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

This study was conducted to determine the concentration of toxic metals in soil, forage and blood plasma of lactating and non-lactating buffaloes in the district Jhang, Punjab, Pakistan. Soil samples were collected from varying distances from the road side. Plasma separation was achieved by centrifugation. The concentration of arsenic (As), selenium (Se), cadmium (Cd), chromium (Cr), iron (Fe), zinc (Zn), copper (Cu) and cobalt (Co) were determined by using Atomic Absorption Spectrophotometer. The results of the study showed that the mean As, Se and Cd concentrations in soil samples were lower while Cr, Fe, Zn, Cu and Co were higher than the official guidelines. In plasma samples, mean concentration values of Co, Zn, Fe, Cd, Se and As were lower while Cu and Cr were higher than the recommended concentrations. According to the results of the study there was no potential exposure of toxicity in buffaloes of the study area.

Potential Toxic Metal Accumulation in Soil, Forage and Blood Plasma of Buffaloes Sampled from Jhang, Pakistan

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

| Micro-minerals (iron, manganese, zinc, copper, and cobalt) content of some wild legumes and grasses from arid environment of central Punjab (Pakistan) was evaluated during the rainy and dry seasons. The micro-mineral contents of legumes were significantly higher in dry season than rainy season except iron. Legume contents of all minerals except iron were higher during dry season compared to those found during the rainy season under the same environment. Grass forages contained higher values of manganese, zinc, and copper during rainy season and the reverse was true for grasses iron and cobalt during the dry season. Results indicated that legumes were the best sources of manganese and zinc than grasses during both seasons, and grasses had higher amounts of copper and cobalt than legumes while both legumes and grasses were at par with respect to iron. All mean mineral forage values except iron at both seasons were below the critical levels required for ruminants for their growth and reproductive aspects, thus mineral supplements are warranted to alleviate the problems of deficiency in livestock grazing there in legume and grass pastures.

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Evaluation of deficiency and toxicity of wild forage micro-minerals as potential hazards for grazing livestock under semi-arid environmental conditions.

Z. I. Khan

Papers

Evaluation of deficiency and toxicity of wild forage micro-minerals as potential hazards for grazing livestock under semi-arid environmental conditions.

Proximate composition evaluation of wild forages in relation to requirement of grazing ruminants in a semi arid environment of Punjab Pakistan.