According to the data shown above, heavy metal pollution is more prevalent in Asian countries. Rapid population increase and industrialization have resulted in land-use changes across the Asian subcontinent, necessitating persistent efforts to improve agricultural productivity in restricted geographical regions to provide appropriate quantities of food. Unfortunately, to achieve that goal, wastewater, treated effluent, and sludge loaded with heavy metals have frequently been utilized as low-cost irrigation supplies in portions of Asia and Africa, causing food quality and hence health to suffer. The buildup of dangerous heavy metals in plants may easily be transmitted to the human system, resulting in heavy metal bioaccumulation in human tissues. The outcomes of such might have serious ramifications in the future.
Impact of SS on the Human system
According to existing studies, heavy metals in urban soils can enter the human body through skin absorption and dust inhalation, among other routes, and so directly affect, particularly children’s health. The toxicity levels of several chosen metals in humans are as follows: Co Al, Cr Pb, Ni Zn, Cu Cd Hg (Mansourri & Madani 2016). The toxicity of heavy metals in humans is determined by their dose, rate of emission, and duration of exposure. Hg, Cd, and Pb are three heavy metals that have attracted more attention in recent decades (Valavanidis, & Vlachogianni, 2010). In humans, the negative health consequences of Hg and mercuric compounds include potential carcinogens, brain, lung, and kidney damage, fetal harm, high blood pressure or heart rate, vomiting and diarrhea, skin rashes, and eye irritation (Martin, & Griswold, 2009). The US EPA has set a regulatory limit of 2 parts per billion (ppb) for Hg in drinking water (Martin, & Griswold, 2009).
Chronic Cadmium toxicity in children includes lung, kidney, skeletal, and cardiovascular system damage, as well as the development of malignancies of the lungs, kidneys, prostate, and stomach (US-EPA 2010; WHO 2011). People are exposed to Cadmium via consuming contaminated food, smoking cigarettes, and working in cadmium-laden environments and primary metal industries (Paschal 2000).
Lead exposure can occur through the inhalation of contaminated dust particles and aerosols, as well as through the consumption of contaminated food and drink. Lead poisoning affects the kidneys, liver, heart, brain, bones, and neurological system in humans. Headache, dullness, memory loss, and irritability are some of the initial signs of lead poisoning (Flora et al., 2006).
Hexavalent Chromium compounds, which include Ca, Zn, Sr, and Pb chromates, are extremely soluble in water, poisonous, and carcinogenic. Furthermore, Chromium compounds have been linked to delaying the healing of ulcers. Chromate chemicals have also been discovered to be capable of destroying the DNA in cells (Matsumoto, 2006).
Thallium is a soft, tasteless, odorless whitish-blue metal that, when exposed to oxygen, oxidizes to thallium oxide. Thallium can be found in electronics, optical glasses, semi-conductors, and mercury lamps, among other places. Thallium enters the body by eating, inhalation, and cutaneous contact. Thallium is very poisonous, with a fatal dosage ranging from 6 to 40 mg/kg. Thallium poisoning causes anorexia, vomiting, gastrointestinal bleeding, abdominal discomfort, polyneuropathy, alopecia, renal failure, skin erythema, seizures, mood disturbances, autonomic dysfunction, cardiotoxicity, and coma, among other symptoms (WHO 2011).
Humans are exposed to Ni through food, air, and water. Previous research has shown that ingestion of nickel-contaminated dust was the primary exposure pathway for local populations, as opposed to inhalation and cutaneous exposure (Sobhanardakani 2019). Other heavy metals, such as Arsenic (As), have been linked to dermatitis, bronchitis, and poisoning. A high Zn content might induce skin rashes and damage to nerve membranes. Cu may cause intestinal discomfort as well as liver and renal damage (Singh et al., 2011). The permissible limits of the heavy metal in the human body & drinking water have been documented below (Table 3)
Table 3: Permissible limit of the heavy metals in the Human body and Drinking water according to the different regulatory bodies (Source Singh et al., 2011; Paul 2017)