Environmental pollution in India: heavy metals and radiogenic elements in Nacharam Lake.
The Nacharam Industrial Development Area is situated in the northeastern part of Hyderabad, the capital city of the state of Andhra Pradesh in India. Approximately 100 industries, including steel manufacturing, chemical manufacturing, and breweries, are located in the area. Residents in the surrounding area use groundwater for their day-to-day needs. It is therefore essential to determine the level of contamination of the water. The National Geophysical Research Institute (NGRI) has been studying the extent of pollution from natural as well as anthropogenic sources in Nacharam Lake. Special attention has been paid to radiogenic elements such as uranium and thorium.
Contamination of soils with heavy metals has posed problems for quite some time in industrialized countries (1). The formation of complexes with dissolved inorganic and organic ligands and high background concentrations of metals increases the mobility of trace metals in soil. Mobility also is influenced by pH, soil cation exchange capacity, soil redox potential, and organic complexation (2). In India, a tropical country, organic matter has a very, high decomposition rate. Basically, metals are accommodated in three reservoirs: water, sediments, and biota. Nevertheless, heavy metals accumulate in the soil and present a serious long-term hazard (3-5). Not all heavy metals are harmful to humans, but very high concentrations are toxic in nature. Studies have shown that toxic metals in soil influence plants (6-10).
This study took water, soil, and rock samples from Nacharam Lake and surrounding areas and analyzed them to ascertain the extent of pollution from natural and anthropogenic sources such as industrial effluents and sewage discharge. An effort was also made to find out the extent of radiogenic [TABULAR DATA FOR TABLE 1 OMITTED] [TABULAR DATA FOR TABLE 2 OMITTED] elements present in the granites and lake sediments of the area.
Geology of the Area
Unclassified exposed Archean crystalline rocks in and around Hyderabad consist mainly of granite and gnieses and form part of the largest of all granite bodies recorded in peninsular India. Exposed granite batholith covers an area of 5,000 square kilometers and extends over several adjoining districts. To the west and north, the margins of this formation and its relationship with other rock formations are concealed by the Deccan trap lava flows. To the northeast, the formation is bounded by Pakhal metasediments, and to the south, it abuts the folded and highly disturbed metasediments of the Cuddapah formations.
Geology of the Study Area
The study area consists of one major rock formation of medium- to coarse-grained granite. The granite can be divided into two major varieties according to color: gray granite and pink granite. Both varieties occupy large parts of the area, and it is practically impossible to draw a line of demarcation between two types; they intermingle with no sharp points of contact. These granites are presumed to be part of the peninsular gneissic complex and to contain basic enclaves of aplite, pegmatite, epidote, and quartz veins. Dolerite dykes frequently traverse the granite as well.
Hydrogeologically, the area is classified as hard rocks composed of Archean granite. Groundwater generally occurs under the water table and in semiconfined conditions. Wells dug in this area have low capacity and tap only upper aquifers. The climate is tropical, characterized by a mean annual temperature of 20 [degrees] C. The dry season prevails for seven months from November to May.
In 1995, 1996, and 1997, water samples were collected from different parts of the lake during May, when the lake water recedes. Water samples were taken from the shore to avoid local contamination. Each sample was collected in two 1-liter polyethylene bottles. The water was immediately filtered, and a part of the sample was acidified and stored in a cool place for trace-metal analysis.
Most of the soil samples were collected from the surface - that is, from depths of 0 to 15 centimeters (cm). Some samples were also collected from a variety of depths of up to 100 cm. Soil samples were stored in sealed polyethylene bags so that evaporation could be checked.
Concentrations of trace elements in water, soil, and rock samples were analyzed with a Plasmaquad inductively coupled plasma (ICP) mass spectrometer. As an internal standard, a stock rhodium solution with a concentration of 1 milligram per liter (mg/L) was added to water and soil samples, forming 10 percent of the resulting working solution (11). Multi-element standard solutions with concentrations of 100 mg/L were used to calibrate for water analysis. National Institute of Standards and Technology (NIST) standard water samples 1643B and 1643C were used as reference materials for water analysis. For the soil analysis, Canadian reference samples SO-1 to SO-4 were used to check the accuracy of the data. International rock standards for granite were used to prepare the calibration curves for the analysis of the rock samples. Detection limits for all the trace elements were better than 1 nanogram per milliliter (ng/mL) (12).
Major oxides were determined with a Philips PW 1400 microprocessor-controlled, fully automatic X-ray fluorescence spectrometer with an on-line computer, a 100 kilovolt-ampere (kVA) X-ray generator, and a 72-position automatic sample changer (13). Soil samples were air-dried first and then dried overnight in an oven at 105 [degrees] C. Next, the samples were finely powdered, to a mesh size of -250. Twenty tons of pressure with a HERZOG hydraulic press produced 40-millimeter (40 mm) pressed pellets.
Results and Discussion
The diffusion and convection of water and industrial effluents through soil involve a series of complex processes that are very important in environmental studies (14). Trace-element data for the soil samples are reported in Table 1. Concentrations of heavy metals, such as lead, zinc, strontium, nickel, copper, and barium, exceeded the average abundance of these elements in soil (15, 16). Concentrations of other elements, such as scandium, vanadium, chromium, and cobalt, were well within the limits. Lead is removed rapidly from water when the water passes through soil or sediment because organic matter has a high capacity to bind lead firmly. As a result, lead concentration generally is low in water and quite high in soil samples. This study found concentrations of lead as high as 260 ppm; the normal lead content of surface soil is around 29 ppm (17, 18). In soil samples [TABULAR DATA FOR TABLE 3 OMITTED] collected in 1995, lead concentrations were lower than in samples collected in 1996. The difference may be due to anthropogenic activity.
TABLE 4 Trace Elements in Groundwater Samples(*) Element Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Vanadium 137.40 52.88 44.43 58.73 32.46 Manganese 89.14 112.40 9.04 7.39 8.48 Iron 60.39 63.80 42.30 27.81 66.54 Zinc 179.10 47.95 54.96 285.00 112.70 Arsenic 40.25 16.05 10.92 12.13 8.84 Selenium 4.55 2.77 1.34 4.07 7.14 Strontium 3881.00 916.30 632.20 1963.00 1457.00 Molybdenum 6.28 1.76 8.88 1.82 1.65 Barium 156.30 117.30 115.90 146.70 297.40 Lead 81.57 90.49 37.29 50.88 67.82 * Concentrations are in nanograms per milliliter. Samples 1, 2, and 3 are open-well samples. Sample 4 and Sample 5 are bore-well samples.
The synergistic effects of lead, copper, zinc, cadmium, and other heavy metals vary significantly with physical, chemical, and biological conditions (19). Organic material and organic-rich rocks, soil, sediments, and leaf litter collect and concentrate most of the heavy metals, thereby acting as a filtering system. This phenomenon poses a special problem under acidic conditions, which can release toxic metals (20). Lead concentrates in the soil surface. It moves downward with time, but movement is generally quite slow because lead compounds are relatively insoluble and surface organic fractions have significant binding capabilities (21, 22). It is well known that small amounts of lead can be taken up into the edible portion of plants and that larger amounts are found in plant roots.
Copper concentrations of up to 400 ppm were found in soil from the study area. This value is very high compared with the world average of 30 milligrams per kilogram (mg/kg) (10, 23). Barium concentrations of up to 2,200 ppm were found; the world average is rarely more than 570 ppm (24). The strontium concentration was double the world average of 280 ppm. Nickel values of 200 ppm were found, which also is very high for granitic terrain. Some forms of nickel are well-known carcinogens and may cause other kinds of diseases as well (25). Other highly toxic metals, which pose well-known health hazards, were found at concentrations higher than the permissible limits. In some samples, the concentration of cadmium was as high as 15 ng/mL. Arsenic was found at 40 ng/mL; the limit set by the World Health Organization (WHO) is only 10 ng/mL. Selenium was observed at just below the tolerance limit.
Table 1 shows uranium and thorium concentrations that were much higher than the world averages of 1 to 3 ppm for uranium and 10 to 15 ppm for thorium (18). Although these values are very high, they occur naturally in some parts of the granitic terrain of Hyderabad and do not have anthropogenic sources. Figure 1 shows locations from which samples were taken. When the high concentrations of uranium and thorium were found, samples were recollected and re-analyzed. After the results had been validated, the samples were sent to the Bhabha Atomic Research Center in Bombay for neutron activation analysis. The values found by this method were in good agreement with the data reported by the ICP mass spectrometer laboratory of NGRI. This process established that natural sources have produced abnormally high concentrations of uranium and thorium in the soil samples taken from some parts of Nacharam. The presence of radiogenic elements can cause lung cancer, kidney failure, and many other diseases and may lead to environmental pollution. Proper care must be taken to prevent migration of these radiogenic elements to plants, animals, and the food chain.
Samples also were collected from the surrounding rocks, as well as from boulders in the middle of the lake. These samples were analyzed for all the major, minor, and trace elements. Trace-element concentrations presented in Table 2 fell within the normal range for granitic terrain, demonstrating that the high concentrations of these elements in soil or lake sediments did not derive from the surrounding rocks but likely were due to anthropogenic sources. Concentrations of uranium and thorium in the rock samples were 9.2 ppm and 68 ppm respectively, while much higher concentrations of 22 ppm for uranium and 83 ppm for thorium were found in the soil samples [ILLUSTRATION FOR FIGURE 2, FIGURE 3 OMITTED].
Figures 4 through 8 show that concentrations of heavy metals such as lead, nickel, copper, zinc, strontium, and barium were above permissible limits. Although these elements originated from surrounding industries, they were spread almost uniformly through Nacharam lake. (Strontium values varied in different parts of the lake because the background value of the strontium in the host rocks is quite high - up to 450 ppm.)
Table 3 presents trace-element data for lake water, and Table 4 presents data for groundwater. Concentrations of some heavy metals were above permissible limits. Lake water samples showed high concentrations of heavy metals such as strontium (1,141 ng/mL), cadmium (14.8 ng/mL), and barium (127 ng/mL). Well water samples had high concentrations of vanadium (137 ng/mL), manganese (112 ng/mL), zinc (285 ng/mL), strontium (3,881 ng/mL), barium (297 ng/mL), and lead (91 ng/mL). Most of the samples clearly demonstrated contamination by heavy metals both in lake water and in groundwater.
This study found that the soil in and around the Nacharam Industrial Development Area is highly contaminated with lead, nickel, copper, zinc, strontium, and phosphorus pentoxide. Concentrations of other heavy metals, such as scandium, vanadium, cobalt, and chromium fall well within permissible limits. Abnormally high concentrations of uranium and thorium were found in the sediment samples taken from Nacharam lake. Rock samples from the surrounding granitic terrain show high concentrations of uranium, thorium, strontium, and barium, indicating that the source of these elements is natural rather than industrial. Granitic rocks in Hyderabad have higher concentrations of uranium and thorium than the world average for acidic rocks.
In sediments, toxic metals may migrate vertically as well as horizontally. Toxic metals also may reach the groundwater by percolating through soil and may contaminate the water aquifer. Water samples from the lake indicate contamination by strontium, cadmium, and barium. Concentrations of some of the highly toxic metals such as arsenic and selenium were just below the permissible limits. The concentration of cadmium in two samples was slightly above the tolerance limit at 12 to 15 ng/mL. In lake sediment samples, concentrations of many heavy metals fell into normal ranges: this was the case for scandium, chromium, and cobalt. The well water samples showed pollution by vanadium, strontium, barium, and lead, which indicated that these heavy metals had percolated through the soil and contaminated the groundwater. In one groundwater sample taken from an open well (Groundwater Sample 2), arsenic concentration was 40 ng/mL which is considered high; WHO has reduced the arsenic tolerance limit from 50 to 10 ng/mL. A few sediment samples showed contamination by nickel, copper, and zinc. Most of the groundwater in the area is contaminated with heavy, metals and is not potable. The contamination was found to be uniformly distributed among dug wells and bore wells.
Regional geochemical mapping may provide useful baseline data that show the distribution of chemical elements naturally present in lake sediments, soil samples, and surrounding rocks. Mapping this kind of information will help delineate pollution that has anthropogenic sources and will help ascertain natural levels of radioactive elements such as uranium and thorium in and around Hyderabad.
Acknowledgements: The authors are extremely grateful to Dr. S. M. Naqvi of the National Geophysical Research Institute (NGRI) in Hyderabad for his keen interest, encouragement, and useful discussions. Thanks also are due to Dr T. M. Krishnamurty of the Bhabha Atomic Research Center in Bombay, who provided instrumental neutron activation analysis data for uranium and thorium. Dr. H. K. Gupta, NGRI director, very kindly supported and encouraged this study. The authors also thank Dr. Gupta for the permission to publish this paper.
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Corresponding Author: P K. Govil, Geochemistry Group, National Geophysical Research Institute, Council of Scientific and Industrial Research, Uppal Road, Hyderabad 500 007, INDIA.
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|Author:||Rao, T. Gnaneswara|
|Publication:||Journal of Environmental Health|
|Date:||Apr 1, 1999|
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