Vegetables contain a wide variety of micronutrients that are essential for human health. Scientific evidence shows that vegetables have enormous health benefits for those who consume sufficient quantities [1]. Human diet habit is responsible for about 33% of cancer-related health consequences and about 50% of cardiovascular problems [2]. Biologically active micronutrients in vegetables have antioxidants, anti-carcinogens, and anti-immunological effects on the human body. In addition, it provides essential vitamins, minerals and dietary fibre to the human body [2–5]. The physical and chemical properties of micronutrients in vegetables, with their medicinal and protective properties, denote a source of nutraceuticals and phytonutraceuticals [3–4, 6]. Observe, for instance, (a) ascorbic acid is found in almost all vegetables and has therapeutic effects on cardiovascular disease and immunity; (b) alpha and beta carotenes are found in almost all vegetables and offer protection from diabetes, coronary artery disease, cancer, and night blindness; (c) dietary fibre in vegetables helps to prevent diabetes, heart disease and colorectal cancer; and (d) folates in dark green vegetables like spinach and broccoli have potential health benefits including improving fertility, preventing cancer, and heart disease [3, 4]. Even so, several studies found that a plant-based healthy diet could reduce coronavirus development and severity [7, 8]. Thus, in the new-normal situation of the world, the interest to vegetables in the human diet has increased (27%) worldwide [7]. Globally, health authorities like WHO promote sufficient intake of vegetables, recommending 220gm of vegetables per person per day [9].
Vegetables and other agri-foods require a sufficient supply of nutrients to grow, and soil health is essential to ensure a sustainable supply of nutrients. Recently, in different parts of the world, experts and regulators have been trying to sustain soil health in several innovative ways like applying nanotechnology, foliar fertilization, organic farming, fertilizer variation, carbon regeneration, and crop rotation [10–13]. However, soil health management is challenging because of recording the inflow and outflow of nutrients in the soil [10, 14]. Several inflows of nutrients to the soil system like decomposition of biomass; enduring of soil minerals; fertilizer applications; N-fixation by legumes; ground rock products; inorganic industrial byproducts; atmospheric deposition, such as N and S from acid rain or N-fixation by lightning discharges; deposition of nutrient-rich sediment from erosion and flooding. Again the outflows of nutrients from soil like runoff loss of dissolved nutrients in water moving across the soil surface; erosion-based loss of nutrients are removed from fields by wind or water movement; leaching loss of dissolved nutrients in the water that moves down through the soil to groundwater or out of the land through drain lines; gaseous losses to the atmosphere through volatilization and denitrification; crop uptake and removal of nutrients from the farm in harvested products [14, 15]. So the most dependable and proven way to sustain a soil's nutrient cycle is the controlled application of fertilizer in the farmland. It is the best way to produce quality yield of vegetables and other crops [16–18]. Chemical fertilizers mainly contain phosphate, nitrate, ammonium and potassium salts [18]. In developing countries with densely populated areas, such as Bangladesh, conventional chemical fertilizers are supplied to farms regularly, patronized by the government stages, to increase commercial yield [14, 19]. Between 1971 and 2020, fertilizer consumption in Bangladesh grew substantially from 12.9 to 320.9 kilograms per hectare [20]. In 2020, fertilizer consumption for Bangladesh was 320.9 kilograms per hectare which are much more than different countries like turkey (100.4 Kg/ha), China (301.5 Kg/ha), Britain (287.5 Kg/ha), Germany (205.4 Kg/ha) France (180.1 Kg/ha) US (160.8 Kg/ha) Italy (126.4 Kg/ha), India (121.4 Kg/ha), Greece (115.4 Kg/ha), and Indonesia (106.9 Kg/ha) [18]. Besides this, the excessive and improper use of traditional fertilizers has a widespread detrimental effect on the ecosystem [21–24, 25]. The commercial fertilizer also contained substantial amounts of toxic metals and could contribute to the accumulation of toxic metals such as lead, cadmium, arsenic, chromium, and radioactive elements in the soil [17, 18, 21, 24, 26]. Accordingly, it decreases the nutrient density in consumed plants [24]. Aside from this, pesticides are used around the world to ensure the quality of vegetables and other agro-crops, as well as to increase their yield, thus ensuring food security [14, 27, 28]. Approximately three billion kilograms of pesticides are used worldwide each year, with an annual increase of 11% [27]. In Bangladesh, with highly demandable and quickly degradable crops like vegetables and fruits, farmers are extensively using pesticides on them [29]. About 40,000 metric tons of pesticide has produced each year at a 6% incremental rate [29]. Organochlorin substances, organophosphates, carbamates, pyrethroid and heterocyclic pesticides, nitro compounds and amides are commonly used as pesticide chemicals for the cultivation of vegetables, fruits and crops [29, 30]. But the worst part is that pesticide chemicals adversely affect the human body both acutely and chronically [27, 28, 30]. In addition, it might carry significant amounts of toxic heavy metals that contaminate vegetables and other edible agro-foods [5, 27, 30]. However, several sources of elements or components such as climate change, unwanted seasonal variation, excessive use of fertilizer and pesticides, industrial effluent, electronic waste, man-made waste, poor management of agricultural land, etc. [31–35] that influence or hamper the balance of the nutrient cycle affects overall soil health and plant nutrients [15].
Currently, toxic heavy metals integration into the soil nutrients, at a threatening level, gradually hampers food health with the human body by affecting soil biology [21, 36]. The translocation of heavy metals from soil to plants is maintained a dynamic equilibrium using the soil's physical, chemical, and biological properties [26, 37]. So the toxic metals can smoothly accumulate from the soil systems to plants' roots and shoots. Hence, the rapid urbanization, industrialization and climate change issues in the last 30–40 years of the history of Bangladesh have remarkably decreased the agricultural land [13, 14, 35]. At that time, to ensure food self-sufficiency, hybrid seeds have used with imbalanced practices of fertilizers and pesticides. Perhaps farmed soil is now facing severe environmental health risks [13, 14]. The cultivation of vegetables in contaminated soil absorbs heavy metals as well as from the air also. The uptake of vegetables containing heavy metals over the permissible limit is the ultimate risk to human health [38]. The heavy metals become toxic when exposed at a chronic level by the human body but are not perfectly metabolic [38]. The undesirable heavy metals then associate harmful effects after several years of exposure. The deleterious effects can be non-carcinogenic and carcinogenic based on heavy metal exposure to the human body over a time period [38]. Exposure to heavy metals can direct consumption of contaminated vegetables and ingestion, inhalation and dermal absorption of workers and residents/non-residents from the soil and fertilizer/pesticides [39, 40]. But about 90% of the heavy metal exposure to human health contributes to the consumption of vegetables only [37]. The easiest instrumental methods of assaying the heavy metals in the different matrices are flame atomic absorption spectrometry (F-AAS) and graphite furnace atomic absorption (GF-AAS). Therefore, in this study, the heavy metal exposure by fertilizer and pesticides used commercially in selected areas is essential to monitor using F-AAS and GF-AAS as toxic metal sources. Also, soil quality indexing regarding harmful metal exposure is necessary to determine any ecological risk in industrial and non-industrial areas. Finally, human health risk implications due to the consumption of vegetables in industrial and non-industrial regions need to assess urgently.