Freshwater ecosystems are increasingly at risk from microplastic contamination. However, information on the sub-lethal toxicity of polymer-specific microplastics in freshwater fish remains limited. The current study assessed the toxicological effects of polyvinyl chloride microplastics (PVC-MPs) with a particle size range 1 to 2500 μm in juvenile Oreochromis mossambicus under controlled laboratory conditions. A 96-h median lethal concentration (LC50) of 90.2 mg/L (95% CI) was determined, and O. mossambicus were subsequently exposed to three sub-lethal concentrations (7.05, 15.63, and 40.04 mg/L) for 14 days. Following exposure, fish were euthanized to determine PVC-MPs accumulation in gill, gut, liver, and muscle. PVC-MPs accumulated in a concentration-dependent manner, with tissue-specific bioaccumulation following the order gill > gut > liver > muscle. PVC-MPs exposure significantly altered the Oxidative stress biomarkers such as superoxide dismutase (SOD), catalase (CAT), thiobarbituric acid reactive substances (TBARS), glutathione (GSH), and hepatic biomarkers, alanine aminotransferase (ALT) and alkaline phosphatase (ALP). Alteration in proximate composition (total protein, total carbohydrates and total lipids) indicated disturbance in energy metabolism. Hematological analysis revealed significant reduction in erythrocyte related indices accompanied by elevated leukocyte counts, while genotoxicity assessment showed significant increase in micronucleus frequency, demonstrating chromosomal damage. Histopathological analysis further revealed progressive epithelial lifting, hyperplasia, lamellar fusion, interlamellar cell mass alteration and erythrocyte aggregation, with lesion severity increasing with exposure concentration. Collectively, these findings demonstrate that sublethal PVC-MPs exposure induces tissue-specific bioaccumulation, oxidative stress, metabolic dysfunction, hematological alterations, genotoxicity and gill pathology in juvenile O. mossambicus, highlighting the ecological risks of PVC-MPs in freshwater ecosystems.
Microplastic exposure in filter-feeding megafauna is commonly assessed using seawater sampling, despite growing evidence that biological aggregation processes may strongly influence particle availability. This study quantified microplastics associated with bulk plankton-net samples collected in Djibouti, an important whale shark (Rhincodon typus) aggregation area in the western Indian Ocean. Using a multi-year dataset (2016 - 2025), microplastic abundance, spatial and temporal variability, and potential exposure for whale sharks were investigated. Mean microplastic abundance was 18.1 ± 21.9 MP m−3, while concentrations expressed on a biomass basis ranged from 0.07 to 1.42 MP mg−1. Fibers accounted for 64.4% of all particles. Most fragments were <100 μm (90%), whereas fibers were mainly within the 100 - 500 μm range (59%). No significant spatial differences in microplastic concentrations were detected among sampling sites, indicating widespread distribution across the Gulf of Tadjoura. Microplastic abundance was strongly correlated with sample biomass (Spearman r = 0.756, p < 0.0001), indicating a close association between particle availability and biomass within the feeding habitat. Exploratory analyses revealed lower zooplankton biomass and whale shark abundance in more recent sampling years, suggesting that ecosystem productivity may influence both particle availability and the intensity of whale shark aggregations. By integrating microplastic concentrations with bulk plankton-net sample biomass and species-specific filtration rates, whale shark exposure was estimated at approximately 5900 MP h−1 (∼4 × 104 MPs day−1). These values fall within the range reported for large planktivorous vertebrates and suggest that seawater-based assessments could underestimate microplastic exposure in filter-feeding species by overlooking biologically mediated pathways.
With accelerating urbanization, fine particulate matter (PM2.5) pollution in cities has become increasingly severe. Understanding variations in PM2.5 concentrations requires consideration not only of the types and locations of emission sources but also of modulating factors such as meteorological conditions and vegetation. To elucidate this, seasonal changes in PM2.5 concentrations, stable carbon and nitrogen isotope ratios (δ13C, δ15N), meteorological variables, and a vegetation index were monitored in two urban forest regions. Potential source locations were also estimated using receptor modeling. In Gomae, sites were located at increasing distances from an expressway into the forest interior, whereas in Sihwa, they were in an industrial complex, a residential area, and the urban forest separating them. During the growing season, δ13C was depleted, suggesting an increased biogenic influence. δ15N implied a strong influence of vehicle emissions in both regions, although its increase in Sihwa during the non-growing season pointed to a possible rise in coal combustion. Among the modulating factors, wind and vegetation appeared to be the key drivers of PM2.5. Wind not only influenced which local sources dominated but also contributed to the long-range transport of PM2.5. Vegetation, in turn, was associated with significantly lower PM2.5 concentrations at sites within the urban forests during the growing season. This difference, however, disappeared even in the evergreen forest during the non-growing season, when air-quality management is most critical. Thus, although urban forests can help reduce PM2.5, their effect is seasonally limited, and emission reduction at the source should take priority.
Retrospective and prospective power analyses were conducted to evaluate the ability of the UK pollutant monitoring programme to detect trends in PCB lipid concentrations (the sum of 25 congeners of polychlorinated biphenyls) in stranded harbour porpoises (Phocoena phocoena). Using data from 415 juveniles stranded between 1991 and 2019, we assessed statistical power to detect these trends within Harbour Porpoise Assessment Units and OSPAR Assessment Areas. Retrospective analyses showed sufficient statistical power (80% at α=0.05) to detect the observed annual declines ranging from 2.64% to 5.10%. At the UK level (England, Scotland and Wales), the current programme can detect a 3.06% annual decline with only 3 samples per year over the full time series (29 years), and 8 samples per year over a 20-year period. Prospective simulations indicated that a six-year monitoring period, akin to reporting under the EU Marine Strategy Framework Directive (MSFD), is sufficient to detect annual declines of 10%–15% depending on the spatial unit/area in question. Extending the monitoring period to ten years, consistent with OSPAR’s Quality Status Reporting cycles, substantially improved sensitivity, enabling detection of smaller declines (5%–10%) with relatively modest sampling effort. Overall, these results demonstrate that the existing monitoring programme is adequately powered to support OSPAR and MSFD reporting requirements, once sufficient individuals are sampled, and provide clear guidance for optimizing future sampling design in data-limited areas. Although focused on harbour porpoises, the framework is applicable to other OSPAR indicator species, including common dolphins, for which PCBs likewise pose the greatest contaminant risk for persistent organic pollutants.
For its high toxicity and frequent detection, the ecological and human health risks of nitrobenzene should be assessed based on freshwater quality criteria (WQCs) in surface freshwaters in China. The short- and long-term WQCs of nitrobenzene were 10,225 μg/L and 898 μg/L for protecting aquatic life derived via Monte Carlo simulation in China, respectively. The WQCs for protecting human health for non-carcinogenic effects of nitrobenzene were determined as 8.20 μg/L with a distributions ranging from 4.39 to 36.16 μg/L for consumption of both water and organisms, 8.60 μg/L with a distributions ranging from 4.72 to 41.80 μg/L for consumption of water only, and 271.76 μg/L with a distributions ranging from 148.38 to 1065.00 μg/L for consumption of organisms only in China, respectively. The concentrations of nitrobenzene ranged from 0 to 3.690 μg/L, with a mean concentration of 0.085 μg/L and a detection frequency of 11.2% in 2249 surface freshwater samples collected at 750 sampling sites in China from January 2023 to December 2025 and analyzed by solid-phase extraction coupled with GC-MS. The insignificant ecological risks and low human health risks of nitrobenzene were successfully estimated by the Monte Carlo-PRA method. This study provided the integrated Monte Carlo-PRA methodology to calculate both ecological and human health risks in aquatic ecosystems based on WQCs.
