Metal(loid)s Toxicity and Bacteria Mediated Bioremediation 169

metals such as beryllium may be hazardous. However, the necessary elements or metals, such as

iron (Fe), could be poisonous. Metals in certain oxidation phases may also be toxic, such as Cr (III) is

an essential micronutrient, whilst the other form Cr (VI) is a potential carcinogen. The consequences

of heavy metal toxicity include decreased fitness, problems with reproduction, cancers and mortality.

Organometallic forms, such as methyl Hg (mercury) and tetraethyl Pb, may be extremely hazardous,

while organometallic derivatives, such as cobaltocenium cation, are less toxic. Radium, which is a

radioactive heavy metal, mimics the property of calcium as it gets absorbed in bones and, along with

Pb and Hg, causes several health complications. However, there are exceptions in cases of Barium

(Ba) and Aluminum (Al), which are rapidly eliminated by the kidneys.

10.3 Effects of Toxic Metals

In the environment, toxic metals are present significantly in effluents, waste streams and sediments,

affecting bacterial diversity, population size, and overall activity (Xie et al. 2013). Toxicity induced by

metals is frequently documented as an environmental health challenge which causes bioaccumulation

of toxic metals in the food chain. The severe consequences are seen in humans, animals and plants

(Aycicek et al. 2008). The impacts of poisonous trace metals are reliant on a number of variables,

including the element’s dietary content, absorption by the body, maintaining homeostasis for these

toxic metallic elements, and the number of animals affected by these elements (Rajaganapathy

et al. 2011). Furthermore, the oxidation state of a hazardous metal influences its toxicological and

biological impacts on the environment. The functional and structural changes in DNA, RNA and

proteins, along with challenges of oxidative phosphorylation and osmotic imbalances, are widely

observed due to metal toxicity (Yao et al. 2008). Toxic metal contamination has occurred as a severe

health issue due to industrial waste streams and agricultural residues. Humans are typically exposed

not only orally but also via cutaneous contact, inhalation and ingestion. The severity of a single

compound’s harmful effects (including immunotoxin) may be altered by interactions with one or

more other heavy metals or xenobiotics. As a result, the synergistic interactions of insecticides and

heavy metals may lead to different health problems.

10.3.1 Effects of Toxic Metals on Human Health

A large fraction of the population in most developing nations faces the challenge of toxic metal

contamination in food items (D’Souza and Peretiatko 2002, Cheng 2003, Meharg 2004). These

toxic metals promote serious health complications in the human body because their introduction

causes the malfunctioning of crucial cellular processes by displacing important metals from their

correct positions (Vieira et al. 2011). People who are more exposed to trace element-polluted areas

or those who work in metal mines are continuously being jeopardized with rising health issues

(Table 10.1). Metal poisoning in humans may cause slow development in children, dementia in

adults, nervous system related problems, renal illnesses, liver diseases, insomnia , depression and

visual abnormalities (Jan et al. 2011).

Toxic metal transmission in humans is rather complicated. Lead (Pb) is taken up by the body

mainly through the stomach and respiratory tracts before it enters the circulatory system. Phosphate

enters the respiratory tract and digestive tract in the form of soluble salts, protein complexes and ions

with a concentration of more than 95% insoluble Pb accumulating for bones build-up (Okereafor

et al. 2020). It is also a strong pro-organizational element that alters and damages the kidney,

liver, reproductive organs, neurological functioning and digestive system. The urinary system, the

immunological networking and the cells performing fundamental physiological processes and gene

expression (Mahurpawar 2015) are also affected. A longer duration of exposure to Pb results in

brain damage, short-term memory loss, adapting skills and coordination complexities in children.

Prenatal Pb exposure may lead to a decrease in immunity and weight of new born babies. It is

one of the main reasons why certain babies are associated with asthma and allergies. Studies have