Environmental pollution has increased many folds in recent years and in some places has reached levels that are toxic to living things. Among pollutant types, toxic heavy metals and metalloids are among the chemicals that pose the highest threat to biological systems (Jjemba 2004). Unlike organic pollutants, which are biodegradable, heavy metals are not degraded into less hazardous end products (Gupta et al. 2001). Low concentrations of some heavy metals are essential for life, but some of them like Hg, As, Pb and Cd are biologically non-essential and very toxic to living organisms. Even the essential metals may become toxic if they are present at a concentration above the permissible level (Puttaiah and Kiran 2008). For example, exposure to Zn and Fe oxides produce gastric disorder and vomiting, irritation of the skin and mucous membranes. Intake of Ni, Cr, Pb, Cd and Cu causes heart problems, leukemia and cancer, while Co and Mg can cause anemia and hypertension (Drasch et al. 2006). Similarly, various studies indicated that overexposure to heavy metals in air can cause cardiovascular disorders (Miller et al. 2007; Schwartz 2001), asthma (Wiwatanadate and Liwsrisakun 2011), bronchitis/emphysema (Pope 2000), and other respiratory diseases (Dominici et al. 2006).

Toxic Metal Pollution in Pakistan and Its Possible Risks to Public Health

Plant-based foods satisfy more than 70% of the human energy and nutrition requirements. However, such foods may be contaminated by heavy metal(loid)s. The dietary exposure to excessive levels of these contaminants is detrimental to human health. In this chapter, we have reviewed the reported contamination levels of arsenic (As), cadmium (Cd), lead (Pb), mercury (Hg) and nickel (Ni) in cereals, vegetables, fruits, nuts, pulses and plant oils. The reported concentrations in different plant-based foods were up to 2.9 mg As kg−1, 24 mg Cd kg−1, 61 mg Pb kg−1, 0.10 mg Hg kg−1 and 506 mg Ni kg−1. Concentrations of the studied contaminants in plant oils were within permissible levels in all the listed studies. Moreover, Hg was within permissible levels in all the studies. However, some samples of vegetables, fruits, cereals, pulses and nuts were reported to be contaminated by As, Cd, Pb and Ni to levels toxic to humans. The contamination levels in plant-based foods were related to contamination of agricultural soils, irrigation waters, atmosphere and crop inputs. The occurrence of contaminated plant-based foods is more common in the densely populated developing and underdeveloped countries in the world. Wastewater treatment, soil remediation and control of the emission of air pollutants have become increasingly important for sustainable agriculture. In the absence of effective remediation, food plants should not be grown in contaminated areas or near the sources of contamination.

Arsenic and Heavy Metal (Cadmium, Lead, Mercury and Nickel) Contamination in Plant-Based Foods

Combined contamination of lead (Pb), cadmium (Cd), and arsenic (As) in soils especially wastewater-irrigated soil causes environmental concern. The aim of this study is to develop a soil amendment for simultaneous immobilization of Pb, Cd, and As in combinative contaminated soil. A soil amendment of iron hydroxyl phosphate (FeHP) was prepared and characterized, and its potential application in simultaneous immobilization of Pb, Cd, and As in combined contaminated soil from wastewater-irrigated area was evaluated. The effects of FeHP dosage, reaction time, and soil moisture on Pb, Cd, and As immobilization in the soil were examined. The immobilization efficiencies of Pb, Cd, and As generally increased with the increasing of FeHP dosage. With FeHP dosage of 10 %, the immobilization percentages of NaHCO3-extractable As and DTPA-extractable Pb and Cd reached 69, 59, and 44 %, respectively. The equilibrium time required for immobilization of these contaminants was in the following order: NaHCO3-extractable As (0.25 days) < DTPA-extractable Cd(3 days) < DTPA-extractable Pb (7 days). However, the immobilization efficiencies of Pb, Cd, and As have not changed much under soil moisture varied from 20 to 100 %. According to the results of the sequential extraction, the percentages of Pb, Cd, and As in residual fractions increased after the application of FeHP amendment, while their percentages in exchangeable fractions decreased, illustrating that FeHP can effectively decrease the mobilities and bioavailabilities of Pb, Cd, and As in the soil. Moreover, the application of FeHP will not have soil acidification and soil structure problem based on the soil pH measurements and soil morphology. FeHP can immobilize Pb, Cd, and As in the combinative contaminated soil from wastewater irrigation area simultaneously and effectively. Thus, it can be used as a potential soil amendment for the remediation of Pb, Cd, and As-combined contaminated soil.

Simultaneous immobilization of lead, cadmium, and arsenic in combined contaminated soil with iron hydroxyl phosphate

In the developing world, vegetables are commonly grown in suburban areas irrigated with untreated wastewater containing potentially harmful elements (PHEs). In Pakistan, there is no published work on the bioaccessibility aspect of PHEs and dietary minerals (DMs) in sewage-irrigated soil or the vegetables grown on such soils in Pakistan. Several industrial districts of Pakistan were selected for assessment of the risk associated with the ingestion of vegetables grown over sewage-irrigated soils. Both the total and bioaccessible fraction of PHEs (Cd, Co, Cr, Ni, and Pb) and DMs (Fe, Cu, Mn, Zn, Ca, Mg, and I) in soils and vegetable samples were measured. The concentrations of these PHEs and DMs in sewage-irrigated and control soils were below published upper threshold limits. However, compared to control soils, sewage irrigation over the years decreased soil pH (7.7 vs 8.1) and enhanced dissolved organic carbon (1.8 vs 0.8 %), which could enhance the phyto-availability of PHEs and DMs to crops. Of the PHEs and DMs, the highest transfer factor (soil to plant) was noted for Cd and Ca, respectively. Concentrations of PHEs in most of the sewage-irrigated vegetables were below the published upper threshold limits, except for Cd in the fruiting portion of eggplant and bell pepper (0.06–0.08 mg/kg Cd, dry weight) at three locations in Gujarat and Kasur districts. The bioaccessible fraction of PHEs can reduce the context of dietary intake measurements compared to total concentrations, but differences between both measurements were not significant for Cd. Since the soils of the sampled districts are not overly contaminated compared to control sites, vegetables grown over sewage-irrigated soils would provide an opportunity to harvest mineral-rich vegetables potentially providing consumers 62, 60, 12, 104, and 63 % higher dietary intake of Cu, Mn, Zn, Ca, and Mg, respectively. Based on Fe and vanadium correlations in vegetables, it is inferred that a significant proportion of total dietary Fe intake could be contributed by soil particles adhered to the consumable portion of vegetables. Faecal sterol ratios were used to identify and distinguish the source of faecal contamination in soils from Gujranwala, Gujarat, and Lahore districts, confirming the presence of human-derived sewage biomarkers at different stages of environmental alteration. A strong correlation of some metals with soil organic matter concentration was observed, but none with sewage biomarkers.

Health risk assessment of potentially harmful elements and dietary minerals from vegetables irrigated with untreated wastewater, Pakistan

Wastewater is a source of some nutrients essential for soil fertility, but it includes various types of contaminants like heavy metals that pollute the soil and crops. In this regard, this study aimed to evaluate the possible health risks of copper (Cu) accumulation in forages irrigated with wastewater. Forages both of summer and winter were grown with different water treatments (sewage water and tap water) in the Department of Botany, University of Sargodha. The concentrations of copper in water, root and forage samples were determined. Moreover, the bioconcentration factor, pollution load index, daily intake of metals and health risk index were calculated. In tap water, the copper value was 0.072 mg L and that in sewage water 0.077 mg L. In soil, the calculated copper value was lower than the USEPA standards. The maximum copper in root was determined in winter forages (0.208 mg kg). The maximum bioaccumulation factor for copper was observed in Trifolium resupinatum (8.2230) grown in winter. The maximum pollution load for copper was found in Brassica campestris (0.2853) grown in winter. The maximum value for the daily intake of metals observed was 0.045, and maximum observed health risk index was 1.136.

Copper bioaccumulation and translocation in forages grown in soil irrigated with sewage water

In the present study, 12 heavy metals (Cr, Mn, Ni, Cd, Co, Cu, Pb, Zn, Fe, Se, As, and Mo) were assessed in a potential vegetable Luffa cylindrica. The vegetable was collected randomly from two different sites located at Jhang, Punjab Pakistan. The analyses of variance of data collected from soil showed non-significant effect on Se, Zn, As, Cr, Ni, Mo and Pb while significant effect on Fe, Co, Mn, Cu and Cd metals. Concentrations of all 12 heavy metals in the soil samples were low at sampling site-I as compared to those at site-II except Ni. These concentrations were found below the safe limits except that of Cd. At site-I, the concentrations recorded for different heavy metals were: As > Fe > Pb > Mn > Cd > Co > Cu > Mo > Zn > Ni > Se > Cr while at site-II were: As > Fe > Mn > Pb > Co > Cd > Cu > Mo > Zn > Ni > Se > Cr. Enrichment coefficient of Cr was higher which showed that root of luffa plant accumulated more Cr concentration from the contaminated soil. The order of enrichment co-efficient was recorded at site-I as: Cr > Zn > Mn > Cu > Fe > Ni > Mo > Pb > As > Se > Co > Cd, and at site-II Cr > Zn > Mn > Ni > Cu > Fe > Mo > Pb > Se > As > Co > Cd. The transfer co-efficient of Mn was higher which indicates that more contents of Mn were transferred from roots to upper edible part. The order of transfer coefficient at site-I was: Ni > Se > Mo > Cr > Zn > Fe > Mn > Cd > Pb > As > Cu > Co and at site-II was Mn > Zn > As > Fe > Pb > Se > Cd > Co > Mo > Cu > Ni > Cr. Correlation analysis showed that Mn, Se, Co, Cd, Ni, Mo and Pb had positive non-significant correlation, whereas a negative and non-significant correlation for Zn, As, Fe and Cr. The order of pollution load index at site-I was Cd > Mo > Se > Pb > Cu > Co > As > Fe > Mn > Ni > Zn > Cr and at site-II: Cd > Mo > Se > Pb > Cu > Co > As > Fe > Mn > Ni > Zn > Cr. Overall, at both sites, lowest concentration of Cr and highest of As were observed which need substantial awareness. Health risk index depends on soil characteristics, chemical composition, rate of consumption and type of a vegetable. In the present study, the order of health risk index due to these heavy metals at site-I was as As > Mo > Mn > Pb > Ni > Cd > Zn > Se > Fe > Co > Cr > Cu and at site-II as As > Mn > Mo > Pb > Cd > Zn > Ni > Se > Fe > Co > Cr > Cu.

Bioaccumulation of heavy metals and metalloids in luffa (Luffa cylindrica L.) irrigated with domestic wastewater in Jhang, Pakistan: a prospect for human nutrition

R. Parveen

Papers

Bioaccumulation of heavy metals and metalloids in luffa (Luffa cylindrica L.) irrigated with domestic wastewater in Jhang, Pakistan: a prospect for human nutrition