Heavy metal toxicity: A comprehensive review of forms, exposure routes, toxicokinetics, and effects on infants

Heavy metals are the elements that occur naturally in the environment. They have high atomic weight, electrical conductivity, and density and are called “toxicants.” Their applications in certain fields like industries, technology, medicine, domestic, and agriculture increase their distribution in the environment, raising ill effects on human beings and the environment. Secondary data suggested that heavy metals can produce adverse toxic effects in infants, even at low concentrations. The degree of toxicity depends on many factors like the form of toxicant, age, gender, metabolism, exposure frequency, solubility, oxidative metal status, duration of exposure, route of exposure, dose, and many more. Heavy metals can affect infants in several ways, like inhalation of contaminated air, ingesting contaminated food and water, finger-mouth/hand-mouth ingestion of toxicants, dermal contact, injection, or even before birth (prenatal exposure). Prenatal exposure to these heavy metals is the most common exposure and affects an infant’s early developmental stages. Heavy metals act as systematic toxicants, i.e., they tend to cause multiple organ damage even at low concentrations. These metals follow numerous routes of toxicokinetics. In general, every toxicant follows the ADME pathway (where “A” refers to adsorption, “D” refers to distribution, “M” refers to metabolism, and “E” refers to elimination). Heavy metal primarily targets cellular organelles and compartments such as cell membranes, mitochondria, lysosomes, endoplasmic reticulum, nuclei, and some enzymes. These organelles play a vital role in metabolism, detoxification, and DNA repair. Moreover, they induce certain deformities in various body organs; that individual has to survive with those deformities, or it causes death. This results in several neurological, genotoxicity, neurodevelopmental, immunological, cognitive, cardiovascular, neurological, respiratory, renal, and hemopoietic deformities in an individual. Moreover, these heavy metals, producing reactive oxygen species and oxidative stress, induce various carcinogenic toxicity in the body. This study systematically reviews the forms, exposure routes, toxicokinetics, and affected organs by arsenic, lead, mercury, and cadmium.