Mining operations in Canada, including uranium mining and milling, generate by-products containing radionuclides, including radium-226 (226Ra), a long-lived, bioaccumulative calcium (Ca2+) analog. Despite strict discharge regulations, there is limited evidence to suggest that current thresholds for 226Ra adequately protect aquatic organisms. Furthermore, Canada lacks a federal water quality guideline for 226Ra, underscoring the need for protective limits to safeguard aquatic ecosystems. Hence, this research aimed to generate data on 226Ra toxicity to the model aquatic invertebrate Daphnia magna. For this purpose, two 21-day chronic toxicity tests with D. magna were conducted, with survival and reproduction as the endpoints, as well as a reduced water hardness experiment, a multigenerational study, and a bioaccumulation assay. These experiments demonstrated that a high activity concentration (nominal 50Bq/L) of 226Ra can significantly impact the survival of D. magna. 226Ra was also found to bioaccumulate in D. magna with a BAF of 72.8. Since the Canadian Metal and Diamond Mining Effluent Regulations (MDMER) monthly mean effluent limit is currently set at 0.37Bq 226Ra /L, the limit for composite samples at 0.74Bq/L 226Ra, andthe limit for grab samples at 1.11Bq/L 226Ra, it is unlikely that toxic effects to aquatic cladocerans like D. magna from 226Ra will be observed downstream of Canadian mines and mills.

Environmental risk assessments of very hydrophobic organic compounds (VHOCs) in soils are often difficult because multiple processes (e.g., sorption, volatilization, biodegradation) can complicate the interpretation of results. A standardized soil dosing and aging procedure is presented for assessing bioavailability of VHOCs in a synthetic soil, which was used to evaluate the phytotoxicity of VHOCs. The soil preparation protocol resulted in relatively stable freely dissolved concentrations of test substance compared to bulk soil concentrations with some losses likely due to volatility and biodegradation. This dosing method was used in a chronic terrestrial plant toxicity bioassay to evaluate the potential toxicity of VHOCs on complex reproductive endpoints like inflorescence and seed bud formation. Testing included representative hydrocarbons and three very hydrophobic lubricant substances (logKow > 10). The toxicity data were used to evaluate existing predicted no-effect concentrations (PNECs) that had originally been derived with the target lipid model, which did not have these higher order chronic plant endpoints. The initial exposure concentrations were set at the PNECs to provide an independent validation of the PNEC. This evaluation was performed to expand the domain of applicability of the PNEC to VHOCs and for the chronic terrestrial plant endpoints. No effects were observed on plant biomass or inflorescence production at these low exposure concentrations, demonstrating that the established PNEC is protective of long-term plant health. The results of the present study confirm that the new dosing method is fit for purpose, and that the existing PNEC framework can be extended to chronic plant endpoints for VHOCs.

Historical changes of sediment characteristics and levels of inorganic and organic contaminants were studied in dated sediment cores from the Visovac Lake, situated in the Krka National Park, Croatia, to identify the main sources of anthropogenic pressures on this highly protected system. Depth distributions of lithogenic elements showed a steady decrease of terrigenous inputs due to the reduction in agricultural activities in the area, which was particularly pronounced during the 1991-1995 war in Croatia. Vertical and longitudinal distributions of Cd and Zn indicated that they are predominately of anthropogenic origin. The historical profiles of these toxic metals coincide well with the recorded production of metal industry in the upper reach of the Krka River with a sharp decrease reflecting the interruption by the war and slow recovery afterwards. By contrast, the recovery of the tourist industry in Krka NP after the war was accompanied by increasing contamination by elements characteristic of boat and car traffic (Sn, Cu, Pb) as well as oil pollution. The contamination with polycyclic aromatic hydrocarbons and polychlorinated biphenyls was only moderate. Although levels of metallic and organic contamination can be considered relatively low, the observed shift from industrial to tourism-related sources indicated that touristic activities should also be regarded as a possible threat for this vulnerable karst aquatic ecosystem.

Geothermal vents can constitute local significant sources of mercury (Hg) in the environment. The geothermal power plant of Bouillante (Guadeloupe, Lesser Antilles) artificially enhances the release of hydrothermal water in shallow areas of the bay. To assess the impact of this release on the Hg transfer in the environment, Hg concentrations were assessed in sediments, sulphur-oxidising bacteria and six animal species (urchin, sponges and fish) with various diets and trophic levels from the Bouillante Bay and a distant Control Site. Concentrations of Hg in all samples from Bouillante were greater than those from the Control Site (2-627 times higher). A comparison with the Hg concentrations reported in the literature for similar sample types reveals that they are abnormally high in most Bouillante samples suggesting a local Hg contamination imputable to the release of Hg hydrothermal water. Rocky pebbles of the shallow discharge channel are covered by a mat of sulphur-oxidising bacteria presenting high concentration of Hg (13µgg-1). Through analysis of species with various diet, two pathways of Hg integration into Bouillante's food webs were emphasised. First, greater Hg concentrations in filter feeders (sponges ×3 and bivalves ×10) not consuming bacterial mats and liver/muscle ratios in fishes suggest that discharge waters enhance the exposure of marine organisms to dissolved inorganic Hg (i.e., waterborne pathway). Second, greater Hg concentrations in opportunistic animals such as the fish Acanthurus bahianus (×49) and the sea urchin Diadema antillarum (×50) known to ingest sulphur-bacterial mats from the discharge channel suggest that these chemosynthetic bacteria play a role in the integration (i.e., dietary pathway) and transfer of Hg in local biota, which enlightens the consideration of vent fields as natural sources of Hg.

Delhi's agricultural hub, nestled along the Yamuna floodplains, faces soil and water contamination issues. Utilizing organic waste composts is gaining traction to improve soil quality, but uncertainties remain about their efficacy in reducing harmful elements. The study examined three Amaranthaceae cultivars, comparing organic waste composts with chemical fertilizer to evaluate correlations between heavy metals, antioxidants, and antinutrients to assess their bioremediation potential. "Heavy metals" or "potentially toxic elements (PTE)" levels in soil and leaves were measured by ICP-MS, while antioxidants and antinutrients were analyzed with UV-VIS spectroscopy. The study revealed higher PTE levels in floodplain soil, with Cr, Ni, and Cd exceeding safe limits in all cultivars. Compost amendments reduced these pollutants by 28% compared to chemical fertilizers, decreasing bioaccumulation by 20%. Health risk assessments showed lower risks in compost-amended cultivars. Additionally, compost amendment displayed a stronger negative correlation between PTE and antioxidants, suggesting effective bioremediation. Overall, compost amendments offer promise for mitigating PTE in metropolitan floodplains.

Stable isotopes (SI) and fatty acid (FA) biomarkers can provide insights regarding trophic pathways and habitats associated with contaminant bioaccumulation. We assessed relationships between SI and FA biomarkers and published data on concentrations of two pesticides [dichlorodiphenyltrichloroethane and degradation products (DDX) and bifenthrin] in juvenile Chinook Salmon (Oncorhynchus tshawytscha) from the Sacramento River and Yolo Bypass floodplain in Northern California near Sacramento. We alsoconducted SI and FA analyses of zooplankton and macroinvertebrates to determine whether particular trophic pathways and habitats were associated with elevated pesticide concentrations in fish. Relationships between DDX and both sulfur (δ34S) and carbon (δ13C) SI ratios in salmon indicated that diet is a major exposure route for DDX, particularly for individuals with a benthic detrital energy base. Greater use of a benthic detrital energy base likely accounted for the higher frequency of salmon with DDX concentrations > 60ng/g dw in the Yolo Bypass compared to the Sacramento River. Chironomid larvae and zooplankton were implicated as prey items likely responsible for trophic transfer of DDX to salmon. Sulfur SI ratios enabled identification of hatchery-origin fish that had likely spent insufficient time in the wild to substantially bioaccumulate DDX. Bifenthrin concentration was unrelated to SI or FA biomarkers in salmon, potentially due to aqueous uptake, biotransformation and elimination of the pesticide, or indistinct biomarker compositions among invertebrates with low and high bifenthrin concentrations. One FA [docosahexaenoic acid (DHA)] and DDX were negatively correlated in salmon, potentially due to a greater uptake of DDX from invertebrates with low DHA or effects of DDX on FA metabolism. Trophic biomarkers may be useful indicators of DDX accumulation and effects in juvenile Chinook Salmon in the Sacramento River Delta.

The mining and smelting site soils in South China present excessive Cd pollution. However, the transport behavior of Cd in the highly weathered acidic soil layer at the lead-zinc smelting site remains unclear. Here, under different conditions of simulated infiltration, the migration behavior of Cd2+ in acid smelting site soils at different depths was examined. The remodeling effect of Cd2+ migration behavior on microbial community structure and the dominant microorganisms in lead-zinc sites soils was analyzed using high-throughput sequencing of 16S rRNA gene amplicons. The results revealed a specific flow rate in the range of 0.3-0.5mL/min that the convection and dispersion have no obvious effect on Cd2+ migration. The variation of packing porosity could only influence the migration behavior by changing the average pore velocity, but cannot change the adsorption efficiency of soil particles. The Cd has stronger migration capacity under the reactivation of acidic seepage fluid. However, in the alkaline solution, the physical properties of soil, especially pores, intercept the Cd compounds, further affecting their migration capacity. The acid-site soil with high content of SOM, amorphous Fe oxides, crystalline Fe/Mn/Al oxides, goethite, and hematite has stronger ability to adsorb and retain Cd2+. However, higher content of kaolinite in acidic soil will increase the potential migration of Cd2+. Besides, the migration behavior of Cd2+ results in simplified soil microbial communities. Under Cd stress, Cd-tolerant genera (Bacteroides, Sphingomonas, Bradyrhizobium, and Corynebacterium) and bacteria with both acid-Cd tolerance (WCHB 1-84) were distinguished. The Ralstonia showed a high enrichment degree in alkaline Cd2+ infiltration solution (pH 10.0). Compared to the influence of Cd2+ stress, soil pH had a stronger ability to shape the microbial community in the soil during the process of Cd2+ migration.

Ground applications of adulticides via a specialized truck-mounted sprayer are one of the most common practices for control of flying adult mosquitoes. Aerosols released to drift through a targeted area persist in the air column to contact and kill flying mosquitoes, but may also drift into adjacent areas not targeted by the applications where it may affect nontarget insects such as imperiled butterflies. This study compared the risk of permethrin to adult mosquitoes and adult butterflies to assess the likelihood that the butterflies would be affected following such sprays. Permethrin toxicity values were determined for Aedes aegypti and Culex quinquefasciatus (LD50s of 81.1 and 166.3 ng/g dw, respectively) and then combined with published toxicity data in a species sensitivity distribution for comparison with published permethrin toxicity data for adult butterflies. The sensitivity distributions indicated adult butterflies and mosquitoes are similarly sensitive, meaning relative risk would be a function of exposure. Exposure of adult butterflies and adult mosquitoes to permethrin was measured following their exposure to ULV sprays in an open field. Average permethrin concentrations on adult mosquitoes (912–38,061 ng/g dw) were typically an order of magnitude greater than on adult butterflies (110–11,004 ng/g dw) following each spray, indicating lower risk for butterflies relative to mosquitoes. Despite lower estimated risk, 100% mortality of adult butterflies occurred following some of the sprays. Additional studies could help understand exposure and risk for butterflies in densely vegetated habitats typical near areas treated by ULV sprays.

We analyzed total mercury content (THg) and carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in fish, subtidal macrobenthos, and particulate organic matter (POM) as a proxy for pelagic phytoplankton and attached microalgae as a proxy for microphytobenthos to investigate the mercury exposure pathway in fish. For four seasons, samples of the above-mentioned organisms were collected on five occasions (July and October 2018 and January, April, and July 2019) in Minamata Bay. Isotope analysis showed that Minamata Bay food web structures were almost entirely fueled by microphytobenthos. The THg values of the fish and macrobenthos species were positively correlated with their δ13C. This indicates that their diets, which were highly fueled by microphytobenthos, led to high THg bioaccumulation in both macrobenthos and fish. The feeding habits of fishes differ depending on the species, and they prey on organisms of many taxa, including fish (mainly Japanese anchovy), crabs, shrimp, copepods, annelids, and algae. Fish species that preyed on benthic crustaceans had high THg. These results suggest that the main pathway of Hg bioaccumulation in fish from Minamata Bay is the benthic food chain, which is primarily linked to benthic crustaceans fueled by microphytobenthos.

Chemical activation of waste materials, to form activated carbon, (AC) is complicated by the large amounts of chemical activating agents required and wastewater produced. To address these problems, we have developed an optimized process for producing AC, by phosphoric acid activation of construction waste. Waste wood from construction sites was ground and treated with an optimized phosphoric acid digestion and activation that resulted in high surface areas (> 2000 m2/g) and a greater recovery of phosphoric acid. Subsequently the phosphoric acid activated carbon (PAC), was functionalized with iron salts and evaluated for its efficacy on the adsorption of selenite and selenate. Total phosphoric acid recovery was 96.7% for waste wood activated with 25% phosphoric acid at a 1:1 ratio, which is a substantially higher phosphoric acid recovery, than previous literature findings. Post activation impregnation of iron salts resulted in iron(II) species adsorbed to the PAC surface. The iron(II) chloride impregnated AC removed up to 11.41 ± 0.502mg selenium per g Iron-PAC. Competitive ions such as sulfate and nitrate had little effect on selenium adsorption, however, phosphate concentration did negatively impact the selenium uptake at high phosphate levels. At 250ppm, approximately 75% of adsorption capacity of both the selenate and the selenite solutions was lost, although selenium was still preferentially adsorbed. Peak adsorption occurred between a pH of 4 and 11, with a complete loss of adsorption at a pH of 13.