This study introduces a non-invasive method for monitoring environmental pollution by analysing metal(loid)s in the faeces of sentinel species. We measured the concentrations of four metal(loid)s, arsenic (As), chromium (Cr), cadmium (Cd), and lead (Pb), in the droppings of four large wading bird species (Little Egret, Great Egret, Reef Heron, and Striated Heron) from 2020 to 2024 in the wetland ecosystem of the Eastern Province of Saudi Arabia, a part of the Central Asian Flyway. Our results revealed significant level of the metal(loid)s in the bird droppings, indicating environmental pollution likely linked to industrial activities, agricultural runoff, and urban expansion. All metal(loid)s exhibited significant temporal variation, with increasing concentrations observed across species. Pb and Cd also showed rising trends but exhibited species-specific effects. While the metal(loid)s analysis confirms exposure and accumulation, it does not by itself allow definitive identification of pollutant sources. Based on previous environmental assessments and land-use data, the studied wetlands are known to be influenced by anthropogenic activities, suggesting that the metal(loid)s in bird faeces predominantly originate from local pollution. However, we acknowledge that further source-tracing analyses would strengthen this inference. This study highlights the need for continuous monitoring of metal(loid)s pollution to safeguard wildlife health and maintain ecological stability. Given the study area's proximity to industrial zones, these findings advocate for enhanced pollution control measures and targeted management strategies to mitigate risks and conserve wetland habitats.

Gadolinium (Gd) and Lanthanum (La) are rare earth elements (REEs) widely employed in contemporary technologies due to their unique physicochemical properties. However, their increasing release into aquatic environments has raised concerns about potential ecotoxicological effects. This study assessed the acute biochemical and molecular response of fourth-instar Chironomus sancticaroli larvae exposed to Gd and La at 0.03, 0.30, 3.00, and 30 μg L. Exposure to La at 0.03 and 3.00 μg L induced a significant increase in acetylcholinesterase (AChE) activity, suggesting potential neurotoxic effects that may alter synaptic transmission and behavioral responses in larvae, whereas Gd did not affect AChE activity. Furthermore, La inhibited esterase-α activity, while Gd inhibited esterase-β activity in larvae exposed to 0.30, 3.00, and 30 μg L, suggesting specific alterations in detoxification and metabolic processing pathways. Both REEs triggered oxidative stress, as evidenced by the increase in catalase and glutathione S-transferase activities at specific concentrations, which may reflect a compensatory response to increased reactive oxygen species. Lipid peroxidation was detected only at the highest La concentration (30 μg L), indicating membrane damage and potential impairment of cellular integrity. Gene expression analysis showed downregulation of hemoglobin D across all La concentrations and hemoglobin E across all Gd concentrations, potentially compromising oxygen transport and respiratory efficiency of larvae. These sublethal alterations suggested that C. sancticaroli larvae are sensitive to both elements, with La exerting broader physiological disruption, in addition, these findings rise concern about the ecological risk of REE contamination in freshwater ecosystems.

This study provides comprehensive information on the abundance of microplastics (MPs) in wastewater effluents, sand, and seawater samples collected from areas in Northern Greece. Sampling was conducted over a one-year period to account for seasonal variations in MP abundance. The collected samples were analyzed using microscopic and spectroscopic techniques, yielding valuable insights into the physicochemical characteristics of MPs. MPs concentrations in sand samples ranged from 15.5 ± 6.2 to 174.7 ± 17.3 items kg of dry sand, while the highest concentrations were recorded in winter. Among aqueous matrices, the highest MP concentrations were found in wastewater effluents, ranging from 0.43 ± 0.17 to 1.72 ± 0.45 items L, with greater loads detected during wet seasons. In seawater samples, MP abundance ranged from 0.078 ± 0.011 to 0.989 ± 0.35 items m, with the highest concentrations recorded during the summer season. Regarding polymer identification, the analysis of MPs was conducted using micro-FTIR instrumentation, and the most frequently detected polymers in the examined samples were PE (poly(ethylene), PP (polypropylene), PET (poly(ethylene terephthalate)), and PA (polyamide). Morphological analysis revealed that fibers were the dominant MP shape across all matrices. Size distribution analysis indicated that most MPs particles were small-sized (< 1 mm). The morphological and chemical characteristics of MPs indicate strong links among matrices. SEM-EDX analysis revealed metals on MPs from sand samples, reinforcing these connections. This study investigates MP abundance across environments, uncovering their sources, inter-matrix relationships, and interactions with pollutants, offering insights into patterns of environmental contamination.

This study aimed to comprehensively analyze the accumulation and distribution patterns of polycyclic aromatic hydrocarbons (PAHs) in plankton across varying exposure durations within a simulated planktonic food chain, consisting of Tetraselmis chuii (phytoplankton), Brachionus rotundiformis (rotifers), and Apocyclops sp. (copepods) cultured in a gas purging system with a continuous supply of PAHs. The investigation revealed three distinct temporal phases of PAH accumulation: before 1 h, 1-24 h, and 24-120 h. Notably, PAH concentrations exhibited substantial fluctuations during the initial two intervals but approached a steady state after 24 h of exposure. An intriguing observation was the differential accumulation of high solubility (> 1) PAHs, which were found in higher quantities in copepods compared to rotifers and phytoplankton. Conversely, low solubility (< 1) PAHs were significantly more abundant in phytoplankton, indicating potential selectivity in PAH uptake among planktonic organisms. Principal component analysis (PCA) elucidated a clear demarcation between phytoplankton and zooplankton, suggesting distinct PAH accumulation patterns influenced by trophic levels. Linear relationship was found between the bioconcentration factor (BCF) and PAH hydrophobicity (K) for all PAHs within the planktonic food chain. The varying slopes in the linear regression between log BCF and log K for phytoplankton, rotifers, and copepods underscored the existence of diverse pathways for PAH accumulation among planktonic organisms. This study offers valuable insights into the complex dynamics of PAH bioaccumulation, with potential implications for understanding the broader ecological impacts of PAHs.

Studies on temporal variation of metal concentrations and their relationship with metal-binding proteins in crocodilians remain scarce. This study aimed to assess interannual changes in physiological (Cu and Zn) and xenobiotic (Hg and Cd) metals, as well as metallothioneins (MTs) levels in blood plasma of 17 semicaptive Morelet's crocodiles (Crocodylus moreletii) sampled twice (n = 34 samples) in 2016 and 2018. Metal concentrations were quantified in plasma samples, and MTs were measured as biomarkers of metal exposure. Results showed a 1.4-fold increase in Hg and 3.5-fold increase in Cd concentrations over time, possibly reflecting dietary exposure or other unmonitored environmental factors. In contrast, Cu concentrations decreased, while Zn remained stable. MTs levels did not differ significantly between years; however, linear models suggested associations between MTs and both Cu and Cd, highlighting their potential role in homeostasis and detoxification. Although based on a small sample size and limited to plasma, these findings offer insights into metal dynamics under semicaptive conditions and support the value of MTs as candidate biomarkers for future monitoring. Improved temporal frameworks and direct environmental or dietary data are needed to better interpret these trends and support conservation strategies for this endangered species.

This study analyzed microplastics (MPs; target size: 0.1-5 mm) in freshwater fish and aquatic plants in an urban lake in Kumamoto, Japan. MPs were detected in 82% of the collected sample of herbivorous fish species, Nile tilapia (Oreochromis niloticus) and Redbelly tilapia (Tilapia zillii) at mean level of 10 ± 13 items ind, which was more than 10 times higher than the levels found in two carnivorous fish species, largemouth bass (Micropterus salmoides) and snakehead (Channa argus). Fish samples near the outlets of stormwater runoff and a wastewater treatment plant showed higher abundances of MPs than fish collected from other locations in the lake. Polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) were dominant polymers in fish, accounting for 83%. These three polymers were also commonly detected in three species of aquatic plants, which retained MPs at 4.6-35 items g dry weight. A comparison of the characteristics of the MPs detected in the herbivorous fish and aquatic plant samples collected at the same station showed similar profiles in terms of polymer types, shape, and colors. This indicates that herbivorous fish are exposed to MPs adsorbed onto the surface of aquatic plants through their feeding activity. Our findings highlighted that aquatic plants act as a mediator to increase the bioavailability of MPs in freshwater fish by trapping MPs on the plant surface.

This study investigated ontogenetic growth changes in total mercury (THg) concentrations, δC, δN, and δO values of harbour porpoises stranded along the coast of Hokkaido, Japan, focusing on differences between males and females. Body length (BL) of the studied harbour porpoises was greater in females than in males. THg preferentially accumulated in the livers rather than in the muscles. The THg concentrations in male and female livers increased sharply and moderately when the BLs exceeded approximately 1.5 m and 1.6 m, respectively, at which BL the harbour porpoises reached sexual maturity. Significant positive correlations were found between the BL and the log Hg concentrations in the livers and muscles of both males and females. δN levels in muscles were higher in calves than in weaned porpoises, likely due to the consumption of N-enriched milk. The δC and δN values in immature males and females varied considerably, probably due to the variety of prey species at low THg concentrations. The δC and δN values in mature males and females increased with increasing BL, suggesting an increase in the trophic level of preys and a possible association with increases in the THg concentrations in their muscles and livers. A significant positive correlation was found between the BLs and the δO values in the muscles from both males and females. A significant correlation was also found between the log THg concentrations and the δO values but not with the δC values and δN values. These correlations suggest feeding shifts towards deep benthic waters with growth.

Soil contaminated with trivalent chromium (Cr) induced manganese (Mn) mobilization potentially leading to increased ecological toxicity. Although Cr is relatively immobile in soil, its interaction with soil minerals indirectly increases Mn bioavailability, which poses risks to soil organisms. The objective of this study was to assess the bioavailability and potential ecological toxicity of Mn and Cr in Cr contaminated soil using chemical extractions, earthworm (Eisenia fetida) toxicity tests, and dehydrogenase activity (DHA) as bioindicators. The mitigation of Mn toxicity in Cr contaminated soil was evaluated following amendments with biochar and calcium carbonate (CaCO). Both amendments increased soil pH and reduced bioavailable Mn concentrations by 44-100% through sorption and pH induced immobilization. While bioavailable Cr concentrations also decreased, the effect was less significant because Cr was originally immobile in the soil. Earthworm survival and loss in biomass was not significantly affected by biochar treatment. Dehydrogenase activity was enhanced in biochar and CaCO amended soils, indicating improved microbial activity. Principal component analysis confirmed that biochar and CaCO amendments reduced bioavailability and metal toxicity to levels comparable to uncontaminated soils. The assessment of bioavailability through chemical extraction and toxicity using earthworm and DHA showed similar trends in this experiment. However, high amounts of biochar may negatively affect earthworms, and a holistic approach is required to effectively evaluate amendments for mitigating metal toxicity in soils.

Ingestion of lead (Pb) derived from ammunition used in the hunting of game animals is recognised as a significant potential source of Pb exposure in wild birds globally. While Pb poisoning in wild birds has been studied extensively in North America and Europe, the prevalence of Pb exposure in bird populations elsewhere, particularly in Africa, remains understudied. To address this gap in knowledge, we examined Pb concentrations in the feathers and bones of four waterfowl species (n = 37) from a region in South Africa where recreational hunting regularly occurs. Lead was detected in all feather and bone samples. While most birds had bone Pb concentrations consistent with low-level exposure (< 10 mg kg), three individuals displayed concentrations (maximum = 63.5 mg kg) associated with lethal Pb poisoning. Lead isotopic ratios in bone samples suggested that Pb shot was the most probable source of Pb in birds with high exposure. These findings align with recent studies on vultures, suggesting that Pb poisoning is more widespread in southern Africa than is currently recognised, affecting not only scavenging species but also waterfowl. The prevalence of elevated bone Pb concentrations compatible with lethal poisoning (8.1%) indicates that Pb exposure could have significant implications for waterfowl populations in the region. Furthermore, substantial indirect risks exist for scavenging and predatory species, as well as for humans consuming meat contaminated with Pb shot. Our findings highlight the importance of addressing the unregulated use of Pb-ammunition across southern Africa, particularly given the large hunting industry the region supports.

Invasive aquatic plants threaten the health of aquatic ecosystems, and demand for chemical control is likely to increase as nuisance levels are reached. Diquat is a contact herbicide registered in many countries to control invasive aquatic plants. The objective of our study was to assess the effects of the aquatic herbicide diquat (Reward®) on North American native and non-native plants, algal communities, an amphipod and an amphibian using outdoor mesocosms to simulate natural systems. Our experimental design included a control and five nominal concentrations of diquat ranging from 100% (18.3 L/ha; 1153 µg/L) to 6.4% (1.2 L/ha; 74 µg/L) of the label rate of a single diquat application. Effects of diquat were found to vary among study organisms. All four plant species were negatively affected at all concentrations, exhibiting either mortality or severe reductions in dry biomass (< 1% the biomass of the controls). In contrast, phytoplankton biomass increased 7 d following diquat application concomitant with significant changes in algal community structure. A concentration-response relationship was observed for amphipod survival (LC at 6 weeks = 155 µg/L) with 100% mortality in the highest treatment after two weeks. In contrast, diquat had a significant positive effect on tadpole survival, growth and development, possibly because of the higher algal biomass and decaying plant tissues. A lower label rate than currently recommended, at least in waterbodies with low turbidity, could provide effective control of target species while reducing effects on non-target biota.

Oil and gas extraction, refining, reforming and transport are important production activities mainly conducted in the Southern Patagonia region of Argentina. Several threats to natural ecosystems have been associated with this industry, most of them related to the increase in toxic metals and metalloids in the environment and biota. Birds of prey are widely used to assess metals and metalloids pollution in the environment. This study determined levels of selected trace elements including both essential and toxic metals in the blood of Crested Caracara (Caracara plancus) nestlings and evaluated relationships between the trace elements composition levels and the distance between nests and oil production plants and the prevailing wind in Southern Patagonia, Argentina. Pb, As, Zn, Se, Ni, Cu, Cr, Cd and V were determined by inductively coupled plasma-mass spectrometry. Two groups of trace elements were correlated according to the blood levels detected (As-V-Cr; Zn-V-Cr), suggesting a common source of exposure to these trace elements. The prevailing wind constituted a promising mechanism to explain an association between the oil pipe-derived trace elements and the exposure of nestlings. Nestlings showed elevated levels of As, Se, Cd, Ni and Zn, which were higher than reference levels reported for other raptor populations. These results indicate that nestling Crested Caracaras are exposed to toxic trace elements in Southern Patagonia. This is the first report of trace elements in the blood of Crested Caracara nestlings inhabiting Southern Continental Patagonia, Argentina, and provides baseline data of this contamination in this species.

Dust palliatives are used to reduce fugitive dust in areas susceptible to erosion by wind and rain. In 2015, the Bureau of Land Management (BLM) temporarily approved the use of polymer-based dust palliatives during the construction and operation of a solar energy facility and, in 2019, on a mining access road in Clark County, Nevada. The areas treated with palliative are habitat to the desert tortoise. The desert tortoise consumes water opportunistically from puddles, saturated soils, or by the collection of precipitation on their carapaces. Since little is known about the toxicity of polymeric substances to the desert tortoise, the BLM is concerned with the exposure of the desert tortoise to palliative in stormwater runoff. The BLM collaborated with the US Geological Survey (USGS) to evaluate the transport of butyl acrylate vinyl acetate (BA-VA), the copolymer ingredient in the dust palliatives applied in the study, away from areas of application. BA-VA concentrations were measured in soils treated with palliative up to 90 days post-treatment, after which the copolymer became undetectable (< 0.55 mg/g). BA-VA concentrations in all stormwater samples within and outside treated areas were consistently below detection (< 0.20 mg/mL). Although stormwater and treated soils eroded from the solar facility application area were found to have BA-VA concentrations below detection (< 0.55 mg/g), it is likely that some BA-VA (parent or degradation product) was transported with suspended material. It is also likely that the amount of BA-VA transported away from areas of application was a small fraction of that applied.

This paper presents the results of a study of the physicochemical conditions and contamination of a peat deposit in a representative northern boreal bog with the persistent organic pollutants (POPs), hexachlorobenzene (HCB), pentachlorobenzene (PeCB), and pentachlorophenol (PCP), as well as compounds from another organochlorine compounds, the chlorinated phenols (CPs). Despite the remoteness from the industrial sources of these compounds, a wide range of the organochlorine compounds were detected in the studied peat deposit. The maximum concentrations of HCB, PeCB, and PCP reached 9.4 ng/g, 0.5 ng/g, and 2.6 ng/g, respectively. Moreover, the total CPs content exceeded 1400 ng/g. It was established that the main pathway of the input of POPs into peat deposit was the atmospheric deposition of particulate matter (ash particulates) transported from local emission sources and sources located in low-latitude territories and adjacent regions. The low mobility of POPs, as well as the high sorption capacity of high-moor peats in relation to compounds with similar properties, lead to their concentration in the upper aerated 40 cm layer of the peat deposit, the formation of which coincides with the age of the "chloroorganic society." Factor and correlation analysis revealed that the key factor determining the distribution of these compounds in normally functioning bogs is the mineral component (ash content of peat and pore water mineralization).

This study investigates airborne concentrations of six insecticides widely used on crops grown in agricultural, semi-urban, and rural areas of Bursa Province, Türkiye. Sorbent-impregnated passive air samplers (SIP-PASs), consisting of polyurethane foam (PUF) disks impregnated with XAD-2 resin, were deployed at ten strategically selected sites representing diverse agricultural and demographic profiles within the province. Analytes were quantified using gas chromatography-mass spectrometry (GC-MS) for depuration compounds and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for target insecticides. Although this study focused solely on insecticides, future research should expand monitoring to include herbicides and fungicides-especially those applied to fruit crops-to provide a more comprehensive evaluation of airborne pesticide exposure. Spatial and temporal concentration patterns were analyzed, alongside Clausius-Clapeyron and back-trajectory analyses to assess temperature-driven volatilization and potential source regions. Health risks were evaluated for various age groups, with emphasis on children. The results offer new insights into CUP behavior and associated inhalation risks in intensively farmed regions. Average CUP concentrations were three times higher in agricultural areas than semirural, and nine times higher than rural zones, with peak levels in Ağaköy, Kestel, Demirtaş, and Mudanya. Concentrations were significantly elevated during warm periods. Temperature effects were evaluated using the Clausius-Clapeyron equation, while cluster analysis indicated long-range transport. Inhalation risk assessment showed hazard quotients below 1 and most lifetime cancer risk values under 10⁻, indicating low health risks.

Pollution from past industrial activities can remain unnoticed for years or even decades because the pollutant has only recently gained attention or been identified by measurements. Modeling the emission history of pollution is essential for estimating population exposure and apportioning potential liability among stakeholders. This paper proposes a novel approach for reconstructing the history of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) pollution from municipal solid waste incinerators (MSWIs) with unknown past emissions. The proposed methodology relies on the search for technical and operational data on the pollution source in archives, the extraction of representative data from the scientific literature, and the use of kinetic models of the formation and decomposition of PCDD/Fs within combustion chambers. This new methodological tool allows to estimate any MSWI's stack emission and relative profile of seventeen PCDD/F congeners over time. The approach is validated through a case study of an MSWI in Switzerland. The modeled congener profile achieved a Pearson correlation coefficient of 0.98 with measurements in fly ash washwater. Additionally, the simulated soil quantity (1,115-1,419 gTEQ or 1,283-1,698 gTEQ) agrees in order of magnitude with the estimated quantity from measurements (371 gTEQ or 425 gTEQ ).

Karst water bodies are vital groundwater resources particularly vulnerable to pollution. Protecting their water quality requires documenting contaminants traditionally associated with anthropogenic activities (metals, nutrients, and fecal indicator bacteria) as well as emerging contaminants, such as antibiotic-resistant organisms (AROs) and perfluoroalkyl substances (PFAS). This study detected contaminants in karst-associated water bodies on the Yucatán Peninsula, including 10 sinkholes (cenotes) and one submarine groundwater discharge (SGD) site. The concentrations of metals (strontium, cadmium, nickel, lead), nutrients (phosphate, silicate, ammonium, nitrate, and nitrite), and fecal indicator bacteria (fecal coliforms, Escherichia coli) were consistent with previous reports, sometimes exceeding recommended standards for groundwater or the protection of aquatic life. This included elevated lead (80.3 µg/L) and nitrate (413 μmol/L) concentrations at two cenotes, and elevated E. coli levels (167 - 1800 CFU/100 mL) in five cenotes. Additionally, 34 antibiotic-resistant E. coli strains were identified in nine cenotes and most strains were multidrug-resistant. Perfluorooctanesulfonic acid (PFOS) and perfluorohexanoic acid (PFHxA) were also detected in eight cenotes and the SGD, with total PFAS concentrations from 0.68 to 10.71 ng/L. The absence of associations between contaminants and urban cover suggests karst hydrology influences contaminant cycling-stable isotope signatures (δO, δH) confirming that most systems are interconnected to regional groundwater flows, that could allow contaminants to travel long distances. The Yucatán Peninsula's karst is an important freshwater reservoir used for consumption and recreation; the presence of contaminants and the karst's vulnerability to their spread raises concerns and highlights the need for continued monitoring and conservation.

This study utilized the methodology of digital soil mapping (DSM) to investigate the spatial prediction of toxic metals and their environmental covariates in the Ghorveh Plain, western Iran. The environmental covariates are defined as the factors that control the distribution of toxic metals at the geographical scale under investigation. They could be used for predicting the sources and monitoring of pollution. A total of 150 soil samples (0-30 cm) were analyzed for toxic metal concentrations and some soil properties. A comprehensive set of environmental variables was obtained from remote sensing imagery, DEM, and ancillary data, which were identified as likely to control the spatial distributions of toxic metals. The genetic algorithm was utilized to identify "all-relevant" environmental covariates for each toxic metal. Three machine learning algorithms, namely random forests (RF), cubist, and regression trees (RT), were employed to establish the statistical relationships between toxic metals and the environmental covariates. The RF model exhibited the most optimal prediction performance. All three models, particularly the RF, demonstrated robust performance, exhibiting minimal impact on the model's functionality when confronted with alterations in the training and testing data. Consequently, the optimal model, RF, was integrated with a bootstrapping method to generate prediction and uncertainty maps. The soil properties and hydrologic factors were the primary variables influencing the spatial distribution of each toxic metal. This study indicates that the integration of DSM techniques with machine learning models and supplementary datasets offers a viable approach to the generation of maps for monitoring and prioritizing remediation measures in areas contaminated by toxic metals.

Lead (Pb) poisoning poses a significant threat to wildlife. A primary cause of Pb poisoning is the unintentional ingestion of Pb ammunition and fishing weights, which are still used for hunting and fishing in numerous regions globally. While the effects of Pb poisoning on birds and mammals are well established, impacts on reptiles are less well documented and difficult to assess under field conditions. In this study, we investigated the effects of extreme Pb exposure on captive sub-adult Nile crocodiles (Crocodylus niloticus; n = 18). We administered Pb dosages in the form of fishing weights (54-215 g) and monitored changes in blood lead concentrations, packed cell volumes, urine Pb concentrations, growth, and body condition over a 48-week period. Crocodiles exhibited a remarkable tolerance to exceptionally high Pb exposure over the duration of the study. Despite the lack of obvious clinical signs of Pb toxicity, elevated BPb concentrations were linked to lower PCVs, indicating anaemia across all treatment groups by week eight. However, crocodiles showed a sustained erythropoietic response which may be contributing to their resilience to acute Pb toxicity. While Pb exposure did not significantly affect body condition, it was associated with a discernible reduction in weight gain over the duration of the study. Our estimation of a 5.8-7.3-year timeframe for complete dissolution of the Pb fishing weights in the experimental crocodiles' stomachs carries significant implications for wild populations, which are likely to be exposed to Pb for far longer than 48-week duration of this study.

Urban freshwater streams across northern latitudes are undergoing increasing salinization due, in part, to road salt inputs during winter months. Road salt contamination has been monitored across Canada for over 40 years; however, the scale of contamination in the Pacific Northwest, which experiences relatively mild and rainy winters, is not well understood. A network of almost 40 water quality loggers in the Lower Mainland of Vancouver, B.C., Canada (VLM) was leveraged to better understand the scale of road salt inputs to local streams and identify factors that influence the magnitude and occurrence of these contamination events. Specific conductance data from these loggers indicate that road salt is entering creeks, resulting in brief salt pulses that typically last 1 day or less. Road salt pulses occur as frequently as three times per week in winter months and can attain maximum chloride concentrations above British Columbia's acute guideline for chloride (600 mg/L Cl) by as much as 11-fold in streams. The amount of road salt entering creeks is influenced by the extent of impervious surface in the surrounding catchment basin, with more urbanized creeks receiving higher inputs. Interestingly, cumulative salt inputs do not correlate with winter severity and remain consistent even during mild winters. Acute pulses of road salt occur in VLM streams between November and March, coinciding with the spawning and incubation period of locally important Pacific salmon species such as coho and chum salmon. This timing poses a direct risk to developing salmonids, and the benthic invertebrates which sustain them later in development.

Microplastics have been found in every part of the planet and in almost every tissue type that has been tested. They are a complex class of pollutants with multiple direct and indirect effects. There is an urgent and growing need to understand their toxicological impacts. Here we measured the effects of two size classes (13.2 µm ± 8.1 and 595.7 µm ± 187.3) of aged polyethylene microplastics, in the presence or absence of copper (10 μg/L), on the behavior of zebrafish and on their ability to respond to a conspecific alarm cue. Additionally, we measured the effects of the microplastics and copper on metal bioaccumulation and induction of metallothionein. Exposure to microplastics decreased the swimming speed of the zebrafish but may have reduced some of the effects of copper. Fish exposed to copper and microplastics had higher swimming velocities than fish exposed to copper alone. However, large microplastics also increased copper bioaccumulation and metallothionein production. Fish that were not exposed to copper decreased their swimming speed after addition of the alarm cue, but there was also an interaction with microplastics. Multivariate analysis of swimming behavior showed that fish exposed to small microplastics and copper formed a distinctive group after addition of the alarm, suggesting that it altered their behavioral responses. Our results show complex interactions between microplastics and copper and highlight the need for comprehensive risk assessment under different environmental scenarios. Fish rely on olfaction to find food and avoid predators. It is well established that metals can inhibit olfaction in fish. Microplastics may interact with metallic pollutants to increase their impact.