Health Risk Associated with Copper Intake through Vegetables in Different Countries

Sustainable development goals aim to attain food security by 2030. To attain food security, it becomes extremely important to target various aspects of food security where safety of food is a major factor. In order to meet the growing population demand, efforts are being made to increase production of food and thus the safety aspect is often ignored. Irrational anthropogenic activities have impacted and deteriorated the ambient environment. Degradation of soil and water has resulted in buildup of contaminants in these spheres and further transfer of contaminants into the food chain. Increase in heavy metals in our surroundings is reported in many parts of the world. Further, increase in concentration of metals in soil and water result in the transfer of these metals into food chain. Unlike other metals copper is although is an essential element for living organisms but excessive consumption of copper is known to cause toxic impacts to living organisms. Green leafy vegetables are considered as hyperaccumulators for copper. The excessive concentration of copper in vegetables is not limited to any one region of the world. The present review summarizes the reports of copper content in vegetables in various parts of the world and health effects associated with it.


INTRODUCTION
Sustainable development goals target to achieve food security for all by 2030. In order to meet with the demands of growing population, the focus of agriculture is to increase the production of food and thus the quality and safety of the food is neglected [1], [2]. Cultivation of crops using wastewater and on polluted lands result in the uptake of contaminants. Increase in heavy metal content in various food crops have been reported in various parts of the world [3]- [5]. Among all food crops, many proteins, and lipids, but also vitamins, minerals and enzymes. Beneficial effects of vegetable for human well-being are well known. The health promoting effects of vegetables have been associated with antioxidative potential of variety of compounds like ascorbic acid, carotenoids, tocopherols, glutathione, phenolic acids, and flavonoids found in them. Vegetables are typically grown on soil, which is the ultimate source of crop nutrients. Contaminated soils, on the other hand, are a source of various pollutants like heavy metals, pesticides etc. that are directly taken up by the plant root system and accumulate in tissues. Post-harvest vegetables may also be at risk from air pollution during transportation and marketing, resulting in higher levels of heavy metals in the produce [6]- [8].
One of the primary and most often discussed ecotoxicological issues is heavy metal poisoning of ecosystem. Among inorganic pollutants (heavy metals, non-metallic salts, acids and bases), heavy metals are the most common inorganic pollutants, and their severe toxicity, non-biodegradability, and high mobility and availability have made them an increasing source of concern around the world a [9]- [12], posing a potential threat to the environment and human health. Despite their poor mobility in soil, these elements alter biochemical processes in organisms, impacting physiological functions even at low concentrations When present in trace amounts, some heavy metals (Cu, Fe, Zn, Mn, etc.) are necessary for plant growth and development, but at high concentrations, they are hazardous. Essential elements have a very different physiology and behaviour than non-essential elements. In risk assessment approaches for essential metals, it is critical to take these processes into account, which include homeostasis, baseline and normative nutritional requirements, and bioavailability. Copper is one such metal.
Copper is essential for plants and being a micronutrient, it plays an important role in number of physiological processes [13]- [16]. Cu in high concentrations pollutes the environment and is hazardous to plants, animals and humans.

CONTAMINATION SOURCES
Heavy metal poisoning of soil is becoming a global problem due to its negative effects on environmental safety. The increase in heavy metal levels in the environment can be attributed to both natural and manmade activities. Parent geologic rock material, volcanic eruptions, spontaneous contributions, or forest fires are natural sources of contamination in soil. Heavy metals accumulate in soil mostly as a result of anthropogenic activity, particularly the application of agrochemicals. Cu is found in nature as native copper [17]- [20], copper sulphides, copper sulfosalts, copper carbonates, and copper (I) and copper (II) oxides. Batteries, pigments and paints, fuel, alloys, catalysts, pesticides and fertilisers are all possible industrial and agricultural sources of copper. Tailings, overburden boulders, and abandoned mines are the main sources of heavy metal contamination in the mining zone. They're all sulfide-rich, and while the metal content isn't high enough to extract economically, it's high enough to pollute the environment. On exposure to oxygen and water, sulphides in tailings, overburden rocks, and abandoned mines produce acid metal drainage. The extraction of low-grade ore is expanding in tandem with the rising demand for Cu. More trash is produced during the extraction of low-grade ore. From 2012 to 2017, global copper (Cu) production increased from 16,692 to 20,029 thousand metric tonnes. With total Cu output of 11,042 thousand metric tonnes, the American continent leads, followed by Asia with 4246.5 thousand metric tonnes.

COPPER IN VEGETABLES
Copper is an important redox active transition metal and exists as Cu 2+ and Cu + in physiological conditions. In plants, copper (Cu) is involved in photosynthetic electron transport, mitochondrial respiration, oxidative stress responses, cell wall metabolism, hormone signalling and as a structural element in regulatory proteins. As a result, plants require Cu as an essential element for appropriate growth and development; when this ion is deficient, plants exhibit distinct symptoms, majority of which harm reproductive organs and young leaves (Copper participates in numerous physiological processes, however, problems arise when excess copper is present in cells). The redox characteristics that contribute towards the essentiality of Cu also make it a toxic element. The generation of highly harmful hydroxyl radicals can be catalysed by redox cycling between Cu 2+ and Cu + , causing damage to biomolecules like proteins, DNA, lipids, and protein In some soils, Cu is naturally present in higher concentrations while in others, the toxic level of Cu is due to human activities like agriculture, smelting, mining and manufacture. Cu has been proven to impede growth and interfere with critical cellular activities including photosynthesis and respiration at concentrations above those required for optimal function.

UPTAKE MECHANISM
Vegetables planted near industrial set ups and busy roads, as well as crops exposed to municipal and agricultural effluents, have a higher concentration of certain elements. Bedrock is the natural source of metals in soil. Some quantity of metal is introduced in the agricultural soil by fertilizers. Surface and ground water, soil, and eventually crop plants may be contaminated with metals. The toxic potential of heavy metals is due to their ability to form stable coordinated compounds with a variety of organic and inorganic ligands, so even at low concentration they serve as biological poisons.  surface also leads to accumulation of heavy metals. This is especially true for vegetables like lettuce, spinach, and endive.

HEALTH RISK DUE TO COPPER IN VEGETABLES
Depending on growth stage and fertiliser treatment, plant species have different capacities for accumulating Cu. Because Cu is quickly absorbed by plant roots and not readily translocated to aboveground portions of the plant, the effect of Cu toxicity is mostly on root growth and shape. Cu transfer into aboveground plant parts is effectively controlled by the substantial concentration of Cu in roots. Some earlier studies on Amaranthus spinosus, Boehmeria niveaL., Eclipta alba, Oryza sativa, Phyllostachys pubescens,Triticum aestivum, Trigonella foenum-graecum, and Willows(Salix spp.), have shown Cu to have a tendency for getting accumulated in root tissues with little upward migration towards shoots. Copper tolerance is related to a plant's ability to store copper in its roots and effectively prevent it from being translocated to photosynthetic regions.
Despite the fact that the plants had an enhanced copper content and had suffered some damage as a result of the Cu treatment, they appeared to be in good health. It was proposed that Chinese cabbage with high Cu level but no obvious signs of damage could pose a risk to human health due to transfer of metal to food.
There is a little difference between the necessary, beneficial, and harmful concentrations of Cu in living systems, which varies significantly depending on Cu speciation and the form of living organisms. As a result, monitoring its bioavailability, speciation, exposure levels, and pathways in live organisms is critical. The main source of heavy metal toxicity in humans is the consumption of Cu-laced food crops.
An overview of the global scenario for contamination of vegetables with Cu is given in Table 1 which summarises recent research on copper contents in different vegetables mainly from 2011 -2021, however a few earlier reports are also included. A study conducted by in Romania (Baia Mare, the mining district) showed that copper accumulated in higher quantities in root vegetables like carrot (2.7 -8.6 mg/kg fw), kohlrabi (0.9 -25.9 mg/kg fw) and parsley (3.3 -49.3 mg/kg fw). Lettuce (0.8 -4.5 mg/kg fw) proved to be a high copper accumulator among leafy vegetables. [2]reported that Copper is present in higher concentration in leafy vegetables (33.22 -6.76μg/g). also showed that leafy and tuberous vegetables accumulate higher level of copper as compared to fruity vegetables.

Regulatory Authorities
Metal industry associations and scientists worldwide, as well as regulatory bodies in Canada, Europe,