of the Bed Sediments of Yamuna . Vll Chapter I presents a brief background of environmental pollution with special reference to metal pollution in the riverine system. A review of pertinent literature available on the metal pollution of river waters and sediments has been presented. The need of metal speciation in water and sediment samples is highlighted and various approaches for measurement are discussed. Based on the available information, the objectives of the work embodied in the thesis have been defined. Chapter II deals with a detailed description of topography, lithology, soil types, climatic features, industrial activities and land-use of the Yamuna basin. The relevant details of the sites and the activities are cited. ^Chapter III gives the details of the mode of sampling and its frequency, preservation of samples and the methodology used for the analysis of the physico-chemical parameters. The procedures followed for speciation of metals in river water and bed sediments are also given. Metal analysis was carried out using Inductively Coupled Plasma Atomic Emission Spectrometer (Plasmalab 8440). Voltammetric measurements were made with PARC Polarographic Model 384B in combination with static Hg drop electrode and Ag/AgCl reference electrode.^/^ Chapter IV presents the results of the physico-chemical parameters in the river water. The pH, alkalinity and suspended solids ara consistently higher in the postmonsoon season. This reflects on the alkaline nature of the washouts added during the Vlll monsoon season. At Dakpathar COD, BOD and TDS are invariably the lowest. This is beacause of no intense human activity upstream. The river downstream receives different types of pollutants due to various industrial and domestic activities and there is an increasing trend in their values. The dissolved oxygen at ITO bridge, Delhi is exceptionally low and ammonical nitrogen is quite high in winters and summers because of accumulation of large amount of organic matter. The chlorides show a gradual increase from Dakpathar to Agra because of the prominence of domestic activities. Hardness values are the highest in the winters as the river is basically fed with ground water during this season. With a few exceptions, there are no significant spatial and temporal variations in the total cadmium content. Slightly higher values of cadmium concentration observed in winters at Mathura and Agra can be attribued to more intense activity of dyeing industries located in the region. Soluble cadmium shows a more or less constant value throughout the stretch in all the seasons. Total copper which is about tenfold higher in postmonsoon season than that in winter and summer seasons, remains more or less constant throughout the entire stretch of investigation. The higher values in the postmonsoon may be attributed to the washouts added to the river during monsoon season in its flow in the upper hilly stretch. This is confirmed by the fact that most of the copper is in the particulate form. In the winters and the summers both total and dissolved copper shows a gradual increase downstream from Dakpathar to Agra. The IX concentration of lead increases gradually from Dakpathar to ITO bridge and suddenly shoots up at Okhla barrage, Delhi, and thereafter remains almost constant. The appreciably high value at Okhla barrage is due to the confluence of Hindon river with Yamuna at this site. Hindon water is reported to have high lead concentration. The soluble lead, with a few exceptions, shows a trend of gradual increase from Dakpathar to Agra. The zinc concentration increases beyond Dakpathar probably due to contribution from agricultural runoff and industrial effluents. Chapter V presents the results of metal speciation of the river water. The three physico-chemical forms distinguished are particulate bound, bound in the dissolved form and labile. The studies indicate that a larger percentage of copper, zinc, cadmium and lead are in the bound form (particulate or dissolved) while lead is labile. An attempt has also been made to further classify the soluble metal into very labile, moderately labile, slowly labile and inert fractions by using Anodic Stripping Voltammetry in conjunction with ion exchange (chelex resin) chromatography. This study conducted on the postmonsoon samples reveals that cadmium is mostly found in very labile and moderately labile fractions; copper and zinc in moderately labile and slowly labile forms while significant fraction of lead is inert. No prominent spatial variations in the above pattern have been observed. . Chapter VI contains the results of the sediment characteristics and the metal speciation in them. The sediment characteristics do not show any prominent variation except that carbonate content is consistently higher in postmonsoon season due to the leaching of limestones in the upper hilly stretch of the river during monsoon. Silicon and aluminium are most abundant elements and the essential minerals are quartz and biotite. The speciation results reveal that out of the elements studied, cadmium concentration in the sediments is the lowest but it is mostly in the mobile form. As the total lead in the sediments is quite high, even its lower percentage bound to carbonate can pose environmental problems. Most of copper and zinc are associated with organic matter, Fe-Mn oxides and residual fractions, thus being less labile. Positive correlations are obtained between some of the sediment constituents and the various fractions of metals associated with them. An attempt has also been made to correlate the water quality and the bed sediment characteristics and also the speciation profiles observed in the two phases.