Heavy metals in vegetables: screening health risks involved in cultivation along wastewater drain and irrigating with wastewater
© Sharma et al. 2016
Received: 8 August 2015
Accepted: 8 April 2016
Published: 19 April 2016
Irrigation of agricultural land with wastewater leads to continuous buildup of metals at these sites which gets accumulated in the vegetables and crops growing on these sites. Not just the crops irrigated with wastewater are hazardous, in present study, we have found that vegetables growing in vicinity of wastewater drain are also not safe for human consumption. The risk associated with consumption of vegetables was assessed by calculating hazard quotient and results revealed that the hazard quotient for leafy and tuberous vegetables was higher than the safe limits in all the sites irrespective of mode of irrigation. Spinach was the most hazardous among all as the hazard quotient with respect to cobalt and copper was highest in spinach. Uptake trend of metals in all vegetables: Iron > Cobalt > Copper > Cadmium > Lead. Cadmium, a potential carcinogen was found in concentrations higher than permissible limits in many vegetables from all sites. Highest level of cadmium (1.20 mg/kg) and copper (81.33 mg/kg) was reported in site which was in vicinity of waste water drain but irrigated with ground water. Concentration of copper and lead in vegetable samples from different sites exhibited no statistically significant difference with respect to different sites.
Injudicious use of resources and haphazard urbanization have over-exploited the natural resources and caused detrimental effects on the environment. Unplanned economic development has led to pressure on cultivable land and suitable water for irrigation. To meet the food demands of exponentially growing human population, cultivation of food crops is carried out at places which are not suitable for agriculture like along wastewater drains or other polluted sites. To address water crisis, irrigation using the large amount of wastewater discharged from the rapid growing industries is being carried out in many parts of the world. Wastewater used for irrigation has many contaminants mainly heavy metals depending upon the source of discharge (Huibers and Van Lier 2005; Pedrero et al. 2010). In most of the developing countries, the wastewater discarded from industrial or residential areas is not treated and even, if it is treated the treatment process involves only primary processes which generally, do not remove heavy metals from the water. Long term use of wastewater for irrigation can cause accumulation of these metals in soil which can be further translocated to food crops and thus enter food chain (Arora et al. 2008; Gupta et al. 2010; Singh and Agrawal 2010). Though, such cultivation strategies help in addressing the issues of unemployment and increase the crop yield but the global food security is not attained. According to World Health Organization (WHO), food security is achieved when “everyone and always” have access to “sufficient and safe” food. Intake of metals through diet is reported across the globe and health hazards associated with these metals are also known (Arora et al. 2008; Orisakwe et al. 2012; Petroczi and Naughton 2009; Singh et al. 2010; Zhuang et al. 2009). Metals being persistent keep accumulating and magnifying with increase in trophic level of food chain. Accumulation of heavy metals beyond permissible limits affects vital organs like, kidneys, bones, liver and blood and causes serious health hazards. Health effects associated with heavy metals like, cadmium, copper, lead and chromium include gastrointestinal effects, renal impairment, neurological disorders, cardiovascular troubles, bone problems, convulsions, paralysis etc. Metals, because of their solubility in water, are toxic and the toxicity can be acute or chronic dependent upon exposure-time (Dorne et al. 2011; Järup 2003). Toxicological studies have found heavy metals to be carcinogenic, teratogenic, mutagenic and neurotoxic (European Union 2002).
Vegetables are important component of human platter because of high nutritional value and antioxidants. Leafy and tuberous vegetables tend to accumulate higher concentration of heavy metals than grains and fruits. Many studies across the globe have reported high content of heavy metals in vegetables cultivated with wastewater (Boamponsem et al. 2012; Flores-Magdaleno et al. 2011; Mathur et al. 2006). Water can percolate and infiltrate from wastewater drain to the adjoining areas and the content of metals in plants growing in the vicinity of wastewater drain can also be significantly elevated which can cause serious repercussions to the society. Present study aims to compare the metal content (copper, cadmium, lead, iron and cobalt) in vegetables irrigated with wastewater and those irrigated with ground water but cultivated across wastewater drain in agricultural sites of Punjab, India. Furthermore comparison of hazard quotient associated with intake of these metals in adults (male and female) and children is also assessed.
Vegetable samples collected from experimental sites
Vegetable (common name)
Leaf and stem
Site 1 Site was located at north-west of Amritsar across the Tung-Dhab drain, and upstream of a Village named Mahal where number of cancer cases is increasing at high rate. This drain carries effluents from two drains (Gumtala drain and Verka drain). The discharge of municipal waste and effluents from various industries (Dairy plant, Paper Mill, Textile industry and Iron foundries) are released into the drain. This site was nearest to the industrial discharges. Agricultural fields at this site are irrigated with ground water.
Site 2 Also, located across Tung-Dhab drain and downstream of Village Mahal. The site was 15 km downstream of Site 1. Main source of irrigation at this site was also ground water.
Site 3 Site on the southern side of city. Municipal wastewater drain flows across this area and the agricultural fields at this site are irrigated with municipal wastewater.
Sample collection and preparation
Edible parts of vegetables growing across each site were coded and collected in triplicate. They were brought to laboratory and wrapped in absorbent paper after sufficient washing with distilled water and initial air-drying. Samples were then oven-dried at 70 °C to remove all moisture content. Dried samples were crushed using pestle and mortar.
Digestion of samples
0.5 g of dried vegetable sample was digested using Tri-Acid mixture (HNO3:H2SO4:HClO4 = 5:1:1) till we obtained transparent fumes. Samples were cooled and filtered using Whatman filter paper no. 1. The final volume was made 50 ml using double distilled water. Heavy metal content of samples was analyzed using Atomic Absorption Spectrophotometer (Model: 240FSAA Make: Agilent Technologies).
Standard solution (1000 mg/l) of different metals viz. copper, cobalt, iron, lead and cadmium were procured from Agilent technologies. Standard curve was prepared using various concentrations made from standard solution. Digested samples were then analyzed for the metal content.
Content of heavy metals in vegetable samples was estimated. Apart from content, following parameters were assessed to estimate risk associated with uptake of metals:
Metal pollution index
Statistical significance of variation in content of heavy metals in vegetables from different sites was tested using two way ANOVA followed by post hoc Tukey HSD test for metal concentration in vegetables from different sites. All the statistical calculations were done using SPSS 17.0.
Results and discussion
Content of heavy metals in vegetables
Two way ANOVA summary table
Site × vegetables
Summary of post hoc Tukey HSD test with respect to sites
Cadmium mean difference (i–j)
Cobalt mean difference (i–j)
Copper mean difference (i–j)
Iron mean difference (i–j)
Metal pollution index
Apart from various other toxicity affects, US EPA (2015) identifies cadmium to target kidney, cobalt to target endocrine gland and copper and iron to target gastrointestinal tract. Thus these metals can cause serious health effects at their target organs. The hazard quotient and metal concentration in food crops in sites irrigated with wastewater was in accordance with previous studies (Guerra et al. 2012; Gupta et al. 2010; Masona et al. 2011; Orisakwe et al. 2012; Pedrero et al. 2010; Singh and Agrawal 2010). In the present study, we observed that plants growing in vicinity of wastewater drain also pose a significant threat to human health. Various studies have reported increase in number of cancer cases, DNA damage and high frequency of micronuclei in buccal mucosa in people from a Village Mahal across the wastewater drain (Gandhi and Kumar 2004; Sambyal et al. 2004). This can be attributed to consumption of these vegetables.
The healthy and balanced diet is considered to be one which is having many servings of vegetables in a day but due to injudicious agricultural practices this can cause a serious threat to human population. The sites irrigated with wastewater due to lack of water resources are the most risky ones but the sites which are in close vicinity with wastewater drains are also of significant consideration due to percolation of water. No significance difference was observed in copper and lead uptake by vegetables growing in sites irrigated with wastewater and those irrigated with ground water but are in close vicinity with wastewater drain. The regular consumption of vegetables grown in sites can cause detrimental effects to the human population. The authors strongly recommend that consumption of tuberous and leafy vegetables from these sites should be restricted and continuous monitoring of vegetables from these sites should be done. Efforts should be made to amend the soil to reduce the uptake of metals in vegetable crops or these sites should be used for cultivation of non-food crops.
AS was involved in design of sampling, chemical analysis and statistical analysis initial drafting of manuscript. JKK participated in analysis of results and helped in revising manuscript. AVN provided resources, helped in designing and critically revising manuscript. All authors read and approved the final manuscript.
Authors are thankful to University Grants Commission, India for providing the financial assistance.
The authors declare that they have no competing interests.
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