Mercury Contamination and Spill-over at Human-Wildlife-Environment Interface

1. Introduction

Pollution is a resultant detrimental effect on the ecosystem attributed to hazard discharges and mismanagement [1, 2]. Contamination on the other hand is attributed to presence of hazards in the biological systems and these act as sources of toxicity to flora and fauna [3]. Potential toxic elements (PTEs), another type of inorganic pollutant, make up one of the most significant groups of pollutants that are released into environment by chemical and allied industries such as pharmaceuticals, fertilizers, and refineries. These PTEs can pollute the environment if their concentration is higher than the allowable limits [4]. There is a possibility that these inorganic pollutants cannot be broken down by biological processes, and as a result, they remain in the environment for a while, ultimately causing disruptive effects, not only on public health but also on the flora and fauna of aquatic and terrestrial environment [5, 6]. Potentially toxic elements are a threat on a global scale since they are not biodegradable and have a propensity to build up in living organisms through the food chain. Different body organs in both humans and animals are impacted by a number of potentially toxic substances’ causing acute and chronic toxic effects [1, 6]. In many Sub-Saharan African countries, anthropogenic activities that occur within an ecosystem, as well as the natural sources, are the two main contributors to PTEs pollution. The vast majority of pollution is caused by human activities, such as the search for new sources of energy [7, 8]. Since the beginning of time, coal and oil have been sources of energy for a wide variety of applications across the globe.

In Uganda, oil exploration in the Lake Albert Graben that began as early as 1938 in Butiaba, Buliisa with geological explorations, has today evolved into the construction of an oil pipeline [9]. Such pipelines come along with the threat of pipeline accidents where oil spills are eminent [10]. The Uganda environmental policy stipulates that oil spills are one of the disasters whose level of contamination of the environment would warrant attention [9]. According to Kassim [2], oil resources should be managed in cognition of the negative effects such as pollution and contamination. The environmental policy stipulates that oil spills are one of the disasters whose level of contamination of the environment would warrant attention [11]. The pollution cited in this situation is that of potentially toxic elements, especially mercury and lead. Since “oil spill” is often a new phenomenon in the area, the ecosystems should be able to adapt in a compatible way otherwise the ecosystem collapses. The theory of sustainable utilization for oil resources in the Lake Albert Graben focuses on three main areas namely; availability of the resources, adaptability and flexibility, and homeostasis [12]. The resources targeted at the Albertine Graben include water, assets, and entitlements, and not so much of PTEs research [13]. For instance, much of the work executed about water levels of mercury, levels of mercury in fish, and risk burden thereafter, is documented better in developed countries compared to the developing countries, like Uganda. The use of consumption advisories is where most of the information in developed countries is stored. The assets in the biodiversity hot spot include flora and fauna uniquely found in this site [14]. In addition to the animal species and plants in the protected area, lies a whole new industrial park as part of the oil city. The much-anticipated livelihood from this oil city creates an entitlement to the community around the oil drilling area [14]. However, conflicts might result in negative catastrophes, such as oil leaks, if the delicate balance between entitlement and livelihood is not realized. In the Murchison Falls Conservation Area (MFCA), wildlife, domestic animals, and human ecosystems are documented as resilient systems, initiated by anthropogenic activities [15]. The presence of oil and gas prospecting in MFCA as major anthropogenic activities translates into ecosystem resilience, coping, and tolerance as a result of the possible oil spills [15]. Oil and gas production is one of the precursors of mercury in the environment, should there be an oil spill [16]. The surrounding communities are being empowered through a socioecological approach that focuses on sustainability of the ecosystem proponents.

This chapter, therefore, discusses the detrimental effects of mercury on an ecosystem that lies at the wildlife, domestic animal, and human interface. These effects are on around an oil spill framework that encompasses terrestrial and aquatic environments, species, and habitats as illustrated in Figure 1.

The likely exposure factors include exposure time, exposure quantity, and analytic chemicals, that is, mercury and lead. The species-related factors include species identity, development stage, generation time, feeding mode, and mobility. The habitat related factors include depth at which species thrive, environmental stressors, i.e., deforestations, erosion, anthropogenic activities and climatic conditions. These triad factors also are both inter and intra linked.

Location and habitat.

In the Lake Albert region, oil exploration often excites the population. However, the location of oil wells in MFCA biodiversity hot spots and forests has led to loss of habitat and ecosystem for biodiversity. The location of MCFA has been illustrated in Figures 2 and 3.

Regardless of where the oil spill occurs, whether terrestrial or aquatic, the impacts are devastating, as they can lead to accumulation of potentially toxic elements, especially mercury in the terrestrial and aquatic environment, causing toxicities in animals and humans. Mercury in particular bioaccumulates and is magnified along trophic levels, often bioconcentrate in plants and animals and the flora acts as sources of the potentially toxic substances/mercury.

On the other hand, there have been positive impacts on development, that is, infrastructure, road networks, and improved livelihoods of the surrounding communities. A balance is needed in utilization of the oil resource since it is perishable but can also have vast negative impacts, which include the oil spills.

2. Species

The conservation world is aware of the burden of oil spills in the areas where oil exploration and extraction exist. These oil spills mainly negatively affect the wildlife (flora and fauna), fishing communities, and the communities in and around the wildlife-protected areas. To safeguard these vulnerable populations at the animal-environment-human interface, solutions on how to mitigate the levels of potential toxic substances found in water, plants, and animals need to be found. This information is displayed as a distribution map of the key levels of lead and mercury in food eaten by communities in the protected areas, and associated health risks. The adverse effects of lead and mercury on wildlife, aquatic species, and environment also need to be documented. These documents translate into the food consumption advisories for lead and mercury in the MFCA. The awareness of risks and benefits associated with eating fish, plants, and wildlife from MFCA is vital for tourists and communities around the protected area. Since most of the mercury is taken in through fish consumption, vulnerable populations should watch out for the fish species eaten, especially the carnivorous fish. The vulnerable populations include children less than 12 years, women of childbearing age, and elderly.

3. Anthropogenic activities

Anthropogenic activities offer a delicate balance between the needs of a community/government and the biodiversity spots and their contribution to nature [21]. The country’s development process should be in tandem with the environmental concerns [20]. Therefore, activities like oil exploration in biodiversity spots should be allowed to execute with guiding regulations and policy. If the works go on unregulated, the destruction to the environment and the associated costs of restoration are quite prohibitive. The cost of an oil spill to wildlife range from losses due to acute toxicity of the aquatic and terrestrial species, the cost of rehabilitation of those that can be recovered, and the cost of clean up to and the length of 1300 km length of the oil pipe for crude oil. The work on oil spills is much needed in the Lake Albert Graben given the fact that 4 million gallons per day in the kingfisher project shall be produced come 2023. The Lake Albert Graben has over 7 blocks of which the kingfisher project lies in one of the blocks [2, 22]. The Lake Albert Graben is synonymous with the Niger delta in Nigeria. Oil-related studies in Nigeria exhibited a range of between 230 and 1200 spills per year in the Niger delta between 1981 and 2015 [3]. The amounts per oil spill in the oil mining areas and between the path of oil pipelines can only be estimated to be between 50,000 barrels and 300,000 barrels per year in the same study period in Niger delta [3]. Based on the oil spills, fish are contaminated with potentially toxic substances and this not only leads to health risks in high-level trophic fish but also has a negative effect on fish breeding in the water sources. Adding the restoration costs to the 3.5 billion US$ initial cost of construction of the pipeline is a tall order [3].

3.3 Mercury entry into the ecosystem

At the human-animal-environment interface, mercury can exist in three forms; elemental (or metallic) mercury, inorganic mercury compounds, and organic mercury compounds. At this point, mercury can be highly persistent, bioaccumulative, and toxic. Mercury occurs naturally in the environment, but it is generally safely contained in minerals and does not present any significant risk, except when anthropogenic activities precipitate its release in large amounts into the environment, consequently circulating freely for a long time [31]. An environment can grossly become polluted with mercury following oil and gas leaks, alkali and metal processing, coal incineration, gold and mercury mining, and from improper medical and other waste disposals. In the environment, microbial organisms can uptake the elemental form of mercury and this signals the transcription of the genes hgcA and hgcB are transcribed to synthesize the HgcA and HgcB proteins [32].

These proteins can then start the methylation reaction to form methylmercury. Mercury and methylmercury exposure to sunlight (specifically ultra-violet light) has an overall detoxifying effect. Sunlight can break down methylmercury to Hg(II) or Hg(0), which can leave the aquatic environment and reenter the atmosphere as a gas as shown in Figure 4.

In the food chain, each rung of the food chain consumes more mercury because animals acquire it faster than they expel it. Small ambient quantities of methylmercury can easily build in fish, fish-eating species, and people. Even at low atmospheric deposition rates in remote regions, mercury biomagnification can be harmful to aquatic food chain consumers.

Mercury-associated risks at the wildlife-domestic animal-environment interface.

mercury in water and sediments is the primary concern, as it is in a highly toxic form and can easily be taken up by animals, thus finding its way into the human food chain. Health concerns in Uganda center on human and animal consumption of fish and fish products contaminated with methylmercury. Particularly in humans, neurotoxicity is the most important concern associated with mercury exposure. When methylmercury reaches the bloodstream, it is distributed to all tissues and can cross the normally protective blood–brain barrier to the brain. Methylmercury can also readily move through the placenta to the developing fetus(es) and, therefore, of more concern to pregnant women and women of childbearing age. Mercury exposure in humans (RfD between 1.0 and 3.0×10⁻⁴ mg/kg per day) can lead to a variety of negative health effects, including neurological, kidney, gastrointestinal, genetic, cardiovascular, and developmental disorders, and even death [32]. Wildlife and domestic animals that consume fish and fish products, depending on their feeding behavior, may ingest large amounts of methylmercury in their diet, often interfering with their reproductive potential. Raptorial bird species, otters, and others that commonly consume water-based foods are at the greater risk of mercury contamination. In birds, reproductive problems are the primary concern related to mercury poisoning. Other mercury effects in wildlife and other animals are liver damage, kidney damage, and neurobehavioral effects.

4. Health risk and burden due to mercury

The exposure diet intake is linked to the Hazard Quotient (HQ), which signifies the relationship between the exposure obtained in the diet and the oral reference dose for mercury [28]. Choice of the oral reference dose is critical in determining the health risks the vulnerable community is exposed to, that is, use of the general population or vulnerable population oral reference dose [34]. The oral reference doses for mercury in the vulnerable and general population are 1 × 10⁻⁴ and 3 × 10⁻⁴ mg/kg per day, respectively [35, 36]. Therefore, there is a need to send out a message to this vulnerable group about the health hazard they are encountering daily by consumption of food contaminated with mercury. Use of specific messages for different target groups was demonstrated in the USA during a study by Ref. [34], which involved pregnant women and children and observed that there is a need for a unique message for the vulnerable group.

Hazard Index (HI) for both vulnerable and general populations if computed can spell out the health risk. For the vulnerable populations, if the hazard quotients from the study are added and the hazard index is greater than one spells out probable health risks from the mercury consumed. These results are in agreement with Poulin et al. [29] who documented higher HI levels in carnivorous than herbivorous fish, a pointer toward the hazard index points toward noncarcinogenic risk attributed to mercury uptake in fish parts, especially the Lake Albert Nile perch.

5. Conclusions

Mercury and other potentially toxic substances associated with oil spills are a common occurrence in areas of oil exploitation. The negative effects of oil spills can be reduced by environmentally friendly human approaches and the resilience of the ecosystem. Oil exploitation is an investment that should be executed carefully in accordance with guidelines and policy. This oil investment can transform community and country livelihoods positively if managed in accordance with the eco-friendly guidelines and negatively if the sole focus of oil extraction is that of resource generation for country expenditures.

Acknowledgments

We acknowledge the support from Makerere University. We recognize all staff of various colleges who read, advised, and critiqued this work.

I am thankful to the Wildlife and Aquatic Animal Resources Department for spear leading this research. I am grateful to Biosecurity, Ecosystem Health, and Veterinary Public Health Department for the support and guidance, especially Dr. Innocent Rwego.

Last but not the least; I am grateful to the mentors Professor Ejobi Francis, Professor Charles Muyanja, Dr. Irene Naigaga, and Dr. Jesca Nakavuma.

Conflict of interest

There is no known conflict of interest to declare on behalf of the authors.

Notes/thanks/other declarations

Thanks to Intech open Publishers for sharing an opportunity for the publication of the chapter.