Stable isotopes as a tool for determining transformation and fate of sulphur in AMD affected water bodies in Meghalaya

Meghalaya, also known as ‘abode of clouds’, is a state located in north-eastern part of India, blessed with abundance of water resources. In the last few decades, extensive coal mining in different parts of Meghalaya has caused detrimental changes in the environment, particularly the aquatic systems. Acid and metal loaded effluents (also known as acid mine drainage or AMD), resulting from the exposure of sulphide mineralization to oxidizing conditions from abandoned or active mining areas, are the principal environmental problems today. Sulphate (SO₄^2-) is a major contaminant and attracts widespread attention as the dominant form of sulphur in coal mining affected aquatic systems. The increased presence of SO₄^2- in ecosystems affected by mining activities has immense negative environmental and human health effects. Low pH and high heavy metal concentrations have been reported from streams flowing in and around the coal mining area in Meghalaya rendering the water quality to be very poor  and unfit for use as potable water.

Stable isotopes have emerged as a promising environmental tracer to understand different environmental functions and processes. Valuable information on the sources and processes can be obtained from the stable isotope ratios of chemical elements in environmental samples as the sources and processes influence history of the samples. Stable isotopes analysis combined with hydrochemical analysis enhances our understanding of transformation and environmental fate of different compounds in water bodies and can provide precise information about factors responsible for controlling water chemistry of different water bodies.

Stable isotopes of sulphur and oxygen combined with hydrochemical parameters were used as a tool for determining origin, transformation and fate of sulphur in AMD affected water bodies in Meghalaya.The study was conducted on two rivers affected by AMD, viz. Myntdu River and Lunar-Lukha River, flowing in the Jaintia Hills region of Meghalaya. The water samples collected are analysed for hydrochemical parameters and stable sulphur and oxygen isotopes (δ³⁴S and δ¹⁸O in aqueous SO₄^2-). The stable isotopes of sulphur and oxygen were also analysed in the coal samples from the nearby mining areas. The result provided an insight into the transformational processes of sulphur in these two AMD affected rivers and the environmental fate of sulphur.