Selected HMs, their anthropogenic sources, provisional maximum tolerable daily intake (PMTDI) according to WHO, symptoms and resultant diseases when consumed beyond the PMTDI dose. This table has been adapted from ref. 68 with permission from MDPI, copyright 2019.

HMs	Anthropogenic sources	PMTDI (mg L−1)	Symptoms and diseases	Ref.
As	Discarded wastes from industries, mining activities, insecticides, ceramics, pesticides herbicides, components of electronics, arsenic-based additives, electrical generation, biosolids, tanning, fertilizers, pyrite oxidation (FeS), arsenopyrite (FeAsS), feed additives, textile, and veterinary medicine, and metallurgy	10	Skin, bladder, kidneys, and lungs cancer, impact the peripheral nervous system (PNS), central nervous system (CNS), and results in heart and pulmonic diseases, and arsenicosis	69–71
			Diseases of the gastrointestinal tract, haemopoietin, genitourinary, skin, fetus and teratogen, brown skin-coloring and hyper-pigmentation, edema that is localized, and anorexia
Cd	Electroplating industries, batteries made up of nickel and cadmium, combustion of coals, plastic stabilizers, alloying industry, synthetic rubber, photographic and engraving process, petroleum refining photoconductors, paints, pigments, photovoltaic cells, electroplated parts, and plastics	3	Pulmonary fibrosis, hypertension, malformation of the skeleton, lymphocytosis, diabetes mellitus, toxicity in the renal system, loss of weight and strength, microcytic hypochromic anemia, and emphysema	72 and 73
			Osteomalacia, peripheral neuropathy, cancer of the lungs, osteoporosis, atherosclerosis, and hyperuricemia
Cr	Chemicals, coasting operations, data storage, textiles, leather tanning, pigments, wood treatment, metallurgy, achrome, and electroplating industries	50	Skin rash and ulcers, irritations and bleedings in the nose, debilitated immune system, mutation of genetic material, liver and kidney impairment, teratogenicity, toxicity in reproduction, embryotoxicity, causes mutation and cancer, dermatitis, septum perforation, and adverse reactions	71 and 74–77
Co	Aerospace, Li-ion batteries, porcelain, preparation of semiconductors, grinding wheels, hydrometers, nuclear medicine, electroplating, materials, enamel, and painting on glass	2	Diarrhea, irritations in the lung, defects of the bones, low blood pressure, genetic mutations in cells, and paralysis	78
Cu	Mining processes, kitchenware, pharmaceutical and chemical apparatus, manufacturing of papers	1500	Alzheimer's, convulsions, Parkinson's diseases, Wilson, liver and eye problems, cramps, vomiting, and Menkes	79
Fe	Mining, corrosion of metals, steel, and iron industries	N/A	Cancer, hemochromatosis, heart diseases, and eyes disorder	80
Pb	Sanitation PVC pipes, lead rich batteries, fuels, even lunch boxes, PVC lead paints recycling, electronics parts manufacturing, processing of metals, pigments of painting, electroplating, mining activities, leather tanning, agriculture, jewelry, and lead batteries	10	Damage in the reproductive systems, damage of the CNS, kidney and liver diseases, barriers to protective blood in the brain which signifies a cause of Alzheimer's disease alongside doddering dementia, lowering of IQ and reduces the growth of the bones, attitudinal dysfunctions, hyperirritability, stupor, and ataxia	81–84
Hg	Fungicides, facilities for plating metals, tanneries, pharmaceuticals, solders, vapor from mercury lamps, chemical compounds, emissions from volcanoes, filling of the teeth, catalysts, rectifiers, coal, solid and municipal waste burning, and, mining activities	1	Damage in the reproductive systems, impairment of the CNS, liver syndromes, distorted development of the neurons, impacts on the digestive and immune systems, kidneys, lungs, eyes, and skin, Minamata, acrodynia, surges in salivation, hypertension, and hypotonia	85
Mn	Manganese steels production, alloys of ferromanganese, and iron pipe corrosion	500	Psychological disorders, trembling, respiratory diseases, and lethargy	86
Ni	Surgical implants, nickel-based steel, super-alloys, electroplating, magnets from alnico, coinage, non-ferrous alloys, catalysts, microphone pods, rechargeable batteries, plumbing fittings plating, and dental prostheses	20	Anaemia, encephalopathy, hepatitis, lung, diarrhea, kidney impairment, gastrointestinal pain, pulmonic fibrosis, renal edema, dermatitis of the skin, dysfunction of the CNS	87 and 88
Zn	Zn alloys, anti-corrosion coating, rubber industry, cans, chemical industry producing pigments, paints, batteries, and soldering	3000	Respiratory breakdown, loss of appetite, diarrhea, headaches, lethargy, fever from metal fume, leukocytes of bronchiolitis, neuronal illness, risks of prostate cancer, macular deterioration, depression, and impotence	89–92
Ag	Copper refineries, zinc–nickel, gold, electroplating, and jewelry industries	100	Gastroenteritis, neuronal ailments, knotting, argyria, cytopathological influences in fibroblast, keratinocytes, rheumatism, mast cells, cartilage, and mental tiredness	93 and 94
Cu	Tanning, fertilizers, and photovoltaic cells	1300	Kidney dysfunctions, anemia, allergies, arthritis, diabetes, hemorrhaging, alopecia, adreno-cortical hyperactivity, autism, and cystic fibrosis	95