**2.1 Heavy metal toxicity**

Some heavy metals are essential to the human biological process, but depending upon their dosage intake leads some unexpected hazardous effects on health and the physiological system. According to [9] studies shows that despite of its beneficiary health effects, heavy metals are acting as carcinogenic agents. Dissolved forms of these metals through different forms as soil pollutants, water pollutant and air pollutants entering into food chain and finally ending in humans, these are leading to severe damage to the cellular system and leading to expose towards cancer. According to the reports of the International agency for research on cancer nonessential heavy metals (As, Cd, Cr) are major cancer- causing agents [9].

#### **2.2 Sources, exposure, and environmental impacts of lead**

The sources of lead varies with different countries based on old and new usage of lead products. It is not limited to the processing of gold ore and recycling of used lead products. It is found that the decrease in blood lead levels in the population of the countries in which unleaded gasoline is in usage [15].

A recent study [16] has reported elevated blood levels in pregnant women in a rural village in Bangladesh. In this study, they found more than 30% of women they sampled were had lead levels in blood in the range of above 5 μg/dL. They found the major source of lead exposure to these women were identified as food storage cans. Nearly 18% of food storage cans (out of the tested) were having lead soldering insides and are responsible for lead contamination in these women. Another study in China [17] determined the blood lead levels (BLL's) in children who are taking treatment in lead specialty clinics. In this study, they found the BLL's ranging from 5 to 126 μg/dL. The major reasons they found for the higher lead levels in their blood as industrial sources and folk medicine which is popular in China. Another important thing was determined as it is difficult to find lead poisoning in children due to non-specific symptoms. A very recent study from Australia [18] determined the higher lead levels in children due to the high concentration of lead in soil and pretty dish dust at their premises. This study found that the population who are living in old houses built before 1940 are diagnosed with higher lead levels due to pretty dish dust.

In Nigeria, lead poisoning in the population was observed in the area of Zamfara state which contains gold mining activities. Mahuta [19] reported that in Nigeria, the sources of the lead include mining of gold, lead pipes used for drinking water, and cultural usage of lead.

Based on the studies in all parts of the world it is assumed that the sources of lead are historical usage of lead, industrial activities, and leaded gasoline. Major studies reported that children are the most common victims of lead poisoning. The way of exposure includes the inhalation through the nose and ingestion through drinking water and soil.

There are several ways to minimize the lead levels in the environment such as remediation techniques (in soil), using adsorbents (in water), and using unleaded gasoline (the air). After the identification of leaded gasoline as a source of lead poisoning by US EPA, a major decline in their levels was found by replacing it with unleaded gasoline. Dongre [20] reported the toxicological profile, remedial solutions for lead levels in water by using polymeric materials, such as chitin and chitosan.

Zaltauskaite and Kniuipyte [21] reported the impact of lead concentration in soil on *Eisenia fetida* (earthworm). They found that lead in soil inhibits the growth of earthworms. Lead in soil can enter into human food by the vegetation in the contaminated soil [22]. The Types of carcinogenic effects of lead toxicity was explained in **Figure 1**. The lead toxicity in humans causes intestinal cancer, lung cancer, and central nervous system.

*Heavy Metals - Their Environmental Impacts and Mitigation*

**Figure 1.** *Carcinogenic effect of Lead.*
