# Environmental Toxicants and Their Role in the Spread of Infectious Diseases: Implications for Public Health in Low-Resource Settings

Oche Joseph Otorkpa

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## To cite this version:

Oche Joseph Otorkpa. Environmental Toxicants and Their Role in the Spread of Infectious Diseases: Implications for Public Health in Low-Resource Settings. National Institute of Environmental Health (NIEH). 2025. [https://hal-05173467](https://hal-05173467)

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# Environmental Toxicants and Their Role in the Spread of Infectious Diseases: Implications for Public Health in Low-Resource Settings

Oche Joseph Otorkpa

Department of Public Health, Faculty Of Health Sciences, National Open University Of Nigeria, Abuja, Nigeria; drochejoseph@gmail.com

<figure><img src="image_3.png" /></figure>

## Abstract

In low-resource settings, the interplay between environmental toxicology and infectious diseases presents a growing public health crisis. This chapter explores how widespread exposure to heavy metals, pesticides, and mycotoxins exacerbates disease vulnerability by weakening immune defenses, contaminating food and water sources, and fostering antimicrobial resistance. Drawing on case studies and data from sub-Saharan Africa and similar regions, it illustrates how poor sanitation, unregulated industrial activity, and inadequate infrastructure create synergistic pathways for both toxic and infectious hazards. The chapter further examines how environmental contaminants disrupt water systems, food chains, and immune function, while contributing to the evolution of resistant pathogens. It advocates for integrated strategies such as strengthened WASH (Water, Sanitation, and Hygiene) interventions, robust surveillance systems, and multisectoral policy coordination. By highlighting the need for systems-based solutions, it underscores the urgency of building resilient health systems that can anticipate, detect, and mitigate the dual threats of environmental toxicants and infectious diseases in vulnerable populations.

## 1. Introduction

In low-resource settings, the burden of infectious diseases is compounded by widespread exposure to environmental toxicants such as heavy metals, pesticides, and mycotoxins [1]. These contaminants not only degrade air, water, and food quality but also weaken immune defenses and alter microbial ecosystems, increasing vulnerability to infections [1,2]. Poor sanitation, unsafe waste disposal, and inadequate infrastructure further facilitate disease transmission, while toxic exposures foster antimicrobial resistance (AMR) in both community and healthcare environments [3]. As environmental and public health threats increasingly intersect, traditional approaches to disease control become insufficient. This chapter explores how environmental toxicology directly and indirectly influences infectious disease patterns in resource-limited contexts. Drawing on data from sub-Saharan Africa and other affected regions, it underscores the need for integrated strategies including improved water, sanitation, and hygiene (WASH), environmental monitoring, and robust surveillance systems to build resilient health systems capable of anticipating and mitigating toxicological and infectious threats in vulnerable populations.

### 1.1 Methodology

To ensure a comprehensive and evidence-informed synthesis, this chapter employed a narrative literature review approach focused on identifying peer-reviewed articles, grey literature, and relevant case studies that illustrate the linkages between environmental toxicants, immunosuppression, and infectious disease dynamics, particularly in low-resource settings. Literature searches were conducted using databases including PubMed, Scopus, Web of Science, and Google Scholar between January 2000 and April 2025. Search terms included combinations of keywords such as "environmental toxicants," "heavy metals," "pesticides," "mycotoxins," "immune suppression," "infectious diseases,"
"antimicrobial resistance," and "low-resource settings." Inclusion criteria encompassed English-language publications reporting empirical data, reviews, or case studies relevant to the chapter's focus. Studies were prioritized if they provided insight into mechanisms of action, public health impacts, or surveillance strategies. Exclusion criteria included non-peer-reviewed opinion pieces, studies lacking relevance to environmental health or disease transmission, and publications focused solely on high-income settings without generalizable implications for low-resource environments. Reference lists of key papers were also reviewed to identify additional sources.

**2. Environmental Contaminants in Low-Resource Settings**

In many low-resource settings, particularly in sub-Saharan Africa and some parts of Asia, environmental contaminants are widespread due to weak regulatory frameworks, informal industrial practices, and limited public health infrastructure [4]. These toxic substances often present in soil, water, air, and food pose a dual threat by directly affecting human physiology and indirectly facilitating the transmission and severity of infectious diseases. Among the most critical contaminants are heavy metals, pesticides, and mycotoxins.

**2.1. Heavy Metals**

Over the past century, the rapid pace of globalization and industrialization has significantly increased the demand for the exploitation of natural resources often with little regard for environmental consequences. This trend has been particularly pronounced in low-income countries, where weak regulatory oversight has led to the unchecked release of environmental toxicants, such as heavy metals, into ecosystems [5]. Heavy metals such as lead, arsenic, mercury, and cadmium accumulate in the environment through artisanal mining, industrial effluents, and unsafe waste disposal [6]. Ingestion or inhalation of these metals disrupts hematologic, neurologic, and immune function. Long-term exposure weakens host immunity, increasing vulnerability to infectious diseases such as tuberculosis, respiratory tract infections, and diarrheal illnesses [7].

Case Example: In Zamfara State, Nigeria, extensive lead contamination resulting from informal gold mining led to widespread lead poisoning, particularly among children. Alongside fatal neurotoxicity that resulted in the death of over 400 children, these exposures were linked to increased bacterial infections, highlighting the immunosuppressive effects of chronic heavy metal exposure [8,9].

**2.2. Pesticides**

Effective pest management is crucial for agriculture and public health. Chemical pesticides have played a key role in reducing crop losses and controlling disease vectors like mosquitoes, thereby contributing to food security and saving countless lives [10,11]. The 20th-century population growth was made possible by increased food production, heavily reliant on pesticides. Roughly one-third of global agricultural output depends on pesticide use. Without them, fruit, vegetable, and cereal yields would decline by 78%, 54%, and 32% respectively [10]. However, the long-term overreliance on chemical pesticides has proven ecologically and economically unsustainable. Excessive pesticide use can severely disrupt natural ecosystems by eliminating beneficial predators, accelerating the emergence of pesticide-resistant pests, and causing outbreaks of secondary pest species [12]. Alarmingly, experimental and field-based studies have shown that over 98% of sprayed insecticides and 95% of herbicides often fail to reach their intended targets, with the majority of the chemicals dispersing into surrounding environments air, soil, and water through processes such as spray drift, surface
runoff, and volatilization [13]. These estimates, drawn from both controlled laboratory simulations and real-world agricultural trials, highlight the significant inefficiencies of conventional pesticide application methods. As a result, not only are production costs driven up due to the need for repeated applications, but the unintended environmental dispersion of these chemicals also has far-reaching consequences for ecosystem integrity and human health.

Available data indicates that while the majority of pesticides are applied in high-income countries, approximately 99% of pesticide poisoning cases and pesticide-related deaths occur in low-and middle-income countries, where regulatory oversight, healthcare systems, and farmer education are limited [14]. In these contexts, many farmers overuse pesticides without adequate knowledge of their health risks, often driven by the fear of reduced yields. Moreover, chemicals banned or heavily restricted in industrialized nations are still widely used in developing countries due to weak regulatory enforcement [15]. Cultural perceptions and local farming practices also influence how pesticides are applied introducing persistent organic pollutants (POPs) into local ecosystems and food chains. These substances bioaccumulate in human tissues and interfere with endocrine and immune regulation. Pesticide-driven ecological imbalances such as the reduction of beneficial insect populations can lead to a resurgence of vector-borne diseases like malaria, as natural mosquito predators are eliminated [16,17].

## 2.3. Mycotoxins

Mycotoxins, such as aflatoxins and fumonisins, are toxic fungal metabolites that commonly contaminate staple crops like maize, groundnuts, and sorghum, particularly in humid climates or during poor storage [18]. An estimated 25% of the global food and feed supply is affected by mycotoxins, posing serious threats to food safety and public health. Alarmingly, their prevalence is increasing rapidly in developing countries, particularly across Africa, due to climate change, poor post-harvest handling, and weak regulatory frameworks [19]. Chronic exposure can result in liver damage, immune suppression, and greater susceptibility to bacterial, parasitic, and viral infections, including hepatitis B and rotavirus [20, 21]. Children in regions like sub-Saharan Africa are especially vulnerable, and even low-level exposure in malnourished populations significantly heightens disease burden and mortality.

## 2.4 Emerging Contaminants

While this chapter focuses primarily on well-established environmental toxicants such as heavy metals, pesticides, and mycotoxins, emerging contaminants especially per- and polyfluoroalkyl substances (PFAS) are gaining increasing attention for their immunomodulatory effects. However, the lack of data from low-resource environments represents a critical research gap, especially given the compounding risks posed by weak regulatory oversight, inadequate waste management, and limited public awareness.

## 3. Pathways Linking Environmental Toxicants and Infectious Diseases

Environmental toxicants not only pose direct chemical hazards but also interact with infectious disease dynamics in complex and synergistic ways. These interactions compromise public health through multiple pathways, particularly in
low-resource settings where exposure levels are high and health systems are often
fragile.

**3.1. Compromised Water Systems**

Contaminated water sources serve as dual threats, carrying both chemical pollutants and pathogenic organisms. When industrial waste, agricultural runoff, or mining byproducts contaminate surface waters with heavy metals like arsenic, mercury, or lead alongside microbial pathogens from fecal matter the risk of waterborne disease outbreaks increases dramatically [23,24]. In addition, events such as floods and droughts exacerbate the situation by overwhelming sanitation infrastructure and concentrating toxins and pathogens in limited water supplies this leads to increased risks of waterborne diseases as pathogens and toxins are more easily spread through contaminated water supplies [25]. Cholera, typhoid fever, and cryptosporidiosis are common outcomes, especially in informal settlements and refugee camps [26]. Furthermore, Artisanal and small-scale mining (ASM), particularly gold mining, is widespread in many developing countries and low-resource settings, often resulting in severe water contamination. These activities typically involve the use of hazardous substances such as mercury and generate toxic byproducts that leach into surrounding water bodies [27]. A recent study in Ghana which adopted a systematic approach to gather and analyze relevant literature revealed alarming levels of heavy metals in freshwater sources, with concentrations of arsenic (0.28 mg/L), cadmium (0.13 mg/L), lead (0.30 mg/L), and mercury (0.03 mg/L) all exceeding World Health Organization (WHO) permissible limits. Sediment samples from the same sites also contained elevated levels of these metals, including 22.92 mg/kg of arsenic, 5.41 mg/kg of cadmium, 98.01 mg/kg of lead, and 0.81 mg/kg of mercury, surpassing international sediment quality guidelines [28]. These pollutants can severely impact aquatic ecosystems and human health, affecting water sources used for drinking, agriculture, and other purposes which compromises the immune system, they weaken the immune system by disrupting immune cell function, making individuals more vulnerable to infections [29].

**3.2. Contaminated Food Chains**

Foodborne exposure to toxic substances often originates at the foundational levels of the agricultural production chain specifically the soil and water used for cultivation. When crops are grown in soils that have been contaminated by industrial waste, mining runoff, or excessive pesticide application, they readily absorb harmful substances such as heavy metals (e.g., lead, cadmium, arsenic), pesticide residues, and persistent organic pollutants [30]. Similarly, irrigation with polluted water often drawn from rivers or streams impacted by untreated sewage, agricultural discharge, or chemical effluents introduces additional toxicants. These contaminants accumulate in edible plant tissues and enter the food chain, posing serious health risks to consumers over time [31]. In addition, livestock grazing in such contaminated environments are also at risk of bioaccumulating these hazardous substances in their tissues over time. As animals consume grass, forage, and water tainted with heavy metals, pesticide residues, and other toxicants, these compounds can concentrate in their muscles, organs, and milk. This bioaccumulation not only threatens animal health leading to reduced productivity, reproductive issues, and disease but also poses significant risks to human health when contaminated meat, milk, or other animal products are consumed [32]. The situation is particularly concerning in low- and middle-income countries, where environmental regulations and routine monitoring of soil and water quality are often lacking, increasing the likelihood of chronic exposure through daily dietary intake [33]. The accumulation of environmental toxicants in the food chain can cause a range of illnesses that
weaken the immune system, making individuals more susceptible to infections [34].

### 3.3. Weakened Immunity

Many environmental toxicants such as polychlorinated biphenyls (PCBs), dioxins, and heavy metals like lead, mercury, and cadmium can significantly disrupt the body's immune system [35]. These substances interfere with immune function by altering cytokine signaling, suppressing the production and activity of white blood cells, and damaging lymphoid tissues such as the spleen and thymus [36]. As a result, the body's ability to recognize and respond to pathogens becomes compromised. This immune suppression heightens vulnerability to a wide range of infectious agents [37]. In communities already facing high burdens of immunocompromizing conditions such as HIV/AIDS, chronic malnutrition, or prolonged stress the effects of toxicant exposure are often magnified. These synergistic interactions increase the frequency and severity of opportunistic infections, including tuberculosis, toxoplasmosis, and candidiasis. Such infections not only complicate diagnosis and treatment but also contribute to higher morbidity and mortality rates, particularly in low-resource settings [38].

### 3.4. Antimicrobial Resistance (AMR)

Environmental reservoirs of toxicants also play a critical role in the evolution of antimicrobial resistance. Heavy metals, disinfectants, and residual antibiotics in agricultural runoff and wastewater apply selective pressure on microbial communities, encouraging the survival of resistant strains. These toxicants can induce stress responses in bacteria, promoting horizontal gene transfer and the spread of resistance genes across species [39]. Resistant pathogens can enter the human population through direct contact, contaminated water, or food, creating a public health crisis that undermines the effectiveness of existing antimicrobial therapies not just in hospitals but across entire ecosystems [40].

### 3.5. Environmental Toxicants and COVID-19

The ongoing COVID-19 pandemic has reinforced the importance of a well-functioning immune system in preventing severe outcomes from viral infections. Emerging evidence suggests that exposure to environmental toxicants such as heavy metals, pesticides, and persistent organic pollutants can impair immune responses critical for mounting defenses against viruses, including SARS-CoV-2 [41,42,43]. These substances disrupt cytokine signaling, reduce the effectiveness of T-cell and antibody-mediated responses, and may exacerbate chronic inflammation, all of which increase susceptibility to respiratory viruses and worsen outcome of SARS-CoV-2 infection [42,43]. Populations in low-resource settings, where exposure to multiple toxicants is common and healthcare infrastructure is weak, may face compounded risks.
<figure><img src="image_4.png" /><figcaption>**Figure 1** *Environmental Toxicants and the Transmission Dynamics of Infectious Diseases*</figcaption></figure>

**4. Surveillance and Response Mechanisms**

Effective management of the complex interactions between environmental toxicants and infectious diseases requires robust surveillance and responsive health systems. Integrated approaches that combine epidemiological, environmental, and behavioral data are essential for timely intervention and informed policy-making to combat the transmission dynamics as shown in figure 1 above.

**4.1. Integrated Disease Surveillance and Response (IDSR)**

The IDSR framework has emerged as a cornerstone for early warning and response to disease outbreaks, particularly in low-resource settings [44]. By streamlining data collection across various diseases and levels of the health system, IDSR facilitates rapid detection, reporting, and containment of public health threats. Incorporating environmental indicators such as air and water quality, soil contamination, and climatic variables into IDSR enhances its predictive capacity and enables a more comprehensive understanding of outbreak drivers, including those linked to toxic exposures [45].

**4.2. Environmental Monitoring**

Establishing environmental surveillance systems is vital to complement pathogen tracking efforts [46]. Sentinel sites that routinely monitor soil, water, food, and air for contaminants such as heavy metals, pesticides, and persistent organic pollutants provide early warning signs of potential health hazards [47]. Coupled with geospatial mapping, these data can identify high-risk exposure hotspots and inform targeted interventions. Integration with health data systems
enhances the ability to trace disease outbreaks to environmental origins, facilitating multi-sectoral response strategies [48].

### 4.3. Risk Communication

Risk communication plays a pivotal role in bridging the gap between surveillance data and community action. Public awareness campaigns that clearly articulate the connections between environmental hazards and health outcomes can empower individuals to adopt safer practices [49,50]. For instance, disseminating information about the dangers of using contaminated water or improper pesticide handling can reduce exposure and disease incidence. Effective messaging must be culturally sensitive, locally relevant, and delivered through trusted communication channels to foster sustainable behavior change.

## 5. Water, Sanitation, and Hygiene (WASH) as a Crosscutting Strategy

WASH interventions serve as foundational pillars for both environmental health and infectious disease prevention. By addressing the upstream drivers of exposure, contaminated water, inadequate sanitation, and poor hygiene WASH strategies offer broad protective effects against chemical and biological hazards alike.

### 5.1. Safe Water Access

Ensuring access to clean and safe drinking water is critical. In resource-constrained settings, decentralized and low-cost technologies such as solar disinfection (SODIS), ceramic filtration, and biosand filters offer practical solutions [51, 52]. These methods effectively reduce microbial pathogens while also lowering concentrations of certain chemical contaminants. Scaling up such technologies can significantly mitigate the co-occurrence of toxicants and waterborne infectious agents.

### 5.2. Sanitation Infrastructure

Improved sanitation systems such as ventilated improved pit (VIP) latrines, eco-san toilets, and community-led total sanitation (CLTS) programs are essential for preventing environmental contamination. Proper waste management reduces the leaching of fecal matter and chemicals into surrounding soils and water bodies, thereby limiting transmission of enteric pathogens and reducing the emergence of AMR in environmental reservoirs.

### 5.3. Hygiene Promotion

Promoting good hygiene practices, particularly handwashing with soap at critical times, has been consistently shown to reduce the incidence of enteric and respiratory diseases. Additionally, hygiene education can decrease chemical exposure, such as washing pesticide residues from fruits and vegetables or using protective gear during pesticide application. Integrated hygiene promotion campaigns should be embedded in school curricula, community health outreach, and media platforms to maximize reach and impact.

## 6. Health System Resilience and Policy Integration

Strengthening the resilience of health systems is essential for addressing the complex interplay between environmental toxicants and infectious diseases. This requires not only robust service delivery and surveillance but also coordinated policies that span multiple sectors and levels of governance.

### 6.1. Capacity Building

Empowering frontline health workers with skills in environmental health, toxico-surveillance, and outbreak response is critical to early detection and containment of health threats. Training programs should include modules on identifying environmental risk factors, collecting and interpreting exposure data,
and engaging with communities on behavior change. Strengthened human resource capacity at the local level enhances overall system responsiveness and helps bridge the gap between scientific knowledge and practical, on-the-ground action.

## 6.2. Multisectoral Coordination

Environmental health challenges are inherently cross-cutting, requiring coordinated efforts across multiple sectors. Effective collaboration among ministries of health, environment, agriculture, education, and water resources can facilitate a unified response to complex risk interfaces. Joint planning, data sharing, and policy alignment such as One Health frameworks enable integrated approaches to managing environmental hazards, infectious disease risks, and food safety concerns. Building such coordination mechanisms into national emergency preparedness plans strengthens collective resilience.

## 6.3. Policy Recommendations

To support system-wide resilience and reduce disease burden, several policy actions are essential:

* Strengthen and enforce environmental regulations, particularly those governing industrial discharge, mining runoff, and the use of agricultural chemicals such as pesticides and fertilizers. Regulatory compliance should be monitored through independent audits and community reporting mechanisms.

* Invest in early warning systems that integrate environmental surveillance with disease data. Such systems should include real-time geospatial mapping, climate modeling, and automated alert mechanisms to facilitate proactive interventions.

* Develop and implement national AMR action plans that explicitly include environmental dimensions. These plans should address the role of pollutants in fostering resistance and promote integrated waste management strategies for healthcare and agricultural sectors.

## 7. Future Directions

As climate change, rapid urbanization, and population growth accelerate, the convergence of environmental toxicants and infectious disease risks will intensify especially in low- and middle-income countries. To navigate this evolving landscape, future strategies must harness innovative technologies and integrated frameworks. Tools such as mobile health (mHealth) platforms can expand real-time data collection and community engagement, while satellite imaging enables environmental monitoring at scale. In addition, genomic surveillance can offer early insights into the spread and evolution of AMR.

Research and policy efforts should prioritize:

* Longitudinal studies exploring the link between chronic toxic exposures and increased susceptibility to infections

* Routine integration of environmental indicators into national and sub-national health surveillance systems

* Development and deployment of context-specific WASH innovations tailored for fragile and resource-limited settings

These forward-looking approaches can guide more resilient, data-driven, and equitable public health responses.

## 8. Conclusion

The intersection of environmental toxicology and infectious diseases represents a critical yet often overlooked frontier in global health especially in low-resource settings, where the burden is most acute. Addressing these
interconnected challenges requires moving beyond siloed responses to adopt a systems-level approach. This includes integrating environmental monitoring into disease surveillance, empowering communities through risk communication, and implementing sustainable, cross-sectoral policies. Acknowledging and acting on the deep interlinkages between environment and health can help reduce disease burden, strengthen resilience, and achieve lasting public health gains.

**Acknowledgments**

The author would like to acknowledge the staff of Public Health Nigeria for their valuable support and provision of data related to the lead poisoning crisis in Zamfara State and the flooding events in Maiduguri. Their contributions were instrumental in enriching the environmental and public health analysis presented in this work.

**Conflict of Interest**

The authors declare no conflict of interest.

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