Muscle melanisation in sand flathead is visible as black spots in the normally white flesh of fish. It is widespread in Tasmania, including at the Tamar Estuary, with increasing frequency of reporting by recreational fishers. The phenomenon is more prevalent in areas impacted by heavy metal pollution and has been linked to heavy metal accumulation. In this study, image processing software ImageJ was employed to study the phenomenon and to establish an objective rating system. A longitudinal profile plot was used to study the greying of the fillet. The degree of melanisation was rated based on the percentage surface area melanised on the surface and in transverse sections of fillets. A muscle melanisation scoring system for sand flathead was established based on visual interpretation using the macroscopic melanisation scoring criteria: melanisation scores 0 = <0.5%, 1 = 0.5–5%, 2 = 5–20%, and 3 = >20% (% = melanised surface area in proportion to the whole fillet). A refined image analysis technique was developed to quantify the percentage of melanised muscle surface area and the muscle melanisation scoring system was statistically validated. Sand flathead fillet with higher melanisation score was shown to be linked to increased intensity of greyness and greater numbers and size of black spots on the surface of fillets and within the flesh. The greying and black spots were primarily concentrated at the anterior region of fillet and around the dorsal vertebrae zone on transverse section of fillets. Overall, findings from this study established the use of image analysis techniques to validate visual inspection and to give a standardised and objective method to determine the degree of melanisation in sand flathead. As muscle melanisation appears to be linked to heavy metal pollution, the standardised scoring system would facilitate future research for environmental pollution and monitoring purposes.

The impacts of microplastic particulates in benthic freshwater organisms have been largely unexplored despite abundant plastic accumulation in the sediments of these systems. We investigated the uptake of plastic particles by benthic filter feeding quagga mussels (Dreissena bugensis) and associated toxicity exhibited through impacts on mortality, filtration rate, reproduction and oxygen consumption. Matrix Assisted Laser Desorption/Ionization Imaging Mass Spectrometry (MALDI-IMS) technology was used to assess the microplastic inclusion. For this purpose, quagga mussels were exposed to four treatments ranging from 0.0 to 0.8 g/L of a high density fluorescent red polyethylene powder in the size range of 10–45 μm for 24-h, and the targeted endpoints were quantified. Identification of several micrograms of microplastics in the digestive tract suggests rapid clearance from the water column by filtering. At the higher concentrations, about 95% of the microplastics ingested remained in the mussels after 24-h. Microplastics were found in the gills which correlated with decreasing filtration rate at higher microplastic concentrations. Despite large-scale ingestion, plastic exposure did not affect survivorship, reproduction rates, or oxygen consumption in the period examined. MALDI-IMS identified unique mass spectra that correlated with microplastic inclusion. This research suggests that microplastics can impair feeding through decreased filtration rates of filter feeding organisms, potentially resulting in a reduction of overall fitness over time and that MALDI-IMS may have the potential to identify microplastics and changes in tissue at the borders of plastic inclusion.

Current understanding on the fate and behavior of microplastics (MPs) in complex soil media remains inadequate. We characterized the aging and hetero-aggregation of a MP sampled in farmland soil, and explored its vertical downward transport in natural loamy sand. The MP was identified with FTIR spectrum as polypropylene, a plastic lighter than water. FTIR spectrum combined with SEM imaging confirmed the MP was highly aged, generating colloidal plastic fibers and carbonyl groups. SEM imaging coupled with EDX analysis suggested hetero-aggregation of the MP with soil minerals. Soil leaching tests performed with the clean MP (without soil minerals) (CMP), the raw MP (RMP) (with soil minerals), and the RMP with humic acid (HA) (RMP + HA) demonstrated that the mobility was insignificant for the CMP, moderate for the RMP and highest for the RMP + HA, resulting in a maximal downward traveling distance of 0 cm, 3–4 cm, and 9–10 cm, respectively. Correlation between the maximal traveling distance and zeta potential of the CMP, RMP, and RMP + HA confirmed surface charge as a dominant control on the MP mobility; while the increasing density of the MP, due to hetero-aggregation with soil minerals, was identified as a driving mechanism for its downward transport, despite its intrinsic density lower than water. Occurrence of only the lower-sized rod-shaped plastic fibers at the maximal traveling distance suggested the natural aging, a process leading to plastic vibration and fragmentation, was conducive to plastic translocation. The three explored classes of antibiotic resistance genes (ARGs) (tetracycline, beta-lactam and sulfonamide) were all detected in the plastic surface, suggesting the MP may function as a potential pathway for the dissemination of ARGs to the deeper soil layer. These findings are important to understand the concentration distribution of both the MPs and ARGs in agriculture impacted soils, a natural reservoir of both emerging contaminants.

As a strong reductant and highly active alkali, hydrazine (N2H4) has been widely used in chemical industry, pharmaceutical manufacturing and agricultural production. However, its high acute toxicity poses a threat to ecosystem and human health. In the present study, a ratiometric fluorescent probe for the detection of N2H4 was designed, utilizing dicyanoisophorone as the fluorescent group and 4-bromobutyryl moiety as the recognition site. 4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-enyl) phenyl 4-brobutanoate (DDPB) was readily synthesized and could specially sense N2H4 via an intramolecular charge transfer (ICT) pathway. The cyclization cleavage reaction of N2H4 with a 4-bromobutyryl group released phenolic hydroxyl group and reversed the ICT process between hydroxy group and fluorophore, turning on the fluorescence in the DDPB-N2H4 complexes. DDPB exhibits a low cytotoxicity, reasonable cell permeability, a large Stokes shift (186 nm) and a low detection limit (86.3 nM). The quantitative determination of environmental water systems and the visualization fluorescence of DDPB test strips provides a strong evidence for the applications of DDPB. In addition, DDPB is suitable for the fluorescence imaging of exogenous N2H4 in HeLa cells and zebrafish.

Odontarrhena muralis is one of the most promissing plant species for Ni phytomining, and soil amendments can further increase its Ni phytoextraction ability. Here we investigated whether Ni phytomining/phytoremediation using this Ni hyperaccumulator can benefit from applying citric acid to a serpentine soil that is naturally enriched in Ni (>1000 mg kg⁻¹). Synchrotron micro X-ray fluorescence (μ-SXRF) was used to image Ni and other metal distributions in whole fresh leaves of O. muralis. Leaf Ni accumulation in plants grown on citric acid-amended soil increased up to 55% while Co, Cr, Fe, Mn, and Zn concentrations were 4-, 14-, 6-, 7- and 1.3-fold higher than the control treatment. O. muralis presented high bioconcentration factors (leaf to soil concentration ratio) to Ni and Zn whereas Cr was seemingly excluded from uptake. The μ-SXRF images showed a uniform distribution of Ni, preferential localization of Co in the leaf tip, and clear concentration of Mn in the base of trichomes. The citric acid treatments strongly increased the Co fluoerescence intensity in the leaf tip and altered the spatial distribution of Mn across the leaf, but there was no difference in Ni fluorescence counts between the trichome-base region and the bulk leaf. Our data from a serpentine soil suggests that citrate treatment enhances Ni uptake, but Co is excreted from leaves even in low leaf concentrations, which can make Co phytoming using O. muralis unfeasible in natural serpentine soils.

As one type of the most widespread and long-lasting anthropogenic contaminants, microplastics have become a global environmental concern. While numerous studies have demonstrated effects of microplastics on aquatic organisms, the potential influence on terrestrial faunas is relatively less known, even though soil is a primary recipient and sink of plastics. In this study, earthworm Eisenia fetida was exposed to different levels (0, 1, 5, 10, and 20% d.w.) of polyethylene (PE, ≤300 μm) and polystyrene (PS, ≤250 μm) particles in an agricultural soil to evaluate the oxidative stress. Fluorescence imaging, after dying with Nile Red, clearly indicated the ingestion of PE and PS particles by E. fetida. Exposure to PE or PS particles at the highest rate (20%) for 14 d significantly (p < 0.05) increased the activity of catalase and peroxidase and the level of lipid peroxidation, while inhibited the activity of superoxide dismutase and glutathione S-transferase in E. fetida. However, no discernible effect was detected at amendment rates ≤10% for the majority of biochemical endpoints, suggesting that microplastic-induced oxidative stress would not occur in E. fetida under most environmental conditions. The influence of microplastics on bioaccumulation of PAHs and PCBs was also evaluated in E. fetida exposed to different levels (0, 0.1, 1, 5, and 10% d.w.) of PE and PS particles. The tissue concentrations of PAHs and PCBs were reduced in the presence of microplastics at amendment rates ≥1%, suggesting that microplastics did not act as a carrier to enhance contaminant uptake. This was attributed to competitive sorption of microplastics for contaminants and the specific feeding behavior of earthworm. Biodynamic model analysis confirmed that ingestion of microplastics contributed negligibly to contaminant bioaccumulation. Findings of this study suggested that under environmentally relevant conditions, microplastics should not cause significant toxic effects to E. fetida, nor enhance its accumulation of hydrophobic contaminants.

Microplastics pose a great threat to entire marine ecosystems, but little is known about their impacts on phytoplankton, especially for the harmful dinoflagellates. In this study, effects of micro polyvinyl chloride (mPVC) on the growth, chlorophyll content and photosynthetic efficiency of the dinoflagellate Karenia mikimotoi at different periods (0, 24, 48, 72 and 96 h) were assessed using gradient concentrations (0, 5, 25, 50 and 100 mg L⁻¹) of mPVC with a size of 1 μm. PVC microplastics had dose-dependent adverse effects on K. mikimotoi growth, chlorophyll content and photosynthetic efficiency. The density of algal cell decreased with increasing mPVC concentrations and the highest inhibitory rate (IR) was 45.8% at 24 h under 100 mg L⁻¹ of mPVC. The total chlorophyll content and chlorophyll content in a single algal cell decreased at 96 h and the ФPSⅡ and Fv/Fm decreased 25.3% and 17.1%, respectively. The SEM images provided an intuitive visual method to observe the behaviors and interactions between microplastics and microalgae. It was found from the SEM images that microalgae was wrapped by microplastic beads. The physical blockage and aggregation were also responsible for the cytotoxicity of K. mikimotoi. Our study clarified that PVC microplastics can reduce algal growth, chlorophyll content and photosynthetic efficiency, and it is beneficial to evaluate the possible impact of plastics on aquatic ecosystems.

Hardpans are massively indurated layers formed at the top layer of sulfidic tailings dams, which develop cementation structures and result in heavy metal immobilization. However, the micro-structural and complex forms of the cementing materials are not fully understood, as well as the mechanisms by which Zn and Pb are stabilized in the hardpans. The present study deployed synchrotron-based X-ray fluorescence microscopy (XFM) to have characterized the cementing structures, examined the distribution of Fe, Zn and Pb, and obtained laterally-resolved speciation of Zn within the hardpans using fluorescence X-ray absorption near-edge structure (XANES) imaging. The XFM analyses revealed that the Fe-rich cement layers consisted of Fe (oxyhydr)oxides coupled with amorphous Si materials, immobilizing Zn and Pb. Through laterally-resolved XANES imaging analyses, Zn-ferrihydrite-like precipitates were predicted to account for >76% of the total Zn within the Fe-rich cement layers. In contrast, outside of the cement layers, 9–63% of the Zn was estimated as labile ZnSO4.7H2O, with the remainder in the form of Zn-sulfide. These findings demonstrated that the Fe-rich cement layers were critical in immobilizing Zn and Pb within hardpans via mineral passivation and encapsulation, as the basis for long-term geochemical stability in the hardpan layer of sulfidic mine tailings.

In the present study, we evaluate our previously developed non-destructive soil algal toxicity method using species from a different class of algae; Class Trebouxiophyceae (Chlorella vulgaris and Chlorella sorokiniana), and directly measure the photosynthetic activity of these species adsorbed onto the soil as a new toxicity endpoint. This study shows that non-destructive soil algal toxicity method is applicable to non-specific test species, including those of Class Trebouxiophyceae as well as Class Chlorophyceae (Chlorococcum infusionum and Chlamydomonas reinhardtii). Furthermore, by performing photosynthesis image analysis, we verify that it is possible to measure the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soils without the need to extract algal cells from the soil. We propose that the non-destructive soil algal toxicity method represents a novel technique for 1) evaluating pollutants in soil using non-specific algae and 2) conveniently and rapidly assessing the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soil as a new toxicity endpoint.

The Athabasca Oil Sands Region (AOSR) in Alberta, Canada, is an important source of atmospheric pollutants, such as aerosols, that have repercussions on both the climate and human health. We show that the mean freezing temperature of snow-borne particles from AOSR was elevated (−7.1 ± 1.8 °C), higher than mineral dust which freezes at ∼ −15 °C and is recognized as one of the most relevant ice nuclei globally. Ice nucleation of nanosized snow samples indicated an elevated freezing ability (−11.6 ± 2.0 °C), which was statistically much higher than snow-borne particles from downtown Montreal. AOSR snow had a higher concentration (∼2 orders of magnitude) of >100 nm particles than Montreal. Triple quadrupole ICP-(QQQ)-MS/MS analysis of AOSR and Montreal snow demonstrated that most concentrations of metals, including those identified as emerging nanoparticulate contaminants, were much more elevated in AOSR in contrast to Montreal: 34.1, 34.1, 16.6, 5.8, 0.3, 0.1, and 9.4 mg/m³ for Cr, Ni, Cu, As, Se, Cd, and Pb respectively, in AOSR and 1.3, 0.3, 2.0, <0.03, 0.1, 0.03, and 1.2 mg/m³ in Montreal snow. High-resolution Scanning Transmission Electron Microscopy/Energy-dispersive X-ray Spectroscopy (STEM-EDS) imaging provided evidence for various anthropogenic nano-materials, including carbon nanotubes resembling structures, in AOSR snow up to 7–25 km away from major oil sands upgrading facilities. In summary, particles characterized as coming from oil sands are more efficient at ice nucleation. We discuss the potential impacts of AOSR emissions on atmospheric and microphysical processes (ice nucleation and precipitation) both locally and regionally.