Are heavy metals found in plants near agriculture


Are food crops and medicinal plants affected by heavy metals?

In some case studies using the TF, food crops and medicinal plants were found to affected by heavy metals in the atmosphere, which has serious human health implications ( Jarup, 2003; Cui et al., 2004; Chary et al., 2008; Cao et al., 2010; Street, 2012; Amaya et al., 2013; Sahoo and Kim, 2013; Gall et al., 2015; Kohzadi et al., 2018 ).

Where do heavy metals come from in vegetable greenhouses?

In case studies on vegetables in China ( Xu et al., 2015; Fan et al., 2017) and Europe ( Facchinelli et al., 2001; Acosta et al., 2011 ), the sources of heavy metals in greenhouses were primarily anthropogenic.

Do heavy metals exist naturally in the soil?

Heavy metals exist naturally in soil in complex forms with other minerals (see Table 1showing the average abundance of total heavy metals in the earth’s crust and in typical soils). Table 1. Average abundance (mg/kg = ppm) of total heavy metals in the earth’s crust and in typical soils (Source; Plant and Raiswell. 1993).

How do plants colonize heavy metals?

Heavy metals are naturally occurring in the earth‘s crust but anthropogenic and industrial activities have led to drastic environmental pollutions in distinct areas. Plants are able to colonize such sites due to several mechanisms of heavy metal tolerance.


Why do animals absorb toxic metals?

In laboratory animals, absorption of toxic metals may occur as a result of chronic deficiencies of calcium and magnesium in the body. In other cases, excess levels of aluminum mobilizes calcium and heavy metals to move from bones to the central neural tissue.

What is the most common cause of heavy metal poisoning in adults?

Arsenic is a common cause of acute heavy metal poisoning in adults — although the source is not from soils but from the process of smelting copper, zinc, and lead in from the manufacture of chemicals and glass. Lead, the leading cause of heavy metals poisoning, primarily comes from soils.

What to do with soil high in lead?

Another option for soils high in lead is to use container or raised-bed gardening with clean soils and installing a barrier (such as a geotextile fiber) between good soils and the contaminated soil below. Table 2.

How to reduce lead in soil?

If your soil tests for lead higher than 50 ppm, you might need to use some soil amendments to reduce lead toxicity. These include: 1 Maintaining a neutral soil pH above 6.5. Lead uptake by plants is reduced when pH is above 6.5. 2 Add phosphorus when soil tests indicate a need. Phosphorus reacts with lead to form insoluble compounds, therefore reducing toxicity. 3 Add organic matter, which in turn binds lead and makes it less soluble in soil water. When adding organic material, soil pH soil should be maintained above 6.5 to reduce uptake by plants. 4 What about lead in water? If you still have leaded water pipes, you should test your water for lead content. It is recommended to replace these pipes or keep water off edible plants.

How to get rid of lead in garden?

Use clean soil in raised beds or containers for vegetable gardening. Plants do not absorb or accumulate substantial amounts of lead. Lead does not readily accumulate in the fruiting part of vegetables and fruit crops (such as corn, beans, squash, tomatoes, strawberries and apples).

What is the specific gravity of a heavy metal?

A heavy metal is a chemical element with a specific gravity at least five times that of water, whose specific gravity is 1 at 39 ° F. Specific gravity measures the density of a given amount of a solid substance when compared to an equal amount of water. Heavy metals that fall into this category include arsenic, cadmium, iron, lead, chromium, …

How long does lead last in soil?

Lead has a half-life of 53,000 years and does not biodegrade. If your soil tests for lead higher than 50 ppm, you might need to use some soil amendments to reduce lead toxicity. These include: Maintaining a neutral soil pH above 6.5. Lead uptake by plants is reduced when pH is above 6.5.

What are the sources of heavy metals in food crops?

The sources of heavy metals in food crops vary in the developing and developed world. The deposition of PM on food crops and the use of industrial effluents and sewage sludge as fertilizers are the primary contamination sources in soil–crop systems in developed countries.

How are heavy metals transferred to plants?

Heavy metals are transferred from soil pores to plants in ionic forms, which can vary by metal ( McLaughlin et al., 2011 ). The biospeciation of heavy metals can also vary by food crop. Vegetables such as iceberg lettuce, cherry belle radishes, Roma bush beans, and Better Boy tomatoes all accumulate heavy metals with different concentrations in the roots, leaves, and fruits ( Cobb et al., 2000 ). Pb uptake in lettuce was higher than that in tomatoes and beans, and Cd and As uptake in the same plants was lower than Zn uptake ( Cobb et al., 2000 ). Pb, Cd, Cu, Zn, and As bioaccumulated in 22 vegetables grown in China in the following decreasing order: leaves > stalk/root/solanaceous > legume/melon vegetables. The THQ reached 5, indicating that all the vegetables had a high potential to cause severe health risks upon ingestion ( Zhou et al., 2016 ).

What is biochar in soil?

Biochar application is considered to be a potent eco-remediation strategy to alleviate heavy metal contamination in soil and confer multifaceted benefits. Biochar derived from waste could effectively sequester heavy metals by altering the physicochemical conditions of soil and reducing the phytoavailability of hazardous elements ( Jiang et al., 2012; Khan et al., 2014; Gul et al., 2015; Igalavithana et al., 2017; Peng et al., 2018 ). Composting and biochar can act as ecological solutions to improve the soil nutrient cycle, cation exchange capacity, and humification and effectively reduce soil metal concentrations (as revealed by the measure-monitor model) ( Beesley et al., 2014; Wu et al., 2017 ). Li et al. (2018) found that biochar combined with metal-resistant bacteria such as Pseudomonas chenduensis remarkably reduced Cd bioavailability in contaminated paddy soil.

What are the causes of heavy metal pollution?

The root causes of this problem are generally held to be the rapid pace of urbanization, land use changes, and industrialization, especially in developing countries with extremely high populations, such as India and China ( UN-HABITAT, 2004 ). Since the industrial revolution and economic globalization, the diversity of environmental contaminants has increased exponentially, with countless anthropogenic sources. Therefore, the diverse and emerging issues of food security have become a global concern, particularly their inextricable association with human health ( Clarke, 2011; Säumel et al., 2012; Toth et al., 2016; Rai, 2018a ).

What are the benefits of root-associated metal transporters in food crops?

In several food crops, root-associated metal transporters assist in the sequestration of hazardous elements, such as Cd, and minimize their bioaccumulation in seeds after their transfer from the root to the stem.

What are the functions of polysaccharides in food?

Polysaccharides (with –COOH, –OH, and –SH functional groups assisting in binding heavy metals to the root ) in the root cell walls of food crops also play an important role in the avoidance and tolerance of metal stress.

What are the indices of soil and plant metal transfer and health risks?

Indices of soil–plant metal transfer and health risks have been proposed to describe the translocation of heavy metals in soil and plant systems (plant uptake factors) and to assess the extent of risk from the dietary intake of vegetables and other food crops ( Yang et al., 2018 ). This section discusses the different indices used to determine the ecotoxicological effects and health risks from the intake of contaminated food crops.

Why are heavy metals found in soil?

Heavy metals, such as arsenic, cadmium and lead are in all plants that grow in healthy soil because they are natural constituents of the Earth’s crust and have existed on earth since its formation (Agency for Toxic Substances and Disease Registry, 2011). If heavy metals are not naturally occurring, and instead due to pollution, …

What is the cadmium level in California?

If heavy metals are not naturally occurring, and instead due to pollution, they appear in significantly higher levels, including cadmium at levels of 57 to 160 ppm (Agency for Toxic Substances and Disease Registry). Proposition 65, the Safe Drinking Water and Toxic Enforcement Act of 1986 created to regulate the effect of fracking on California’s …

What is Axiom food?

Axiom, an ethically based food ingredient provider, has been on a mission to educate consumers on all of the aspects of how and why metals naturally occur in vegetables that grow in healthy soil, so they can make informed decisions about their intake and understand if and when those levels are toxic to the organs and other parts of the body. …

Is tungsten toxic to plant protein?

Tungsten testing is new and has not been deemed toxic in any plant protein supplements. Errors can occur in testing and managing levels so close to the detection limit that it can create great variances, even up to 50 percent.

Is Axiom Foods vegetarian?

With vegetarianism on the rise, rice protein purveyor Axiom Foods launches a campaign to educate the masses about the realities of heavy metals. Axiom Foods, whose Oryzatein® enzyme-extracted, brown rice protein is supplied to food and beverage manufacturers throughout the U.S., Europe and other countries, is embarking on a campaign …

Does eating vegan food mean you will not absorb metal?

Just because a food contains a certain level of metal does not mean the body will absorb or retain it; The Agency for Toxic Substances and Disease Registry, for example, only 2 to 6 percent of ingested cadmium is absorbed. According to the Journal of the American Medical Association, vegans are shown to live longer.

Where to test for contamination in food?

Testing for contamination in food products needs to be done in U.S. accredited laboratories, where standards for calibration exist and highly-educated practitioners test with accepted scientific methodologies. Test results can vary vastly based on seemingly insignificant factors.

What do we know about heavy metals in soil?

Metals from air pollution accumulate in the top 1-2 inches of soil and tend to stay put.

What do we know about lead exposure through soil and garden plants?

Lead poses human health hazards when particles are inhaled or ingested.

What do we know about cadmium and arsenic in soils?

Cadmium and arsenic are naturally occurring elements widely distributed in the earth’s crust.

Be cautious about planting vegetables close to older structures

Lead-based paints have not been sold in the U.S. since 1978, but structures built before 1978 were likely painted with lead-based paint.

Are my bees at risk from heavy metal pollution?

Research in an industrialized area found that honey did not contain elevated lead levels, even when bees foraged in contaminated areas.


Most of the agricultural soils around the world are contaminated with heavy metals like cadmium, arsenic, mercury, lead, chromium, and many more. High concentration of heavy metals is toxic to all life forms, from microorganisms to human beings. This chapter would focus on the impacts of heavy metals on plants.


The authors would like to thank Director, DEI, for his continuous support and encouragement. SM is grateful to Dayalbagh Educational Institute, Deemed University, Agra, for sanctioning the Research Project, DEI/Minor Project/2017-18 (iv), as a startup grant. DG is thankful to DST-INSPIRE for providing fellowship.

How do heavy metals affect plants?

The heavy metals available for plant uptake are those present as soluble components in the soil solution or those solubilized by root exudates [10]. Plants require certain heavy metals for their growth and upkeep, excessive amounts of these metals can become toxic to plants and ability of plants to accumulate essential metals equally enables them to acquire other nonessential metals [11]. As metals cannot be broken down, when concentrations within the plant exceed optimal levels, they adversely affect the plant both directly and indirectly and some of the direct toxic effects caused by high metal concentration include inhibition of cytoplasmic enzymes and damage to cell structures due to oxidative stress [12, 13]. Indirect toxic effect is the replacement of essential nutrients at cation exchange sites of plants [14]. The negative influence of heavy metals on the growth and activities of soil microorganisms also indirectly affect the growth of plants. Reduction in the number of beneficial soil microorganisms due to high metal concentration may lead to decrease in organic matter decomposition leading to a less fertility of soil. Enzyme activities are very much useful for plant metabolism, hampered due to heavy metal interference with activities of soil microorganisms. These toxic effects (both direct and indirect) lead to a decrease in plant growth which finally results in the death of plant [15]. The effect of heavy metal toxicity on the growth and development of plants differs according to the particular heavy metal for that process. Metals such as Pb, Cd, Hg, and As which do not play any beneficial role in plant growth, adverse effects have been recorded at very low concentrations of these metals in the growth medium. Kibra [16] noticed significant reduction in height of rice plants growing on the soil contaminated with 1 mg Hg/kg with reduction in tiller and panicle formation. For Cd toxicity which reduces the shoot and root growth in wheat plants when Cd as low as 5 mg/L in the soil[17]. Most of the reduction in growth parameters of plants growing on polluted soils can be attributed to reduced photosynthetic activities, plant mineral nutrition, and reduced activity of some enzymes [18].

How does lead affect plants?

The uptake of lead by the roots of the plant may be reduced with the application of calcium and phosphorus to the soil. Lead (Pb) is one of the ubiquitously distributed most abundant toxic elements in the soil. It exerts adverse effect on morphology, growth and photosynthetic processes of plants. Lead is known to inhibit seed germination of Spartiana alterniflora, Pinus helipensis [103]. Inhibition of germination may result from the interference of lead with important enzymes. Mukherji and Maitra [104] observed 60 µM lead acetate inhibited protease and amylase by about 50% in rice endosperm. Early seedling growth was also inhibited by lead in soya bean, rice [105], maize [106], barley, tomato and certain legumes [107]. Lead also inhibited root and stem elongation and leaf expansion in Allium species barley [108] and Raphanus sativas. The degree to which root elongation is inhibited depends upon the concentration of lead and ionic composition and pH of the medium [109]. Concentration dependent inhibition of root growth has been observed in Sesamum indicum [110]. A high lead level in soil induces abnormal morphology in many plant species. For example, lead causes irregular radial thickening in pea roots, cell walls of the endodermis and lignification of cortical parenchyma [111]. Lead also induces proliferation effects on the repair process of vascular plants [112]. Lead administrated to potted sugar beet plants at rates of 100–200 ppm caused chlorosis and growth reduction [113]. High Pb concentration also induces oxidative stress by increasing the production of ROS in plants [114].

What is the effect of chromium on plants?

Chromium is known to be a toxic metal that can cause serve damage to plants and animals. Chromium induced oxidative stress involves induction of lipid peroxidation in plants that causes severe damage to cell membranes. Oxidative stress induced by chromium initiates the degradation of photosynthetic pigments causing decline in growth. High chromium concentration can disturb the chloroplast ultra structure there by disturbing the photosynthetic process. Since seed germination is the first physiological process affected by Cr, the ability of a seed to germinate in a medium containing Cr would be indicative of its level of tolerance to this metal [87]. Seed germination of the weed Echinochloa colona was reduced to 25% with 200 µM Cr [88]. High levels (500 ppm) of hexavalent Cr in soil reduced germination up to 48% in the bush bean Phaseolus vulgaris [89]. Peralta [87] found that 40 ppm of Cr (VI) reduced by 23% the ability of seeds of Lucerne (Medicago sativa) to germinate and grow in the contaminated medium [90]. Reductions of 32–57% in sugarcane bud germination were observed with 20 and 80 ppm Cr, respectively [91]. The reduced germination of seeds under Cr stress could be a depressive effect of Cr on the activity of amylases and on the sub sequent transport of sugars to the embryo axes. Protease activity, on the other hand, increases with the Cr treatment, which could also contribute to the reduction in germination of Cr treated seeds [92]. Decrease in root growth is a well documented effect due to heavy metals in trees and crops [93]. Prasad [94] reported that the order of metal toxicity to new root primordia in Salix viminalis is Cd > Cr > Pb, whereas root length was more affected by Cr than by other heavy metals studied. Chromium stress is one of the important factors that affect photosynthesis in terms of CO2 fixation, electron transport, photophosphorylation and enzyme activities [95].

What is the limit of cadmium in soil?

The permissible limit of cadmium (Cd) in agricultural soil is 100 mg/kg soil [70]. Plants grown in soil containing high levels of Cd show visible symptoms of injury reflected in terms of chlorosis, growth inhibition, browning of root tips and finally death [71,72,73]. The inhibition of root Fe (III) reductase induced by Cd led to Fe (II) deficiency, and it seriously affected photosynthesis. In general, Cd has been shown to interfere with the uptake, transport and use of several elements (Ca, Mg, P and K) and water by plants [74]. Cd also reduced the absorption of nitrate and its transport from roots to shoots, by inhibiting the nitrate reductase activity in the shoots [75]. Appreciable inhibition of the nitrate reductase activity was also found in plants of Silene cucubalus [76]. Nitrogen fixation and primary ammonia assimilation decreased in nodules of soybean plants during Cd treatments [77]. Metal toxicity can affect the plasma membrane permeability, causing a reduction in water content; in particular, Cd has been reported to interact with the water balance [78]. Cadmium treatments have been shown to reduce ATPase activity of the plasma membrane fraction of wheat and sunflower roots [79]. Cadmium produces alterations in the functionality of membranes by inducing lipid peroxidation [79] and disturbances in chloroplast metabolism by inhibiting chlorophyll biosynthesis and reducing the activity of enzymes involved in CO2 fixation [80].

What are the main sources of soil pollution?

Wastes are the major source of soil pollution originates from mining, chemical, metal processing industries, and other allied industries. These wastes include varieties of chemicals like heavy metals, phenolic, organic, non-metals, etc. Heavy metals are the intrinsic component of the environment with essential and non essential both types. Soils polluted with heavy metals have become common due to increase in geologic and anthropogenic activities. It is the unplanned disposal of municipal waste, mining, use of extensive pesticides, insecticides, fungicides, and other agrochemicals uses were significant causes of environment pollution and causes of most concern. Heavy metals, such as cadmium, copper, lead, chromium, manganese, iron and mercury is major environmental pollutants, particularly in areas with high anthropogenic pressure. Heavy metal accumulation in soils is of concern in agricultural production due to the adverse effects on food safety, marketability and crop growth due to phytotoxicity, and environmental health of soil organisms. The influence of these heavy metals on plants and their metabolic activities caused by the geological and biological redistribution of heavy metals through pollution of the air, water and soil were briefly discussed in this article.

What is the role of manganese in plants?

Manganese (Mn) is an essential plant mineral nutrient, playing a key role in several physiological processes, particularly photosynthesis. Manganese deficiency is a widespread problem, most often occurring in sandy soils, organic soils with a pH above 6 and heavily weathered, tropical soils. Mn is readily transported from root to shoot through the transpiration stream, but not readily remobilized through phloem to other organs after reaching the leaves [130]. Necrotic brown spotting on leaves, petioles and stems is a common symptom of Mn toxicity [131]. This spotting starts on the lower leaves and progresses with time toward the upper leaves [132]. With time, the speckles can increase in both number and size resulting in necrotic lesions, leaf browning and death [133]. Another common symptom is known as ‘‘crinkle leaf’’, and it occurs in the youngest leaf, stem and petiole tissue. It is also associated with chlorosis and browning of these tissues [131, 133]. Manganese toxicity in some species starts with chlorosis of older leaves moving toward the younger leaves with time. This symptom starts at the leaf margins progressing to the interveinal areas and if the toxicity is acute, the symptom progresses to marginal and interveinal necrosis of leaves [134]. Excess Mn is reported to inhibit synthesis of chlorophyll by blocking a Fe concerning process [135]. Manganese toxicity is a relatively common problem compared to other micronutrient toxicity. It normally is associated with soils of pH 5.5 or lower, but can occur whenever the soil pH is below 6.0 symptoms include chlorosis and necrotic lesions on old leaves, dark brown or red necrotic spots, accumulation of small particles of MnO2 in epidermal cells of leaves or stems, often referred to as “measles”, drying leaf tips, and stunted roots. In the broad bean (Vicia faba) Mn accumulation in shoot and root; reduction in shoot and root length; chlorosis [22]. Otherside in spearmint (Mentha spicata) Mn decrease the chlorophyll a and carotenoid content; increase accumulation of Mn in plant roots [23]. Moreover, Mn in pea (Pisum sativum) reduces chlorophylls a and b content; reduction in relative growth rate; reduced photosynthetic O2 evolution activity and photosystem II activity [24]. However, in tomato (Lycopersicon esculentum) Mn slower plant growth; decrease in chlorophyll concentration [25].

Why do plants turn yellow?

Leaves get discolor when the soil is deficient in zinc and plant growth is stunted [136]. Zinc deficiency causes leaf discoloration called chlorosis tissue of the veins to turn yellow. Chlorosis by zinc deficiency usually affects the base of the leaf near the stem. Chlorosis appears on the lower leaves first, and then gradually moves up to the plant. In severe cases, the upper leaves become chlorotic and the lower leaves turn brown or purple and die. When plants show symptoms this severe, it’s best to pull them up and treat the soil before replanting. Zinc (Zn) is an essential micronutrient that affects several metabolic processes of plants [60] and has a long biological half life. The phytotoxicity of Zn and Cd is indicated by decrease in growth and development, metabolism and an induction of oxidative damage in various plant species such as Phaseolus vulgaris [61] and Brassica juncea [62]. Cd and Zn have reported to cause alternation in catalytic efficiency of enzymes in Phaseolus vulgaris [63] and pea plants [64]. Concentrations of Zn found in contaminated soils frequently exceed to those required as nutrients and may cause phytotoxicity. Zn concentrations in the range of 150–300 mg/kg have been measured in polluted soils [65]. High levels of Zn in soil inhibit many plant metabolic functions; result in retarded growth and cause senescence. Zinc toxicity in plants limited the growth of both root and shoot [66].


Concentrations of heavy metals in agricultural land near highways are a major concern for humans. This study was conducted to investigate the contamination level of heavy metals in soil, canola crop, and the potential health risk for honeybee and human.


Canola, ( Brassica napus L.), is used as one of the most important sources of edible oil in the world, especially in the USA after soybean oil (Hayward 2012 ), and it is considered raw material in the chemical industry such as an alternative regenerative fuel (Nedić et al. 2013 ). In addition, its by-products are used as animal fodder (Paula et al.

Materials and methods

The study area is Ghazala Farm, which covers an area of 84,000 m 2, in Ghazalet Al Khais, near the highway, between the city of Zagazig (Sharkia Governorate) and Ismailia Governorate, Egypt.

Results and discussion

The average pH value in canola soil was predominantly alkaline (8.50), with low organic C (average 0.85%), which affected the reservation of metal in the soils (Troeh and Thompson 2005 ).


Nine heavy metals (Fe, Co, Cr, Ni, Pb, Hg, Mn, and Cu) in canola soil, canola crop (roots, stem, and pods), honey, pollen, and propolis near the highway between Zagazig city (Ash Sharqia Governorate) and Ismailia governorate, Egypt, and associated health risk assessment for honeybee via honey and pollen consumption and human via soil ingestion and pollen and honey consumption were detected.


The author gratefully acknowledges the all stuff in Central Laboratory for soil, food and feedstuffs ISO-17025, Faculty of Development and Technology, Zagazig University, Zagazig, Egypt, In particular Professor Mustafa Abdel-Rahim director of the Central Laboratory, for their collaboration in this research.

Additional information

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What Is A Heavy Metal?

Heavy Metals and Plants

  • In plants, uptake of heavy metals depends on the plant species and bioavailability of the metal in the soil. Since most of the ingestion of heavy metals in humans occurs from the consumption of plants, addressing how plants acquire heavy metals can aid in controlling heavy metal toxicity. The ingestion of heavy metals is not enough to cause toxicit…

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Sources of Heavy Metals

  • Arsenic is a common cause of acute heavy metal poisoning in adults — although the source is not from soils but from the process of smelting copper, zinc, and lead in from the manufacture of chemicals and glass. Lead, the leading cause of heavy metals poisoning, primarily comes from soils. Excess levels of lead in soils greater than 400 ppm result from prior use of lead paint arou…

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Testing Your Soil

  • If you think you might have lead contamination in your farm or home, the best procedure is to collect soil samples and have them analyzed for lead content. OSU publications Analytical Laboratories Serving Oregon(link is external) (EM 8677) and A Guide to Collecting Soil Samples for Farms and Gardens(link is external)(EC 628) list laboratories that can do heavy metal soil tes…

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Taking Preventive Steps

  • Lead contamination is more likely to come from external lead on unwashed produce than from actual uptake by plants. Consumers should always wash their produce before eating or cooking, and growers should always wash their leafy vegetables before marketing them, since lead-laden dust can blow in from distant places. Soil contaminated with lead looks and smells like normal s…

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