Microplastics change soil properties, plant performance, and bacterial communities in salt-affected soils.

Microplastics (MPs) are emerging contaminants found globally. However, their effects on soil-plant systems in salt-affected habitats remain unknown. Here, we examined the effects of polyethylene (PE) and polylactic acid (PLA) on soil properties, maize performance, and bacterial communities in soils with different salinity levels. Overall, MPs decreased soil electrical conductivity and increased NH4+-N and NO3--N contents. Adding NaCl alone had promoting and inhibitive effects on plant growth in a concentration-dependent manner. Overall, the addition of 0.2% PLA increased shoot biomass, while 2% PLA decreased it. Salinity increased Na content and decreased K/Na ratio in plant tissues (particularly roots), which were further modified by MPs. NaCl and MPs singly and jointly regulated the expression of functional genes related to salt tolerance in leaves, including ZMSOS1, ZMHKT1, and ZMHAK1. Exposure to NaCl alone had a slight effect on soil bacterial α-diversity, but in most cases, MPs increased ACE, Chao1, and Shannon indexes. Both MPs and NaCl altered bacterial community composition, although the specific effects varied depending on the type and concentration of MPs and the salinity level. Overall, PLA had more pronounced effects on soil-plant systems compared to PE. These findings bridge knowledge gaps in the risks of MPs in salt-affected habitats.

Population origin and heritable effects mediate road salt toxicity and thermal stress in an amphibian.

Human impacts on wild populations are numerous and extensive, degrading habitats and causing population declines across taxa. Though these impacts are often studied individually, wild populations typically face suites of stressors acting concomitantly, compromising the fitness of individuals and populations in ways poorly understood and not easily predicted by the effects of any single stressor. Developing understanding of the effects of multiple stressors and their potential interactions remains a critical challenge in environmental biology. Here, we focus on assessing the impacts of two prominent stressors associated with anthropogenic activities that affect many organisms across the planet - elevated salinity (e.g., from road de-icing salt) and temperature (e.g. from climate change). We examined a suite of physiological traits and components of fitness across populations of wood frogs originating from ponds that differ in their proximity to roads and thus their legacy of exposure to pollution from road salt. When experimentally exposed to road salt, wood frogs showed reduced survival (especially those from ponds adjacent to roads), divergent developmental rates, and reduced longevity. Family-level effects mediated these outcomes, but high salinity generally eroded family-level variance. When combined, exposure to both temperature and salt resulted in very low survival, and this effect was strongest in roadside populations. Taken together, these results suggest that temperature is an important stressor capable of exacerbating impacts from a prominent contaminant confronting many freshwater organisms in salinized habitats. More broadly, it appears likely that toxicity might often be underestimated in the absence of multi-stressor approaches.

Salt-Induced Early Changes in Photosynthesis Activity Caused by Root-to-Shoot Signaling in Potato.

Salinity is one of the most dangerous types of stress in agriculture. Acting on the root, salinity causes changes in physiological processes in the shoot, especially photosynthesis, which is crucial for plant productivity. In our study, we used potato plants, the most important crop, to investigate the role of salt-induced signals in changes in photosynthesis activity. We found a salt-induced polyphasic decrease in photosynthesis activity, and the earliest phase started several minutes after salt addition. We found that salt addition triggered rapid hydraulic and calcium waves from root to shoot, which occurred earlier than the first phase of the photosynthesis response. The inhibition of calcium signals by lanthanum decreased with the formation of rapid changes in photosynthesis. In addition to this, a comparison of the characteristic times of signal propagation and the formation of a response revealed the role of calcium waves in the modulation of rapid changes in photosynthesis. Calcium waves are activated by the ionic component of salinity. The salt-induced decrease in transpiration corresponds in time to the second phase of the photosynthetic response, and it can be the cause of this change. The accumulation of sodium in the leaves occurs a few hours after salt addition, and it can be the cause of the long-term suppression of photosynthesis. Thus, salinity modulates photosynthetic activity in plants in different ways: both through the activation of rapid distant signals and by reducing the water input and sodium accumulation.

Assessing the Toxicity of Sea Salt to Early Life Stages of Freshwater Mussels: Implications for Sea Level Rise in Coastal Rivers.

Sea levels across the planet are rising, particularly along the eastern coast of the United States. Climate-induced sea level rise can result in the inundation and intrusion of seawater into freshwater drainages. This would alter salinity regimes and lead to the salinization of coastal freshwater ecosystems. Increased salinity levels in freshwater can negatively affect freshwater-dependent species, including native mussels belonging to the order Unionida, which are highly sensitive to changes in water quality. Sea salt is largely made up of sodium and chloride ions, forming sodium chloride, a known toxicant to freshwater mussels. However, sea salt is a mixture that also contains other major ions, including potassium, sulfate, calcium, strontium, and magnesium, among others. Freshwater mussels exposed to sea salt would be exposed to each of the sea salt ions at the same time, resulting in a mixture toxicity effect. The mixture toxicity of these ions on early life stages of freshwater mussels is largely unknown because most research to date has evaluated individual salt ions in relative isolation. Therefore, we conducted acute toxicity tests on early life stages (glochidia and juvenile) of three freshwater mussel species that inhabit Atlantic Slope drainages (nonsalinity-adapted Atlanticoncha ochracea, salinity-adapted A. ochracea, Sagittunio nasutus, and Utterbackiana implicata). Glochidia and juveniles of each species were exposed to a control and six concentrations of Instant Ocean® Sea Salt (IOSS), a synthetic sea salt that closely resembles the ionic composition of natural sea salt. Exposure concentrations were 1 part(s) per thousand (ppt), 2 ppt, 8.5 ppt, 12.5 ppt, 17 ppt, and 34 ppt. We calculated the median effect concentration (EC50) for each of the eight acute toxicity tests and found that glochidia were more sensitive than juveniles to IOSS. At hour 24 EC50s for the glochidia ranged from 0.38 to 3.6 ppt, with the most sensitive freshwater mussel being the nonsalinity-adapted A. ochracea, exhibiting an EC50 of 0.38 ppt (95% confidence interval [CI] 0.33-0.44). Juvenile freshwater mussels exhibited EC50s at hour 96 ranging from 5.0 to 10.4 ppt, with the least sensitive freshwater mussel being the nonsalinity-adapted A. ochracea, exhibiting an EC50 of 10.4 ppt (95% CI 9.1-12.0). Our results show that acute exposure to sea salt adversely affects freshwater mussel viability, particularly glochidia. This information can be used to enhance freshwater mussel conservation strategies in regions that are or will be impacted by climate-induced sea level rise and associated freshwater salinization. Environ Toxicol Chem 2023;42:2478-2489. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Ecotoxicological response surface analysis of salt and pH in textile effluent on Bacillus subtilis and Lactuca sativa.

Textile effluents, although their composition can vary considerably, typically contain high levels of dissolved salts and exhibit wide variations in pH. Ecotoxicological studies regarding the effects of these parameters, however, have been limited owing to the need for sensitive and easy-to-handle bioindicators that require low amounts of sampling, are cost-effective, time-efficient, and ethically endorsed. This kind of study, additionally, demands robust multi-factorial statistical designs that can accurately characterize the individual and combined relationship between variables. In this research, Response Surface Methodology (RSM) was used to calculate the individual and interaction effects of NaCl concentration and pH value of a Simulated Textile Effluent (STE) on the development rate (DR) of the bioindicators: Bacillus subtilis bacteria and Lactuca sativa lettuce. The results demonstrated that the bioindicators were sensitive to both NaCl and pH factors, where the relative sensitivity relationship was B. subtilis > L. sativa. The quadratic equations generated in the experiments indicated that increased concentrations of 50-250 mg L-1 of NaCl caused a perturbance of 1.40%-34.40% on the DR of B. subtilis and 0.50%-12.30% on L. sativa. The pH factor at values of 3-11 caused an alteration of 27.00%-64.78% on the DR of the B. subtilis and 51.37%-37.37% on the L. sativa. These findings suggest that the selected bioindicators could serve as effective tools to assess the ecotoxicological effects of textile effluents on different ecological systems, and the RSM was an excellent tool to consider the ecotoxicological effects of the parameters and to describe the behavior of the results. In conclusion, the NaCl and pH factors may be responsible for disrupting different ecosystems, causing imbalances in their biodiversity and biomass. Before discharge or reuse, it is suggested to remove salts and neutralize pH from textile effluents and, mostly, develop novel, eco-friendlier textile processing techniques.

Ecophysiological responses of Glycine max L. under single and combined cadmium and salinity stresses.

Soil contamination by cadmium (Cd) and degradation by salinity are likely to become one of the most important problems hindering food production and human health. However, their combined effect on crops is still ambiguous. A hydroponic study was made to investigate the separate and combined exposure of 100 µM Cd and 150 µM NaCl on soybeans (Glycine max L.) growth, photosynthetic pigment, and antioxidant systems for 7 days. Both Cd and NaCl, applied separately decreased the seedlings growth, chlorophyll contents and caused oxidative stress. However, the toxic effects of salinity applied alone were more pronounced. Interestingly, combined exposure of Cd and NaCl induced higher decreases in all growth parameters and lipid peroxidation than single exposure suggesting synergistic effects. The results implicate that the phytotoxicity of both stressors can be associated with redox status imbalance. Our finding may provide insight into the physiological mechanisms of heavy metal exposure and salinity stress tolerance in soybeans and suggest that saline stress changes the effects of Cd toxicity on crops in Cd-salt-polluted soils.

Pre-exposure to seawater or chloride salts influences the avoidance-selection behavior of zebrafish larvae in a conductivity gradient.

The risk assessment of freshwater salinization is constructed around standard assays and using sodium chloride (NaCl), neglecting that the stressor is most likely a complex mixture of ions and the possibility of prior contact with it, triggering acclimation mechanisms in the freshwater biota. To date, as far as we are aware of, no information has been generated integrating both acclimation and avoidance behavior in the context of salinization, that may allow these risk assessments upgrading. Accordingly, 6-days-old Danio rerio larvae were selected to perform 12-h avoidance assays in a non-confined 6-compartment linear system to simulate conductivity gradients using seawater (SW) and the chloride salts MgCl2, KCl, and CaCl2. Salinity gradients were established from conductivities known to cause 50% egg mortality in a 96-h exposure (LC50,96h,embryo). The triggering of acclimation processes, which could influence organisms' avoidance-selection under the conductivity gradients, was also studied using larvae pre-exposed to lethal levels of each salt or SW. Median avoidance conductivities after a 12-h of exposure (AC50,12h), and the Population Immediate Decline (PID) were computed. All non-pre-exposed larvae were able to detect and flee from conductivities corresponding to the LC50,96h,embryo, selecting compartments with lower conductivities, except for KCl. The AC50,12h and LC50,96h overlapped for MgCl2 and CaCl2, though the former is considered as more sensitive as it was obtained in 12 h of exposure. The AC50,12h for SW was 1.83-fold lower than the LC50,96h, thus, reinforcing the higher sensitivity of the parameter ACx and its adequacy for risk assessment frameworks. The PID, at low conductivities, was solely explained by the avoidance behavior of non-pre-exposed larvae. Larvae pre-exposed to lethal levels of salt or SW were found to select higher conductivities, except for MgCl2. Results indicated that avoidance-selection assays are ecologically relevant and sensitive tools to be used in risk assessment processes. Stressor pre-exposure influenced organisms' avoidance-selection behavior under conductivity gradients, suggesting that under salinization events organisms may acclimate, remaining in altered habitats.

Halotolerant plant growth-promoting bacteria, Bacillus pumilus, modulates water status, chlorophyll fluorescence kinetics and antioxidant balance in salt and/or arsenic-exposed wheat.

Seed priming is an effective and novel technique and the use of eco-friendly biological agents improves the physiological functioning in the vegetative stage of plants. This procedure ensures productivity and acquired stress resilience in plants against adverse conditions without contaminating the environment. Though the mechanisms of bio-priming-triggered alterations have been widely explained under induvial stress conditions, the interaction of combined stress conditions on the defense system and the functionality of photosynthetic apparatus in the vegetative stage after the inoculation to seeds has not been fully elucidated. After Bacillus pumilus inoculation to wheat seeds (Triticum aestivum), three-week-old plants were hydroponically exposed to the alone and combination of salt (100 mM NaCl) and 200 µM sodium arsenate (Na2HAsO4·7H2O, As) for 72 h. Salinity and As pollutant resulted in a decline in growth, water content, gas exchange parameters, fluorescence kinetics and performance of photosystem II (PSII). On the other hand, the seed inoculation against stress provided the alleviation of relative growth rate (RGR), relative water content (RWC) and chlorophyll fluorescence. Since there was no effective antioxidant capacity, As and/or salinity caused the induction of H2O2 accumulation and thiobarbituric acid reactive substances content (TBARS) in wheat . The inoculated seedlings had a high activity of superoxide dismutase (SOD) under stress. B. pumilis decreased the NaCl-induced toxic H2O2 levels by increasing peroxidase (POX) and enzymes/non-enzymes related to ascorbate-glutathione (AsA-GSH) cycle. In the presence of As exposure, the inoculated plants exhibited an induction in CAT activity. On the other hand, for H2O2 scavenging, the improvement in the AsA-GSH cycle was observed in bacterium priming plants plus the combined stress treatment. Since B. pumilus inoculation reduced H2O2 levels against all stress treatments, lipid peroxidation subsequently decreased in wheat leaves. The findings obtained from our study explained that the seed inoculation with B. pumilus provided an activation in the defense system and protection in growth, water status, and gas exchange regulation in wheat plants against the combination of salt and As.

Lethal and Sub-lethal Implications of Sodium Chloride Exposure for Adult Unionid Mussel Species: Eurynia dilatata and Lasmigona costata.

The elevated use of salt as a de-icing agent on roads in Canada is causing an increase in the chloride concentration of freshwater ecosystems. Freshwater Unionid mussels are a group of organisms that are sensitive to increases in chloride levels. Unionids have greater diversity in North America than anywhere else on Earth, but they are also one of the most imperiled groups of organisms. This underscores the importance of understanding the effect that increasing salt exposure has on these threatened species. There are more data on the acute toxicity of chloride to Unionids than on chronic toxicity. This study investigated the effect of chronic sodium chloride exposure on the survival and filtering activity of two Unionid species (Eurynia dilatata, and Lasmigona costata) and assessed the effect on the metabolome in L. costata hemolymph. The concentration causing mortality after 28 days of exposure was similar for E. dilatata (1893 mg Cl-/L) and L. costata (1903 mg Cl-/L). Significant changes in the metabolome of the L. costata hemolymph were observed for mussels exposed to non-lethal concentrations. For example, several phosphatidylethanolamines, several hydroxyeicosatetraenoic acids, pyropheophorbide-a, and alpha-linolenic acid were significantly upregulated in the hemolymph of mussels exposed to 1000 mg Cl-/L for 28 days. While no mortality occurred in the treatment, elevated metabolites in the hemolymph are an indicator of stress.

Ethanol and NaCl-Induced Gold Nanoparticle Aggregation Toxicity toward DNA Investigated with a DNA/GCE Biosensor.

Engineered nanomaterials are becoming increasingly common in commercial and consumer products and pose a serious toxicological threat. Exposure of human organisms to nanomaterials can occur by inhalation, oral intake, or dermal transport. Together with the consumption of alcohol in the physiological environment of the body containing NaCl, this has raised concerns about the potentially harmful effects of ingested nanomaterials on human health. Although gold nanoparticles (AuNPs) exhibit great potential for various biomedical applications, there is some inconsistency in the case of the unambiguous genotoxicity of AuNPs due to differences in their shape, size, solubility, and exposure time. A DNA/GCE (DNA/glassy carbon electrode) biosensor was used to study ethanol (EtOH) and NaCl-induced gold nanoparticle aggregation genotoxicity under UV light in this study. The genotoxic effect of dispersed and aggregated negatively charged gold nanoparticles AuNP1 (8 nm) and AuNP2 (30 nm) toward salmon sperm double-stranded dsDNA was monitored by cyclic and square-wave voltammetry (CV, SWV). Electrochemical impedance spectroscopy (EIS) was used for a surface study of the biosensor. The aggregation of AuNPs was monitored by UV-vis spectroscopy. AuNP1 aggregates formed by 30% v/v EtOH and 0.15 mol·L-1 NaCl caused the greatest damage to the biosensor DNA layer.

Salicylic acid and trehalose attenuate salt toxicity in Brassica juncea L. by activating the stress defense mechanism.

Two significant soil degradation processes that pose a hazard to our ecosystems are soil salinization and sodification. The information on potential of salicylic acid (SA) and trehalose (Tre) to induce abiotic stress signaling and triggers physio-biochemical responses in crop plants is limited. Therefore, the present study was aimed to investigate the efficacy of 5 µM SA and/or 10 mM Tre in improving the growth, photosynthesis, ion homeostasis, nutrient acquisition, antioxidant defense system and yield of mustard plants growing under sodium chloride (NaCl) stress (0, 50, 100 and 150 mM NaCl). The data showed that increasing NaCl stress concentration decreased growth, photosynthesis, membrane permeability, ion homeostasis and yield in a dose-dependent manner while increasing considerably enzymatic antioxidant enzyme activities, compatible solute accumulation, sodium ion and oxidative stress biomarkers linearly with increasing NaCl stress concentration. The spray of SA, Tre, and SA + Tre played diversified roles in enhancing NaCl stress tolerance in mustard at morpho-physiological and biochemical levels. The combined SA + Tre application proved best and completely neutralized the NaCl stress-induced suppression in growth, photosynthesis, ion homeostasis, nutrient acquisition and yield by significantly enhancing the activities of enzymatic antioxidants, compatible solutes accumulation, water status and membrane permeability, while reducing considerably osmotic stress, reactive oxygen species generation, lipid peroxidation, cell death and sodium uptake in mustard. The SA + Tre application enhanced relative water content by 23%, net photosynthetic rate by 48%, superoxide dismutase activity by 51% and seed yield per plant by 64%, while decreased superoxide anion content by 26%, sodium ion content by 36% and malondialdehyde content by 25% over 0 mM NaCl treatment. Our findings indicate that the co-application of SA + Tre can be a suitable approach to palliate the ill effect of NaCl stress in mustard plants.

Cation Composition Influences the Toxicity of Salinity to Freshwater Biota.

The effects of salinization on freshwater ecosystems have been estimated by testing sodium chloride (NaCl) since it is the most widely used salt as a deicing agent and Na+ and Cl- ions are the most representative in seawater composition. However, calcium, magnesium, and/or potassium are starting to be proposed as potential surrogates for NaCl, but for which ecotoxicological effects are less explored. This study aimed to identify (i) the less toxic salt to freshwater biota to be suggested as a safer alternative deicer and (ii) to contribute to the lower tiers of salinity risk assessment frameworks by identifying a more suitable surrogate salt than NaCl. The battery of ecotoxicity assays with five key trophic level species showed that among the tested salts (MgCl2, CaCl2, and KCl), KCl and CaCl2 seemed to induce the highest and lowest toxicity, respectively, compared with NaCl. CaCl2 is suggested as a safer alternative for use as a deicer and KCl as a surrogate for the risk assessment of seawater intrusion in coastal regions. These results enrich the salt toxicity database aiming to identify and propose more suitable surrogate salts to predict the effects of salinization to a broader extent.

Physiological and transcriptome analyses demonstrate the silver nanoparticles mediated alleviation of salt stress in pearl millet (Pennisetum glaucum L).

Pearl millet (Pennisetum glaucum L.) is a highly nutritive-value summer-annual forage crop used for hay, silage, grazing, and green chop. However, abiotic stresses including salinity negatively affect its growth and productivity. Furthermore, the nanotechnology is attaining greater consideration to reduce the impact of environmental stresses in plants. In the present study, transcriptome responses of silver nanoparticles (AgNPs) in pearl millet under salinity were investigated. The treatments were given as Control, NaCl (250 mM), AgNPs (20 mg/L), and NaCl + AgNPs to pearl millet seedlings after thirteen days of seed sowing. After 1 h of given treatments, leaf samples were collected and subjected to physio-chemical examination and transcriptome analyses. Salt stress increased the hydrogen peroxide (H2O2), malondialdehyde (MDA) content, and proline as compared to other treatments. In addition, the combined applications of NaCl + AgNPs ameliorated the oxidative damage by increasing antioxidant enzymes activities including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Furthermore, RNA sequencing data showed 6016 commonly annotated Differentially Expressed Transcripts (DETs) among various treated combinations. Among them, 427 transcripts were upregulated, and 136 transcripts were downregulated at nanoparticles vs control, 1469 upregulated and 1182 downregulated at salt vs control, 494 upregulated and 231 downregulated at salt + nanoparticles vs control, 783 upregulated and 523 downregulated at nanoparticles vs salt. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that Mitogen-activated protein kinase (MAPK) signaling pathway, biosynthesis of secondary metabolites, and plant hormonal signal transduction pathway were the enriched among all identified pathways. In addition, Reverse transcription quantitative real-time polymerase chain reaction (qRT-PCR) showed that salinity up regulated the relative expression of DETs in pearl millet while, AgNPs optimized their expression that are associated with various molecular and metabolic functions. Overall, AgNPs treatments effectively improved the morphology, physiology, biochemistry, and gene expression pattern under salinity which could be attributed to positive impacts of AgNPs on pearl millet.

Mixture Toxicity of Three Unconventional Gas Fracking Chemicals, Barium, O-Cresol, and Sodium Chloride, to the Freshwater Shrimp Paratya australiensis.

The 96-h acute toxicity of barium (Ba2+ ), o-cresol, and sodium chloride (NaCl) to Paratya australiensis was assessed in single, binary, and ternary combinations in addition to three biochemical assays: glutathione S-transferase, acetylcholinesterase, and sodium-potassium adenosine triphosphatase. The 96-h lethal concentrations that expressed 50% mortality (LC50) in the single-toxicant exposures were Ba2+ = 23.4 mg/L, o-cresol = 12.2 mg/L, and NaCl = 4198 mg/L. Mortality from o-cresol exposure occurred between 11 and 22 mg/L, whereas Ba2+ was more gradual across 10-105 mg/L, and most of the NaCl mortality occurred between 2050 and 4100 mg/L. Toxic units were used to assess the binary and ternary interactions of the toxicants. A more than additive effect was observed for most combinations in the binary chemical exposures, with the ternary combinations yielding highly synergistic interactions. Greater synergism was observed with the 96-h LC50 of o-cresol in combination with the three concentrations of NaCl (1025, 2050, and 3075 mg/L) compared with Ba2+ , with toxic units of 0.38, 0.48, and 0.10 (o-cresol) and 0.71, 0.67, and 0.50 (Ba2+ ). No notable enzyme activity trends were observed in the enzyme biomarker responses from both individual and mixture exposures. Although acute single-species toxicity tests tend to underestimate the effects of Ba2+ , o-cresol, and NaCl on populations, communities, and ecosystems in seminatural (e.g., mesocosms) and natural systems, there are currently no published acute toxicity data available for P. australiensis and the three toxicants used in the present study. The present study shows that chemicals with different toxicity mechanisms can potentially lead to more synergistic responses. Environ Toxicol Chem 2023;42:481-494. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Morphological and antioxidant responses of Cicer arietinum L. genotypes exposed to combination stress of anthracene and sodium chloride.

Various mutagenic, carcinogenic pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs) are released into the environment posing a negative effect on plant metabolism. All the pollutants that are emitted into the atmosphere, ultimately find their way into the plant. Soil salinity stress is one of the major determinants of crop productivity. Different plants respond differently to different abiotic stress present alone or in combination. One such combination of abiotic stress is PAHs and salinity stress. The present research aims to study the effect of the application of NaCl and Anthracene alone and in various combinations on two chickpea genotypes GPF2 and PDG4. A 21 days laboratory experiment was conducted in petriplates and growth pouches. Different concentrations of NaCl and Anthracene were given to two chickpea genotypes viz. GPF2 and PDG4, alone as well as in combinations to study morphological, physiological and antioxidant responses. Results obtained were further analyzed by using various statistical measures such as Principle Component Analysis and Two-way ANOVA. Results indicated that under the dual presence of NaCl and Anthracene, GPF2 exhibited higher activities of antioxidant enzymes and was shown to have a negative correlation with plant height and chlorophyll content. Based on the results of the present investigation, it was concluded that GPF2 was a better performing chickpea genotype towards the combined presence of Anthracene and NaCl as compared to PDG4.

Influence of Test Method Variables on Sensitivity of Neocloeon Triangulifer to a Reference Toxicant in Short-Term, Effluent Style Evaluations.

Recent literature has demonstrated the sensitivity of mayflies to environmental contaminants. However, to date, there are no methods approved by the US Environmental Protection Agency for using sensitive insects like mayflies in whole-effluent toxicity or receiving water toxicity tests. The parthenogenetic mayfly Neocloeon triangulifer has been shown to be amenable to continuous culture in the laboratory, and methods have been described for its use in both acute and chronic toxicity studies. The goal of the present study was to investigate aspects of N. triangulifer testing and culturing methods that might require adjustment so that they are applicable for testing effluents and receiving waters in a short-term exposure. To this end, the influence of organism age, test duration, and test temperature on sensitivity to NaCl as a reference toxicant were tested (concentrations ranging from 182 to 2489 mg/L). Further studies were conducted to assess the utility of commercially available diets and the influence of nutrient amendment of water on organism growth and sensitivity. Seven-day NaCl tests started with less than 24-h-old larvae were similar in sensitivity to 14-day and full life chronic tests, and were much more sensitive than those started with 7-day-old organisms. Reducing test temperature from 25 °C to 22 °C had a minor influence on culture timing, and little impact on sensitivity to NaCl. In other experiments, reconstituted test water supplemented with nutrients to potentially improve in-test food quality had minimal effect on growth at 7 days and did not significantly alter acute sensitivity to NaCl relative to unamended reconstituted water. A suitable commercially available, ready-to-feed diet substitute for cultured diatoms was not found. Testing N. triangulifer in effluents or receiving waters with the methods recommended will complement similar methods for Ceriodaphnia dubia. Environ Toxicol Chem 2022;41:2758-2768. © 2022 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Exogenous melatonin promotes the growth of alfalfa (Medicago sativa L.) under NaCl stress through multiple pathways.

Salinity is one of the most common factors affecting alfalfa (Medicago sativa L.), and NaCl is one of the main factors of salinity stress which can cause heavy losses in agricultural production in the world. The application of exogenous melatonin (MT) plays a major role in numerous plants against various stress environments. The effects of exogenous MT on the NaCl tolerance of alfalfa treated with the control, 100 µmol L-1 MT, 150 mmol L-1 NaCl, or 150 mmol L-1 NaCl+ 100 µmol L-1 MT were investigated. The results showed that MT increased growth parameters, inhibited chlorophyll degradation and promoted photosynthetic gas exchange parameters (photosynthetic rate, conductance to H2O, and transpiration rate) and stomatal opening under NaCl stress. Osmotic regulation substances such as soluble sugar, proline and glycine betaine were the highest in the NaCl treatment and the second in the NaCl+MT treatment. Nitrogen, phosphorus, potassium, calcium and magnesium were reduced and sodium was increased by NaCl, whereas these levels were reversed by the NaCl+MT treatment. MT inhibited cell membrane imperfection, lipid peroxidation and reactive oxygen species (ROS) accumulation caused by NaCl stress. MT up-regulated the gene expression and activity of antioxidant enzymes and increased the content of antioxidant non-enzyme substances to scavenge excessive ROS in NaCl-treated plants. In addition, all indicators interacted with each other to a certain extent and could be grouped according to the relative values. All variables were divided into PC 1 (89.2 %) and PC 2 (4 %). They were clustered into two categories with opposite effects, and most of them were significant variables. Hence, these findings reveal that exogenous MT alleviates the inhibitory effects of NaCl stress on photosynthesis, stomata opening, osmotic adjustment, ion balance and redox homeostasis, enhancing tolerance and growth of alfalfa. Furthermore, it suggests that MT could be implemented to improve the NaCl tolerance of alfalfa.

Lead exposure of rats during and after pregnancy induces anti-myelin proteolytic activity: a potential mechanism for lead-induced neurotoxicity.

Toxic effects of lead (Pb) are principally manifested in the central nervous system (CNS) and a mounting body of evidence indicates that excessive chronic exposure to Pb participates in the pathological processes of numerous neurodegenerative disorders in humans.In this study we evaluated whether the prolonged pre- and postnatal exposure of rat pups to lead, administrated through ingestion in drinking water, as a typical environmental exposure, can determine alterations of the protein pattern of CNS myelin and the induction of myelin-associated proteinases. Pregnant dams were given distilled water or 0.3 mg/mL lead acetate in drinking water during gestation and lactation. At postnatal day (PND) 21, pups born from mothers poisoned with Pb continued the treatment with the metal. On PND 35 and 56, pups were sacrificed, and brains were subjected to myelin purification and extraction of myelin-associated proteinases. The SDS-PAGE analysis of protein pattern of myelin incubated in vitro with an oxidative system indicated that myelin proteins from Pb-treated pups were more sensitive to the toxicity of reactive oxygen species in comparison with those from untreated pups. The zymografic analysis of NaCl-extracts from myelin of Pb-treated pups showed a band of digestion of 54 kDa that increased in pups sacrificed at PND 56 in comparison with those sacrificed at PND 35 and correlated with the concentration of Pb, detected in purified myelin. The incubation of the NaCl-extract from Pb-treated pups with purified myelin basic protein (MBP) evidenced the presence of different MBP-degrading activities. These results suggest that Pb may influence the integrity of the myelin sheath, probably through the induction of anti-myelin proteinases.

The joint effects of salt and 6PPD contamination on a freshwater herbivore.

Using sodium chloride (NaCl) for de-icing roads is known to have severe consequences on freshwater organisms when washed into water bodies. N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, also known as 6PPD, is an antiozonant mainly found in automobile tire rubber to prevent ozone mediated cracking or wear-out. Especially the ozonated derivate, 6PPD-quinone, which is washed into streams after storm events, has been found to be toxic for coho salmon. Studies on other freshwater organisms could not confirm those findings, pointing towards distinct species-specific differences. Storm events result in greater run-offs from all water-soluble contaminants into freshwater bodies, potentially enhancing the concentrations of both chloride and 6PPD during winter. Here we show that these two contaminants have synergistic negative effects on the population growth of the rotifer Brachionus calyciflorus, a common freshwater herbivore. Hence, while only high concentrations of 6PPD and even higher concentrations of 6PPD-quinone, beyond environmentally relevant concentrations, had lethal effects on rotifers, the addition of NaCl enhanced the sensitivity of the rotifers towards the application of 6PPD so that their negative effects were more pronounced at lower concentrations. Similarly, 6PPD increased the lethal effect of NaCl. Our results support the species-specific toxicity of 6PPD and demonstrate a synergistic effect of the antiozonant on the toxicity of other environmentally relevant stressors, such as road salt contamination.

Seawater intrusion: an appraisal of taxa at most risk and safe salinity levels.

Seawater intrusion into low-lying coastal ecosystems carries environmental risks. Salinity levels at these coastal ecosystems may vary substantially, causing ecological effects from mortality to several sublethal endpoints, such as depression of rates of feeding, somatic growth, or reproduction. This review attempts to establish safe salinity levels for both terrestrial and freshwater temperate ecosystems by integrating data available in the literature. We have four specific objectives: (i) to identify the most sensitive ecological taxa to seawater intrusion; (ii) to establish maximum acceptable concentrations-environmental quality standards (MAC-EQSs) for sea water (SW) from species sensitivity distributions (SSDs); (iii) to compile from the literature examples of saline intrusion [to be used as predicted environmental concentrations (PECs)] and to compute risk quotients for the temperate zone; and (iv) to assess whether sodium chloride (NaCl) is an appropriate surrogate for SW in ecological risk assessments by comparing SSD-derived values for NaCl and SW and by comparing these with field data. Zooplankton, early life stages of amphibians and freshwater mussels were the most sensitive ecological receptors for the freshwater compartment, while soil invertebrates were the most sensitive ecological receptors for the terrestrial compartment. Hazard concentration 5% (HC5 ) values, defined as the concentration (herein measured as conductivity) that affects (causes lethal or sublethal effects) 5% of the species in a distribution, computed for SW were over 22 and 40 times lower than the conductivity of natural SW (≈ 52 mS/cm) for the freshwater and soil compartment, respectively. This sensitivity of both compartments means that small increments in salinity levels or small SW intrusions might represent severe risks for low-lying coastal ecosystems. Furthermore, the proximity between HC5 values for the soil and freshwater compartments suggests that salinized soils might represent an additional risk for nearby freshwater systems. This sensitivity was corroborated by the derivation of risk quotients using real saline intrusion examples (PECs) collected from the literature: risk was >1 in 34 out of 37 examples. By contrast, comparisons of HC5 values obtained from SSDs in field surveys or mesocosm studies suggest that natural communities are more resilient to salinization than expected. Finally, NaCl was found to be slightly more toxic than SW, at both lethal and sublethal levels, and, thus, is suggested to be an acceptable surrogate for use in risk assessment.