Assessment of inherent toxicity of certain rocks and its impact on environment


        Rocks are made of various minerals and are different in different rock types. In contact with the atmosphere, rocks disintegrate and degrade by natural agencies like wind and water and forms soil. Both rock and soil plays important role in groundwater quality as rainwater percolates through soil and rock and reaches the aquifer.  Calcium, Magnesium, Fluoride. Etc are some of the important ions in groundwater but intake of them above permissible limits as suggested by BIS, 1992 results in health risks like kidney stones and fluorosis. A plant growing in a place which is rich in such ions in mineral composition of rock and soil absorbs them and enters the food chain. Intake of fruits, vegetables and pulses bearing large amount of calcium and fluoride leads to health defects in human and other living beings. Thus the impact of rock on human health by different ways must be studied and measures must be taken.


The project emphasizes on the impact of rock and soil on water quality and the integrated effect on human health, at Pambar River Sub-Basin, Northwest Tamil Nadu.  And so the specified objectives are


·         To investigate the relationship between the geological processes and the diversity and uptake of toxic elements by flora.

·         To quantify the rate and path of transport of the toxic substances from the rocks to the biological environment and its   impact on   ecosystem and         


·         To analyze the impact on human health of toxic substances in particular with crystal deposition diseases.

·         To identify suitable methods to treat soil and water contamination by toxic elements.



1.         Dr. L. Elango – Geochemical characterization of groundwater, groundwater quality assessment and its relation to rock/sediment.


2.         Dr. R. Nagendra - Sedimentological and mineralogical studies of fluvial deposits, identification of toxic element bearing minerals in fluvial deposits.


3.         Dr. S. Sanjeevi - Thematic mapping using satellite data, studying the major shear zones, intensity of weathering.


4.         Hema Achyuthan - Soil micro-morphology and soil formation, soil characteristics which is responsible for the release of toxic substances geochemistry. Modeling of transport

             processes through groundwater and Overall co-ordination.


5.         Dr. S. Srinivasalu - Mineralogy of the rocks, and geochemical characters of the rocks and soil to identify the source minerals of toxic elements.


6.         Dr. S. Narayana Kalkura – Characterization of pathological stones of humans, identification of sources.


7.         Dr. K. Palanivelu - Identifying suitable methods of treatment of contaminated water/soil.


8.         Dr. V. Murugesan – Methods of treatment of water contaminated by Fluoride and Arsenate.


9.         Dr. R. Ramesh – Characterization of organic and inorganic constituents in Sediments.      




The study will help to identify the impact of inherent toxicity in the rocks on environment. Its impact on sediments, soil and water will be brought out. Further, the presence of toxic elements in rocks/soil/water and its impact on human health, particularly with kidney stones and fluorosis will be understood. In order to minimize the impact of inherent toxicity on human health, cost effective methods of treatment of contaminated water will be suggested.           





Apatite is widely distributed in all rock types; igneous, sedimentary and metamorphic, but is usually just small disseminated grains or cryptocrystalline fragments. Large well formed crystals though can be found in certain contact metamorphic rocks. Bands of apatite occur in Sevattur carbonatite complex. Apatite is fluorapatite as generally is the case with carbonatite apatites. In paragenetic sequence it is later than pyrochlore and iron oxides and carbonates. Lens shaped bodies or bands of apatite ± magnetite ± olivine are present in Sevattur. Soils upto 2.4% of apatite has been found due to weathering of the carbonatite body.




            Near Sevattur, vermiculite occurs in the northern part of a pyroxenite band, traversed by carbonatite. The vermiculite bearing ultrabasic rocks are seen on a small high ground, situated about a mile to the east of Kagankarai Railway station. The entire area occupied by the ultrabasic rocks is covered by a black colored soil which is the only indication of the underlying ultrabasic rocks. The mineral, which occurs as pods and lenses, shows an exfoliation index upto 15 times the original volume when heated to 850ºC. A total reserve of 1.93 lakh tonnes has been estimated upto a depth of 9 m.



Magnetite and hematite are the main iron oxide minerals presence in various sizes. Weathering of these magnetite occurring along the stream courses.  The magnetite has probably been formed as skarn mineral due to the intrusion of granitic rocks. In Sevattur many magnetite rich pockets have been found either alone or along with apatite. In some carbonatite rocks they are found as clusters within the rock.



The aqueous alteration of ultramafic rocks shows the serpentinization in Onnakkarai Carbonatite Complex.



In Kankar, calcium carbonate is formed as nodules in soils of semi-arid regions. Dunite is the core of this kankar – Kanjanur dunite.




            In Sevattur carbonatites are primary type, contains predominantly of coarse grained carbonate grains. The Sevattur carbonatite occurs as an inwardly dipping arcuate body sandwiched between a large syenitic stock and pyroxenite near village Sevattur as ring dykes and veins amidst syenites, pegmatites and aplites, as cavity fillings, breccia and diatremes within some contact metasomatic carbonaceous rocks. During the weathering process the calcite is forms the typical dark brown color soil. 



1.      Clay - shows chemical etching and long resistance time under water, may be below the water table.

2.      Sand – attrition and abrasion indicating transportation. No/little chemical weathering and the mineral’s        

          angular structure indicating low intensity/ short transportation. Probably it is a debris flow deposit.

3.      Clay - shows high intensity of chemical etching and so it has undergone both oxic and anoxic conditions.









Rainwater is pure until it reaches the ground surface. After falling on the surface and while percolates through unsaturated zone before reaching the water table, the water concentration gets changed. The extent of modification depends on factors like the type of rock that forms the aquifer system, depth of the wells, circulation time of water in aquifer, and climatic conditions of the area. These results in higher concentration of some major, minor and trace ions in groundwater which in turn becomes contaminated in terms of such ions. Even though some ions like calcium, magnesium and fluoride are important they are toxic when present above acceptable limits. The water becomes hard on increased amount of calcium and magnesium. Hard water reduces the efficiency of water for domestic purposes as that retards the formation of foams in soaps and detergents. When groundwater becomes the drinking source of an area such ions enter into the food chain and results in health risks like development of kidney stones. Fluoride is one of the essential ions in groundwater and it helps in the strengthening of bones and teeth but prolonged exposure of excess fluoride causes dental and skeletal fluorosis. The water present in the study area are hard to very hard in nature and are higher in fluoride concentration of up to 4.4 mg/l where 0.6 to 1.5 is the permissible range for fluoride to be present in drinking water.






·        Kidneys are largely responsible for the regulation of water, electrolyte and acid-base balance in the body.


·        Urinary stone diseases which is also known as renal calculi causes from various factors such as metabolic abnormalities, bacterial infection, low urine volume, intake of water and environmental factors. Kidney stones may contain various combinations of chemicals.


·        The most common type of stone contains calcium in combination with either oxalate or phosphate.


·        This is a commonly occurring disease affecting around 1 -20% of the population in Asia, 12% in India, 13% in North America and 5- 9% in Europe.






Calcium oxalate stone shows the micro-Spherule and crystalline layer in the nucleus and platy morphology in the core region




The Uric acid stone shows the layered pattern arrangement in the outer layer and fibrous growth morphology in the core region.




 The Struvite stone shows the fractured surface in the outer layer and orderely arranged layered  crystals in the core.