Contamination of food crops by heavy metals (HMs) is a public health concern that is gradually becoming a global challenge. There is rising concern about food safety and human health due to the unceasing release of HMs into the environment by various forms of anthropogenic activities and natural processes. HMs are highly persistent and when they contaminate the food chain a sustainable circle is created in the food web, the metals will be revolving between the environment, food crops and the human body. This article intended to provide an overview of the sources of HMs and their consumption through food crops. The study reviewed relevant literature published online between January 2018 and December 2020. The leading sources of food crop contamination are sewage and industrial effluents, mining, smelting, illicit dumping of solid waste, abuse of agrochemicals, atmospheric deposit and chemical processing. Leafy vegetables in general and wheat grains are the most contaminated food crops. Pb, Cr and Cd were the most reported HMs in food crops in the last three years. The rate of food crops HMs contamination in the last three years was found to be in the following order: Pb>Cd>Cr>As>Zn>Ni>Cu>Mn>Fe>Hg>Co>Al.
Food is a basic requirement for life, its safety is a basic right to human (Fung et al., 2018) and food security cannot exist without food safety (Vipham et al., 2020; Sharma and Nagpal, 2020). Food safety, human health and environmental contamination are intimately connected (Rai et al., 2019).
The contamination of food crops by HMs possess a serious challenge to human health (Vatanpour et al., 2020; Zwolak et al., 2019). HMs are potentially harmful substances that are highly persistence and non-biodegradable (Garrigues et al., 2019; Liao et al., 2016), their presence in food can be dangerous to human health (Massoud et al., 2019) and when consumed can accumulate in different body organs (Ngure and Kinuthia, 2020).
The geochemical behaviour and health risk indices of many HMs are not well understood in agro-system (H. Wang et al., 2020). Understanding their effects on human health is even more complicated because of the diversity of their sources and some own some biological functions at minute and regulated quantities (Afonne and Ifediba, 2020). The consequences of environment and food HMs contaminations attracted public attention (L. Wang et al., 2020), meanwhile professionals and regulatory bodies have great concern on the safety of foods since many foods can mask chemicals that a dangerous to human health (Gallo et al., 2020).
Sources of heavy metals
The most common sources of HM to food crops are contaminated sewage and industrial effluents, mining, smelting, illicit solid waste dumping, misused of agrochemicals, atmospheric deposit, rock weathering, traffic pollution and chemical processing such as leather and textile processing wastes (Table 1). The sources identified in this research are very similar to those reported by Sawut et al. (2018), El-Radaideh and Al-Taani (2018) and Zwolak et al. (2019).
In addition to the aforementioned, thermal power plant, e-wastes and electroplating were also reported by Rai et al. (2019). HMs have their ways into soil and food crops through wastewater irrigation and production in contaminated soil. Soil HM concentration significantly increased in recent decades due to the hasty urbanisation and industrialisation (Rai et al., 2019; Hanfi et al., 2020). Irrigation water is contaminated with HMs from natural and anthropogenic sources (M. Deng et al., 2020).
The incessant use of wastewater for irrigation (Chaoua et al., 2019) and excessive use of agrochemical allied are among the major reasons for food crops HM-contamination (Margenat et al., 2018). Areas with a history of industrial activities possess higher levels of HMs contaminants (J. Peng et al., 2019; Liu et al., 2020) and chances of contamination for both humans and animals are higher in these areas and its environs (Bala et al., 2020). The activities of chemical and mining industries continue to intensify environmental contamination since the inception of the industrial revolution (Saadati et al., 2020). Atmospheric deposit, use of sewage sludge and industrial effluent as fertilization and irrigation with untreated industrial effluent also contributed (Rai et al., 2019). The variation in the HM concentration in different locations is an indicator of anthropogenic activities intensity (S. Sharma et al., 2018), hence, the rate of food crops HMs contamination can, to some extent, be related to the population of a location. China, Pakistan and Nigeria were the most reported nations with the highest levels of food crops metal contamination in recent years (Table 1).
Food Crops HMs Contamination
HMs contamination of food crops is more common in developing nations with limited access to foods and clean water (Shakoor et al., 2017). Most of these countries don’t have established guidelines for regulations of HM concentrations in foods and environments (Edogbo et al., 2020). Nevertheless, the menace is also affecting developed nations (El-Hassanin et al., 2020; Y. Sun et al., 2019). Weber et al. (2019) reported that the Pb, Zn, Cu, As, and Cr contents of the soil in some private vegetable gardens in Sheffield exceed England permissible limits, also the concentration of Mo, Ni, Pb, and As in the soil of gardens around Barcelona exceed Spanish permissible limit (Margenat et al., 2018). Amazingly, illicit waste dumping and burning in agricultural land is still a habit in Giugliano, Italy (Melai et al., 2018). Deviller et al. (2020) also identified shortfalls (that can lead to health and environmental problems) that were not properly addressed by the existing EU regulations on the use of the recycle wastewater for agricultural purposes. Also, many European countries lack definite regulations for wastewater reuse (Chojnacka et al., 2020).
Food crops normally absorb HMs through their roots and in rare cases through the leaves (Edelstein and Ben-Hur, 2018). Transpiration rate, plant species and soil conditions such as pH, organic matter content, temperature, texture, cation exchange capacity, presence of microorganisms and other metals affect bioavailability and mobility of trace elements in the soil (Gupta et al., 2019). HMs can accumulate in food crops and subsequently have their way into the food chain (Rai et al., 2019). Once a food chain is contaminated it will become very difficult to be safe, a sustainable circle is created in the food web where the metals will be revolving between the environment, food crops and the human body (S. Kumar et al., 2019). The contamination can be severe and can rich all the nooks and crannies in the food chain, down to the level of milk production and oil extraction as reported by Samiee et al. (2019) in human breastmilk, X. Zhou et al. (2019) in cow milk and Zaanouni et al. (2018) in olive oil. Even the organic foods which are now considered the safest foods can be contaminated with HMs when off-farm manure is used in their production (Zhen et al., 2020). Nevertheless, Tibu et al. (2019) recommended the use of compost from municipal solid waste in the production of organic vegetables. Likewise, the concentrations Cd and Pb in local and imported organic cereal-based products sold in Thessaloniki, Greece exceed recommended thresholds (Skendi et al., 2020). Abdallah et al. (2020) discovered nanoscale HMs fragments in plants naturally grown in HMs-contaminated soil, similarly, Singh et al. (2018) recommend bio-extraction of HM nanoparticles from the plant.
There is variation in the global distribution of HM (Afonne and Ifediba, 2020). HMs contamination levels varies with location and depend greatly on the HMs properties of the growing locations (Jafari et al., 2018). Ebrahimi-Najafabadi et al. (2019) reported variation in the HM contents between local and imported rice in Iran. Rapid urbanisation and vigorous industrial activities make China the global epicentre for food crops HMs contamination. China reported dangerous levels of HMs in food crops than any other nation in the last three years (Table 1).
HMs Consumption Through Food Crops
Consumption of foods contaminated with HMs presents critical challenges to global food security and human health (Afonne and Ifediba, 2020), it causes complicated health problems including cancers (Yu et al., 2019). Some HMs have no known biological role and can disrupt biological processes even at minute concentrations, and their rate of accumulation in biological tissues is always higher than the rate of excretion (Ngure and Kinuthia, 2020). Other species of HMs such as Co, Cu, Fe, Mn, Ni, Mo, Se and Zn are essential micronutrients and at required concentrations, they play important roles in many biological processes (Giri et al., 2020). HMs with great health worries are As, Cd, Cr, Pb and Hg (Bhagwat, 2019), they can cause severe health problems even in a small quantity (Vardhan et al., 2019). Pb contamination is now a global challenge, it was the most reported HM in food crops, other toxic HMs reported by researchers in recent years were Cr and Cd (Table 1). The data in Table 1 shows that the rate of food crops HMs contamination in the last three years was found to be in the following order: Pb>Cd>Cr>As>Zn>Ni>Cu>Mn>Fe>Hg>Co>Al. Pb, Cd, As and Hg contaminated foods and beverages more than any other HM (Massoud et al., 2019). Cd, As, Cr and Ni are the most consumed HMs with high cancer risks (V. Kumar et al., 2019). Arsenic is the most ingested HM by both children and adults (V. Kumar et al., 2019), while Cd and Pb are the most soluble and mobile HMs (Elmi et al., 2020). Cd and Hg are the potential dangerous HMs due to their bioavailability caused by their high solubility and exchange capability (L. Sun et al., 2019). Cd and Pb are dangerous and cause serious health problems to both humans and livestock even at minute levels (Sharifan et al., 2020). Hg, Pb and Cd are associated with kidney and neural damages (Fung et al., 2018). Arsenic is a chronic carcinogen, and its toxicity can also cause respiratory disorder, skin lesion, diabetes and heart-related diseases (Nachman et al., 2017). Direct consumption of As either through foods or drinking water is considered a life-threatening issue (Shakoor et al., 2017). Mercury in the form of methylmercury can cause severe health problems that can lead to loss of consciousness and death (Reis and Mizusawa, 2019). Food contaminated with Pb, Mn and Cd can lower immunity and affect the functions of vital organs (Obiora et al., 2019) Increase blood Pb level in children damage kidney and lead to the formation of cancer cells (Obiora et al., 2019).
HMs are consumed more through staple foods; cereals and vegetables are the most common carriers (Liu et al., 2019; Yu et al., 2019; Zheng et al., 2020). Lower amounts are consumed through tree-fruits and their nuts (Wu et al., 2019). Y. Huang et al. (2019) reported that vegetables and paddy farms accumulate more HMs than other upland areas. HMs intake through rice consumption is becoming a threat to human health (X. Deng et al., 2020). Contamination of rice is now a global concern and many health problems are associated with the consumption of contaminated rice due to its ability to accumulate dangerous HMs such as As, Cd, Pb, Ni, and Cr among others (Ali et al., 2020; Khanam et al., 2020). Wheat consumption also contributed greatly and account for over 60 % of human health risks (S. Wang et al., 2019). Baruah et al. (2019) reported a higher transfer rate for Pb, Cu and Cd in wheat seedling. Leafy and other vegetables are the most contaminated foods with Pb among all other foods consumed in Northern Italy (Malavolti et al., 2020). Infant foods and vegetables contain more Pb than other food categories in Brazil (Neto et al., 2019). Dangerous levels of different HMs were reported in various food crops by many researchers in different parts of the World. A summary of recent findings reported dangerous levels of HMs were presented in Table 1. Different standards, both local and international, were used by researchers in arbitrating the toxicity levels of different HMs in different food crops. The international standards commonly used as references are the Joint FAO/WHO Food Standards published by Codex Alimentarius Commission in 2001, 2007, 2010, 2011, 2013 and 2016, and European Commission regulations published in 1997 (194/97), 2006 (1881/2006) and 2008 (629/2008).
• Effective monitoring and enforcement of environmental protection laws and the establishment of operational food safety inspection and investigation systems can minimize the consumption of HMs and other food contaminants.
• Massive awareness through socio-environmental campaign can change the attitude of people that are careless about the soil and water safety.
• Sensitisation campaigns to the farmers and other stakeholders in the production chain on the dangers associated with food production on the contaminated field and that of using contaminated water for irrigation will contribute a lot.
• Creating awareness on the danger associated with consuming contaminated food will guide consumers to make a better decision on choosing good quality foods.
• Dangers associated with HMs contamination can be minimised by choosing crops with less metal accumulation capacity and those with low affinity to most dangerous HM species.
• Organic foods are healthier than food produced through conventional agriculture, they contain less HMs and other contaminants, and possess better nutritional qualities.
Vigorous industrial activities, hasty urbanization, poor environmental policy, failure to enforce environmental protection laws, illiteracy, poverty, and food scarcity are among the leading factors that caused HMs contamination in food crops. The leading sources of food crop contamination are sewage and industrial effluents, mining, smelting, illicit dumping of solid waste, abuse of agrochemicals, atmospheric deposit and chemical processing. Leafy vegetables in general and wheat grains are the most contaminated food crops. Pb, Cr and Cd were the most reported HMs in food crops in the last three years. The rate at which food crops are contaminated with HMs in recent years is observed to be in this order: Pb>Cd>Cr>As>Zn>Ni>Cu>Mn>Fe>Hg>Co>Al.
Abdallah B.B., Zhang X., Andreu I., Gates B.D., El Mokni R., Rubino S., Landoulsi A., Chatti A. (2020). Differentiation of Nanoparticles Isolated from Distinct Plant Species Naturally Growing in a Heavy Metal Polluted Site. Journal of Hazardous Materials, 386: 1–8.
Afonne O.J., and Ifediba E.C. (2020). Heavy metals risks in plant foods – need to step up precautionary measures. Current Opinion in Toxicology, 22: 1–6.
Alam M., Khan M., Khan A., Zeb S., Khan M.A., Amin N. ul, Sajid M., Khattak A.M. (2018). Concentrations, dietary exposure, and human health risk assessment of heavy metals in market vegetables of Peshawar, Pakistan. Environmental Monitoring and Assessment, 190: 1–15.
Ali W., Mao K., Zhang H., Junaid M., Xu N., Rasool A., Feng X., Yang Z. (2020). Comprehensive review of the basic chemical behaviours, sources, processes, and endpoints of trace element contamination in paddy soil-rice systems in rice-growing countries. Journal of Hazardous Materials, 397: 1–24.
Ametepey S.T., Cobbina S.J., Akpabey F.J., Duwiejuah A.B., Abuntori Z.N. (2018). Health risk assessment and heavy metal contamination levels in vegetables from tamale metropolis, Ghana. International Journal of Food Contamination, 5: 1-8.
Awino F.B., Maher W.A., Krikowa F., Lynch A.J.J. (2020). Occurrence of Trace Metals in Food Crops Grown on the Mbale Dumpsite, Uganda, and Human Health Risks. Integrated Environmental Assessment and Management, 16: 362–377.
Bala M., Sharma A., Sharma G. (2020). Assessment of heavy metals in faecal pellets of blue rock pigeon from rural and industrial environment in India. Environmental Science and Pollution Research, 27: 43646-43655.
Baruah N., Mondal S.C., Farooq M., Gogoi N. (2019). Influence of Heavy Metals on Seed Germination and Seedling Growth of Wheat, Pea, and Tomato. Water, Air, and Soil Pollution, 230: 1–15.
Bhagwat V.R. (2019). Safety of water used in food production. In R. L. Singh & S. Mondal (Eds.), Food Safety and Human Health (first, pp. 219–247). Elsevier Inc.
Chaoua S., Boussaa S., El Gharmali A., Boumezzough A. (2019). Impact of irrigation with wastewater on accumulation of heavy metals in soil and crops in the region of Marrakech in Morocco. Journal of the Saudi Society of Agricultural Sciences, 18: 429–436.
Cheshmazar E., Arfaeinia H., Karimyan K., Sharafi H., Hashemi S.E. (2018). Dataset for effect comparison of irrigation by wastewater and ground water on amount of heavy metals in soil and vegetables: Accumulation, transfer factor and health risk assessment. Data in Brief, 18: 1702–1710.
Chojnacka K., Witek-Krowiak A., Moustakas K., Skrzypczak D., Mikula K., Loizidou M. (2020). A transition from conventional irrigation to fertigation with reclaimed wastewater: Prospects and challenges. Renewable and Sustainable Energy Reviews, 130: 1–14.
Cooper A.M., Felix D., Alcantara F., Zaslavsky I., Work A., Watson P.L., Pezzoli K., Yu Q., Zhu D., Scavo A.J., Zarabi Y., Schroeder J.I. (2020). Monitoring and mitigation of toxic heavy metals and arsenic accumulation in food crops: A case study of an urban community garden. Plant Direct, 4: 1–12.
Deng M., Yang X., Dai X., Zhang Q., Malik A., Sadeghpour A. (2020). Heavy metal pollution risk assessments and their transportation in sediment and overlay water for the typical Chinese reservoirs. Ecological Indicators, 112: 1–8.
Deng X., Yang Y., Zeng H., Chen Y., Zeng Q. (2020). Variations in iron plaque, root morphology and metal bioavailability response to seedling establishment methods and their impacts on Cd and Pb accumulation and translocation in rice (Oryza sativa L.). Journal of Hazardous Materials, 384: 1–8.
Deviller G., Lundy L., Fatta-Kassinos D. (2020). Recommendations to derive quality standards for chemical pollutants in reclaimed water intended for reuse in agricultural irrigation. Chemosphere, 240: 1–8.
Doabi S.A., Karami M., Afyuni M., Yeganeh M. (2018). Pollution and health risk assessment of heavy metals in agricultural soil, atmospheric dust and major food crops in Kermanshah province, Iran. Ecotoxicology and Environmental Safety, 163: 153–164.
Ebrahimi-Najafabadi H., Pasdaran A., Rezaei Bezenjani R., Bozorgzadeh E. (2019). Determination of toxic heavy metals in rice samples using ultrasound assisted emulsification microextraction combined with inductively coupled plasma optical emission spectroscopy. Food Chemistry, 289: 26–32.
Edelstein M., Ben-Hur M. (2018). Heavy metals and metalloids: Sources, risks and strategies to reduce their accumulation in horticultural crops. Scientia Horticulturae, 234: 431–444.
Edogbo B., Okolocha E., Maikai B., Aluwong T., and Uchendu C. (2020). Risk analysis of heavy metal contamination in soil, vegetables and fish around Challawa area in Kano State, Nigeria. Scientific African, 7: 1–10.
Eissa M.A., Negim O.E. (2018). Heavy metals uptake and translocation by lettuce and spinach grown on a metal-contaminated soil. Journal of Soil Science and Plant Nutrition, 18: 1097–1107.
Ekere N.R., Ugbor M.C.J., Ihedioha J.N., Ukwueze N.N., Abugu H.O. (2020). Ecological and potential health risk assessment of heavy metals in soils and food crops grown in abandoned urban open waste dumpsite. Journal of Environmental Health Science and Engineering, 18: 711-721.
El-Hassanin A.S., Samak M.R., Abdel-Rahman G.N., Abu-Sree Y.H., Saleh E.M. (2020). Risk assessment of human exposure to lead and cadmium in maize grains cultivated in soils irrigated either with low-quality water or freshwater. Toxicology Reports, 7: 10–15.
El-Radaideh N.M., Al-Taani A.A.A.K. (2018). Geo-environmental study of heavy metals of the agricultural highway soils, NW Jordan. Arabian Journal of Geosciences, 11: 1–14.
Elmi A., Al-Khaldy A., AlOlayan M. (2020). Sewage sludge land application: Balancing act between agronomic benefits and environmental concerns. Journal of Cleaner Production, 250: 119512.
Fung F., Wang H.S., Menon S. (2018). Food safety in the 21st century. Biomedical Journal, 41: 88–95.
Gallo M., Ferrara L., Calogero A., Montesano D., Naviglio D. (2020). Relationships between food and diseases: what to know to ensure food safety. Food Research International, 137: 1–16.
Garrigues S., Esteve-Turrillas F.A., de la Guardia M. (2019). Greening the wastes. Current Opinion in Green and Sustainable Chemistry, 19: 24–29.
Gebeyehu H.R., Bayissa L.D. (2020). Levels of heavy metals in soil and vegetables and associated health risks in Mojo area, Ethiopia. PLoS ONE, 15: 1–22.
Giri S., Mahato M.K., Bhattacharjee S., Singh A.K. (2020). Development of a new noncarcinogenic heavy metal pollution index for quality ranking of vegetable, rice, and milk. Ecological Indicators, 113: 106214.
Gupta N., Yadav K.K., Kumar V., Kumar S., Chadd R.P., Kumar A. (2019). Trace elements in soil-vegetables interface: Translocation, bioaccumulation, toxicity and amelioration - A review. Science of the Total Environment, 651: 2927–2942.
Hanfi M.Y., Mostafa M.Y.A., Zhukovsky M. V. (2020). Heavy metal contamination in urban surface sediments: sources, distribution, contamination control, and remediation. Environmental Monitoring and Assessment, 192: 1–21.
Hasan A.B., Reza A.H.M.S., Kabir S., Siddique M.A.B., Ahsan M.A., Akbor M.A. (2020). Accumulation and distribution of heavy metals in soil and food crops around the ship breaking area in southern Bangladesh and associated health risk assessment. SN Applied Sciences, 2: 1–18.
Hou S., Zheng N., Tang L., Ji X., Li Y. (2019). Effect of soil pH and organic matter content on heavy metals availability in maize (Zea mays L.) rhizospheric soil of non-ferrous metals smelting area. Environmental Monitoring and Assessment, 191: 1–10.
Hu B., Shao S., Fu Z., Li Y., Ni H., Chen S., Zhou Y., Jin B., Shi Z. (2019). Identifying heavy metal pollution hot spots in soil-rice systems: A case study in South of Yangtze River Delta, China. Science of the Total Environment, 658: 614–625.
Huang Y., Wang L., Wang W., Li T., He Z., Yang X. (2019). Current status of agricultural soil pollution by heavy metals in China: A meta-analysis. Science of the Total Environment, 651: 3034–3042.
Idrees M. (2020). Analysis and Human Health Risk from Selected Heavy Metals in Common Instant Noodles. Biological Trace Element Research, 198: 339-343.
Jafari A., Kamarehie B., Ghaderpoori M., Khoshnamvand N., Birjandi M. (2018). The concentration data of heavy metals in Iranian grown and imported rice and human health hazard assessment. Data in Brief, 16:453–459.
Khanam R., Kumar A., Nayak A.K., Shahid M., Tripathi R., Vijayakumar S., Bhaduri D., Kumar U., Mohanty S., Panneerselvam P., Chatterjee D., Satapathy B.S., Pathak H. (2020). Metal(loid)s (As, Hg, Se, Pb and Cd) in paddy soil: Bioavailability and potential risk to human health. Science of the Total Environment, 699: 134330.
Kilic S., Cam I.B., Tongur T., Kilic M. (2018). Health Risk Assessment of Exposure to Heavy Metals and Aflatoxins via Dietary Intake of Dried Red Pepper from Marketplaces in Antalya, Southern Turkey. Journal of Food Science, 83: 2675–2681.
Kladsomboon S., Jaiyen C., Choprathumma C., Tusai T., Apilux A. (2020). Heavy metals contamination in soil, surface water, crops, and resident blood in Uthai District, Phra Nakhon Si Ayutthaya, Thailand. Environmental Geochemistry and Health, 42: 545–561.
Kumar S., Prasad S., Yadav K.K., Shrivastava M., Gupta N., Nagar S., Bach Q.V., Kamyab H., Khan S.A., Yadav S., Malav L.C. (2019). Hazardous heavy metals contamination of vegetables and food chain: Role of sustainable remediation approaches - A review. Environmental Research, 179:108792.
Kumar V., Parihar R.D., Sharma A., Bakshi P., Singh Sidhu G.P., Bali A.S., Karaouzas I., Bhardwaj R., Thukral A.K., Gyasi-Agyei Y., Rodrigo-Comino J. (2019). Global evaluation of heavy metal content in surface water bodies: A meta-analysis using heavy metal pollution indices and multivariate statistical analyses. Chemosphere, 236:1–14.
Larsen K.V., Cobbina S.J., Ofori S.A., Addo D. (2020). Quantification and health risk assessment of heavy metals in milled maize and millet in the Tolon District, Northern Ghana. Food Science and Nutrition, 8: 4205–4213.
Leblebici Z., Kar M., and Başaran L. (2020). Assessment of the Heavy Metal Accumulation of Various Green Vegetables Grown in Nevşehir and their Risks Human Health. Environmental Monitoring and Assessment, 192: 1–8.
Liang H., Wu W.L., Zhang Y.H., Zhou S.J., Long C.Y., Wen J., Wang B.Y., Liu Z.T., Zhang C.Z., Huang P.P., Liu N., Deng X.L., Zou F. (2018). Levels, temporal trend and health risk assessment of five heavy metals in fresh vegetables marketed in Guangdong Province of China during 2014–2017. Food Control, 92: 107–120.
Liao J., Wen Z., Ru X., Chen J., Wu H., Wei C. (2016). Distribution and migration of heavy metals in soil and crops affected by acid mine drainage: Public health implications in Guangdong Province, China. Ecotoxicology and Environmental Safety, 124: 460–469.
Liu P., Hu W., Tian K., Huang B., Zhao Y., Wang X., Zhou Y., Shi B., Kwon B.O., Choi K., Ryu J., Chen Y., Wang T., Khim J.S. (2020). Accumulation and ecological risk of heavy metals in soils along the coastal areas of the Bohai Sea and the Yellow Sea: A comparative study of China and South Korea. Environment International, 137: 1–12.
Liu Y., Tan H., Zhou S., Dong K.F., Xiao G. (2019). Regional characteristics of dietary lead intake in the Chinese population. Science of the Total Environment, 691: 393–400.
Lizarazo M.F., Herrera C.D., Celis C.A., Pombo L.M., Teheran A.A., Pineros L.G., Forero S.P., Velandia J.R., Díaz F.E., Andrade W.A., Rodriguez O.E. (2020). Heliyon Contamination of staple crops by heavy metals in Sibate, Colombia. Heliyon, 6: 1–10.
Malavolti M., Fairweather-Tait S.J., Malagoli C., Vescovi L., Vinceti M., Filippini T. (2020). Lead exposure in an Italian population: Food content, dietary intake and risk assessment. Food Research International, 137: 1–9.
Margenat A., Matamoros V., Díez S., Cañameras N., Comas J., Bayona J.M. (2018). Occurrence and bioaccumulation of chemical contaminants in lettuce grown in peri-urban horticulture. Science of the Total Environment, 637–638: 1166–1174.
Massoud R., Hadiani M.R., Hamzehlou P., Khosravi-Darani K. (2019). Bioremediation of heavy metals in food industry: Application of Saccharomyces cerevisiae. Electronic Journal of Biotechnology, 37: 56–60.
Mehmood A., Aslam Mirza M., Aziz Choudhary M., Kim K.H., Raza W., Raza N., Soo Lee S., Zhang M., Lee J.H., Sarfraz M. (2019). Spatial distribution of heavy metals in crops in a wastewater irrigated zone and health risk assessment. Environmental Research, 168: 382–388.
Melai V., Giovannini A., Chiumiento F., Bellocci M., Migliorati G. (2018). Occurrence of metals in vegetables and fruits from areas near landfill in Southern Italy and implications for human exposure. International Journal of Food Contamination, 5: 1–13.
Mihaileanu R.G., Neamtiu I.A., Fleming M., Pop C., Bloom M.S., Roba C., Surcel M., Stamatian F., Gurzau E. (2019). Assessment of heavy metals (total chromium, lead, and manganese) contamination of residential soil and homegrown vegetables near a former chemical manufacturing facility in Tarnaveni, Romania. Environmental Monitoring and Assessment, 191: 1–13.
Muhammad S., Ullah R., Jadoon I.A.K. (2019). Heavy metals contamination in soil and food and their evaluation for risk assessment in the Zhob and Loralai valleys, Baluchistan province, Pakistan. Microchemical Journal, 149:1–7.
Mwesigye A.R., Young S.D., Bailey E.H., Tumwebaze S.B. (2019). Uptake of trace elements by food crops grown within the Kilembe copper mine catchment, Western Uganda. Journal of Geochemical Exploration, 207: 1–8.
Nachman K.E., Ginsberg G.L., Miller M.D., Murray C.J., Nigra A.E., Pendergrast C.B. (2017). Mitigating dietary arsenic exposure: Current status in the United States and recommendations for an improved path forward. Science of the Total Environment, 581–582: 221–236.
Neto C. deVasconcelos M., Silva T.B.C., Araújo V.E. de, Souza S.V.C. de. (2019). Lead contamination in food consumed and produced in Brazil: Systematic review and meta-analysis. Food Research International, 126: 1–15.
Ngure V., Kinuthia G. (2020). Health risk implications of lead, cadmium, zinc, and nickel for consumers of food items in Migori Gold mines, Kenya. Journal of Geochemical Exploration, 209: 1–13.
Noh K., Thi L.T., Jeong B.R. (2019). Particulate matter in the cultivation area may contaminate leafy vegetables with heavy metals above safe levels in Korea. Environmental Science and Pollution Research, 26: 25762–25774.
Obiora S.C., Chukwu A., Chibuike G., Nwegbu A.N. (2019). Potentially harmful elements and their health implications in cultivable soils and food crops around lead-zinc mines in Ishiagu, Southeastern Nigeria. Journal of Geochemical Exploration, 204: 289–296.
Oguntade O.A., Adegbuyi A.A., Nassir A.L., Olagunju S.O., Salami W.A., Adewale R.O. (2020). Geoassessment of heavy metals in rural and urban floodplain soils: health implications for consumers of Celosia argentea and Corchorus olitorius vegetables in Sagamu, Nigeria. Environmental Monitoring and Assessment, 192: 1–19.
Olutona G.O., Aderemi M.A. (2019). Organochlorine pesticide residue and heavy metals in leguminous food crops from selected markets in Ibadan, Nigeria. Legume Science, 1: 1–9.
Peng J., Li F., Zhang J., Chen Y., Cao T., Tong Z., Liu X., Liang X., Zhao X. (2019). Comprehensive assessment of heavy metals pollution of farmland soil and crops in Jilin Province. Environmental Geochemistry and Health, 1: 1–15.
Rahmdel S., Rezaei M., Ekhlasi J., Zarei S.H., Akhlaghi M., Abdollahzadeh S.M., Sefidkar R., Mazloomi S.M. (2018). Heavy metals (Pb, Cd, Cu, Zn, Ni, Co) in leafy vegetables collected from production sites: their potential health risk to the general population in Shiraz, Iran. Environmental Monitoring and Assessment, 190: 1–10.
Rai P.K., Lee S.S., Zhang M., Tsang Y.F., Kim K.H. (2019). Heavy metals in food crops: Health risks, fate, mechanisms, and management. Environment International, 125: 365–385.
Rehman ur K., Bukhari S.M., Andleeb S., Mahmood A., Erinle K.O., Naeem M.M., Imran Q. (2019). Ecological risk assessment of heavy metals in vegetables irrigated with groundwater and wastewater: The particular case of Sahiwal district in Pakistan. Agricultural Water Management, 226:1–7.
Rehman Z.U., Khan S., Shah M.T., Brusseau M.L., Khan S.A., Mainhagu J. (2018). Transfer of Heavy Metals from Soils to Vegetables and Associated Human Health Risks at Selected Sites in Pakistan. Pedosphere, 28: 666–679.
Reis J., Mizusawa H. (2019). Environmental challenges for the nervous system and the brain in Japan. Revue Neurologique, 175: 693–697.
Saadati M., Soleimani M., Sadeghsaba M., Hemami M.R. (2020). Bioaccumulation of heavy metals (Hg, Cd and Ni) by sentinel crab (Macrophthalmus depressus) from sediments of Mousa Bay, Persian Gulf. Ecotoxicology and Environmental Safety, 191: 1–7.
Samiee F., Vahidinia A., Taravati Javad M., Leili M. (2019). Exposure to heavy metals released to the environment through breastfeeding: A probabilistic risk estimation. Science of the Total Environment, 650:3075–3083.
Sawut R., Kasim N., Maihemuti B., Hu L., Abliz A., Abdujappar A., Kurban M. (2018). Pollution characteristics and health risk assessment of heavy metals in the vegetable bases of northwest China. Science of the Total Environment, 642: 864–878.
Semenov D.O., Fatjejev A.I., Smirnova K.B., Shemet A.M., Lykova O.A., Tyutyunnyk N. V., Pogromska I.A. (2019). Geochemical and anthropogenic factors of variability of heavy metals content in the soils and crops of Ukraine at the example of copper. Environmental Monitoring and Assessment, 191: 1–9.
Shakoor M.B., Nawaz R., Hussain F., Raza M., Ali S., Rizwan M., Oh S.E., Ahmad S. (2017). Human health implications, risk assessment and remediation of As-contaminated water: A critical review. Science of the Total Environment, 601–602: 756–769.
Sharifan H., Moore J., Ma X. (2020). Zinc oxide (ZnO) nanoparticles elevated iron and copper contents and mitigated the bioavailability of lead and cadmium in different leafy greens. Ecotoxicology and Environmental Safety, 191: 1–8.
Sharma A., Nagpal A.K. (2020). Contamination of vegetables with heavy metals across the globe: hampering food security goal. Journal of Food Science and Technology, 57: 391–403.
Sharma S., Nagpal A.K., Kaur I. (2018). Heavy metal contamination in soil, food crops and associated health risks for residents of Ropar wetland, Punjab, India and its environs. Food Chemistry, 255: 15–22.
Singh J., Dutta T., Kim K.H., Rawat M., Samddar P., Kumar P. (2018). “Green” synthesis of metals and their oxide nanoparticles: Applications for environmental remediation. Journal of Nanobiotechnology, 16: 1–24.
Skendi A., Papageorgiou M., Irakli M., Katsantonis D. (2020). Presence of mycotoxins, heavy metals and nitrate residues in organic commercial cereal-based foods sold in the Greek market. Journal Fur Verbraucherschutz Und Lebensmittelsicherheit, 15: 109–119.
Sun L., Guo D., Liu K., Meng H., Zheng Y., Yuan F., Zhu G. (2019). Levels, sources, and spatial distribution of heavy metals in soils from a typical coal industrial city of Tangshan, China. Catena, 175: 101–109.
Sun Y., Li H., Guo G., Semple K.T., Jones K.C. (2019). Soil contamination in China: Current priorities, defining background levels and standards for heavy metals. Journal of Environmental Management, 251: 109512.
Tibu C., Annang T.Y., Solomon N., Yirenya-Tawiah D. (2019). Effect of the composting process on physicochemical properties and concentration of heavy metals in market waste with additive materials in the Ga West Municipality, Ghana. International Journal of Recycling of Organic Waste in Agriculture, 8: 393–403.
Tokalıoğlu Ş., Çiçek B., İnanç N., Zararsız G., Öztürk A. (2018). Multivariate Statistical Analysis of Data and ICP-MS Determination of Heavy Metals in Different Brands of Spices Consumed in Kayseri, Turkey. Food Analytical Methods, 11: 2407–2418.
Vardhan K.H., Kumar P.S., Panda R.C. (2019). A review on heavy metal pollution, toxicity and remedial measures: Current trends and future perspectives. Journal of Molecular Liquids, 290: 111197.
Vatanpour N., Feizy J., Hedayati Talouki H., Es’haghi Z., Scesi L., Malvandi A.M. (2020). The high levels of heavy metal accumulation in cultivated rice from the Tajan river basin: Health and ecological risk assessment. Chemosphere, 245: 1–8.
Vipham J.L., Amenu K., Alonso S., Ndahetuye J.B., Zereyesus Y., Nishimwe K., Bowers E., Maier D., Sah K., Havelaar A., Grace D. (2020). No food security without food safety: Lessons from livestock related research. Global Food Security, 26: 1–7.
Wang H., Li X., Chen Y., Li Z., Hedding D.W., Nel W., Ji J., Chen J. (2020). Geochemical behavior and potential health risk of heavy metals in basalt-derived agricultural soil and crops: A case study from Xuyi County, eastern China. The Science of the Total Environment, 729: 139058.
Wang L., Peng X., Fu H., Huang C., Li Y., Liu Z. (2020). Recent advances in the development of electrochemical aptasensors for detection of heavy metals in food. Biosensors and Bioelectronics, 147:111777.
Wang S., Wu W., Liu F. (2019). Assessment of the human health risks of heavy metals in nine typical areas. Environmental Science and Pollution Research, 26:12311–12323.
Weber A.M., Mawodza T., Sarkar B., Menon M. (2019). Assessment of potentially toxic trace element contamination in urban allotment soils and their uptake by onions: A preliminary case study from Sheffield, England. Ecotoxicology and Environmental Safety, 170:156–165.
Wei J., Cen K. (2020). Contamination and health risk assessment of heavy metals in cereals, legumes, and their products: A case study based on the dietary structure of the residents of Beijing, China. Journal of Cleaner Production, 260: 1–10.
Wu S., Zheng Y., Li X., Han Y., Qu M., Ni Z., Tang F., Liu Y. (2019). Risk assessment and prediction for toxic heavy metals in chestnut and growth soil from China. Journal of the Science of Food and Agriculture, 99: 4114–4122.
Yu Y., Zhu X., Li L., Lin B., Xiang M., Zhang X., Chen X., Yu Z., Wang Z., Wan Y. (2019). Health implication of heavy metals exposure via multiple pathways for residents living near a former e-waste recycling area in China: A comparative study. Ecotoxicology and Environmental Safety, 169:178–184.
Zaanouni N., Gharssallaoui M., Eloussaief M., Gabsi S. (2018). Heavy metals transfer in the olive tree and assessment of food contamination risk. Environmental Science and Pollution Research, 25: 18320–18331.
Zhang T., Xu W., Lin X., Yan H., Ma M., He Z. (2019). Assessment of heavy metals pollution of soybean grains in North Anhui of China. Science of the Total Environment, 646: 914–922.
Zhen H., Gao W., Jia L., Qiao Y., Ju X. (2020). Environmental and economic life cycle assessment of alternative greenhouse vegetable production farms in peri-urban Beijing, China. Journal of Cleaner Production, 269: 1–10.
Zheng S., Wang Q., Yuan Y., Sun W. (2020). Human health risk assessment of heavy metals in soil and food crops in the Pearl River Delta urban agglomeration of China. Food Chemistry, 316:1–8.
Zhou X., Zheng N., Su C., Wang J., Soyeurt H. (2019). Relationships between Pb, As, Cr, and Cd in individual cows’ milk and milk composition and heavy metal contents in water, silage, and soil. Environmental Pollution, 255: 1–7.
Zhou Y., Jia Z., Wang J., Chen L., Zou M., Li Y., Zhou S. (2019). Heavy metal distribution, relationship and prediction in a wheat-rice rotation system. Geoderma, 354: 1–11.
Zwolak A., Sarzyńska M., Szpyrka E., Stawarczyk K. (2019). Sources of Soil Pollution by Heavy Metals and Their Accumulation in Vegetables: a Review. Water, Air, and Soil Pollution, 230: 1–9.