Contaminants in the Water Environment: Significance from the Perspective of the Global Environment and Health

1. Introduction

Water is essential for all life, yet it faces increasing threats from contamination due to various human activities and natural processes. Pollutants enter the water environment through industrial discharge, agricultural runoff, household waste, and natural processes, leading to the widespread pollution of freshwater and marine ecosystems. These contaminants can be categorized as chemical (e.g., heavy metals, persistent organic pollutants (POPs), pharmaceuticals, and emerging contaminants such as per- and polyfluoroalkyl substances (PFASs)); biological (e.g., microbial pathogens); and physical (e.g., microplastics, sediments) [1,2,3,4]. The presence of these substances in water systems poses significant risks to both environmental and human health.

Water contamination is a global crisis with severe consequences for biodiversity, food security, and public health on an unprecedented scale. Contaminants disrupt aquatic ecosystems, bioaccumulate in the food chain, and contribute to severe health conditions, including cancer, endocrine disruption, and developmental disorders [5,6,7,8,9]. As water contamination transcends geographical boundaries through atmospheric deposition and hydrological cycles, addressing this issue requires a global perspective that integrates scientific research, policy implementation, and technological innovation.

This Special Issue on Contaminants in the Water Environment (https://www.mdpi.com/journal/water/special_issues/4671N8F525: accessed on 22 April 2025) presents a diverse range of studies examining the sources, distribution, and impacts of various pollutants in aquatic ecosystems. Research on nutrient dynamics highlights how human activities and climate factors influence the nitrogen and phosphorus levels in urban river basins. Heavy metal contamination is explored through an assessment of the iron pollution in Egypt’s groundwater and an elemental analysis in Utah Lake using ICP-OES. Microplastic pollution is investigated in Central Europe’s largest shallow lake, while industrial contributions to water pollution are evaluated in Indonesia’s Cikembar sub-watershed. This Issue also addresses the impacts of climate and land use on water quality seen in Colorado’s Fountain Creek watershed and Indonesia’s Cirata Reservoir. Analytical advancements are featured in pathogen surveillance studies comparing methods for the detection of SARS-CoV-2 in hospital wastewater. Additionally, toxicological studies in this Issue assess the combined effects of glyphosate and copper on aquatic organisms and the presence of heavy metals in fish from the Yangtze River, raising concerns in terms of food safety. These contributions collectively provide valuable insights into the complex interactions of contaminants in the water environment, underscoring the urgent need for improved monitoring, regulation, and sustainable water management practices.

2. Sources and Types of Contaminants

Water contaminants can be categorized based on their sources and chemical nature. The major sources include the following:

(a)

Industrial discharge: Factories release heavy metals (e.g., lead, mercury, cadmium), solvents, and POPs, contaminating nearby water bodies;

(b)

Agricultural runoff: Fertilizers, pesticides, and herbicides introduce nitrates, phosphates, and toxic compounds into aquatic systems, leading to eutrophication and ecosystem imbalances;

(c)

Urban wastewater: Household products, pharmaceuticals, and personal care products enter sewage systems, ultimately reaching natural water sources;

(d)

Atmospheric deposition: Airborne contaminants, including polycyclic aromatic hydrocarbons (PAHs) and mercury, settle into water bodies through precipitation, illustrating the global environmental transport of pollutants;

(e)

Natural sources: Environmental processes such as volcanic eruptions, wildfires, dust storms, the natural weathering of heavy metals from soils and rocks, and the decomposition of organic matter contribute to contamination.

3. The Global Impact of Water Contamination

Water contamination has far-reaching implications, potentially destabilizing global ecological balance and socioeconomic stability. Its key consequences include (i) bioaccumulation and biomagnification, where toxic substances accumulate in aquatic organisms and intensify through the food chain, endangering higher trophic levels [10,11]; (ii) eutrophication, where excessive nutrient runoff from agriculture promotes algal blooms, depleting oxygen levels and causing large-scale fish mortality [12,13]; and (iii) habitat degradation, where chemical pollutants reduce biodiversity by negatively impacting aquatic flora and fauna [14,15,16,17]. Additionally, water contamination poses substantial socioeconomic challenges. Polluted water reduces agricultural productivity, increases healthcare costs, and burdens governments and communities financially.

4. The Health Risks Associated with Water Contaminants

Waterborne contaminants, including both legacy and emerging pollutants, contribute to a wide range of health risks, ranging from acute poisoning to chronic diseases, often resulting in fatalities and significant economic losses. For instance, heavy metals such as lead, mercury, and arsenic can cause neurotoxicity, kidney damage, and developmental disorders [18,19,20,21,22]. Pesticides and herbicides can cause endocrine disruption, reproductive toxicity, and an increased risk of cancer [23,24,25]. Pharmaceuticals can contribute to antibiotic resistance and hormonal imbalances in both humans and aquatic organisms [26,27]. Microplastics and nanoparticles can be associated with inflammatory responses, oxidative stress, and potential carcinogenic effects [28,29,30].

Water contamination intensifies global water scarcity and poses a significant threat to food security by reducing the availability of clean water for drinking and irrigation, directly impacting agriculture and global food supply chains. Exposure to waterborne contaminants leads to severe health consequences, resulting in millions of deaths worldwide. According to the World Health Organization, in 2022, at least 1.7 billion people relied on unsafe or contaminated drinking water, with an estimated 1 million deaths annually due to diarrhea caused by unsafe water [31]. Similarly, other contaminants, such as microplastics and antimicrobial-resistant pathogens, also contribute to mortality on a global scale. Figure 1 below illustrates the global distribution of deaths associated with unsafe drinking water, highlighting the disparities in water quality worldwide. Furthermore, the economic burden associated with healthcare costs, water treatment, and ecosystem restoration places significant financial strain on governments and communities worldwide.

5. Advances in Detection and Monitoring

The ability to detect and quantify contaminants is essential for assessing environmental and health risks while developing effective mitigation strategies. Recent advancements in analytical techniques have significantly improved detection capabilities. Gas Chromatography-Mass Spectrometry (GC-MS) and Liquid Chromatography-Mass Spectrometry (LC-MS) allow for the identification of trace contaminants, while high-resolution mass spectrometry, such as Liquid Chromatography-High-Resolution Mass Spectrometry (LC-HRMS) (e.g., Orbitrap and Quadrupole Time-of-Flight [QTOF] and Gas Chromatography-High-Resolution Mass Spectrometry (GC-HRMS), enhances suspect screening for a broader range of pollutants [33,34,35,36]. Additionally, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) provides precise analyses of heavy metal concentrations [37,38]. Artificial intelligence and machine learning can contribute further by enabling predictive modeling of contaminant transport and risk assessments, as well as automating the detection and classification of pollutants through big data approaches [39,40,41,42]. Meanwhile, biosensors and smart technologies can revolutionize real-time water quality monitoring, with portable sensors allowing for rapid field-based assessments [43,44,45]. These innovations collectively enhance the accuracy, efficiency, and timeliness of responses to water contamination, strengthening environmental and public health protection.

6. Conclusions and Call to Action

Water contamination is an escalating global challenge with profound environmental, economic, and health implications. While scientific advancements have improved contaminant detection and regulation, significant gaps remain, particularly as concerns emerging contaminants in the water bodies, policy enforcement, and public awareness. Addressing these challenges requires a collaborative approach involving researchers, policymakers, industries, and communities. Strengthening the global regulations, promoting sustainable water management, and leveraging AI-driven solutions can pave the way for a cleaner and healthier water environment.

To protect future generations, it is important to prioritize research on water quality, advocate for stricter environmental policies, and foster a culture of responsible water use. Taking decisive action today can ensure access to clean and safe water for all. We hope that the articles published in this Special Issue will engage readers and contribute to our scientific understanding of water contamination significantly, advancing global scientific discourse further.