Water Is Described In Classical Sankrit

Published Date: 02 Nov 2017

Introduction

Water is described in classical Sankrit literature as ‘‘Jeevan’ meaning life’ reiterating its importance in survival of biological species and the Greeks called it universal solvent. A colloquial comment is: water is something you can’t live in it and you can’t live without it. Despite this dichotomy, water is an essential component for life; it is also a basic building block to our quality of life. The world wide emphasis of supply of adequate quantity and quality to sustain life needs no more rhetoric. So it is regarded as a "human right" rather than a "human need". Water scarcity, whether pure or polluted, has already adverse effects on all populations in every continent. UNICEF and WHO reports have demonstrated that a large proportion of the world’s population does not have access to adequate and safe sources of water for drinking and other essential purposes (Mara, 2003). Around 1.2 billion people, or almost one-fifth of the world's population, live in areas where the access to close and clean drinking water is not available and 500 million people are approaching this situation. (Ayoob et al., 2008).

Groundwater, constituting 97% of global freshwater and being used for drinking by more than 50% of the world population, serves as the only economically viable option for many communities (Howard et al., 2006). Therefore, groundwater has been appropriately described as the ‘hidden sea’ – because it is hidden in large amounts under the earth’s crust. This is true to a greater extent in the case of developing countries like India where an estimated 80% of domestic consumption in rural and 50% in urban areas are met by groundwater sources alone (Ayoob et al., 2008). However, the presence of several naturally occurring and human induced elements such as fluoride, arsenic, nitrate, sulfate, iron, manganese, chloride, selenium, heavy metals, and radioactive materials may greatly degrade the water quality resulting in health concerns. Roughly, one-sixth of humanity lacks access to any form of improved quality water supply within 1 kilometre of their home (WHO, 2006).

The most harmful pollutants to the human health, recognized worldwide by the World Health Organization (WHO) are contamination of arsenic and fluoride in groundwater (Brunson and Sabatini, 2009). However, fluoride contamination of drinking water receives much less attention as compared to arsenic.

Health Effects of Fluoride

Indeed, fluoride is the only substance in drinking water that can cause divergent health effects on the consumer depending upon its relative presence in dissolved form. A limited amount of fluoride is useful for bone and teeth development and dental health. However, concentrations higher than 1.5 mg L-1 may be detrimental to human health, leading to dental or skeletal fluorosis (Miretzky and Cirelli, 2011). Children in the age group up to 12 years are likely to be most exposed to fluorosis as their body tissues are in growth stage during this period. Moreover, any fluorosis stated is non-reversible and no treatment exists to recover. Its well-known symptoms among others are severe joint and muscular pains. Therefore, the WHO has set a desirable and permissible limit range between 0.5 and 1 mg L-1 in drinking water (WHO, 2006). Effluent standard of 4 mg L-1 for fluoride from the wastewater treatment plants has been described by USEPA (Shen et al., 2003).

Health Effects of Arsenic

Arsenic is present as As (III) and As (V). In water, the most common valence states of arsenic are As(V), or arsenate, which is more prevalent in aerobic surface waters and As(III), or arsenite, which is more likely to occur in anaerobic ground waters. In the pH range of 4 to 10, the predominant As (III) compound is neutral in charge, while the As (V) species are negatively charged. The occurrence of arsenic in groundwater poses even a greater danger than fluoride hazards due to its high toxicity at small concentrations and ability to go undetected especially when it is present as As(III) (Camacho et al., 2011). Arsenic is well known for its carcinogenic effects on humans, which prompts lung, kidney, skin, liver and bladder cancers. Exposure to high levels of arsenic can cause problems in humans ranging from gastrointestinal symptoms to arsenicosis, a chronic disease resulting from extended exposure to As, which occurs mainly via ingestion of water containing As and subsequent accumulation in the body (Villaescusa and Bollinger, 2008; Sharma and Sohn, 2009). Therefore, the WHO recommended a value of 10 µg L-1 for As as safe in drinking water (WHO, 2006). This limit is applicable in the US, India, Taiwan, Vietnam, and Japan (Hug et al., 2008; Reddy and Roth, 2012) while other countries such as Bangladesh, China, and most of South American countries adopted a higher (maximum) contaminant level of 50 µg L-1 (Camacho et al., 2011; Chakraborti et al., 2010).

Health Effects of Combined As and F

When two different types of harmful contaminants go inside human body, they may function independently or synergistically or antagonistically to one another (Chouhan and Flora, 2010). The interaction of As and F in relation to the development of the endemic disease is complicated enough not to have definite mechanism. Notwithstanding, numerous confirmative studies have reported the lethal effects of single fluoride and arsenic exposure, there is a dearth of literature based on the combined effect of these two. Rao and Tiwari (2006) reported that As and F in combination affects integrity of cells genetic material more than the individual exposure. In animal studies for rats, co-exposure of As and F even at low concentrations resulted in decreased comet tail and detrimental effect on liver and kidney (Flora et al., 2009; Mittal and Flora, 2006). Wang et al., (2007) carried out the study of 720 children between 8 and 12 years of age in rural villages in Shanyin county, Shanxi province, China. A standard measure for intelligence quotient (modified classic Raven’s test), weight, height, chest circumference, and lung capacity was used to determine the effects of As and F exposures on children’s growth and it was concluded that children’s intelligence and growth can be affected by high concentrations of As or F. Hence, it is important to remove these toxicants from potable water.

This article critically analyzes the genesis of joint presence of geogenic fluoride and arsenic in groundwater and drinking water in different continents of the world along with the treatment methods for their removal. Also, it deals with the effectiveness of several treatment methods when these two contaminants are present together. Additionally, this is an attempt to focus on some common and different factors and their comparison to better understand the simultaneous actions of these two contaminants. The issue of the concentrated As and F disposal is also dealt with.

2. ORIGIN AND PHYSICO-CHEMICAL PROPERTIES OF As AND F CONTAMINATED GROUNDWATERS

2.1. Regions of predominant F contamination

Although there is evidence of the presence of fluoride in different latitudes such as south-east of Africa, United States, the Middle East of Asia, and South America, the Asian countries China and India top the list of worst hit nations in groundwater contamination with fluoride along (Figure 1). Some substances found naturally in rocks or soils along with fluoride, such as iron, manganese, arsenic, chlorides, sulfates, or radionuclides are commonly found dissolved in ground water.

Fig.1. Probability of occurrence of excessive fluoride concentrations in groundwater (International Groundwater Resource Assessment Centre, http://www.un-igrac.org/)

For past few decades, the areas with arid and semi-arid climates are suffering from the scarcity of water due to the fact that the uptake of groundwater is in far excess than water recharge as well as excessive evaporation leading to decreased availability of water (Jakariya et al., 2003; Jakariya et al., 2007b). Numerous studies have shown that usually these are the regions where fluoride contamination is the greatest. Fluorides are released into the environment naturally through: i) weathering and dissolution of crystalline minerals such as fluorite, biotites, topaz, and their corresponding host rocks such as granite, basalt, syenite and shale, ii) in emissions of volcanoes and, iii) in marine aerosols (Cordeiro et al., 2012). As fluoride primarily originates from fluoride rich rocks, fluoride concentrations are frequently proportional to the degree of leaching/dissolution of crystalline minerals through water-rock interactions. The sources of fluoride in groundwater through rocks rich in fluoride are listed in Table 1.

Table 1: Sources of fluoride contamination (I have prepared it putting formulas)

Mineral Formula Geological setting environment

Flurospar CaF2 Sedimentary rocks, lime stones, sand stone

Cryolite Na3AlF6 Igneous rocks, granite

Fluorapatite Ca5(PO4)3F Igneous rocks, metamorphic rocks

Sellaite MgF2 Bituminous dolomite-anhydrite rock

Regions of predominant As contamination

Arsenic occurs in the environment in several oxidation states. The inorganic forms of arsenic, As(III) (arsenite) and As(V) (arsenate) are commonly found in water. Parsa and Etemad Shahidi, (2010) stated that, unusual large proportions of arsenic are present in potentially soluble form. Studies have shown that over exploitation of shallow (or main) aquifer has been the source of many arsenic problems (Jakariya and Bhattacharya, 2007). Figure 2 shows the regions of world where there is arsenic contamination of groundwaters. Very high concentrations of the arsenic concentration can be seen predominant in Mexico, USA, China, Bangladesh, Vietnam and Pakistan. Recently, groundwaters in Japan and Korea were also found contaminated with arsenic. The most common reason of mobilization of arsenic in groundwater and soils are natural weathering of arsenic bearing minerals and ores and microbiological activities. It is released into waters through: i) erosion and dissolution of rocks, minerals, and ores, ii) anthropogenic processes such as infiltration or runoff from mining, groundwater abstraction and, iii) from atmospheric deposition. The major mechanism that is responsible for the arsenic contamination in groundwater is the desorption from iron oxides or hydroxides from natural rocks and their reductive dissolution (Kim et al., 2012, Li et al., 2012).

Fig.2. Probability of occurrence of excessive arsenic concentrations in groundwater (International Groundwater Resource Assessment Centre, http://www.un-igrac.org/)

Fig.3. Arsenic and fluoride co-occurrence worldwide (International Groundwater Resource Assessment centre, http://www.un-igrac.org/)

Regions of contamination by both As and F

It will be necessary to analyse the presence of As and F in various regions and continents of the world and also where they are present together along with other anions which will have severe effect on the treatment technology. The sources of water contamination by both As and F and the remedial technologies for their removal could then be properly understood. It is not only the removal of these contaminants from water to make it suitable for human consumption is important but also the manner in which they are finally disposed off is equally important in order to avoid future recycle in aquifers. The disposal technologies thus merit even a greater attention.

The action of geological and geochemical processes introduces arsenic and fluoride transfer into the groundwater and soils. Although the mechanism of arsenic release from the sediments is unknown, it is suggested that the link between the kinetics of arsenic release from the sediments and the groundwater residence time in the reservoir is an important factor (Akter and Ali, 2011). Figure 3 represents the co-occurrence of fluoride and arsenic worldwide.

Coexistence of As and F in groundwater is commonly found in many countries including Argentina, China, Mexico, and Pakistan, with concentrations up to 5300 μg L—1 of As and 29 mg L—1 of F in the same groundwater sample (Jing et al., 2012). Recently, Australia, Japan, Korea, and Chile have also been confirmed with elevated As and F co-occurrence (Figure 3) (Richards et al., 2009; Yoshizuka et al., 2010; Chakraborti et al., 2011; Ahn 2012; Fernandez-Turiel et al., 2005).

Arsenic is found to be frequently associated with fluoride in shallow aquifers around the world. A high concentration of arsenic is also found in semi-arid regions that contain oxidized groundwater (Currel et al., 2011). The correlations between these two toxicants are different according to the redox conditions (Kim et al., 2012). The adsorption capacity of Fe-(hydr)oxides on F and As decreases with increase in pH, releasing both components into groundwater indicating that the Fe-(hydr)oxides play an important role for hosting the co-contamination (Streat et al., 2008). High concentrations of As (<10–5300 μg L-1) and F (51–7,340 μg L-1) are reported in shallow groundwaters indicating potential risk of arsenicosis and fluorosis in Chaco-Pampean plain, Argentina. Arsenic and fluoride related diseases affect potentially 2–8 million inhabitants in Argentina itself (Nicolli et al., 2012). Alarcon-Herrera et al. (2012) have reported that the joint presence of arsenic and fluoride in groundwater is linked to volcanism, geothermal, and mining activities.

Physico-chemical properties for groundwaters containing As and F

Selected physico-chemical properties of different samples of the waters around the world are listed in Table 2. High evaporation rates in arid and semi-arid climates, lead to generation of saline groundwaters and alkaline pH, which are correlated to high As and F to concentration in groundwater (Nicolli et al., 2008, Nicolli et al., 2008b). Presence of Na+ and HCO3− are also correlated with simultaneous presence of arsenic and fluoride stating that As and F are generally associated to high concentrations of Na+ and HCO3−. On the other hand, studies in Yuncheng Basin, northern China, have found a moderately positive correlation between pH and As and F concentrations indicating that high pH may favour desorption of fluoride and arsenic, while HCO3- may act as a sorption competitor (Currel et al., 2011). These authors also have reported a strong correlations between As and F suggesting that the enrichment of As and F is governed by a common mechanism and/or set of aquifer conditions.

Table 2. Physico-chemical properties for groundwaters containing As and F

Parameter

Geographical location

Zhijiliang, Inner Mongolia, China

Meoqui City, Chihuahua, México

2 sites

Kalalanwala and Kot Asadullah, Pakistan

2 depths

Un-known site, India

Kyushu, Japan

16 sites

Chihuahua, Mexico

Geumsan County, Korea

Min. and Max.

Santiago del Estero Province, Argentina

pH

7.57

7.2

7.4

8

7.55

7.2

2.8-8.5

7.17

5.78

8.68

6.4-9.3

Temperature, 0C

13

25±2

25±2

20.5

25

12

23

Arsenic, mg L-1

1.10

0.134

0.075

0.235

0.06

0.13

0.01-3.23

0.435

113

0.01-15

Fluoride, mg L-1

1.59

5.9

4.8

11

1.47

5

0.04-3.76

11.8

7.54

0.7-22

Sodium, mg L-1

119

630

273

1.1-1501

250

1.64

66.8

Carbonate, mg L-1

10

121

126

857

410

8.64

239

Turbidity, NTU

311

1.4

1.1

320

1

Hardness, mg L-1

51.5

24.5

58.3