**3. Impact of heavy metals on the quality of vegetables**

Vegetation sensitivity to nutrition and metal concentrations varies, and their reactions can be seen in variations in stain concentration, liquid content, dehydrated weight, as well as development [21–23]. All of these variations in plant properties lead to different light absorption as well as reflectivity characteristics, which can be utilised to determine soil pollution and plant physiological condition. A few research findings have shown that metal and nutritional anxiety in plants contribute to differences in the supernatural reflectivity of the undergrowth [24–26], which may end up causing numerous biological effects in the plants and thus contribute to nutritional availability in veggies increasing or decreasing. Toxicity of metals in plants causes high germination inhibition, significant reductions in rates of growth, variations in photosynthetic efficiency, respiration, and transpiration, as well as changes in nutrient homeostasis and Mn, K, Mg. [27, 28] discovered distinctive leaf symptoms in Raphanus and Phaseolus, as well as a decrease in the root: shoot ratio and ratio of biomass. Higher levels of HM as well as cytochemical localization of Zn in *Raphanus* and *Pha-seolus*, which may cause stress, defence, and detoxification, are attributable to Zn′s direct actions and the combined indirect effects of heavy metal (**Table 1**).


#### **Table 1.**

*Heavy metals impacted vegetables from different areas.*

#### *Heavy Metal Contamination in Vegetables and Their Toxic Effects on Human Health DOI: http://dx.doi.org/10.5772/intechopen.102651*

Growth of plant was inhibited in both treatments of Cd, i.e. leaf chlorosis symptoms at 10 M Cd and necrotic patches at 100 M Cd, according to [36, 37], and browning of root was detected in both dealings. In root abstracts of Cd-exposed plants, the action of phosphoenolpyruvate carboxylase, which is involving in the anaplerotic fixation of CO2 into organic acids, increased. At 100 M Cd, citrate synthase, isocitrate dehydrogenase, and malate dehydrogenase activities increased significantly in leaf extracts, although fumarase activity declined. Membrane damage, electron transport disturbances, enzyme inhibition/ activation, and interactions with nucleic acids are among known effects of metal toxicity [38, 39]. The production of oxidative stress and the substitution of critical cofactors of numerous enzymes, like Zn, Fe, and Mn, are two plausible causes for the development of these illnesses. Various researchers have associated oxidative stress with introduction to high heavy metal concentrations [40, 41]. Heavy metals' influence on plants, according to [42–44], growth suppression, physical harm, and a decay in physical, biological, and plant function are all consequences. Heavy metal toxicity disrupts cell and organelle membrane integrity by blocking enzymes, polynucleotides, and important nutrient and ion transport systems, displacing and/or substituting essential ions from cellular locations, denaturing and inactivating enzymes, and denaturing and inactivating enzymes. At supraoptimal absorptions, heavy metals as Cd, Pb, Hg, Cu, Zn, and Ni impede plant development, growth, and yield.

Interspecies distinctions in metal and nutrient uptake, as well as differences caused by therapeutic interventions within the similar plant, are minor and could be due to plant biomass and root exudes into the soils. The availability of metals and nutrients for plant absorption will be affected when plants develop and roots grow in soil due to biogeochemical interactions of organic acids generated by root oozes. This method may explain why tomato (*Solanum lycopersicum*) and pepper (*Piper nigrum*) plants absorb more Cu as well as Zn than other crops. According to [45, 46], Zn & Cu create organometallic compounds with organic acids found in root exudes, resulting in enhanced plant absorption. Excessive Zn in the growth media was shown to be hazardous to all 3 vegetable crops. Chlorosis in early leaves, searing of coralloid roots, and severe suppression of plant development were all signs of toxicity. With rising Zn concentrations, shoot fresh weight (FW) dropped.

Cu had a negative effect on seed germination in Chinese cabbage, according to [47]. (*Brassica pekinensis*). The germination rate was significantly lowered by the 0.5 mmol L1Cu treatment, with a median fatal dosage of 0.348 mmol L1. In early seedlings, Cu lowered root and shoot lengths, however the0.008 mmol L1treatment resulted in stimulatory elongation of the shoots. The aluminium coagulators had a toxic outcome on the plant growth of vegetable seeds at the tested concentrations. Furthermore, excessive copper levels in growing media harmed all 3 vegetable crops, causing chlorosis in new leaves, brown, stunted, coralloid roots, as well as plant development inhibition [48, 49].

Lin et al. [40] find that under higher Cd concentrations, the content of protein of desolate carrot (Daucus carota) and common sunflower (*Helianthus annuus*) decreased. Increased Zn concentrations reduced the content of protein of algae and Rapeseed (*Brassica napus*), according to [50]. The reduce in content of protein has been linked to increased protease activity speeding up protein breakdown [51, 52] or heavy metals interfering with nitrogen metabolism. Heavy metals, according to [53], may disrupt nitrogen metabolism, reducing protein synthesis in vegetables, and are also reason for a decrease in photosynthesis, which affects protein synthesis [40]. Cd could impair the absorption of Fe, potassium, Mn & calcium [54], and the toxicity amount had been observed to be higher in the case of specific heavy metals.
