Environmental Risk Assessment of Aquatic Environments: From Emerging Contaminants to Ecosystem Management

Aquatic ecosystems, including freshwater lakes, rivers, estuaries, and coastal marine environments, are fundamental to ecological stability, food security, and human well-being. However, these systems are increasingly subjected to complex and overlapping anthropogenic pressures. Rapid industrialization, urban expansion, intensive agriculture, and expanding coastal infrastructure have introduced a diverse spectrum of stressors into aquatic environments, ranging from traditional pollutants such as heavy metals to contaminants of emerging concern (CECs), including pharmaceuticals, plastic-derived chemicals, and engineered nanomaterials [1,2].

Within this context, environmental risk assessment has become a critical scientific framework that bridges chemical monitoring, biological effects, and ecosystem management. Rather than focusing solely on contaminant concentrations, modern risk assessments seek to quantify the probability and severity of adverse outcomes across multiple levels of biological organization, from molecular and cellular responses to population- and ecosystem-level impacts [3]. This Special Issue, Environmental Risk Assessment of Aquatic Environments, was conceived to address these challenges by bringing together interdisciplinary research across chemical analysis, ecotoxicology, biomonitoring, and risk management perspectives. This Special Issue brings together 13 peer-reviewed contributions spanning emerging contaminants, biomonitoring approaches, and risk management implications for aquatic systems.

Among the most pressing challenges in aquatic risk assessment is the widespread presence of biologically active and persistent contaminants. Pharmaceuticals, personal care products, and plastic additives are designed to exert biological effects at low concentrations, raising concerns about their unintended impacts on non-target organisms [1,4]. In this Special Issue, Martinjak et al. (2025) presented a forced degradation study of several antiviral drugs, highlighting the complexity of these pollutants and the importance of understanding chemical stability in environmental matrices. Furthermore, Souza-Silva et al. (2025) provided a comprehensive review of the aquatic ecotoxicology of antiretrovirals, emphasizing the need for focused research on these bioactive compounds. While some compounds pose high risks, risk characterization must be specific; for instance, Batucan et al. (2025) examined low concentrations of ibuprofen and found no adverse effects on mayfly nymphs, highlighting the need for concentration-dependent toxicity data.

Plastic pollution further complicates this landscape. Beyond visible debris, microplastics and nanoplastics act as vectors for chemical additives and sorbed environmental pollutants, while also posing physical and cellular hazards. Their small size facilitates their ingestion across trophic levels and potential internalization at the cellular level, introducing new pathways for toxicity and ecological risk [4]. In this context, Romano et al. (2025) contributed a bibliometric analysis of nanoplastics, specifically focusing on their uptake, bioaccumulation, and cellular internalization, which are critical for future risk assessment models. Expanding the scope to engineered nanomaterials, Diallo and Dewez (2024) characterized the toxicity of zirconium nanoparticles on the aquatic plant Lemna minor, providing insights into the risks posed by metal-based nanomaterials. Additionally, Di Bella et al. (2025) investigated plasticizers and bisphenols in Sicilian lagoon environments, demonstrating how these contaminants pose risks in areas with varying anthropogenic pressures.

While emerging contaminants receive increasing attention, traditional pollutants remain a persistent, significant threats in many aquatic systems worldwide. Heavy metals such as cadmium, copper, zinc, mercury, and lead continue to impact water and sediment quality, particularly in regions affected by mining activities, industrial discharge, and urban runoff [5]. Unlike many organic contaminants, metals do not degrade and can accumulate in sediments and biota, leading to long-term ecological degradation and human health concerns. Addressing these classic toxicological challenges, Cojocaru et al. (2025) evaluated the presence of heavy metal toxicity in Daphnia magna, providing data that reinforces the utility of standard test organisms in monitoring metal pollution.

Risk assessment in metal-contaminated systems relies heavily on biological indicators capable of integrating exposure over time. Organisms such as diatoms, zooplankton, and benthic invertebrates provide sensitive and ecologically relevant measures of metal toxicity, reflecting both acute and chronic stress responses [6]. For instance, Glevitzky et al. (2025) utilized diatom-based bioindicators to assess pollution in the Arieș River, Romania. Similarly, Krupa et al. (2025) assessed the ecological state of floodplain lakes in Kazakhstan using phytoplankton communities. These cases validate the use of biomonitoring in real-world ecosystem health assessment. Moreover, the bioaccumulation and biomagnification of metals such as methylmercury highlight the close linkage between the health of aquatic ecosystems and food safety, reinforcing the need to incorporate dietary exposure and public health considerations into environmental risk frameworks [5]. Directly addressing the human dimension, Spagnolo et al. (2025) evaluated fish consumption patterns and perceptions of the health risks related to methylmercury exposure in an Italian coastal population.

Aquatic environmental risk is not limited to chemical stressors alone. Nutrient enrichment and eutrophication frequently lead to harmful algal blooms, particularly those dominated by toxin-producing cyanobacteria. Cyanotoxins can induce oxidative stress, genotoxic effects, and developmental abnormalities in aquatic organisms, while also posing risks to livestock and human populations [7]. Assessing these biological hazards requires tools capable of capturing both community-level structural changes and sublethal biological responses. In this Special Issue, Kurbatova et al. (2025) assessed the genotoxic effects of water in ecosystems with varying cyanobacterial abundance using the Allium test, offering a practical approach to monitoring biological hazards.

In parallel, physical modifications of aquatic and coastal environments introduce additional dimensions of risk. Shore protection structures, hydrological alterations, and engineered coastal defenses, while designed to mitigate erosion or flooding, can inadvertently modify nearshore hydrodynamics and create hazardous conditions such as rip currents, increasing risks to human safety [8]. Pezzini and Pranzini (2025) addressed this often overlooked aspect by analyzing shore protection structures as contributors to drowning risk in Italy, reminding us that environmental risk assessment must extend beyond chemical and biological endpoints to include physical hazards within integrated management frameworks.

The collective insights of this Special Issue demonstrate that environmental risk in aquatic systems is inherently multidimensional. Chemical, biological, and physical stressors often co-occur, interact, and amplify one another, challenging reductionist assessment approaches [3]. Effective risk assessment therefore requires integration across disciplines, combining advanced analytical techniques, sensitive biological indicators, and conceptual frameworks that explicitly link environmental exposure to ecological and human health outcomes. Future research should prioritize the harmonization of assessment methodologies of emerging contaminants, the incorporation of mixture toxicity and chronic exposure scenarios, and the translation of scientific findings into actionable management strategies. Advances in remediation technologies, early-warning biomonitoring tools, and ecosystem-based management approaches will be essential for mitigating risks and ensuring the long-term sustainability of aquatic environments. In the realm of remediation technologies, English (2024) explored the use of electric field-based ozone nanobubbles for water purification, offering potential solutions for aquaculture and wastewater treatment.

The studies assembled in this Special Issue collectively reinforce the notion that environmental risk assessment is no longer a linear process of measuring pollutant concentrations. Instead, it is an integrative discipline that must account for complex contaminant mixtures, biological responses across multiple scales, and the broader physical and socio-environmental context [3]. By bridging scientific understanding with risk management strategies and policy relevance, this Special Issue aims to contribute to the effective protection and stewardship of aquatic ecosystems in an era of accelerating environmental change.