Sources, Fate, and Ecological Risk of Pollutants in Aquatic Environments

1. Introduction

Following the success of the first edition of the Special Issue “Occurrence and Environmental Risks of Organic Pollutants in Aquatic Environment”, which gathered nine high-quality contributions from international research groups, this second edition has once again proved to be a scientific success, with an equivalent number of published papers. Together, these studies span freshwater and coastal systems, sediments and biota, legacy and emerging pollutants, and combine field observations, laboratory experiments, model derivation, and critical reviews.

Contributions 1–6 examined the occurrence, distribution, bioavailability, and risk of pollutants in surface water, sediments, and aquatic organisms. Zhang et al. derived fluoride water quality criteria and identified high-risk basins in China; Tan et al. linked PFAS contamination to zooplankton community structure in the Weihe River; Musco et al. showed that BDE-47 induces sublethal physiological and behavioural responses in symbiont-bearing foraminifera; Ruiz-Marin et al. assessed heavy-metal enrichment and bioaccumulation in clams from Mexican lagoons; Zhao et al. characterized organochlorine pesticides in plateau-lake sediments; and Chang et al. reviewed PFAS sources and treatment challenges in electroplating wastewater. These studies collectively illustrate that pollutant occurrence is controlled by both anthropogenic sources and site-specific environmental conditions, and that conventional treatment and single-indicator assessments are often insufficient.

Contributions 7–9 focused on long-term remobilization, toxicological mechanisms, and risk-assessment tools. Zhao et al. reconstructed a sediment record showing that eutrophication can remobilize legacy organochlorine pesticides; Xia et al. reviewed evidence that environmental endocrine disruptors induce DNA damage, chromosomal abnormalities, and micronuclei through oxidative stress, DNA damage response interference, and epigenetic dysregulation; and Yuan et al. derived species-sensitivity-based water quality criteria for three quinolone antibiotics. These contributions highlight the importance of integrating historical records, mechanistic toxicology, and criterion derivation into ecological risk assessment.

Collectively, this Special Issue addresses the sources, occurrence, fate, bioavailability, toxicity, ecological risk, treatment, and regulation of legacy and emerging pollutants in aquatic environments. It covers organic contaminants such as PFAS, organochlorine pesticides, BDE-47, and endocrine disruptors, as well as fluoride, heavy metals, and antibiotics, across water, sediment, and biological matrices. The overarching conclusion is that effective aquatic pollution management requires source control, long-term monitoring, integrated multi-method assessment, and science-based water quality criteria that account for pollutant mixtures, environmental gradients, and species-specific sensitivity.

2. An Overview of Published Articles

Zhang et al. (Contribution 1) derived fluoride water quality criteria for protecting aquatic organisms and assessed ecological risks in surface waters. Using globally collected acute and chronic toxicity data and species sensitivity distribution methods, they derived short- and long-term criteria of 17.47 mg/L and 3.334 mg/L, respectively. The authors recommended expanding datasets to improve future criteria derivation and risk assessment.

Tan et al. (Contribution 2) investigated PFAS contamination and zooplankton community structure in the Weihe River, China, using eDNA metabarcoding and PLS-PM. Short-chain PFAS dominated and showed spatial patterns similar to zooplankton. Water chemistry promoted PFAS accumulation, with taxon-specific effects: short-chain PFAS were negatively associated with Cercozoa, while long-chain PFAS correlated with Ciliophora and Rotifera. Some Ciliophora taxa may serve as bioindicators, and higher abundance potentially buffered diversity loss. The research concluded that short-chain PFAS plus water parameters pose higher ecological risk.

In Palermo (Italy), Musco et al. (Contribution 3) exposed symbiont-bearing benthic foraminifera (Peneroplis spp.) to BDE-47. Exposure reduced pseudopodial activity and reproduction and increased symbiont loss, with limited mortality at the higher concentration. Locomotor activity showed a non-monotonic response: the low concentration increased mean distance travelled, whereas the high concentration reduced it relative to the low dose. These sublethal responses support these foraminifera as sensitive bioindicators and suggest potential consequences for carbonate production and trophic transfer in coastal ecosystems.

In Campeche (Mexico), Ruiz-Marin et al. (Contribution 4) assessed heavy metal concentrations in sediments and bioaccumulation in the clam Rangia cuneata across three climatic seasons in the Pom–Atasta lagoons. Sediments were enriched in As, Cr, and Ni, but only Ni exceeded the adverse-effect threshold and showed BSAF > 1. Toxic risk and ecological risk indices indicated low to moderate risk, with Ni as the main concern. The research recommended continuous monitoring to protect benthic fauna and local food safety.

Zhao et al. (Contribution 5) investigated organochlorine pesticides (OCPs) in surface sediments from typical lakes of China. HCHs dominated while DDTs were low, with historical residues and agricultural non-point sources as the main contributors. Overall, contamination was low to moderate, and the closed/semi-closed, low-temperature, weakly scoured plateau-lake settings favoured long-term OCP retention in sediments. The research recommended priority source tracing, continuous monitoring, and risk control at high-risk sites.

Chang et al. (Contribution 6) reviewed PFAS sources, occurrence, and treatment in electroplating wastewater. Chromium plating is the main source, and the shift toward short-chain and substitutive PFAS has increased the diversity and hidden fractions of PFAS in wastewater. Conventional treatment is largely ineffective, while individual technologies show chain-dependent and matrix-limited performance. The research concluded that source control, integrated treatment trains, and non-target screening are essential for effective PFAS management in the electroplating industry.

Zhao et al. (Contribution 7) reconstructed a multi-decadal sediment record from Lake Qilu of China and linked organic matter evolution to organochlorine pesticide (OCP) dynamics. Eutrophication increased algal-derived and hydrophilic organic matter; OCPs showed historical accumulation, post-ban decline, and recent resurgence. Positive correlations with TN, DOM, and hydrophilic matter suggest that eutrophication-derived organic matter complexes hydrophobic OCPs and promotes their upward remobilization. The research conclude that eutrophication can remobilize legacy OCPs, with implications for risk assessment in eutrophic lakes.

Xia et al. (Contribution 8) reviewed the sources, detection methods, in vivo/in vitro evidence, and mechanisms of genotoxicity induced by environmental endocrine disruptors. Bisphenols, phthalates, PBDEs, and some novel substitutes consistently cause DNA damage, chromosomal abnormalities, and micronuclei, mainly via ROS-mediated oxidative stress, DNA damage response interference, and epigenetic dysregulation. Combined low-dose exposures may amplify damage and pose transgenerational risks, supporting high-throughput, multi-omics, and AI-based risk assessment.

Yuan et al. (Contribution 9) derived short- and long-term water quality criteria for norfloxacin, enrofloxacin, and ciprofloxacin using species sensitivity distribution following Chinese guidelines. Toxicity data covered multiple trophic levels, and best-fit models were used to estimate protective concentrations. These criteria provide a scientific basis for regulating emerging pollutants and revising freshwater quality standards.

3. Future Perspectives and Concluding Remarks

Future research should move beyond single-pollutant and short-term assessments toward integrated, environmentally realistic frameworks. For legacy and emerging pollutants, priority should be given to long-term monitoring across water, sediment, and biota, supported by non-target screening to capture unknown transformation products and hidden fractions such as those observed for PFAS. Mechanistic studies should further link sublethal responses, oxidative stress, DNA damage, and epigenetic effects to population- and ecosystem-level outcomes, while accounting for combined exposure at environmentally relevant low doses and possible transgenerational risks. The remobilization of historically buried pollutants under eutrophication and hydrodynamic disturbance also deserves sustained attention, particularly in shallow and plateau lakes. In parallel, treatment technologies for industrial wastewater require integrated trains rather than single processes, with greater emphasis on short-chain compounds, concentrate disposal, and cost-effective operation. Water quality criteria should be expanded and regionally adapted, incorporating species sensitivity, bioavailability, and site-specific environmental conditions to support more robust risk assessment and regulation.

In conclusion, the studies in this Special Issue demonstrate that pollutants in aquatic environments originate from multiple anthropogenic and natural sources, undergo complex fate and remobilization processes, and exert adverse effects across molecular, organismal, and ecological levels. Their risks are modulated by environmental gradients, pollutant mixtures, and species-specific sensitivity, and cannot be reliably captured by conventional treatment performance or single-indicator assessments alone. Effective aquatic pollution management therefore requires source control, continuous monitoring, mechanistic toxicology, improved treatment technologies, and science-based water quality criteria. Integrating these approaches will strengthen the protection of aquatic biodiversity and human health under increasing chemical pressure.