Effect of Heavy Metals on Human Health

A plethora of statements concerning the hazards of heavy metals in AMD on human health have been made by natural scientists, social scientists and activists over decades. However, Garland (2011) argues that whilst there is evidence that shows the effects of AMD on the ecosystem, very little is known about the potential effects of AMD on human health. On the other hand, what is known is that many of the components and pollutants in AMD are dangerous to humans (Garland, 2011). For example, Pb, Cd, Hg and As are widely dispersed in AMD (Peng et al., 2009; Simate and Ndlovu, 2014), and these elements have no beneficial effects in humans, and there is no known homeostasis mechanism for them (Vieira et al., 2011; Morais et al.,

2012). However, the metals are considered to be the most toxic to humans and animals; the adverse human health effects associated with exposure to them, even at low concentrations, are diverse and include, but not limited to, neurotoxic and carcinogenic actions (Castro-Gonzalez and Mendez- Armenta, 2008; Jomova and Valko, 2011; Morais et al., 2012). In addition, many other studies have also indicated that any exposure to heavy metals is capable of causing a myriad of human health effects, ranging from cardiovascular and pulmonary inflammation to cancer and damage of vital organs (Geiger and Cooper, 2010; Alissa and Ferns, 2011; Jaishankar et al., 2014); and many major human physiological systems including the skeletal, nervous, respiratory, excretory and digestive systems may be affected (Ngole-Jeme and Fantke, 2017).

According to Garland (2011), in order for humans to be affected by the pollutants in AMD, they need to be exposed to the pollutants. Besides, there are a number of ways that people can potentially be exposed to the AMD pollutants (Garland, 2011; Ngole-Jeme and Fantke, 2017). The AMD enters the environment as polluted water, either through surface waters such as rivers or through groundwater. As the water moves through the ecosystem, the pollutants in AMD can then enter other parts of the ecosystem. For example, AMD pollutants in a river could be deposited and end up in the river beds where some aquatic species get their food. As discussed already in Section 5.3.2, what is of a major concern is that once heavy metals are accumulated by aquatic organisms, they can be transferred through the upper classes of the food chain (Ayandiran et al., 2009). Carnivores at the top of the food chain including humans obtain most of their heavy metal load from the aquatic ecosystem through their food, especially where fish are present and so there exists the potential for considerable biomagnification (Cumbie, 1975; Mance, 1987; Ayandiran et al., 2009). The depletion of aquatic organisms affected by AMD either through heavy metals or acidity was emphasised by Cotter and Brigden (2006) as it leads to the domino effects up the ecosystem by reducing the food sources available for animals at the top of the marine and human food chain.

Another AMD exposure pathway to humans occurs if AMD-contaminated water is used for irrigating crops, then there is a risk that the soils and plants can become polluted. In addition, if an animal drinks the polluted water or eats the polluted plants, then there is a risk that the animal can take up the pollution as well. Other exposure pathways have been described by Ngole- Jeme and Fantke (2017) and Jaishankar et al. (2014).

Akpor and Muchie (2010) contend that the danger of heavy metal pollutants in water lies in two aspects of their impact. First, heavy metals have the ability to persist in natural ecosystems for an extended period. Second, they have the ability to accumulate in successive levels of the biological chain, thereby causing acute and chronic diseases. In general, the toxicity or poisoning of heavy metals results from the disruption of metabolic functions. According to Singh et al. (2011), heavy metals disrupt the metabolic functions in two ways: (1) they accumulate in vital organs and glands such as the heart, brain, kidneys, bone and liver where they disrupt their important functions and (2) they inhibit the absorption, interfere with or displace the vital nutritional minerals from their original places, thereby, hindering their biological functions. Ideally, heavy metals are toxic because they have cumulative deleterious effects that can cause chronic degenerative changes (Ibrahim et al., 2006; Alissa and Ferns, 2011), especially to the nervous system, liver and kidneys, and, in some cases, they also have teratogenic and carcinogenic effects (International Agency for Research on Cancer, 1987; Alissa and Ferns, 2011). A summary of some of the heavy metals and their effects on human health together with permissible limits is presented in Table 5.4 (Solomon, 2008; Singh et al., 2011; Monachese et al., 2012).


Heavy Metals and Their Effects on Human Health Together with Permissible Limits

Heavy Metal


Permissible Level (mg/L)


Bronchitis, dermatitis, poisoning



Renal dysfunction, lung disease, lung cancer, bone defects, increased blood pressure, kidney damage, bronchitis, bone marrow cancer, gastrointestinal disorder



Mental retardation in children, developmental delay, fatal infant encephalopathy, congenital paralysis, sensor neural deafness, liver, kidney, and gastrointestinal damage, acute or chronic damage to the nervous system, epilepticus



Inhalation or contact causes damage to nervous central system



Damage to the nervous system, protoplasm poisoning, spontaneous abortion, minor physiological changes, tremors, gingivitis, acrodynia characterised by pink hands and feet



Damage to nervous membrane



Damage to the nervous system, fatigue, irritability



Anemia, liver and kidney damage, stomach and intestinal irritation


Sources: Solomon, 2008; Singh et al., 2011; Monachese et al., 2012; Simate and Ndlovu, 2014.

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