Results and Discussion

Heavy metals in vegetables (Varthur): The heavy metal content was high in most vegetables and exceeded their safe limits in India (Awashthi et al., 2000). The concentration of metals in vegetables grown in the command area of Varthur lake is presented in the Table 1 and heavy metal-wise discussed below.

Lead (Pb): In this study Amaranthus sp. showed the highest concentration of Pb, i. e., 148±4.2 mg/Kg, and maize showed the lowest concentration, i. e., 24 mg/Kg that is far exceeding the Indian safe limit of 2.5 mg/Kg (table 1). The Pb contamination in vegetables was found to be due to prolonged irrigation of vegetables using Pb-containing lake water. Discharges from battery industries are the prime sources of Pb contamination. However, plants have the ability to accumulate high levels of Pb without any impact on their appearance or yield (Suruchi and Pankaj, 2011). Due to the high bioaccumulation properties of Pb in plants, its accumulation can exceed several hundred times of the threshold levels permitted for human consumption (Wierzbica, 1995; Suruchi and Pankaj, 2011). Accumulation of lead is mainly due to a large number of small-scale industries, vehicular emissions, resuspended road dust, and diesel generator sets (Ramesh and Murthy, 2012). The uptake of lead in plants is regulated by pH, particle size, and CEC (cation exchange capacity) of soil as well as by root exudation and other physiochemical parameters (Lokeshwari and Chandrappa, 2006). A higher Pb content of 28.4 to 149.5 mg/Kg was found in Palak and 54.69 to 75.5 mg/Kg in Coriander grown near Varthur lake (Ramesh and Yokananda Murthy, 2012).

Similarly, Varalakshmi and Ganeshamurthy (2010), also found elevated levels of Pb in Varthur vegetables. Lead is very toxic to plants and humans; hence high levels recorded in this study are quite alarming. Todd (1996) noted that when lead is accumulated in the human body, it gets sequestered in the bones and teeth, resulting in brittle bones and weakness in the wrists and fingers. Furthermore, lead stored in bones can reenter the bloodstream during periods of increased bone mineral recycling, causing further anomalies (i.e., pregnancy, lactation, menopause, advancing age, etc.). Mobilized lead can be re-deposited in the body's soft tissues and can cause musculoskeletal, renal, ocular, immunological, neurological, reproductive, and developmental effects (ATSDR, 1999b).

(*Note: Safe limits- Pescod, 1992; Indian safe limits- Awashthi et al., 2000; N/D- Not detectable; N/A- Not available).

Cadmium (Cd): The Cd content in palak and corn was highest i. e., 9.7±0.07 9.7±0.2 mg/Kg and lowest in Amaranthus sp. i. e., 6.8±3.8 mg/Kg (table 1). A maximum Cd concentration of 4 mg/Kg was found in spinach grown near Bellandur lake, Bangalore. (Lokeshwari and Chandrappa, 2006). Acute doses (10–30 mg/kg/day) of cadmium can cause severe gastrointestinal irritation, vomiting, diarrhea, and excessive salivation, and doses of 25 mg of Cd/Kg body weight can cause death (cadmium exposure in humans, 2011)). The use of contaminated water for irrigation, fertilizers, sewage, and compost can remarkably increase the Cd uptake into plant tissues (Jackson and Alloway, 1991). Farooq et al., (2008) revealed that plants could readily absorb Cd from the soil where their ingestion will enter into the human food chain based on plant species, their physical and chemical properties. Low-level chronic exposure to Cd can cause adverse health effects, including gastrointestinal, hematological, musculoskeletal, renal, neurological, and reproductive effects (table 2). The most vulnerable organ system affected by Cd exposure is the kidney (ATSDR, 1999a).

Copper (Cu): The Cu content was highest in palak, i. e., 183± 18 mg/Kg and lowest in coriander, i. e., 41.6±12 mg/Kg (table 1). The average content of Cu in plant tissue is ten µg/g dry weight (Baker and Senef, 1995). Typical symptoms of Cu deficiency appear first at the tips of young leaves and then extend downward along the leaf margins. The leaves may also be twisted or malformed and show chlorosis or even necrosis (Marschner, 1995). Demirezen and Ahmet (2006) reported that Cu concentration (22.19-76.50 mg/kg) was found higher in leafy vegetables when compared to non-leafy vegetables in Turkey, and it may be due to the richness of chlorophyll. Chronic exposure to Cu can cause Vineyard sprayer’s lung (if inhaled) and Wilson disease (hepatic and basal ganglia degeneration).

Chromium (Cr): The Cr content in vegetables was highest in palak, i. e., 141±34 mg/Kg and lowest in pudina, i. e., 50.3±54 mg/Kg (table 1). The exposure route of Cr to humans is through nonpoint sources. In fact, Cr can be found in common cereals/grains, vegetables, red wine, beans, fish, lean meat, etc. Naturally, Cr is present in the soil in the form of minerals. A higher Cr content of 127.27 mg/Kg was found in coriander grown in urban districts of Karnataka (Ramesh and Murthy, 2012). Chromium enhances the actions of insulin, a key enzyme that is vital to the metabolism and the storage of carbohydrates, fats, and protein. Chromium (III) is an essential trace element that aids in the metabolism of glucose and fats (Morgan, 2010). Chromium (VI) compounds are carcinogenic as classified by the International Agency for Research on Cancer, whereas chromium (III) compounds are not (Guertin et al., 2004).

Nickel (Ni): The Ni content is maximum in Amaranthus sp. i. e., 90.5±7.7 mg/Kg. Ni was not detectable in palak and maize (Table 1). The Ni was also not detectable in lake water; however, it was high in the soil. A maximum concentration of 14.9 mg/Kg Ni was obtained for Spinach sp. grown near Vrishabhavathi River, Bangalore, Karnataka (Jayadev and Puttaih, 2012). Ni is an essential metal in the diet of humans but at low concentrations. Excess levels of Ni in humans can lead to various forms of cancer. Ni is mainly found in the soil as an ore together with iron. Other anthropogenic sources are dust/gases released by power plants which settle on the soil or precipitate with raindrops (table 2). When the soil pH is acidic, Ni becomes immobile and is taken up by plants.

In a similar study in West Bengal, the heavy metal content in vegetables like Pudina, Spinach, and Coriander were found to exceed their Indian safe limits (Gupta et al., 2012). The average Cd content in vegetables ranged from 9.4 to 13.2, Cu content from 25 to 32.1, Pb from 21 to 47.7, Cr from 44.1 to 95.8and Ni from 51 to 68.6 mg/Kg. The heavy metal content in Amaranthus sp. grown near Vrishabhavathi River, Bangalore, were observed to be 6.1 mg/Kg for Pb, 16 mg/Kg for Cu, 11.9 mg/Kg for Ni, and 10 mg/Kg dry weight of Cr (Jayadev and Puttaih, 2013).

(Jarup L., 2003; Ali et al., 2013; Xu et al., 2014; Wang et al., 2010)

Heavy metals in lake water and soil from the vegetable farm at Varthur

Among the metals analyzed, Ni was not detectable in the lake water sample (table 3). The concentration of Cd was found to be 0.6±0.07 mg/L exceeding the safe limits for irrigation, i.e., 0.01 mg/L. Cr level in water was observed to be 0.5±0.14 mg/L and exceeded the safe limits (0.1 mg/L). Similarly, high Cu levels were observed (1.4±0.1 mg/L), exceeding the safe limits (0.5 mg/L). Pb content in water was found to be within the limit, i.e., 2.0 mg/L. Heavy metal analysis by Jumbe and Nandini (2009) reveals metals like Cd, Cr, Cu, Pb, and Ni at a concentration of 0.12, 2.13, 0.32, 2.72, and 1.03 ppm. A study by Varalakshmi and Ganeshamurthy (2010) in Varthur lake reported undesirable concentration of heavy metals as Cd (0.03 mg/L), Pb (0.07 mg/L), Cr (0.28 mg/L), and Ni (0.03 mg/L). A similar study conducted by Lokeshwari and Chandrappa (2006) in Bellandur lake, showed reasonably high values of Cu (12 mg/L), Ni (3 mg/L), Cr (6 mg/L), Pb (9 mg/L), and Cd (0.7 mg/L), respectively.

In the case of soil 20.5±3.4, mg/Kg and 189±71 mg/Kg of Cd and Ni were observed, respectively. They were found to exceed the safe limits, i.e., 3-6 mg/Kg and 135-270 mg/Kg (Pescod, 1992). Varalakshmi and Ganeshamurthy (2010), reported that the soil near Varthur lake contained metals like Cd, Pb, Cr, and Ni with concentrations of 2.9, 68.12, 56.5, and 57.3 mg/Kg. Similarly, investigations by Ramesh and Murthy (2012), showed substantially high heavy metal content in soil at Ramagondanahalli (in Varthur), i.e., 35.32 mg/kg for Cu, 45.33 for Pb and116.94 mg/Kg Cr. Moreover, Lokeshwari and Chandrappa (2006) analyzed heavy metals in surface soils, i.e., Cu and Cd were 2.5 and 6-fold higher than the natural concentration, respectively. Unequal distribution of heavy metals could be because of myriads of factors depending on the type and genetic features of soil-forming rocks, granulometric soil composition, amount of organic matter, pH, absorption capacity, amount of CaCO₃, and other physical and chemical properties of soil (Naser et al., 2009).

Sodium adsorption ratio (SAR) of Varthur lake water: The wastewater quality for irrigation was determined using the sodium absorption ratio (SAR). The SAR is commonly used as an index for evaluating the sodium hazard associated with an irrigation water supply (Rajendra et al., 2009). The SAR is defined as the square root of the ratio of the sodium to calcium+ magnesium ions (Ca+Mg).

The SAR recorded for Varthur lake water of the two sampling periods was found to be 28.6 (table 3), which poses a very severe degree of restriction for irrigation purposes (FAO, 1985). A SAR of 14.9 was observed in a study conducted by Ackah et al. (2013) in Accra, Ghana. Irrigation waters having higher SAR could lead to build-up of high soil Na levels over time, which in turn can adversely affect soil infiltration and percolation rates (due to soil dispersion). Additionally, excessive SAR levels can lead to soil crusting, poor seedling, emergence, and poor aeration. This problem is also related to factors such as the salinity rate and the type of soil. For example, sandy soils may not get damaged as easily as other heavier soils when it is irrigated with high SAR water. It means excess sodium in irrigation water, relative to calcium and magnesium or total salt content, can affect soil structure, soil aeration, flow rate, permeability, infiltration, etc.