Gupta Abhik - Heavy Metal and Metalloid Contamination of Surface and Underground Water

Heavy Metal and Metalloid Contamination of Surface and Underground Water

Heavy Metal and Metalloid Contamination of Surface and Underground Water

Environmental, Policy, and Ethical Issues

Abhik Gupta

First edition published 2021
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Contents

Human use of metals goes back to antiquity. Implements made by hammering copper have been found from about 7000 bce in eastern Anatolia (Turkey). Objects made of smelted copper dating back to about 3800 bce have been unearthed in Iran (History World 2003). There is evidence of use of copper from Nubia in Sub-Saharan Africa in 4000 bce through imports from Egypt, although copper-smelting might have started there during 26862181 bce , when bronze was also being used by alloying copper with tin (Childs and Killick 1993). The use of copper was prevalent in the pre-Harappan culture in Indus Valley (26002400 bce ) followed by extensive use of copper, bronze (copper and tin), lead, silver, and gold in Harappan culture (23001750 bce ) (Bose et al. 1971). Copper mines are known to have existed in the Balkans by 4000 bce . Bronze was made by smelting copper and tin together, and the Bronze Age is said to have begun by about 2800 bce , followed by the age of iron from about 1500 bce (History World 2003). And then, with improved furnaces reaching higher temperatures, steel could be produced from iron. At first, humans started using native or naturally occurring metals, notably copper, (Roberts et al. 2009) but also gold. Mining for metals and smelting of ores began later.

With the progress in science, newer metals were discovered and technologies evolved to make innovative uses of these, albeit with adverse environmental consequences. For example, cadmium, a toxic metal which is not known to have any biological function, was discovered in 1817, and primarily used as a coating or plating on steel objects to protect them from corrosion (Reardon 2011). Today, cadmium is also extensively used in nickelcadmium batteries, cadmium pigments, stabilizers, and alloys, and in electronic compounds such as cadmium telluride (International Cadmium Association 2003). Chromium, a transition metal, was discovered in 1798, and is added as an alloy in steel to make it more resistant to oxidation and corrosion (Reardon 2011). While trace amounts of chromium are important for health, hexavalent chromium is highly toxic and a carcinogen. Its use in leather tanning is, therefore, fraught with environmental risks and concerns. We could cite numerous such examples of heavy metals used in various industrial activities around us, such as lead in paints and inverter batteries.

With their increasing use in various industrial activities and their release from mining activities, heavy metals along with persistent organic pollutants became the most important classes of chemicals of serious environmental concern. Contamination of our freshwater ecosystems including groundwater by heavy metals, and their accumulation in freshwater biota, therefore, pose a threat to both the environment and public health. And metals are there to remain in the environment for several reasons. As early as the 1990s, it was suggested that though advanced non-metallic materials such as polymers, semiconductors, ceramics, and composites are projected to replace the use of metals, the demand for metals is not expected to diminish, especially in view of the need for growth of infrastructure in developing countries, and maintenance of the standard of living in developed countries (Eagar 1991). And today, with climate change looming large, several metals will be essential for the low-carbon energy technologies to combat this global challenge. Among these are heavy metals such as cobalt, nickel, manganese, copper, chromium, gallium, indium, lead, molybdenum, silver, and zinc, and the metalloid boron. Increase in mining activities for these metals will lead to the contamination of freshwater systems and groundwater, posing problems that will require monitoring and mitigation.

I owe the motivation to write this book to these facts, as well as my research interest in heavy metals, which dates back to the late 1980s and early 1990s, while studying the contamination of urban hill streams in the northeastern region of India. Subsequently, this interest expanded to include the accumulation of these elements in aquatic plants and animals, along with studies on the toxic effects on their morphology, physiology, biochemistry, and behavior. Another major area of concern was arsenic, which entered into groundwater from geogenic sources and created a public health problem of gargantuan magnitude, with its scourge being the most acute in the river valleys of Asia.

While trying to conceptualize this book, it occurred to me that while several booksmostly edited compilations with contributions from expertsover the last couple of decades or more had thrown light on various environmental and biological aspects of heavy metal and metalloid contamination, information was scarce on our understanding of the policy issues pertinent to this problem. It was perhaps needed to put together our policies on water resources and their pollution and critically assess how adequately these covered the specifics of heavy metal and metalloid contamination. Further, I also felt that heavy metal and metalloid contamination of water raised several moral-ethical questions, which warranted some discussion in the light of the different discourses in the field of environmental ethics. This book has accordingly been divided into three broad sections on the environmental, policy, and ethical issues. The sub-sections in the first section on environmental aspects include the ongoing debate on using or discarding the term heavy metals; the geogenic and anthropogenic contamination of surface and underground water by heavy metals; their accumulation and toxicity in biota; the prospects of and the challenges to their mitigation by bioremediation; and the implications of global climate change in their occurrence, distribution, and toxicity. The policy section gives an overview of the policies directly or indirectly pertaining to heavy metals in water adopted by different countries; while the third section on ethical issues looks at the relevance of the existing ethical theories in addressing heavy metal contamination, and the lessons to be learnt from various indigenous worldviews on water and its quality.