Development of a Machine Learning Model to Estimate the Biotic Ligand Model-Based Predicted No-Effect Concentrations for Copper in Freshwater.

The copper (Cu) biotic ligand model (BLM) has been used for ecological risk assessment by taking into account the bioavailability of Cu in freshwater. The Cu BLM requires data for many water chemistry variables, such as pH, major cations, and dissolved organic carbon, which can be difficult to obtain from water quality monitoring programs. To develop an optimized predicted no-effect concentration (PNEC) estimation model based on an available monitoring dataset, we proposed an initial model that considers all BLM variables, a second model that requires variables excluding alkalinity, and a third model using electrical conductivity as a surrogate for the major cations and alkalinity. Furthermore, deep neural network (DNN) models have been used to predict the nonlinear relationships between the PNEC (outcome variable) and the required input variables (explanatory variables). The predictive capacity of DNN models was compared with the results of other existing PNEC estimation tools using a look-up table and multiple linear and multivariate polynomial regression methods. Three DNN models, using different input variables, provided better predictions of the Cu PNECs compared with the existing tools for the following four test datasets: Korean, United States, Swedish, and Belgian freshwaters. Consequently, it is expected that Cu BLM-based risk assessment can be applied to various monitoring datasets, and that the most applicable model among the three different types of DNN models could be selected according to data availability for a given monitoring database. Environ Toxicol Chem 2023;42:2271-2283. © 2023 SETAC.

Comparison of the Estimation Methods from Acute to Chronic Biotic Ligand Model-Based Predicted No-Effect Concentrations for Nickel in Freshwater Species.

Biotic ligand models (BLMs) and the sensitivities of indigenous species are used to assess the environmental risk considering the bioavailability of metals, such as nickel. However, the BLM-based acute-to-chronic ratio (ACR) is required if the predicted no-effect concentration (PNEC) cannot be derived from the chronic species sensitivity distribution (SSD). The applicability of the ACR approach for estimating BLM-based PNEC for nickel from acute toxicity data was evaluated in the present study. The BLM-based acute SSD for nickel was built using the sensitivities of 21 indigenous species and different taxon-specific BLMs for each taxonomic group. To predict the acute sensitivity of invertebrates, the chronic crustacean nickel BLM with pH effect term, which can account for nickel toxicity at high pH levels, was used. This was used instead of the existing acute BLM for crustacean, which has too narrow a pH range to cover the pH dependency of toxicity. The final BLM-based ACR of nickel, determined within a factor of 1.53 from the species-specific acute and chronic sensitivities of the six species, was more reliable than the typical ACR estimated within a factor of 1.84. A linear relationship (r2 = 0.95) was observed between the PNECs using BLM-based ACR and the PNECs derived from the BLM-based chronic SSD of the European Union Risk Assessment Reports. In conclusion, the BLM-based PNEC for nickel could be derived using the ACR approach, unlike when copper BLM was applied. The BLM-based ACR for nickel is the first result calculated by directly comparing acute and chronic species sensitivities, and will contribute to the application of BLM-based risk assessment in broader ecoregions. Environ Toxicol Chem 2023;42:914-927. © 2023 SETAC.

Derivation of acute copper biotic ligand model-based predicted no-effect concentrations and acute-chronic ratio.

The copper biotic ligand model (BLM) can quantitatively describe the bioavailability depending on various environmental factors and has been used to derive the predicted no-effect concentrations (PNECs). The commonly employed acute BLM tool, HydroQual, which applies the biotic ligand constants of fathead minnow in the same model structure for all taxonomic groups, estimates lower acute copper toxicity values compared to the chronic copper PNECs of the European Union Risk Assessment Reports (EU-RAR), which are based on taxon-specific model structures and biotic ligand constants for vertebrates, invertebrates, and algae. In this study, the full-BLM approach was applied using an appropriate acute BLM for each taxonomic group to derive acute HC5s (fifth percentile value in the species sensitivity distribution [SSD]) and an acute-chronic ratio for copper. Two acute BLMs for vertebrates and invertebrates were used and validated against site waters using the new method to estimate the intrinsic sensitivity for each species across different environmental conditions. To derive acute copper full BLM-based HC5s in Korean freshwater, acute toxicity tests were performed with 10 indigenous species, which were used to build the acute BLM-based SSD at each site. The final estimated acute full-BLM HC5s were higher than the EU-RAR chronic PNECs within the BLM calibration range. Furthermore, a linear relationship was observed between the acute full-BLM HC5s and the EU-RAR chronic PNECs. This linear regression function was suggested as an acute to chronic transformation function that can be applied to calculate chronic PNEC values. In conclusion, if the chronic ecotoxicity database of indigenous aquatic organisms for copper is lacking, it may be more efficient to derive chronic PNECs using an acute-chronic ratio after deriving BLM-based acute copper SSDs for indigenous species within representative taxonomic groups. This study provides a scientific foundation for the derivation of water quality criteria for copper in freshwater.

Development of water quality criteria of ammonia for protecting aquatic life in freshwater using species sensitivity distribution method.

Ammonia is deemed one of the most important pollutants in the freshwater environment because of its highly toxic nature and ubiquity in surface water. This study thus aims to derive the criteria for ammonia in freshwater to protect aquatic life because there are no water quality criteria for ammonia in Korea. Short-term lethal tests were conducted to perform the species sensitivity distribution (SSD) method. This method is widely used in ecological risk assessment to determine the chemical concentrations to protect aquatic species. Based on the species sensitivity distribution method using Korean indigenous aquatic biota, the hazardous concentration for 5% of biological species (HC5) value calculated in this study was 44mg/L as total ammonia nitrogen (TAN). The value of the assessment factor was set at 2. Consequently, the criteria for ammonia were derived as 22mg/L at pH7 and 20°C. When the derived value was applied to the monitoring data nationwide, 0.51%, 0.09%, 0.18%, 0.20%, and 0.35% of the monitoring sites in Han River, Nakdong River, Geum River, Youngsan River, and lakes throughout the nation, respectively, exceeded this criteria. The Ministry of Environment in Korea has been considering introducing water quality standard of ammonia for protecting aquatic life. Therefore, our results can provide the basis for introducing the ammonia standard in Korea.

Seasonal variation in the input of atmospheric selenium to northwestern Greenland snow.

Oxygen isotope ratio (δ(18)O) and concentrations of Al, Na(+), methanesulfonic acid (MSA), SO4(2-), and selenium (Se) in a continuous series of 70 snow samples from a 3.2-m snow pit at a site in northwestern Greenland were determined using ultraclean procedures. Well-defined depth profiles of δ(18)O, Al, and sea-salt-Na(+) allowed the determination of chronology of the snow pit that spanned approximately 6 years from spring 2003 to summer 2009. Se concentrations were at a low pg/g level, ranging from 7.2 to 45 pg/g, and exhibited high variability with generally higher values during winter and spring and lower values during summer and fall. Very high crustal enrichment factors (EFc) of Se averaging approximately 26,600 for the entire time period indicate a small contribution from crust dust. High Se/MSA ratios are generally observed in the winter and spring snow layers, in which the Se concentrations were relatively high (>20 pg/g). This suggests that a significant component of the Se present in the snow layers is of anthropogenic origin. During the summer season, however, high EFc values are accompanied with low Se/MSA, indicating an increased contribution of marine biogenic sources. Significant correlations between Se, Al, and non-sea-salt SO4(2-) highlight that significant inputs of Se to the snow are likely controlled by the seasonality in the transport efficiency of anthropogenic Se from the source regions to the site. Based on the seasonal changes in Se concentrations, Se/MSA, and Se/S ratios observed in the samples, the input of anthropogenic Se to the site appears to be governed by the long-range transportation of Se emitted from coal combustion in East Asian countries, especially in China.

Ecotoxicity of bare and coated silver nanoparticles in the aquatic midge, Chironomus riparius.

Although sediment is generally considered to be the major sink for nanomaterials in aquatic environments, few studies have addressed the ecotoxicity of nanomaterials in the presence of sediment. In the present study, the ecotoxicity of silver nanoparticles (AgNPs) with a range of organic coatings was examined in a freshwater sediment-dwelling organism, Chironomus riparius, using acute and chronic ecotoxicity endpoints, including molecular indicators. The toxicity of AgNPs coated with different organic materials, such as polyvinylpyrrolidone, gum arabic, and citrate, to C. riparius was compared with that of bare-AgNPs and AgNO3 (ionic silver). Total silver concentration was also measured to monitor the behavior of the AgNPs in water and sediment and to determine how ion dissolution affects the toxicity of all AgNPs. The coated- and bare-AgNPs caused DNA damage and oxidative stress-related gene expression. In addition, the bare-AgNPs and AgNO3 had a significant effect on development and reproduction. The surface coatings generally mitigated the toxicity of AgNPs to C. riparius, which can be explained by the reduced number of ions released from coated-AgNPs. Citrate-AgNPs caused the most significant alteration at the molecular level, but this did not translate to higher-level effects. Finally, comparing previously conducted studies on AgNP-induced gene expression without sediments, the authors show that the presence of sediment appears to mitigate the toxicity of AgNPs.