Mechanism and Health Effects of Heavy Metal Toxicity in Humans

Abstract

Several heavy metals are found naturally in the earth crust and are exploited for various industrial and economic purposes. Among these heavy metals, a few have direct or indirect impact on the human body. Some of these heavy metals such as copper, cobalt, iron, nickel, magnesium, molybdenum, chromium, selenium, manganese and zinc have functional roles which are essential for various diverse physiological and biochemical activities in the body. However, some of these heavy metals in high doses can be harmful to the body while others such as cadmium, mercury, lead, chromium, silver, and arsenic in minute quantities have delirious effects in the body causing acute and chronic toxicities in humans. The focus of this chapter is to describe the various mechanism of intoxication of some selected heavy metals in humans along with their health effects. Therefore it aims to highlight on biochemical mechanisms of heavy metal intoxication which involves binding to proteins and enzymes, altering their activity and causing damage. More so, the mechanism by which heavy metals cause neurotoxicity, generate free radical which promotes oxidative stress damaging lipids, proteins and DNA molecules and how these free radicals propagate carcinogenesis are discussed. Alongside these mechanisms, the noxious health effects of these heavy metals are discussed.

Toxic Metal Implications on Agricultural Soils, Plants, Animals, Aquatic life and Human Health

“…Neurological and behavioural disorders such as tremors, insomnia, memory loss, neuromuscular effects, headaches, and cognitive and motor dysfunction [179] Red blood cell accumulation (competes with iron for haemoglobin binding) and inhibition of myelin synthesis in developing fetus and children [180] Immune, enzyme and genetic alterations [181,182] Young's syndrome (Azoospermia sinopulmonary infections) [183] Allergic skin reaction [190] Genotoxicity haematotoxicity, teratogenicity, immunotoxicity and carcinogenicity [191] Pb Headache, loss of appetite, abdominal pain, fatigue, sleeplessness, hallucinations, vertigo, renal dysfunction, hypertension, arthritis, birth defects, mental retardation, autism, psychosis, allergies, paralysis, weight loss, dyslexia, hyperactivity, muscular weakness, kidney damage, brain damage, coma and death [192] Disruption of the intracellular second messenger systems resulting in the alteration of the functioning of the central nervous system [193] Zn Respiratory disorder from inhalation of zinc smoke, epigastric pains, risks of prostate cancer and lethargy [194] Copper deficiency [195] Irritation and corrosion of the gastrointestinal tract, acute renal tubular necrosis and interstitial nephritis [196]…”

Determination and Human Health Risk Assessment of Heavy Metals in Floodbasin Soils in Owerri, Southeastern Nigeria

“…The adverse effects caused due to heavy metals agglomeration in plants eventually enter the food chain in the form of food and dust posing types of health hazards [2]. In humans, they are essential nutrients that are required for various physiological and biochemical functions in the body and may result in deficiency diseases or syndromes if not in adequate amounts but in large doses, they may cause acute or chronic toxicities [3,4].…”

A Detailed Review Study on Potential Effects of Microplastics and Additives of Concern on Human Health

“…Commonly, a density of at least 5 g/cm −3 defines a heavy metal and differentiates it from other "light" metals. Other, broader definitions for "heavy metals" require an atomic mass higher than 23 or an atomic number exceeding 20 [75][76][77]. However, these definitions are confusing and misleading due to the fact that they cause the inclusion of non-metals.…”

“…Even though heavy metals are naturally present in our environment (e.g., in the atmosphere, lithosphere, hydrosphere, and biosphere), their environmental contamination and their exposure to humans have mainly originated from various anthropogenic activities [77].…”

“…Among metals, Al, Sb, As, Ba, Cd, Cr (II), Co, Cu, Pb, Hg, Ni, Se, Sn and V are defined metal-estrogens showing high affinity to estrogen receptors because they can mimic estrogen activation; for this reason, they are considered harmful and potentially linked with breast cancer [89][90][91]. Cadmium has been suggested to take part in the promotion of cellular apoptosis and DNA methylation, in providing oxidative stress, in causing damage to DNA, in increasing bone fractures in postmenopausal women, and in lipid peroxidation [77,92,93].…”