Polycyclic aromatic hydrocarbons (PAHs) are a diverse group of organic compounds characterized by multiple fused aromatic rings. These compounds primarily arise from the incomplete combustion of organic materials, which can occur in various contexts, including vehicular emissions, industrial activities, and natural events such as wildfires and volcanic eruptions. PAHs are pervasive in the environment; they have been detected in air, soil, water, and sediments, and can enter the food chain, leading to bioaccumulation and biomagnification.

The formation and persistence of PAHs in the environment are largely influenced by their hydrophobic nature, which causes them to adhere to particulate matter. This affinity facilitates their transport and enhances their stability, raising significant concerns about their long-term effects on both human health and ecosystems. Epidemiological studies and toxicological research have linked PAH exposure to a variety of adverse health outcomes, including respiratory issues, cardiovascular diseases, and several forms of cancer. Their potential carcinogenic, mutagenic, and endocrine-disrupting properties have been extensively studied, emphasizing the critical need for a deeper understanding of their toxicological mechanisms and exposure pathways.

As environmental pollution escalates, particularly in the context of urbanization and industrialization, addressing the challenges posed by PAHs becomes increasingly urgent. New industrial practices and energy transitions aimed at combating climate change may inadvertently lead to increased PAH emissions, underscoring the importance of ongoing research in this area. By elucidating the complex interactions between PAHs and biological systems, we can gain valuable insights into their impacts and develop effective strategies for risk mitigation.

We invite researchers to contribute to this Collection, which serves as a platform for advancing knowledge on the toxicological implications of PAHs. We encourage submissions that explore a wide range of topics, including environmental fate, human exposure assessments, mechanistic studies, and risk characterization, with the ultimate goal of informing effective regulatory measures and public health interventions.

Topics of interest include, but are not limited to:

- Mechanisms of PAHs toxicity

- Human health risk assessments for PAHs exposure

- Environmental fate and transport of PAHs

- Strategies for PAHs remediation

- Novel analytical techniques for PAHs detection

This Collection supports and amplifies research related to SDG 3.

Keywords: Polycyclic Aromatic Hydrocarbons; PAHs; exposure assessment; toxicology; mechanism of action; health effect; risk assessment; bioanalysis; bioavailability

Microplastics (plastics less than 5 mm) are the breakdown of larger plastic items. They are now widespread in freshwater environments, including rivers, lakes, streams and livestock, and domestic supply dams and reservoirs. These particles primarily come from sources like household waste, industrial activities, personal care products, atmospheric fallout, recreational activities, and fishing activities. The scientific concern around microplastics in freshwater ecosystems is multifaceted. Aquatic organisms, such as fish and invertebrates (prawns, mussels), can mistakenly ingest these particles, which may lead to physical harm like digestive blockages, reduced feeding efficiency, starvation, and reproductive issues. Furthermore, microplastics can adsorb harmful chemicals (e.g., DDT, heavy metals, and oil compounds) from the surrounding water environment, which may then enter the food chain when consumed by fish and other aquatic organisms. In addition, microplastics contaminated freshwater or irrigation water used can contaminate crops, fruit, and vegetables via the root systems. The presence of microplastics also disrupts the natural balance of aquatic ecosystems. While the long-term ecological consequences are still being studied, research suggests that microplastics may alter habitat conditions, affect nutrient cycling, and impact biodiversity. Additionally, they may serve as carriers for harmful pathogens, further compromising ecosystem health.

Understanding the pathways, impacts, and long-term consequences of microplastics in freshwater environments is crucial for developing effective mitigation strategies and policies to address this growing environmental challenge. The proposed Collection will publish articles on different aspects of microplastic contamination and their risk assessment in freshwater ecosystems, highlight the urgent need for better waste management strategies, and encourage more research about the toxicological impacts of microplastics on freshwater ecosystems.

The major aspects of this collection will cover:

• Toxicological effects of microplastics on freshwater fish

• Toxicological effects of microplastics on crops or vegetables via contaminated freshwater

• Toxicological effects of microplastics in freshwater drinking sources

• Contamination of water and food with freshwater microplastics and risks to humans

• Harmful chemicals adsorbed by microplastics from the surrounding water environment and their possible toxic effects on freshwater ecosystems

Keywords: Microplastics; Aquatic pollution; River pollution; Lake contamination; Microplastic degradation; Microplastic ingestion; Microplastic toxicity; Environmental monitoring