HC5 Values Research Articles

Risk assessment of Arsenic in surface water of China water systems based on a time-dependent species sensitivity distribution (SSD) method

Arsenic (As) is a naturally occurring metalloid element widespread in the environment. Assessing the ecological risk of As in surface water, especially the acute risk caused by emergent pollution incidents, is of great significance. However, acute toxicity data including median lethal concentration (LC50) and median effective concentration (EC50) of As derived by toxicology experiment may vary according to the exposure time, which is referred as time dependence effect. Time dependence not only affects toxicity data but also influences the characterization of acute risk in the ecosystem. However, previous research on the time dependence effect of As, especially the quantitative influence on the risk assessment is still limited. In this research, acute toxicity data of As(III) and As(V) was collected. Time dependence of toxicology data of inorganic As was studied. Time-dependent species sensitivity distributions of freshwater species were established. The hazardous concentration for 5% of species (HC5) values in different exposure time were further derived. Finally, the dynamic ecological risk of As in major Chinese water basins was evaluated. The results suggested that the toxicity data of inorganic As had a significant linear relationship (p < 0.01) with time. The HC5 values of As (III) and As (V) at an exposure time of four days were reduced by 15.5% and 77.5%, respectively, as compared to the HC5 value of one day. According to the ecological risk characterized by the probability density overlapping area method, the ecological risk of As(III) and As(V) increases with the exposure duration. The Yangtze River had the highest risk, with risk values ranging from 19.9% to 22.6%. According to the results, the time dependence of toxicity data should be fully considered in the formulation of water quality criteria or ecological risk assessment so as to provide better protection for the water ecosystem security.

Derivation of ecological safety thresholds and risk assessment of new SDHI fungicides in farmland system

Succinate dehydrogenase inhibitor (SDHI) fungicides have become some of the top-selling fungicides in recent years. As the utilization of these fungicides intensifies, the corresponding potential risks to the environment proportionately increase. However, there is still limited knowledge about their toxic effects on ecosystems. In this study, acute toxicity data from laboratory assessments of the springtail Folsomia candida, alongside collected data from terrestrial and aquatic non-target species, were utilized to construct a species sensitivity distribution (SSD) model for both terrestrial and aquatic non-target organisms. Subsequently, we derived ecological baseline values for diverse scenarios within ecosystems. The results indicated that benzovindiflupyr exhibited the highest 7-day median lethal concentration (7d-LC50) to Folsomia candida at 2.0 μg cm−2, while the toxicity levels of other SDHI fungicides varied, ranging from 99 to 304 μg cm−2. In agricultural environments, the Hazard Concentration for 5 % of species (HC5) values for fluxapyroxad, boscalid, sedaxane, and isopyrazam were determined to be 8.0, 1240, 12.97, and 25.37 g ha−1, respectively. In aquatic environments, the HC5 values for benzovindiflupyr, fluxapyroxad, boscalid, sedaxane, isopyrazam, and carboxin were 0.0013, 0.022, 1.76, 0.372, 0.013, and 0.161 mg L−1, respectively. In an evaluation of typical agricultural scenarios within China, SDHI fungicides were found to exert substantial ecological risks to terrestrial non-target fauna and aquatic ecosystems around agricultural fields. Specifically, isopyrazam and fluxapyroxad were identified as posing heightened ecological risks to Typhlodromus pyri and Aphidius rhopalosiphi. Moreover, the application of benzovindiflupyr, carboxin, isopyrazam, and fluxapyroxad in paddy field environments is associated with unacceptable risks to groundwater. The findings of this study contribute significantly to the environmental risk evaluation of SDHI fungicides within farmland system, thereby informing the development of policy frameworks for their scientifically grounded application.

Derivation of environmental quality standards for free cyanide incorporating censored data into species sensitivity distributions

Free cyanide is considered to be the most toxic form of cyanides to aquatic life. Due to its broad range of uses and subsequent potential widespread emissions to surface water, the environmental effects of free cyanide have been extensively researched. Regulatory bodies have proposed water quality standards for free cyanide, but these are regularly debated and implementation has been inconsistent due to monitoring challenges. The aim of the present study was therefore to derive new environmental quality standards (EQS) for free cyanide according to the Water Framework Directive (WFD). Ecotoxicity data from previous derivations and an additional literature search were gathered and individually (re) evaluated on reliability. The pooled acute ecotoxicity dataset consisted of reliable results for 35 species, distributed over 8 taxonomic groups. The pooled chronic ecotoxicity dataset consisted of results for 13 species, distributed over 7 taxonomic groups. WFD criteria for deriving a species sensitivity distribution (SSD) were met, if censored data points were included. Using the R-package ETX 3.0, an SSD including censored data was constructed and acute and chronic HC5 values of 17 and 0.66 μg/L, respectively, were derived. Comparisons were made with alternative SSDs constructed by transforming or discarding the censored data. Applying a default assessment factor (AF) of 10 to the HC5 from the acute SSD resulted in a MAC-EQS of 1.7 μg CN/L for freshwater and marine water. Careful consideration was given to addressing the uncertainty around the chronic HC5 value for the selection of an AF of 3, resulting in an AA-EQS of 0.22 μg CN−/L for freshwater and 0.044 μg CN−/L for marine water by applying an additional AF of 5. It is concluded that the current environmental quality standards for free cyanide are the first to be derived according to the WFD guidance, using only reliable data and including censored values.

Predicting the ecological risk thresholds of soil metals in Europe using the quantitative ion character-activity relationships (QICAR) model

Metal pollutants have become increasingly diverse. Therefore, managing the ecological risks associated with these elements in soil is urgently required. However, determining the soil ecological risk thresholds of elements through routine toxicological tests is time-consuming and laborious, establishing prediction models is vital to risk management. Accordingly, this study aimed to predict the element toxicity to soil organisms by collecting the toxicological data of eight elements to soil organisms at 18 European and 17 Chinese sites through literature and toxicology databases, using the quantitative ion character-activity relationship (s-QICAR) model. Firstly, the toxicity values (logEC10) of eight elements to five biological species and three microbial processes were obtained through clustering and soil normalization methods in three typical soil scenarios. Correlation analysis revealed that for different species and microbial processes, there are three to six physicochemical properties of elements related to their toxicity, among which, the covalent radius of the element was the best significantly correlated with logEC10 of all organisms (R2 = 0.77–0.95). Based on this, the s-QICAR model was established and used to predict the logEC10 of Sc, Ti, V, Cr, Co, Ni, Cu, and Zn to eight organisms. Furthermore, along with the species sensitivity distribution curve, the HC5 values (i.e., 95% species protection level) for the above eight elements were calculated. Following correction, the predicted no-effect concentrations of these elements ranging from 9 to 189 mg/kg, and the ecological risk threshold map has been produced. In summary, we present a new method to quantify the ecological risk of metal-induced pollution in European soils without routine toxic measurements, and provide important insights into soil pollution risk assessment and management.

Ecological risk threshold for chromium in Chinese soils and its prediction models

The derivation of chromium (Cr) ecological risk thresholds in soils remains limited, despite their importance as measurement standards and indicators for enacting soil protection policies. In this study, toxicity of Cr in soil to different species was tested based on Log-Logistic dose-effect relationship. On this basis, combined with Cr toxicity measurement data in literature, the ecological risk threshold HC5 for protecting 95% species safety in soils with different properties was obtained by fitting species sensitivity distribution curve (SSD). This research collected various Cr toxicological data from Chinese cropland soils, based on 31 different endpoints covering soil fauna, functional indicators of microorganisms, terrestrial plants, etc., sourced from both our laboratory and existing literature. We applied the SSD method to estimate the hazardous concentration of Cr for HC5 and ultimately established a predictive model according to HC5 and different soil properties. As a result, the EC10 (an effective concentration of Cr resulting in 10% suppression of terminal biological activity) based on 7 different soils and 4 endpoints ranged from 16.8 to 148.0 mg kg−1, and the hormesis of Cr induction reached up to 109%. Overall, the toxicity (EC10) to microorganisms was much lower, while it was higher for graminoids. All the toxicity data were corrected through an aging factor with up to 540 days of equilibration before fitting the SSD curves. After that, a prediction model considering HC5 values and soil properties was established as LogHC5 = 3.003LogpH +0.651LogOC +0.013LogCEC - 0.476. The model was well-verified in field experiments, as the actual and predicted values fell within a 2-fold error range. This approach offers a rigorous scientific foundation for determining the Cr ecological risk threshold and could be important for the conservation of ecological species in soils.

Derivation of ecotoxicologically acceptable Cu concentrations in soil from different land uses in South Korea

This study aimed to establish ecotoxicologically acceptable Cu concentrations for soil-residing species by integrating the biotic ligand model and the species sensitivity distribution. Statistical analyses were performed on 35 soil solution samples collected from four distinct land use sites: residential, agricultural, forested, and industrial regions. The environmental parameters of these samples, including pH, dissolved organic carbon (DOC), Ca2⁺, Mg2⁺, K⁺, and Na⁺ concentrations, exhibited wide variations across the four regions. Specifically, pH and the concentrations of Mg2⁺, K⁺, and Na⁺ showed significant variability. Additionally, a strong correlation was observed between pH and Ca2⁺, as well as between the DOC concentration and Mg2⁺ and Na⁺. Using the biotic ligand model, we derived the half-maximal effective activities of Cu (EC50{Cu2+}) for 10 soil organisms based on the chemical compositions of the soil solution samples. Additionally, a species sensitivity distribution approach was employed to determine the 5% hazardous concentration (HC5) for soil biota, which was closely associated with DOC and Na⁺ concentrations, with Mg2⁺ playing a secondary role. We attributed these relationships to the formation of DOC complexes that mitigate Cu toxicity, along with competitive interactions with cations. Notably, HC5 values did not differ significantly across sampling sites (p = 0.523). Clustering based on environmental factors grouped the samples into four clusters, each containing soils from different land use types. However, the third cluster included an outlier from agricultural soil due to its unusually high pH and DOC levels. These findings suggest that it is crucial to consider site-specific soil characteristics when determining ecotoxicologically acceptable Cu concentrations, and soil solution characteristics do not always align with specific land use patterns.

A rapid and multi-endpoint ecotoxicological test using Mychonastes afer for efficient screening of metals and herbicides

Microalgal growth-based tests are international standards for ecotoxicity assessment; however, their long exposure times, large sample volumes, and reliance on a single growth-endpoint make them inadequate for rapid toxicity screening. Here, we aimed to develop a rapid and simple ecotoxicological test using the fast-growing green alga Mychonastes afer, with multiple endpoints—growth, lipid content, and photosynthesis. We exposed M. afer to two metals—silver and copper—and two herbicides—atrazine and diuron—for 24 h and identified the most sensitive and reliable endpoints for each toxicant: the maximum electron transport rate (ETRmax) for Ag, Cu and atrazine, and the lipid content for diuron. Lipid content was found to be both a sensitive and reliable biomarker, meeting the effluent limit guidelines in both the Republic of Korea and the USA. The sensitivity of M. afer to Ag and atrazine also closely matched the HC5 values derived from the species sensitivity distribution approach, confirming its reliability for setting regulatory concentrations of these contaminants. Our calculated predicted no-effect concentration (PNEC) values were similar to established European Union PNECs for Ag, Cu, atrazine, and diuron, underlining the utility of these biological endpoints for ecological risk assessment and regulatory decision making. This method required lower sample volume (2 mL vs 100 mL) and exposure time (24 h vs 72–120 h) than conventional green algal tests, and eliminated the need for labour-intensive cell counting, expensive equipment, and chlorophyll fluorescence measurement expertise. Overall, this M. afer test can be a valuable tool for the rapid screening of wastewater for metals and herbicides, contributing to environmental protection and management practices.

Which distribution to choose for deriving a species sensitivity distribution? Implications from analysis of acute and chronic ecotoxicity data

Species sensitivity distributions (SSDs) estimated by fitting a statistical distribution to ecotoxicity data are indispensable tools used to derive the hazardous concentration for 5 % of species (HC5) and thereby a predicted no-effect concentration in environmental risk assessment. Whereas various statistical distributions are available for SSD estimation, the fundamental question of which statistical distribution should be used has received limited systematic analysis. We aimed to address this knowledge gap by applying four frequently used statistical distributions (log-normal, log-logistic, Burr type III, and Weibull distributions) to acute and chronic SSD estimation using aquatic toxicity data for 191 and 31 chemicals, respectively. Based on the differences in the corrected Akaike’s information criterion (AICc) as well as visual inspection of the fitting of the lower tails of SSD curves, the log-normal SSD was generally better or equally good for the majority of chemicals examined. Together with the fact that the ratios of HC5 values of other alternative SSDs to those of log-normal SSDs generally fell within the range 0.1–10, our findings indicate that the log-normal distribution can be a reasonable first candidate for SSD derivation, which does not contest the existing widespread use of log-normal SSDs.

Deriving ecological risk thresholds for soil molybdenum in China based on interspecies correlation estimation and quantitative ion character–activity relationship models

Soil molybdenum (Mo) levels can reach ecologically hazardous levels. China has not yet established the relevant thresholds, posing challenges for environmental management. Therefore, we present our data relevant to Mo toxicity for several important species. By normalizing soil properties, we obtained a correlation model of Mo toxicity to Hordeum vulgare, as well as 31 models for the toxicity of other elements including Cu and Ni to invertebrates and microbial processes. Using interspecies correlation estimation (ICE) extrapolation, the sensitivity coefficient (0.12–0.71) for five plants were found. For invertebrates and microbial processes lacking Mo data, we used regression analysis to establish Mo toxicity models based on the soil quantitative ion character–activity relationships (s–QICAR; R2 =0.70–0.95) and known toxicities of other metal elements to invertebrate and microbial processes. Furthermore, combining species sensitivity distribution calculations, the HC5 values for protecting 95% of soil species from Mo in three typical soil scenarios in China were calculated. After correction, the predicted no-effect concentrations were 6.8, 4.8, and 3.4 mg/kg, respectively. This study innovatively combined ICE and s − QICAR to derive soil Mo thresholds. Our results can provide a basis for decision-making in the assessment and management of soil Mo pollution.

Aquatic life criteria of hydrothermal liquefaction wastewater via ecotoxicity test and modeling

Wastewater resulting from hydrothermal liquefaction (HTL-AP) of biowaste is gaining attention as an emerging hazardous material. However, there is a lack of specific and systematic ecotoxicity studies on HTL-AP. This study addresses this gap by conducting acute toxicity tests on HTL-AP using typical aquatic species and integrating these results with predicted toxicity values from interspecies correlation estimation models to establish aquatic life criteria. HTL-AP exhibited significant toxicity with LC50 of 956.12–3645.4 mg/L, but demonstrated moderate toxicity compared to common freshwater pollutants like commercial microbicides, personal care products, and insect repellents. The resulting hazardous concentration for 5 % of species (HC5), the criterion maximum concentration, and the short-term water quality criteria for aquatic were 506.0, 253.0, and 168.7 mg/L, respectively. Notably, certain organisms like Misgurnus anguillicaudatus and Cipangopaludina chinensis showed high tolerance to HTL-AP, likely due to their metabolic capabilities on HTL-AP components. The significant decrease in HC5 values for some HTL-AP substances compared to pure compounds could indicate the synergistic inhibition effects among HTL-AP compositions. Furthermore, according to the established criteria, HTL-AP required significantly less diluted water (13 t) than carbendazim (1009 t) to achieve biosafety, indicating a safer release. This research establishes a preliminary water quality criterion for HTL-AP, offering a valuable reference for risk assessment and prediction in the utilization of HTL-AP within environmental contexts.

Occurrence, distribution, and ecological risk assessment of heavy metals in Chao Phraya River, Thailand

Understanding heavy metals in rivers is crucial, as their presence and distribution impact water quality, ecosystem health, and human well-being. This study examined the presence and levels of nine heavy metals (Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn) in 16 surface water samples along the Chao Phraya River, identifying Fe, Mn, Zn, and Cr as predominant metals. Although average concentrations in both rainy and dry seasons generally adhered to WHO guidelines, Mn exceeded these limits yet remained within Thailand’s acceptable standards. Seasonal variations were observed in the Chao Phraya River, and Spearman’s correlation coefficient analysis established significant associations between season and concentrations of heavy metals. The water quality index (WQI) demonstrated varied water quality statuses at each sampling point along the Chao Phraya River, indicating poor conditions during the rainy season, further deteriorating to very poor conditions in the dry season. The hazard potential index (HPI) was employed to assess heavy metal contamination, revealing that during the dry season in the estuary area, the HPI value exceeded the critical threshold index, indicating the presence of heavy metal pollution in the water and unsuitable for consumption. Using the species sensitivity distribution model, an ecological risk assessment ranked the heavy metals’ HC5 values as Pb > Zn > Cr > Cu > Hg > Cd > Ni, identifying nickel as the most detrimental and lead as the least toxic. Despite Cr and Zn showing a moderate risk, and Cu and Ni posing a high risk to aquatic organisms, the main contributors to ecological risk were identified as Cu, Ni, and Zn, suggesting a significant potential ecological risk in the Chao Phraya River’s surface water. The results of this study provide fundamental insights that can direct future actions in preventing and managing heavy metal pollution in the river ecosystem.

Determining soil conservation strategies: Ecological risk thresholds of arsenic and the influence of soil properties

The establishment of ecological risk thresholds for arsenic (As) plays a pivotal role in developing soil conservation strategies. However, despite many studies regarding the toxicological profile of As, such thresholds varying by diverse soil properties have rarely been established. This study aims to address this gap by compiling and critically examining an extensive dataset of As toxicity data sourced from existing literature. Furthermore, to augment the existing information, experimental studies on As toxicity focusing on barley-root elongation were carried out across various soil types. The As concentrations varied from 12.01 to 437.25 mg/kg for the effective concentrations that inhibited 10% of barley-root growth (EC10). The present study applied a machine-learning approach to investigate the complex associations between the toxicity thresholds of As and diverse soil properties. The results revealed that Mn-/Fe-ox and clay content emerged as the most influential factors in predicting the EC10 contribution. Additionally, by using a species sensitivity distribution model and toxicity data from 21 different species, the hazardous concentration for x% of species (HCx) was calculated for four representative soil scenarios. The HC5 values for acidic, neutral, alkaline, and alkaline calcareous soils were 80, 47, 40, and 28 mg/kg, respectively. This study establishes an evidence-based methodology for deriving soil-specific guidance concerning As toxicity thresholds.

Aquatic and sediment ecotoxicity data of difenoconazole and its potential environmental risks in ponds bordering rice paddies

Difenoconazole has a widespread agricultural use to control fungal diseases in crops, including rice. In edge-of-field surface waters the residues of this lipophilic fungicide may be toxic to both pelagic and benthic organisms. To allow an effect assessment we mined the regulatory and open literature for aquatic toxicity data. Since published sediment toxicity data were scarce we conducted 28 d sediment-spiked toxicity test with 8 species of benthic macroinvertebrates. Ecotoxicological threshold levels for effects were assessed by applying the species sensitivity distribution approach. Based on short-term L(E)C50’s for aquatic organisms from water-only tests an acute Hazardous Concentration to 5% of the species (HC5) of 100 µg difenoconazole/L was obtained, while the HC5 based on chronic NOEC values was a factor of 104 lower (0.96 µg difenoconazole/L). For benthic macroinvertebrates the chronic HC5, based on 28d-L(E)C10 values, was 0.82 mg difenoconazole/kg dry weight sediment. To allow a risk assessment for water- and sediment-dwelling organisms, exposure concentrations were predicted for the water and sediment compartment of an edge-of-field pond bordering rice paddies treated with difenoconazole using the Chinese Top-Rice modelling approach, the Chinese Nanchang exposure scenario and the Equilibrium Partitioning theory. It appeared that in the vast majority of the 20 climate years simulated, potential risks to aquatic and sediment organisms cannot be excluded. Although the HC5 values based on laboratory toxicity data provide one line of evidence only, our evaluation suggests population- and community-level effects on these organisms due to chronic risks in particular.

Ecological risk assessment for typical organophosphorus pesticides in surface water of China based on a species sensitivity distribution model

The ecological risks posed by widespread organophosphorus pesticide (OPs) pollution in the surface waters of China remain unclear. In this study, species sensitivity distribution (SSD) parametric statistical approaches were coupled with fully acute and chronic toxicity data to fit the sensitivity distributions of different aquatic species to five typical OPs: dimethoate, malathion, parathion-methyl, trichlorfon, and dichlorvos. Crustaceans exhibit the highest sensitivity to OPs, whereas algae are the least sensitive. The acute hazardous concentrations that affected 5 % of the species (HC5) were 0.112, 0.001, 0.001, 0.001, and 0.001 mg/L for dimethoate, malathion, parathion-methyl, trichlorfon, and dichlorvos, respectively, whereas their chronic HC5 values were 0.004, 0.004, 0.053, 0.001, and 0.0005 mg/L, respectively. Hence, dichlorvos is highly toxic and poses greater risk to non-target aquatic species. The evaluation data revealed varying geographical distribution characteristics of the ecological risks from OPs in 15 freshwater aquatic systems across different regions of China. Dichlorvos posed the highest risk in the basins of Zhejiang and Guangdong Provinces, with the highest chronic Risk Quotient (RQ) and Hazard Index (HI) at 9.34 and 9.92, respectively. This is much higher than what was collected and evaluated for foreign rivers (the highest chronic RQ and HI in foreign rivers were 1.65 and 2.24, respectively). Thus, dichlorvos in the surface waters of China poses a substantial ecological risk to aquatic organisms, and may endanger human health.

Estimating species sensitivity distributions for microplastics by quantitatively considering particle characteristics using a recently created ecotoxicity database

Estimation of a species sensitivity distribution (SSD) by fitting a statistical distribution to ecotoxicity data is a promising approach to deriving “safe” concentrations for microplastics. However, most existing SSDs do not quantitatively consider the diverse characteristics of microplastics, such as particle size and shape. To address this issue, based on 38 mass-based chronic no observed effect concentrations (NOECs) obtained from a recently created database, we estimated SSDs that quantitatively consider the influences of three types of microplastic characteristics (particle length, shape, and polymer type) and habitat of the test species (freshwater vs. marine) by using Bayesian modeling. We selected the best SSD model among all possible models using the widely applicable information criterion. The best SSD model included particle length (range: 0.05–280 μm) and a binary dummy variable corresponding to the fiber shape. Lower chronic NOECs were associated with decreasing particle size and with toxicity tests that included fibers in this model. Combined with the fact that the null model (i.e., an SSD model with no predictor variable) was ranked 27th among the 64 candidate SSD models, our results support the need to incorporate particle characteristics such as length and shape (e.g., fiber) into estimations of SSDs for microplastics. The medians of the hazardous concentration of 5% of species (HC5) for microplastic spheres and fragments, estimated by the posterior distributions of individual parameters in the best SSD model, ranged from 0.02 to 2 µg/L, depending on the particle length (0.1–100 μm). For microplastic fibers, the HC5 values were estimated to be approximately 100 times lower than those for microplastic spheres and fragments with the same particle length. However, the 95% Bayesian credible intervals for HC5 estimates for fibers were considerable, expanded by up to five orders of magnitude. Despite many remaining challenges, the Bayesian SSD modeling utilized in this study provides unique opportunities to simultaneously investigate the influences of multiple microplastic characteristics on the NOECs of multiple species, which would otherwise be difficult to discern.

Health Risk Assessment and Environmental Benchmark of Cadmium in Farmland Soils around the Gangue Heap of Coal Mine, Chongqing

To analyze the health risk assessment and environmental benchmark of cadmium in farmland soils surrounding the gangue heap of a coal mine in Chongqing, Hakanson, the ecological risk index and health risk assessment were used. Meanwhile, the soil environmental reference value of the regional cultivated land was inverted based on the species sensitive distribution model (SSD). The results showed that the dryland soil was polluted by Cd, with an over-standard rate of 55.8%, and the paddy field soil was polluted by Cd, with an over-standard rate of 31.6%. The corn was polluted by Cd, with an over-standard rate of 4.4%, and the rice was not polluted by Cd. The Hakanson ecological risk index showed that Cd was mainly characterized in soils by high ecological risk and considerable ecological risk. The health risk assessment indicated that Cd presented low non-carcinogenic risk by corn and rice; however, it showed acceptable carcinogenic risk by corn and unacceptable carcinogenic risk by rice in this study. The sensitivity analysis of health risks showed that the content of Cd was the most sensitive. The SSD inversion showed that the reference values for Cd in dryland soil of pH ≤ 5.5, 5.5<pH ≤ 6.5, 6.5<pH ≤ 7.5, and pH>7.5 had HC5 values of 0.491, 0.382, 0.376, and 0.588 mg·kg-1, respectively, and that for Cd in paddy soil had an HC5 value of 0.807 mg·kg-1. The reverse analysis showed that the HC5 of Cd in dryland soil (pH ≤ 7.5) and paddy soil was relatively relaxed and was higher than the soil risk screening values, which showed that the current standard was relatively loose. However, the HC5 of Cd in dryland soil (pH>7.5) was lower than the soil risk screening values, which showed that the current standard was relatively strict. It is suggested that the current soil standard could be adjusted in this area.

Ecological risk evaluation and sensitivity analysis of heavy metals on soil organisms under human activities in the Tibet Plateau, China.

The Tibetan Plateau (TP), once considered a pristine environment, is now facing increased heavy metal pollution due to human activities, causing unprecedented ecological risks to soil organisms. However, little is known about the sensitivity and tolerance of different soil organisms to heavy metal toxicity in the high-altitude areas of the TP under the background of human activity intensity and future risk control priorities. In this study, we conducted an ecological risk assessment and threshold calculation for 10 heavy metals in soil for typical soil organisms, including Cd, Co, Cr, Cu, Ni, Pb, Zn, Mn, Sb, and Sn, using the species sensitivity distribution (SSD) method in the zone between Ranwu town and Renlongba glacier on the TP. The results revealed that most sampling sites had average levels of Cd, Sb and Ni exceeding their regional soil environmental background values and were the major contaminants. Impressively, the hitherto undeveloped Renlungba Glacier showed relatively high contamination levels of Sb and Ni. From the view of sensitivity differences, the toxicity risks of Cd, Cr, Cu, Ni and Pb were higher for terrestrial plants than for soil invertebrates based on the fitted heavy metal SSD curve trends. In terms of the ecological risk level, the average potentially affected fraction values of Zn and Ni reached 18.5% and 17.0%, respectively, with significant ecological risk at a few sampling sites. In terms of ecological risk thresholds, the Cd concentration at the 5% hazard concentration (HC5) control level was 0.05 mg/kg, which was the heavy metal with the highest risk in this study. Comparing the HC5 values of each heavy metal with the limit values in the current Chinese soil environmental quality standards, the existing administrative policies as a whole lack a powerful prevention of the potential ecological risk posed by heavy metals to soil organisms.

Determination of aquatic hazard concentrations for the oil spill response product class of surface washing agents using species sensitivity distributions

Surface washing agents (SWAs) are a diverse class of oil spill response products intended to facilitate removal of stranded oil from shorelines. This class of agents has high application rates relative to other categories of spill response products, but global toxicity data is generally limited to two standard test species: inland silverside and mysid shrimp. Here, we provide a framework to maximize the utility of limited toxicity data across a product class. To characterize species sensitivity to SWAs, the toxicity of three agents spanning a range of chemical and physical properties were tested in eight species. The relative sensitivity of mysids shrimp and inland silversides as surrogate test organisms was determined. Toxicity normalized species sensitivity distributions (SSDn) were used to estimate fifth centile hazard concentration (HC5) values for SWAs with limited toxicity data. Chemical toxicity distributions (CTD) of SWA HC5 values were used to compute a fifth centile chemical hazard distribution (HD5) to provide a more comprehensive assessment of hazard across a spill response product class with limited toxicity data than traditional single species or single agent approaches can give.

Ecological risk characteristics of sediment-bound heavy metals in large shallow lakes for aquatic organisms: The case of Taihu Lake, China

Heavy metal contamination in the surface sediments of large shallow lakes in China is becoming increasingly serious. However, more attention has been paid to the human health risk of heavy metals in the past, while little consideration has been given to aquatic organisms. Taking Taihu Lake as an example, we explored the spatial and temporal heterogeneity of the potential ecological risks of seven heavy metals (Cd, As, Cu, Pb, Cr, Ni, and Zn) to species at different taxonomic scales using an improved species sensitivity distribution (SSD) method. The results showed that all six heavy metals, except Cr, were exceeded to some extent compared to background levels, with Cd being the most severe exceedance. Based on the hazardous concentration for 5% of the species (HC5), Cd had the lowest HC5 value, implying the highest ecological risk of toxicity. Ni and Pb had the highest HC5 values and the lowest risk. Cu, Cr, As and Zn were at a relatively moderate levels. For the different groups of aquatic organisms, the ecological risk of most heavy metals was generally lower for vertebrates than for the whole species. The risk for invertebrates and algae was higher than that for all species. Zn and Cu had the highest potentially affected fractions (PAFs) for all classification cases, with mean PAFs of 30.25% and 47.2%, respectively. Spatially, the high ecological risk of sediment heavy metals was significantly related to the spatial characteristics of the type and intensity of human activities in the catchment. Administratively, the environmental quality standards for freshwater sediments proposed by America and Canada are insufficient to protected against the ecological risks of heavy metals in Taihu Lake. In the absence of such standards, China urgently needs to establish an approptiate system of environmental quality standards for heavy metals in lake sediments.

Ecological risk assessment for xylenes and propylbenzenes in aquatic environment using a species sensitivity distribution approach

Xylenes and propylbenzenes (PBZs) are volatile aromatic hydrocarbons with high aquatic toxicity. Xylenes can be present in three isomers: o-xylene (OX), m-xylene (MX), and p-xylene (PX), while PBZs include two isomers: n-propylbenzene (n-PBZ) and isopropylbenzene (i-PBZ). Their accidental spills and improper discharges from petrochemical industries can cause severe contamination in water bodies posing potential ecological risks. In this study, the published acute toxicity data of these chemicals for aquatic species were collected to calculate hazardous concentrations protecting 95% species (HC5) using a species sensitivity distribution (SSD) approach. The acute HC5 values for OX, MX, PX, n-PBZ, and i-PBZ were estimated to be 1.73, 3.05, 1.23, 1.22, and 1.46 mg/L, respectively. The risk quotient (RQ) values calculated based on HC5 indicated their high risk (RQ: 1.23 ∼ 21.89) in groundwater, but low risk (RQ < 0.1) in natural seawater, river water, and lake water. When xylenes or PBZs leaked into the sea, they were expected to pose a high risk (RQ > 1) at the start and then a low risk (RQ < 0.1) after 10 days due to natural attenuation. These results may help to derive more reliable protection thresholds for xylenes and PBZs in aquatic environment and provide a basis for evaluating their ecological risks.