Sensitivity Distribution Curves Research Articles

Ecological risk assessment of heavy metals in desulfurized seawater discharged from a coal-fired power plant in Qingdao.

Despite the prevalence of discharge of large volumes of heavy-metal-bearing seawater from coal-fired power plants into adjacent seas, studies on the associated ecological risks remain limited. This study continuously monitored concentrations of seven heavy metals (i.e. As, Cd, Cr, Cu, Hg, Pb, and Zn) in surface seawater near the outfall of a coal-fired power plant in Qingdao, China over three years. The results showed average concentrations of As, Cd, Cr, Cu, Hg, Pb, and Zn of 2.63, 0.33, 2.97, 4.63, 0.008, 0.85, and 25.00 μg/L, respectively. Given the lack of data on metal toxicity to local species, this study investigated species composition and biomass near discharge outfalls and constructed species sensitivity distribution (SSD) curves with biological flora characteristics. Hazardous concentrations for 5% of species (HC5) for As, Cd, Cr, Cu, Hg, Pb, and Zn derived from SSDs constructed from chronic toxicity data for native species were 3.23, 2.22, 0.06, 2.83, 0.66, 4.70, and 11.07 μg/L, respectively. This study further assessed ecological risk of heavy metals by applying the Hazard Quotient (HQ) and Joint Probability Curve (JPC) based on long-term heavy metal exposure data and chronic toxicity data for local species. The results revealed acceptable levels of ecological risk for As, Cd, Hg, and Pb, but unacceptable levels for Cr, Cu, and Zn. The order of studied heavy metals in terms of ecological risk was Cr > Cu ≈ Zn > As > Cd ≈ Pb > Hg. The results of this study can guide the assessment of ecological risk at heavy metal contaminated sites characterized by relatively low heavy metal concentrations and high discharge volumes, such as receiving waters of coal-fired power plant effluents.

Exploring honey bee toxicological data as a proxy for assessing dimethoate sensitivity in stingless bees

The high diversity and distinctive characteristics of stingless bees pose challenges in utilizing toxicity test results for agrochemical registrations. Toxicity assessments were performed on 15 stingless bee species, along with the honey bee, using the insecticide dimethoate, following adapted OECD protocols. Median lethal doses over 24 h (24 h-LD50) were determined for exposure routes (acute oral or contact) and species. Species sensitivity distribution (SSD) curves were constructed and the 5% hazard doses (HD5) were estimated based on 24 h-LD50 values. The SSD curve was adjusted as the body weight and dimethoate response were correlated. Lighter bees (<10 mg) had lower 24 h-LD50 values. Contact exposure for adjusted HD5 suggested insufficient protection for Melipona mondury, whereas the oral exposure HD5 indicated no risks for the other 14 species. Comprehensive risk assessments are crucial for understanding the agrochemical impact on stingless bees, emphasizing the need for a broader species range in formulating conservation strategies.

Analyzing species sensitivity distribution of evidently edible microplastics for freshwater biota

Assessing the ecological risks of microplastics is difficult because of the limited availability of reliable ecotoxicity data. Although freshwater is a valuable sink for microplastics, the current framework for ecological risk assessment using traditional toxicity data is not applicable to freshwater ecosystems. Herein, species sensitivity distribution (SSD) curves were compared for edible and all microplastics exposed to aquatic organisms based on traditional endpoint-based and all-endpoint-based databases. Freshwater toxicity data for microplastics were screened after verifying microplastic presence in test species (56 toxicity datapoints for one microalga, three water fleas, one fish, and one crab; 0.02–100 µm-sized microplastics). SSD and curve parameters were compared with or without non-traditional toxicity endpoints. The HC50 in all endpoint databases was more sensitive than that in the traditional endpoint database and showed a good fit. SSD curves derived from the database for all microplastics were compared and analyzed with edible microplastics. HCx increased for edible microplastics (0.02–100 µm-sized) than for all microplastics (0.02–200 µm-sized), and the size of edible microplastics was lower than of all microplastics. Thus, using non-traditional toxicity data, the SSD approach compensates for the limited ecotoxicity data on microplastics while considering the internalization of microplastics in biota.

Antioxidant enzyme activity and pathophysiological consequences in the sludge worm Tubifex tubifex under acute and sub-lethal exposures to the fungicide Tilt ®

This study aimed to evaluate the effects of propiconazole on the tubificid segmented worm, Tubifex tubifex. The animals were exposed to various concentrations of propiconazole for 96 h to assess the acute effect of this fungicide and for subacute level animals were exposed for 14 days with 10% and 20% of the 96 h LC50 value (0.211 and 0.422 mg/l, respectively). The 96 h LC50 value was determined to be 2.110 mg/l, and sublethal propiconazole concentrations caused significant changes in the oxidative stress enzymes. When compared to control organisms, superoxide dismutase (SOD) and catalase (CAT) activity first decreases and then significantly increases on days 7 and 14. However, GST activity decreases and MDA concentration rises in a concentration- and time-dependent manner throughout the exposure period. In addition, the impacts of propiconazole on Tubifex tubifex were characterized and depicted using a correlation matrix and an integrated biomarker response (IBR) assessment. These findings suggest that exposure to this fungicide distorts the survivability and behavioral response in Tubifex tubifex at the acute level. In addition, it modulates changes in oxidative stress enzymes at the sublethal level. Furthermore, the species sensitivity distribution curve indicates that this tubificid worm has a high risk of survival in the presence of the fungicide propiconazole in aquatic ecosystems.

Copper and cadmium, isolated and in the mixture, impact the Neotropical freshwater Calanoida copepod Notodiaptomus iheringi: A short-term approach with environmental concentrations

Metal discharges in aquatic ecosystems are of concern since they affect different trophic levels, altering the functioning of the aquatic food chain. The metals can interact among them and with other pollutants, resulting in complex mixtures whose effects on biota are unpredictable. The impacts of copper (Cu) and cadmium (Cd), isolated and combined, on the freshwater copepod Notodiaptomus iheringi were assessed in acute and sub-chronic exposures. Species sensitivity distribution (SSD) curves were constructed for both metals. In the acute tests antagonism was observed in mortality, while in sub-chronic, mortality was not affected; however, the eggs produced and percentage of viable eggs were significantly altered. Our data suggest that egg production can be a detoxification route in N. iheringi under Cu and mixture exposure. From the SSD curves, N. iheringi was the most sensitive Brazilian species for Cu and the second most sensitive for Cd.

Toxic Relationships: Prediction of TBT's Affinity to the Ecdysteroid Receptor of Triops longicaudatus.

Tributyltin (TBT) is a biocide introduced in the 1960s in antifouling paints. Despite legislation banning its use, its persistence in the environment still causes significant harm to organisms. Tributyltin is a ligand of retinoid X receptors (RXR) and ecdysteroid receptors (EcRs), which in arthropods act as homologs of RXR. Focusing on Metazoan species, this study used genomic and proteomic information from different sources to compare their three-dimensional structure, phylogenetic distribution, and amino acid sequence alterations. The objective was to identify possible patterns that relate organisms' sensitivity to TBT using the species Triops longicaudatus as the basis for the comparisons. The results showed great conservation of this protein across several species when comparing the interaction amino acids described to RXR (an EcR analog) in Homo sapiens. The three-dimensional comparison of RXR showed little conformational variation between different sequences by maintaining the interaction pocket. As for the Species Sensitivity Distribution (SSD) curve, an HC05 = 0.2649 [0.0789-0.7082] µg/L was obtained with no specific distribution between the different taxa. Protein-ligand docking analysis was then used to confirm the SSD curve ranking of species. Still, the results showed an opposite trend that may be related, for example, to differences in the LC50 values used in the calculations. This study serves as the first step for applying bioinformatics techniques to produce information that can be used as an alternative to animal or cellular experimentation. These techniques could be adapted to various chemicals and proteins, allowing for observations in a shorter timeframe and providing information on a broader spectrum.

Water quality criteria derivation and ecological risk assessment for ibuprofen, a common antifever drug in China

Ibuprofen, an extensively consumed antifever drug, has been inevitably recorded in various aquatic environments in China. However, water quality criteria (WQC) are rarely derived, thereby hindering the ecological risk assessment for this emerging pollutant. This study, therefore, aims to determine the WQC for IBU by screening toxicity data of freshwater and seawater species residing in China and simulating the species sensitivity distribution curves. The ecological risk of IBU in the aquatic environment of China was subsequently assessed through hazard quotient and margin of safety at 10% methods. A total of 15 acute and 9 chronic toxicity data were collected from the literature, and the acute and chronic WQC for IBU were derived as 7.6 mg/L and 2.9 μg/L, respectively. The ecological risk of IBU was generally negligible, with 21.4% of the waters in China at low chronic risk. The long-term effects and environmental existence of IBU, however, warrant further concern considering the shortage of ecotoxicology data and the popularity of usage for this well-known pharmaceutical.

Sensitivity of the Neotropical Solitary Bee Centris analis F. (Hymenoptera, Apidae) to the Reference Insecticide Dimethoate for Pesticide Risk Assessment.

Currently, only Apis mellifera is used in environmental regulation to evaluate the hazard of pesticides to pollinators. The low representativeness of pollinators and bee diversity in this approach may result in insufficient protection for the wild species. This scenario is intensified in tropical environments, where little is known about the effects of pesticides on solitary bees. We aimed to calculate the medium lethal dose (LD50) and medium lethal concentration (LC50) of the insecticide dimethoate in the Neotropical solitary bee Centris analis, a cavity-nesting, oil-collecting bee distributed from Brazil to Mexico. Males and females of C. analis were exposed orally to dimethoate for 48 h under laboratory conditions. Lethality was assessed every 24 h until 144 h after the beginning of the test. After the LD50 calculation, we compared the value with available LD50 values in the literature of other bee species using the species sensitivity distribution curve. In 48 h of exposure, males showed an LD50 value 1.33 times lower than females (32.78 and 43.84 ng active ingredient/bee, respectively). Centris analis was more sensitive to dimethoate than the model species A. mellifera and the solitary bee from temperate zones, Osmia lignaria. However, on a body weight basis, C. analis and A. mellifera had similar LD50 values. Ours is the first study that calculated an LD50 for a Neotropical solitary bee. Besides, the results are of crucial importance for a better understanding of the effects of pesticides on the tropical bee fauna and will help to improve the risk assessment of pesticides to bees under tropical conditions, giving attention to wild species, which are commonly neglected. Environ Toxicol Chem 2023;42:2758-2767. © 2023 SETAC.

Non-traditional species sensitivity distribution approaches to analyze hazardous concentrations of microplastics in marine water

Owing to their ubiquitous nature, microplastics are a major environmental concern. This study reviewed the toxicity data of microplastics in marine water, and analyzed their species sensitivity distribution (SSD) curves and hazardous concentrations (HCs). Toxicity database of no-observed effect concentration (NOEC), 50% effect concentration (EC50), and highest observed no-effect concentration (HONEC), and lethal, developing, reproductive, biochemical, and behavioral toxicity endpoints was used. Using 169 chronic NOEC databases, all non-traditional toxicity endpoint databases showed stronger HC values, better fit, and more variable toxicity sensitivity than those derived from traditional values. Moreover, using 426 chronic NOEC, EC50, and HONEC data points, HC values calculated from traditional plus HONEC toxicity values showed weaker HC values, slightly better fit, and more variable toxicity sensitivity than those derived from traditional toxicity values. The SSD approach using non-traditional toxicity and marine water toxicity data can expand the marine water toxicity database, including information on SSD curves and HCs of diverse microplastics.

Accurate derivation and modelling of criteria of soil extractable and total cadmium for safe wheat production

It is significant to establish an accurate model to predict cadmium (Cd) criteria for safe wheat production. More importantly, for better evaluation of the risk of Cd pollution in high natural background areas, the soil extractable Cd criteria are needed. In the present study, the soil total Cd criteria were derived using the method of cultivars sensitivity distribution integrated with soil aging and bioavailability as affected by soil properties. Firstly, the dataset that meet the requirements was established. Dataset from thirty-five wheat cultivars planted in different soils published in literature of five bibliographic databases were screened using designated search strings. Then, the empirical soil-plant transfer model was used to normalize the bioaccumulation data. Afterwards, the soil Cd concentration for protecting 95 % (HC5) of the species was calculated from species sensitivity distribution curves, and the derived soil criteria were obtained from HC5 prediction models that based on pH. The process of derivation for soil EDTA-extractable Cd criteria was the same way as the soil total Cd criteria. Soil total Cd criteria ranged from 0.25 to 0.60 mg/kg and soil EDTA-extractable Cd criteria ranged from 0.12 to 0.30 mg/kg. Both the criteria of soil total Cd and soil EDTA-extractable Cd were further validated to be reliable using data from field experiments. The results suggested that the criteria of soil total Cd and soil EDTA-extractable Cd in the study can ensure the safety of Cd in wheat grains and thereby enable local agricultural practitioners to develop appropriate management for croplands.

Accumulation of Cr in different vegetables and derivation of soil Cr threshold using the species sensitivity distribution method

Due to its high mobility and bioavailability, hexavalent chromium [Cr(VI)] in agricultural soil can be taken up by crops and pose threat to human being. In this study, two soils (Jiangxi red soil and Shandong fluvo-aquic soil) spiked with Cr(VI) and 8 common vegetable varieties were used to conduct the pot experiment. The bioconcentration factor (BCF) values based on the tetraacetic acid extractable Cr (EDTA-Cr) in soils were used to construct the species sensitivity distribution (SSD) curve. Afterwards, the soil Cr threshold was derived based on the critical BCF value and the permissible limit of Cr for vegetables. The results showed that when spiked with 5.6 mg kg−1 of Cr(Ⅵ), the soil EDTA-Cr concentrations were significantly increased compared with the control except Jiangxi red soil planted with carrot and radish, while the Cr concentrations in the edible parts of vegetables in both soils were below the permissible limit (0.5 mg kg−1 FW). However, there are dramatic differences in the accumulation of Cr by different varieties of vegetables. Apparent discrepancy was observed between the two soils for the bioconcentration of Cr by carrot. Among the leafy vegetables, lettuce and oilseed rape are the most and the least sensitive to Cr pollution, respectively. The safety threshold values of EDTA-Cr were 0.70 mg kg−1 for Shandong fluvo-aquic soil and 0.85 mg kg−1 for Jiangxi red soil, respectively. This study provides information on the safety production of vegetable products in Cr(Ⅵ) polluted soils and is helpful to the revision of soil quality standards of Cr.

Derivation and validation of soil total and extractable cadmium criteria for safe vegetable production

Determining the appropriate soil cadmium (Cd) criteria for vegetable production is important for ensuring that the Cd concentrations of the vegetables meet food safety standards. The soil extractable Cd criteria for vegetable production are also essential for both food safety and environmental management, especially in areas with a high natural background level. In the present study, soil total and extractable Cd criteria were derived using the approach of species sensitivity distribution integrated with soil aging and bioavailability as affected by soil properties. A dataset of 90 vegetable species planted in different soils was compiled by screening the published in literature in five bibliographic databases using designated search strings. The empirical soil–plant transfer model was applied to normalize the bioaccumulation data. After normalization, the intra-species variability was reduced by 18.3 to 84.4%. The soil Cd concentration that would protect 95% (HC5) of the species was estimated by species sensitivity distribution curves that were fitted by the Burr III function. The soil Cd criteria derived from the added approach for risk assessment were proposed as continuous criteria based on a combination of organic carbon and pH in the soil. Criteria for total Cd and EDTA-extractable Cd in the soil ranged from 0.23 to 0.61 mg kg−1 and from 0.09 to 0.25 mg kg−1, respectively. Field experimental data were used to validate the applicability and validity of these criteria. Most of the predicted HC5 values in the field experimental sites were below the 1:1 line. These results provide a scientific basis for soil Cd criteria for vegetable production that will ensure food safety.

Toxicity of fipronil and 2,4-D pesticides in Daphnia similis: a multiple endpoint approach

In Brazil, among the pesticides widely applied simultaneously in sugarcane monocultures are the Regent® 800 WG insecticide (active ingredient (a.i.) fipronil) and the DMA® 806 BR herbicide (a.i. 2,4-D). Thus, this study aimed to investigate, through different endpoints, the effects of the fipronil and 2,4-D pesticides, isolated and as mixtures, on the cladoceran Daphnia similis. To do this, acute toxicity tests were carried out with the compounds acting in isolation and in mixture, where the survival of the organisms was evaluated, and chronic toxicity tests with the isolated compounds, where reproduction and maternal and neonatal body length were evaluated. In this study, the physiological endpoints of D. similis were also analyzed, through the analysis of feeding rates (filtration and ingestion) in exposure and post-exposure scenarios, in order to verify the cladoceran food recovery capacity. In addition, D. similis data were compared with other species when exposed to the studied pesticides, using species sensitivity distribution curves. Acute toxicity tests of the fipronil and 2,4-D showed an average EC50-48h of 66.68μg a.i./L and 327.07mg a.i./L, respectively. In both cases, D. similis showed lower sensitivity compared to other species. For the mixture test, the evaluation by the IA model (independent action) and deviation DR (dose ratio dependent) indicated the occurrence of mostly antagonistic effects. The chronic test with fipronil showed a decrease in the fecundity of the organism at a concentration of 16μg a.i./L, a concentration already found in aquatic environments. For 2,4-D, no significant differences were observed for reproduction at the concentrations tested. Regarding the maternal body length, there were no significant changes when D. similis were exposed to both fipronil and 2,4-D, but these differences were observed in the body length of the neonates only for 2,4-D. There were no significant changes in the feeding rates of the organisms when exposed to both pesticides.

Assessing the impact of antineoplastic drugs in the aquatic environment: State of the art and future perspective for freshwater organisms

Since the late 70s, the continuous pharmaceuticals` input into the environment has raised concerns regarding the eventual risk posed by such compounds to human and environmental health. A major group of pharmaceuticals in terms of environmental impact are the antineoplastic agents (AAs). Herein, we followed a systematic review method to retrieve antineoplastic agents (AAs’) ecotoxicological information regarding freshwater species. In this analysis, data from diverse taxonomic groups, from microorganisms to vertebrate species, looked at different levels of biological organization, including cell lines. Furthermore, this review gathers ecotoxicological parameters (EC50 and LC50) for imatinib (IM), cisplatin (CisPt), and 5-fluorouracil (5-FU) in species sensitivity distribution (SSD) curves and estimates the hazard concentration (HC5) considering the protection of 95% of the ecological community. Lastly, we suggest how we can improve AAs' Environmental Risk Assessment (ERA), considering potential adoptable toxicity endpoints, test duration, AAs metabolites testing, and AAs mixture exposure.

Derivation and validation of soil cadmium thresholds for the safe farmland production of vegetables in high geological background area

Excessive dietary intake of cadmium (Cd) poses toxicity risks to human health, and it is therefore essential to establish accurate and regionally appropriate soil Cd thresholds that ensure the safety of agricultural products grown in different areas. This study investigated the differences in the Cd accumulation in 32 vegetable varieties and found that the Cd content ranged from 0.01 to 0.24 mg·kg−1, and decreased in the order of stem and bulb vegetables > leafy vegetables > solanaceous crops > bean cultivars. A correlation analysis and structural equation model showed that pH, soil organic matter, and the cation exchange capacity had significant effects on Cd accumulation in the vegetables and explained 72.1 % of the variance. In addition, species sensitivity distribution (SSD) curves showed that stem and bulb vegetables were more sensitive to Cd than other types of vegetables. Using the Burr Type III function for curve fitting, we derived Cd thresholds of 6.66, 4.15, and 1.57 mg·kg−1 for vegetable soils. These thresholds will ensure that 20 %, 50 %, and 95 % of these vegetable varieties were risk–free, respectively. The predicted threshold of soil Cd was more than twice that of China's current National Soil Quality Standard (GB 15618–2018) for Cd values. Therefore, soil scenarios and cultivars should be considered comprehensively when determining farmland soil thresholds. The present results provide a new model for setting soil Cd criteria in high geological background areas.

Surrogate species in pesticide risk assessments: Toxicological data of three stingless bees species

Discussions about environmental risk reassessment of pesticides have grown in the last decades, especially in tropical and subtropical regions since the diversity of bee species in these places is quite different. Stingless bees are highly affected by pesticides, and toxicity information is necessary to include them in the regulatory process of countries that hosts a diversity of these species. Therefore, the present study aimed to evaluate the Median Lethal Concentration (LC50), estimate the Median Lethal Dose (LD50) and compared the sensitivity of three species of stingless bees exposed to the commercial formulation of the neonicotinoid thiamethoxam (TMX). The LD50 was estimated based on the LC50 determined in the present study (LC50 = 0.329 ng a.i./μL for Tetragonisca angustula; 0.624 ng a.i./μL for Scaptotrigona postica, and 0.215 ng a.i./μL for Melipona scutellaris). Considering these data, toxicity endpoints were used to fit species sensitive distribution curves (SSD) and determine the sensitivity ratio. The results showed that all the stingless bees tested are more sensitive to TMX than the Apis mellifera, the model organism used in ecotoxicological tests. Regarding the oral LC50, the most susceptible and most tolerant species were M. scutellaris > T. angustula > S. postica > A. mellifera. Following the same evaluated pattern, for the LD50 (considering the weight of the bees - ng a.i./g bee), we have: M. scutellaris > S. postica > T. angustula > A. mellifera, and without the weight considered (ng a.i./bee): T. angustula > M. scutellaris > S. postica > A. mellifera. The different sensitivities among stingless bee species highlight the importance of inserting more than one surrogate species with a variety of sizes in research and protocol development. Additionally, the research suggests the need to investigate patterns regarding the influence of body mass on pesticide sensitivity among stingless bee species.

Assessment of potential ecological risk of bisphenol A in surface waters via evaluation of alternative non-animal approaches

Recently, national regulatory agencies have announced plans to move away from animal testing through the adoption of new approach methods (NAMs) including in silico and in vitro approaches. In this study, we suggest a new approach of environmental risk assessment method for water quality criteria of bisphenol A (BPA) in the surface water of 11 rivers in Asia using an alternative toxicity method based on the in vitro-based cytotoxicity and genetic toxicity. The hazardous concentrations for 5% (HC5) were obtained from the species sensitivity distribution (SSD) curves based on the traditional acute toxicities (TAT), traditional chronic toxicities (TCT), and alterative acute toxicities (AAT) data. The HC5 values for the TAT, TCT, and AAT data were 2019.3 µg/L, 0.92 µg/L, and 0.68 µg/L, respectively. The TAT-based predicted no-effect concentration (PNECTAT), TCT-based PNEC (PNECTCT), and AAT-based PNEC (PNECAAT) values were derived as 1009.65 µg/L, 0.46 µg/L, and 0.34 µg/L, respectively. The TAT-based risk quotient (RQTAT) value of BPA was negligible (<0.1). The AAT-based RQ value (RQAAT) of BPA in Liuxi river (RQAAT = 21.94) of China showed the highest potential ecological risk of the 11 sampled rivers of Asia. In Korea, the highest potential risk assessment (RQAAT = 2.93) was recorded in Gyeonggi-do as the largest administrative region. The results may suggest that the application of AAT in the ecological risk assessment for surface water can replace the previously applied TCT approach.

Global characterization factors for quantifying the impacts of increasing water temperature on freshwater fish

Water temperature is an abiotic master variable for the survival of aquatic organisms. Global warming alters the thermal regimes of rivers and, thus, poses a threat to freshwater biodiversity. To address the impacts of water temperature changes related to global warming on freshwater fish species in life cycle assessment (LCA), we developed spatially explicit characterization factors (CFs) for 207 greenhouse gases under four representative concentration pathways. We calculated fate factors by using the output of a global hydrological model fully coupled with a dynamic water temperature model. We developed six species sensitivity distribution curves for two thermal effects (i.e., lethal and sub-lethal) to derive effect factors, which take the differences in sensitivity between climate regions into account. The regional CFs for CO2 ranged from 2.91 × 10−22 to 6.53 × 10−18 PAF·yr/kg for sub-lethal effects and from 1.98 × 10−22 to 4.58 × 10−18 PDF·yr/kg for lethal effects, depending on the river watersheds and future climate scenarios. To identify the contribution of regional impacts on freshwater fish to their potential global extinction, the regional CFs were converted into global CFs. The largest CFs always occur in the tropical watersheds. The regional impacts in the Amazon watershed contribute the most to the global freshwater fish species extinction. This study contributes to assessing the potential impacts on freshwater biodiversity from global warming from a new cause-effect pathway in LCA.

Probabilistic risk assessment of heavy metals in urban farmland soils of a typical oasis city in northwest China

Previous studies lacked quantitative evaluation studies of the probability of ecology and human health risks from soil heavy metals. This study assessed heavy metal risk level by collecting topsoil samples from a typical oasis city (Wuwei) in northwest China and then quantitatively evaluating the ecological risk from heavy metals by incorporating the uncertainty of health risk model parameters into the risk assessment. This study found that anthropogenic activities have influenced the accumulation of heavy metals in the study area and that the risk of contamination of soil heavy metals was characterized as light to moderate contamination and low ecological risk. On this basis, the species sensitivity distribution curves of heavy metals were constructed using species acute toxicity data, the predicted no effect concentrations of heavy metals were derived, and a probabilistic ecological risk evaluation was conducted. The results show that the current soil environmental quality standards in China are not effective in protecting species diversity. In addition, the probability of ecological risk for Cr, Ni and As in the study area was 63.3%, 23.8% and 7.1%, however, traditional pollution assessment methods underestimate the hazard of Cr. Monte Carlo simulations have shown that the probability of the carcinogenic risk of Cr (adults: 79.4%; children: 94.5%) and As (adults: 78.9%; children: 94.0%) is high, the probability of the total carcinogenic risk exceeding 1E-06 is 99.0%, the probability of the non-carcinogenic risk is low, and the slope factor and reference dose can significantly affect the evaluation of human health risks.

Individual and Combined Effects of Manganese and Chromium on a Freshwater Chlorophyceae.

Manganese (Mn), an essential metal in trace amounts, and chromium (Cr), a nonessential metal to algae, are often found in effluent discharges and may co-occur in contaminated aquatic environments. Therefore, we investigated the effects of Mn and Cr, and their mixtures, on a freshwater Chlorophyceae, Raphidocelis subcapitata, using a multiple endpoint approach. Regarding the single exposure of metals, Mn was 4 times more toxic (median inhibitory concentration at 72 h [IC5072 h ] = 4.02 ± 0.45 µM Mn) than Cr (IC5072 h = 16.42 ± 4.94 µM Cr) for microalgae, considering the effects on the relative growth rate. Moreover, this species was the most sensitive to Mn, according to the species sensitivity distribution curve. Overall, the tested metals did not lead to significant changes in reactive oxygen species production, cellular complexity, and cell relative size but significantly decreased the algal growth and the mean cell chlorophyll a (Chl a) fluorescence at the highest concentrations (3.64-14.56 µM of Mn and 15.36-19.2 µM of Cr). The decreased mean cell Chl a fluorescence indicates an impact on pigment synthesis, which may be related to the observed growth inhibition. In the mixture tests, the reference models concentration addition and independent action were used to analyze the data, and the independent action model was the best fit to describe our results. Therefore, the Mn and Cr mixture was noninteractive, showing additive effects. This is the first study to address the combined toxicity of Mn and Cr regarding freshwater Chlorophyceae. Environ Toxicol Chem 2022;41:1004-1015. © 2022 SETAC.