**3. Heavy metal contaminated abattoir wastes: mechanism of transfer in ecosystem**

Abattoirs have repercussions for the environment because of the way they operate and dispose of their trash. Bleeding, treating wounds, removing the hide, eviscerating the animal (removing its internal organs), preparing the carcass (by cutting and boning it), and so on are all steps in the surgical. In many circumstances, disagreeable odors are produced alongside the massive amounts of solid waste and wastewaters with biochemical oxygen demands (BOD) that might be generated by any of these procedures. The effluents that are relevant and specific to abattoirs in Lagos include blood, excrement, hair, bones, and undigested stomach contents [32].

The processes involved in getting end-products in most abattoirs in Lagos State of Nigeria are unhealthy considering the type of abattoirs found, the personnel and the skills used in the processes [7]. However, these processes used in abattoirs in Lagos, often lead to the introduction, accumulation, and transfer of contaminants like heavy metals such as lead, cadmium, zinc etc. within the ecosystem [33].

Abattoir wastes such as organic and inorganic substances, as well as salts and chemicals added during processing, affects air, water, soil, plants, animals, and humans [33] (**Figure 3**). Heavy metals and other contaminants from the abattoirs *Abattoirs: The Hidden Sources of Plants' Heavy Metals and Other Pollutants in Lagos, Nigeria DOI: http://dx.doi.org/10.5772/intechopen.110339*

firstly caused air pollution to the inhabitants and surrounding commuters very close to the abattoirs, leading to the inhalation of some virulent microorganisms which can cause air borne diseases [34] and irritation to the eyes and nose because of smokes and dust from animal skin (Ponmo) processing often done with burning of vehicular tyres.

Secondly, heavy metals in soil ecosystem (**Figure 3**), through discharge of abattoir effluents on soils thereby increasing heavy metal contaminants and other pollutants [12]. This effluent could kill the soil microbiota or increase the presence of virulent microbes which often causes diseases to plants, animals, and humans. The soil is the complex ecosystem of many plants. Thus, accumulation of metals has been reported in the soil and plants close to the abattoirs [7].

Thirdly, metals in surface and underground waters (**Figure 3**), this occurs through erosion and leaching of heavy metals in abattoir effluents. Improper discharge of effluents could lead to transfer of metals by rainwaters to nearby water bodies and increase the concentrations of metals in the aquatic bodies (**Figure 3**). This often discomfort the aquatic fauna and flora and increase the BOD of the water [28]. Also, leaching of this effluent containing heavy metals such as Pb and other contaminants could predispose the consumers of this water to toxins [35].

Finally, the mobilization of the metals into the air, soil, and water due to poor abattoir wastes management and personnel skills could not free plants, animals, and humans from the heavy metals' poisons [36, 37]. Plants that are contaminated with heavy metals because of bad abattoir practices accumulate these metals in their tissues, herbivores and humans consume these plants, and continuous consumptions of these herbivores and plants by humans leads to bioaccumulations of these metals in tissues and remain in food chain, thereby causing lots of health problems (**Figure 4**).

However, the continuous discharge of abattoir wastes and its poor management overtime, because of bioaccumulation, biomagnification and bioconcentration of heavy metals and other contaminants in the ecosystem in Lagos State, especially as it's involved the heavy metal transfer would pose great threat to air, water, soil, plants,

**Figure 4.** *Trend of pollutants' transfer within the food chain from abattoir wastes.*

animals and human if not properly addressed (**Figure 4**). This in turn, may have negative effects on the economy of the country.
