**1. Introduction**

Lagos State is one of the thirty-six (36) states in Nigeria with population estimated at over 200 million people. It is one the major industrial and business hubs of Nigeria. It has twenty (20) Local Government areas which are subdivided into five main divisions—Ikeja, Badagry, Ikorodu, Lagos and Epe divisions [1]. However, being the cash-driven center of the nation, it is without its own peculiar challenges. One of the prevailing challenges of Lagos, without exceptions from other parts of the country and the world is pollution.

Pollution involves the introduction of any material (solid, liquid or gas) or types of energy (heat, sound, or radiation) that is hazardous to the ecosystem-plants, animals, and human health [2]. Also, it could further be seen as any reaction, by individuals or bodies, which changes the biochemistry, metabolically and/or environment of other living things in a wider or localized area, where the causal link is clearly established [3, 4]. Pollution may be natural like flood, drought, cyclones, and many others and artificially (human activities) mediated and could be grouped into air pollution (affecting the health of the atmosphere), soil pollution (reducing the biodiversity of the soil and its health status) and water pollution (affects the overall quality and safety of water bodies). Several substances have been attributed to the rise in pollution levels in the state and these substances are generally referred to as pollutant [5].

Pollutants are materials that when released into these ecosystems (air, soil, and water) makes them intolerable to the inhabitants. Examples of some pollutants include heavy metals—lead, methane, carbon monoxide, particulate matter, bad smell, plastic, volatile organic compound, and many others have been attributed to pollutions [6]. The majority of man-made fine particles come from domestic sources, specifically biomass-based cooking, and the use of fossil fuels to power homes and vehicles. Some areas near deserts in Africa and West Asia are also important contributors due to windblown dust [6].

However, several sources have been documented which could either be point sources like industries, refineries, mining and many others or non-point sources like car, busses, trains and many more. But abattoirs in Lagos State of Nigeria have also been documented to house several heavy metals and other pollutants [7]. One of these contaminants that is frequently present in trace amounts is heavy metals. Many of these metals, even when present in trace amounts, are harmful to the environment and can accumulate in the bodies of living things through a process called bioaccumulation or bio-concentration [8, 9]. Abattoirs produce a significant quantity of secondary waste materials in the form of massive animal feces [10]. The inappropriate disposal of animal parts, such as flesh, blood, and innards, has been linked to an increase in soil acidity [11, 12]. Soil microorganisms, not just plants, are negatively affected by heavy metals present due to improper treatment of abattoir wastes. When soil is highly concentrated in metals, it can bring heavy metals into the food chain, which can be problematic because of the toxicity of these elements to humans, especially when they bioaccumulate in the body through the ingestion of plants.

### **2. Abattoir as sources of environmental pollutants**

The impacts of pollution on ecosystems are much more pronounced today than they were in the past. Many people assert this, citing various factors such as a decline in soil fertility, a weakening of water quality, several health issues (including those that can lead to metabolic disorder), an ecological impact, and so on [13–15]. A major contributor to these pollutions is the careless disposal of trash in these ecosystems, which disrupts the balance of nature. Since there are no well-established management rules on waste disposal, this is a typical practice in Nigeria. However, the sudden increase in the amount of communicable, non-communicable and zoonotic diseases, for example, cancer and tuberculosis in our localities today makes abattoir waste a disease surveillance focus [16]. Abattoir operations result in the release of various wastes and pathogenic organisms that pollutes the environment and pose serious

*Abattoirs: The Hidden Sources of Plants' Heavy Metals and Other Pollutants in Lagos, Nigeria DOI: http://dx.doi.org/10.5772/intechopen.110339*

threat to human health and quality of life [17]. Tragically enough, most abattoirs in Lagos, Nigeria are known for poor and obsolete structural design which is accompanied with deteriorating environment.

An abattoir is a facility specifically designed to carry out the inspection of animals, the sanitary slaughtering, processing, and proper preservation, and storage of meat products for human consumption and is registered and certified by the regulatory body. A meat processing plant is a specialized building authorized to receive animals for slaughter, hold them, and conduct quality control inspections on meat products prior to their release for sale. Abattoirs aim to improve the efficiency with which consumable parts of the meat processing cycle are recovered for human consumption [10]. However, substantial quantities of secondary waste, such as organic and inorganic substances that aren't fit for further exploitation, are produced anyway [18]. Land degradation, air pollution, water scarcity and contamination, loss of biodiversity (particularly plant life), and climate change are all blamed on animal production and the work of veterinary establishments like slaughterhouses [19, 20]. Abattoir waste is an emerging solid waste whose rate of generation is becoming alarming [21].

The soil and natural water bodies are often seriously threatened by the pollution caused by abattoir activities, which not only generate a large quantity of waste but are also a source of heavy metals, bacteria, and others that threaten plant health and human quality of life [17].

### **2.1 Types of abattoirs**

### *2.1.1 Modern abattoir*

They are the pinnacle of conventional abattoir design, equipment, and services, and are typically constructed and managed by centralized governments with the aid of foreign technical experts. These abattoirs are managed on factory lines and offer a variety of services, including cold storage, processing, by-product usage, and waste recycling. Being commercial or profit-driven establishments, most contemporary abattoirs have little interest in providing low-revenue services, such as direct slaughter for public consumption.

### *2.1.2 Slaughterhouses*

Most public slaughters are performed in these establishments. These establishments essentially provide a place to slaughter animals in accordance with public health, inspection, and marketing regulations for a fee, and are used by licensed butchers and dealers. Typically, only operating in densely populated areas and larger cities, these businesses provide essential services under the watchful eye of state and regional authorities. Two types of slaughterhouses exist, they are:

### *2.1.3 Old slaughterhouses*

These establishments just provide the necessary infrastructure for licensed butchers and traders to slaughter cattle in line with public health, inspection, and marketing standards, for the predetermined costs. They are service businesses supervised by city or state governments, typically catering to residents in densely populated urban regions. Most public slaughters are conducted by them.
