Understanding boron toxicity in aquatic plants (Salvinia natans and Lemna minor) in the presence and absence of EDTA.

Even though boron is a widely used element in various industries and a contributor to water pollution worldwide, few studies have examined the toxicity of boron in aquatic plants. EDTA is used to maintain aquatic plants cultures, however it is possible to modify the toxicity of metals. The objective of this study is to assess the toxicity of boron in aquatic plants and explore the impact of EDTA presence on the resulting toxic responses. Floating watermoss Salvinia natans and duckweed Lemna minor were exposed to concentrations ranging from 5 to 100 mg/L for 7 days and 1 to 60 mg/L for 3 days, respectively. Growth and photosynthetic activity parameters were investigated in the presence and absence of EDTA. Growth inhibitions in both aquatic plants were observed in a concentration-dependent manner, irrespective of the presence or absence of EDTA. For instance, based on the specific growth rate (leaves coverage), EC10 values for S. natans were calculated as 12.7 (9.9-15.3) mg/L and 8.0 (5.8-10.3) mg/L with and without EDTA, respectively. In the case of L. minor, EC10 values were calculated as 1.3 (0.8-1.89) mg/L and 2.0 (0.4-4.3) mg/L with EDTA without EDTA, respectively. Significant effects were also observed on the photosynthetic capacity, however there was no change in the increase of boron concentration. Generally, negligible effects of EDTA to the toxicity of boron were observed in the present study. By comparing toxicity results based on the presence and absence of EDTA, which is an essential element in the test medium, the results of this study are expected to be utilized for the ecological risk assessment of boron in aquatic ecosystems.

Multigenerational effects of microplastic fragments derived from polyethylene terephthalate bottles on duckweed Lemna minor: Size-dependent effects of microplastics on photosynthesis.

The 2019 global coronavirus disease pandemic has led to an increase in the demand for polyethylene terephthalate (PET) packaging. Although PET is one of the most recycled plastics, it is likely to enter the aquatic ecosystem. To date, the chronic effects of PET microplastics (MPs) on aquatic plants have not been fully understood. Therefore, this study aimed to investigate the adverse effects of PET MP fragments derived from PET bottles on the aquatic duckweed plant Lemna minor through a multigenerational study. We conducted acute (3-day exposure) and multigenerational (10 generations from P0 to F9) tests using different-sized PET fragments (PET0-200, < 200 µm; PET200-300, 200-300 µm; and PET300-500, 300-500 µm). Different parameters, including frond number, growth rate based on the frond area, total root length, longest root length, and photosynthesis, were evaluated. The acute test revealed that photosynthesis in L. minor was negatively affected by exposure to small-sized PET fragments (PET0-200). In contrast, the results of the multigenerational test revealed that large-sized PET fragments (PET300-500) showed substantial negative effects on both the growth and photosynthetic activity of L. minor. Continuous exposure to PET MPs for 10 generations caused disturbances in chloroplast distribution and inhibition of plant photosynthetic activity and growth. The findings of this study may serve as a basis for future research on the generational effects of MPs from various PET products.

Salvinia natans microplate assay: A simple and efficient method for evaluating aquatic toxicity.

This study proposes a microplate assay for chemical toxicity evaluation using S. natans; this assay is a miniaturization of a culture dish assay from previous studies. The optimal initial frond number of S. natans in the microplate assay was established and the feasibility of the microplate assay was evaluated. To evaluate the applicability of the developed method, S. natans was exposed to six model chemicals (one metalloid and five heavy metals) and the specific growth rate and photosynthetic activity were compared. We determined that the optimal initial frond number was four fronds for the microplate assay. Additionally, toxicity sensitivity to six model chemicals revealed similar results to the culture dish assay. Therefore, we propose that the S. natans microplate assay is a simple and effective method to assess ecotoxicity as it requires less test solution and area than the culture dish assay. This methodology can be expandable to ecotoxicological research.

Trophic transfer of nanoplastics through a microalgae-crustacean-small yellow croaker food chain: Inhibition of digestive enzyme activity in fish.

This study investigated the effects of nanoplastics on marine organisms via trophic transfer in the food chain. We designed a three-step food chain comprising microalga (Dunaliella salina), small crustaceans (Artemia franciscana), and fish (small yellow croakers; Larimichthys polyactis) and evaluated the effects of trophic transfer in marine organisms, as well as verified the possibility of nanoplastic transfer to humans via trophic transfer. Using amine-modified nanopolystyrene (nPS-NH2) as a pollutant, we conducted both direct-exposure and trophic transfer experiments to determine how pollutants move through the food chain (D. salina → A. franciscana). Exposure of D. salina to nPS-NH2, which was adsorbed on its cell wall, resulted in transfer to A. franciscana with alteration of gut permeability. Additionally, assessment of the adverse effects of nPS-NH2 via a dietary pathway (three-step food chain) on the L. polyactis digestive system revealed that nanoplastics adsorbed to the cell wall of microalgae are gradually transferred to higher trophic level organisms, such as via food resources consumed by humans, inducing the inhibition of digestive enzyme activity (α-amylase). It indicates that human could eventually be exposed to nanoplastics and experience toxicity.

Acute and multigenerational effects of petroleum- and cellulose-based microfibers on growth and photosynthetic capacity of Lemna minor.

Comparative toxicological assessment studies on the effects of petroleum- and cellulose-based microfibers on aquatic plants are limited. Therefore, we evaluated the acute and 10-generational toxicological effects of two types of petroleum- and cellulose-based microfibers on the duckweed Lemna minor. Plant growth and photosynthesis parameters were monitored as bioindicators. The multigenerational test revealed the following ranking of the microfibers according to the severity of their effects on L. minor: polypropylene > lyocell > viscose > polyethylene terephthalate. The acute tests revealed a significant increase in the energy required to initiate photosynthesis, although the growth of L. minor was not adversely affected by any microfiber. Both petroleum- and cellulose-based microfibers induced adverse effects on the growth and photosynthesis of L. minor in multigenerational tests. The results of the generational tests contribute to the understanding of the long-term adverse effects of microfibers on aquatic plants.

Sub-acute exposure to nanoplastics via two-chain trophic transfer: From brine shrimp Artemia franciscana to small yellow croaker Larimichthys polyactis.

This study investigated the trophic transfer of nanoplastics in marine food chains. We fed nanoplastic-exposed Artemia franciscana (brine shrimp) to Larimichthys polyactis (small yellow croaker) daily for eight days. Subsequently, the overall health condition, histopathological damage to the liver and digestive tract, and swimming ability of the fish were measured. After the sub-acute exposure to nanoplastics via trophic transfer, the fish showed inhibited growth, severe liver damage, as well as a poorer swimming ability compared to the control. The swimming ability was especially affected, in terms of the overall movement as well as thigmotaxis. The results thus clarified that even an indirect exposure to nanoplastics could induce neurotoxic effects and affect the swimming ability of the fish. As fish are well-known human food resources, the possibility of such trophic transfers affecting higher trophic level organisms, such as humans, cannot be ruled out.

Species sensitivity distributions for ethylparaben to derive protective concentrations for soil ecosystems.

Ethylparaben is used as an antifungal preservative. Although some countries have implemented regulations for human exposure to parabens, environmental regulations for ethylparaben have not been established. This study provides new toxicological data for ethylparaben, for which data regarding soil organisms were previously lacking. Although ethylparaben toxicity has been reported in other species, we present herein the first comprehensive study of its toxicity in soil organisms. We used 12 test species (Lycopersicon esculentum, Vigna radiata, Hordeum vulgare, Oryza sativa, Eisenia andrei, Folsomia candida, Lobella sokamensis, Caenorhabiditis elegans, Chlamydomonas reinhardtii, Chlorococcum infusionum, Chlorella sorokiniana, Chlorella vulgaris) from eight taxonomic groups for acute bioassays and nine test species (L. esculentum, V. radiata, H. vulgare, O. sativa, C. reinhardtii, C. infusionum, C. sorokiniana, and C. vulgaris) from five taxonomic groups for chronic bioassays. A suite of acute and chronic toxicity tests, using 21 soil species, was conducted to estimate EC50 values, which facilitated the construction of species sensitivity distributions (SSDs) and the calculation of protective concentrations (PCs). Acute and chronic PC95 values (protective concentration for 95% of species) for ethylparaben were estimated to be 14 and 5 mg/kg dry soil, respectively. To the best of our knowledge, this is the first study to evaluate the toxicity of ethylparaben to soil species and derive PCs for soil ecosystems based on SSDs. Therefore, the data presented in this study can be used as a basis for further investigations of paraben toxicity to the soil environment.

Estimation of hazardous concentration of toluene in the terrestrial ecosystem through the species sensitivity distribution approach.

Toluene is a highly flammable and commonly used industrial chemical with severe health consequences on humans upon exposure and ingestion. In this study, multispecies bioassays were conducted using a species sensitivity distribution approach to determine acute and chronic hazardous concentrations of toluene in soil. Acute and chronic toluene toxicity tests were conducted with seven soil species from four taxonomic groups. The results from the toxicity tests were used to estimate the acute and chronic HC5 (hazardous concentration for 5 % of species) of toluene in the terrestrial environment at 58.9 (5.4-639.6) mg kg-1 and 2.2 (0.2-19.8) mg kg-1, respectively. To the best of our knowledge, this is the first study to estimate the hazardous concentration of toluene in soil by conducting a battery of bioassays. These values can be used as references for the environmental risk assessment of chemical accidents involving toluene and estimating its impact on soil to protect the terrestrial environment.

Salvinia natans: A potential test species for ecotoxicity testing.

Although macrophytes are known to play vital roles in aquatic ecosystems, most quantitative aquatic toxicity data focus on fishes, water fleas, or algae, with limited ecotoxicity data published on macrophytes. Salvinia natans is a fast-growing plant commonly found in freshwater habitats. In this study, we verified a suitable disinfectant for preventing foreign contamination and formulated a culture medium for ensuring high productivity of S. natans. Finally, we established methodology for S. natans to be used in ecotoxicity testing of heavy metals and pesticides. As global regulations are being developed to harmonize guidelines and laboratory test species, S. natans is emerging as a potential candidate. The toxicity data publicly available for S. natans are very limited; hence, this study reports an advantageous culturing technique to optimize healthy growth of this species in the laboratory and presents optimal toxicity results, achieved by modifying the currently available test guidelines for Lemna. Our findings expand the currently limited range of test species for aquatic toxicity assays. We conclude that S. natans could serve as a valuable test species for aquatic toxicity assays.

Determination of hazardous concentrations of 2,4-dinitrophenol in freshwater ecosystems based on species sensitivity distributions.

2,4-dinitrophenol (2,4-DNP) is a phenolic compound used as a wood preservative or pesticide. The chemical is hazardous to freshwater organisms. Although 2,4-DNP poses ecological risks, only a few of its aquatic environmental risks have been investigated and very limited guidelines for freshwater aquatic ecosystems have been established by governments. This study addresses the paucity of 2,4-DNP toxicity data for freshwater ecosystems and the current lack of highly reliable trigger values for this highly toxic compound. We conducted acute bioassays using 12 species from nine taxonomic groups and chronic assays using five species from four taxonomic groups to improve the quality of the dataset and enable the estimation of protective concentrations based on species sensitivity distributions. The acute and hazardous concentrations of 2,4-DNP in 5% of freshwater aquatic species (HC5) were determined to be 0.91 (0.32-2.65) mg/L and 0.22 (0.11-0.42) mg/L, respectively. To the best of our knowledge, this is the first report of a suggested chronic HC5 for 2,4-DNP and it provides the much-needed fundamental data for the risk assessment and management of freshwater ecosystems.

Deriving hazardous concentrations of phenol in soil ecosystems using a species sensitivity distribution approach.

Phenol is widely used in many industries, and chemical accidents involving phenol have frequently occurred around the world, resulting in the investigation of phenol toxicity in humans, mammals, and aquatic organisms. However, very few studies have investigated phenol toxicity in terrestrial ecosystems. Therefore, we investigated the acute and chronic toxicity of phenol using various soil organisms, including Chlamydomonas reinhardtii, Chlorococcum infusionum, Folsomia candida, Oryza sativa, Raphanus sativus, Pinus densiflora, and Eisenia fetida. The data obtained were used to calculate hazardous concentrations for 5% of species (HC5) for phenol based on a species sensitivity distribution approach. The acute and chronic soil HC5 values for phenol were estimated to be 18.4 and 0.3 mg kg-1, respectively. To the best of our knowledge, this is the first study to conduct battery testing and calculate hazardous concentrations to assess the risk posed by phenol in terrestrial ecosystems. The results can be used to establish standards or strategies to protect terrestrial environments against unintended phenol contamination.

Multispecies bioassay of propylparaben to derive protective concentrations for soil ecosystems using a species sensitivity distribution approach.

Propylparaben is widely used as a preservative in pharmaceuticals and personal care products and is ultimately excreted by the human body. Thus, propylparaben reaches sewage and enters the soil environment by sludge fertilization and wastewater irrigation. However, there are few existing studies on the toxicity and risks of such chemicals in terrestrial environments. In this study, a multispecies bioassay for propylparaben was performed and protective concentrations (PCs) were derived based on toxicity values by probabilistic ecological risk assessment. Acute and chronic bioassays were conducted on 11 species in eight taxonomic groups (Magnoliopsida, Liliopsida, Clitellata, Entognatha, Entomobryomorpha, Chromadorea, Chlorophyceae, Trebouxiophyceae). Based on the toxicity values calculated, the PC95 values for acute and chronic SSDs were 13 and 6 mg/kg dry soil, respectively. Toxicity varied among taxa, with soil algae emerging as the most sensitive to propylparaben. This may be attributable to differences in exposure pathways among species. The exposure pathway of propylparaben can be altered by adsorption to soil particles. As parabens are presently under-regulated globally in terms of their environmental effects, our findings can serve as the basis to propose standard values for environmental protection.

Effects on photosynthesis and polyphenolic compounds in crop plant mung bean (Vigna radiata) following simulated accidental exposure to hydrogen peroxide.

Hydrogen peroxide (H2O2) is a strong oxidizer and bleaching agent included in the list of substances requiring accident preparedness by the National Chemical Information System, Korea. Although chemical accidents related to H2O2 frequently occur globally, few studies have evaluated its toxicity and risk to soil ecosystems. Herein, accidental exposure to H2O2 was simulated in a microcosm including crop plant mung bean (Vigna radiata), and its long-term effects on photosynthetic activities and polyphenolic compounds were measured. Plants were evaluated based on the concentration and amount of H2O2 exposure, distance from H2O2 source, and duration post exposure. Plants exposed to high concentrations and large amounts of H2O2 at a close distance were most damaged; their photosynthetic activities and polyphenolic compound levels significantly decreased compared to the controls. H2O2 consistently damaged plants and affected their activities, but plants with minor damage recovered their photosynthetic activities and polyphenolic compound levels. Additionally, moderate oxidative stress from H2O2 exposure induced the synthesis of polyphenolic antioxidants including flavonol and anthocyanin. Thus, we suggest that flavonol and anthocyanin levels are the most sensitive indicators of adverse effects of H2O2 exposure in V. radiata. Our results highlight the risk of H2O2 and serve as a reference for chemical accidents.

Ecological risk assessment for perfluorooctanoic acid in soil using a species sensitivity approach.

Perfluorooctanoic acid (PFOA) is one of the persistent organic pollutants that has been listed in Annex A of the Stockholm Convention and has attracted attention owing to its endocrine-disrupting properties. However, there is currently little information available regarding the soil ecotoxicity of PFOA and the associated ecological risks. Accordingly, in this study, we sought to assess the soil ecological risk of PFOA based on a probabilistic approach using data obtained from multispecies bioassays and soil toxicity assessments, from which we generated soil species sensitivity distributions and estimated soil protective concentrations for PFOA. Using the latter distributions, we also undertook a probabilistic ecological risk assessment. On the basis of acute and chronic toxicity estimates obtained from bioassays involving eight soil-associated organisms from six diverse taxonomic groups, we could deduce that PFOA poses a negligible risk to soil ecosystems. However, we also found that this chemical may be more toxic than some of the established endocrine-disrupting chemicals such as bisphenol A, nonylphenol, and methylparaben, thereby indicating that further in-depth studies would be necessary to obtain a better understanding of the toxic potential of this chemical in the soil environment.

Soil ecotoxicity study of DEHP with respect to multiple soil species.

Di (2-ethylhexyl) phthalate or DEHP is classified as an endocrine-disrupting chemical. It is used as a plasticizer and pesticide additive. Moreover, it has a half-life of about 150-300 days. Thus, it is present in the soil environment and soil risk assessments for DEHP are needed. However, a number of studies have focused on the effects of DEHP in a single soil species. In this study, we conducted acute and chronic toxicity testing for DEHP using varied soil species, including plants, earthworms, soil algae, Collembola, and soil nematodes. In the plant toxicity test, no effect was observed at very high concentration except at some endpoints, and no effect was observed in the earthworm toxicity test. However, there were adverse effects on soil algae, Collembola, and nematodes. Notably, in the Collembola assays, the survival of adults decreased significantly at very high concentrations, whereas reproduction was hindered at low concentrations. Similar inhibition of reproduction was noted in the soil nematode assay. This suggests that DEHP has a greater influence on fertility than survival in the adult test species. However, besides hindered reproduction, no effect was observed on soil species at environmentally relevant concentrations.

Estimation of the soil hazardous concentration of methylparaben using a species sensitivity approach.

Methylparaben, which is known to be an endocrine-disrupting chemical, is added to various personal care products, including cosmetics, and is also used as a food preservative and in pharmaceuticals. However, information on the toxicity of methylparaben in soil ecosystems is limited. Furthermore, unlike other substances such as metals and pesticides, there is no regulation of levels or safe concentrations of methylparaben in soil ecosystems. Therefore, the aims of this study were to evaluate the toxicity of methylparaben on soil species and to derive hazardous concentration (HC) values with respect soil ecosystem protection. We conducted acute bioassays on eight species within six taxonomic groups and chronic bioassays on five species within four taxonomic groups. On the basis of the results obtained, we derived an acute HC5 value of 44 mg/kg soil and a corresponding chronic value of 27 mg/kg soil for methylparaben using species sensitivity distribution methodology following Australian and New Zealand guidelines. Given that there has been no proposed standard value for methylparaben in soil in any country, it was not possible to compare the HC values calculated in this study with regulation standard levels. Nevertheless, to our knowledge, this study is first to assess the toxicity of methylparaben against soil-inhabiting species and to estimate acute and chronic HCs for soil fauna and flora. The results of this study will provide valuable fundamental data for the establishment of acceptable levels of methylparaben in soil.

Ecological hazard assessment of methyl ethyl ketone using the species sensitivity distribution approach in a soil ecosystem.

Methyl ethyl ketone (MEK) is a common and widely used industrial solvent. However, few studies have investigated its toxicity, or its effects as a contaminant in soil ecosystems. In this study, acute and chronic toxicity data for MEK were generated, and ecological risk based on a species sensitivity distribution was assessed. Seven soil organisms from six taxonomic groups were used for acute toxicity tests and five soil organisms from four taxonomic groups were used for chronic toxicity tests. Acute and chronic soil HC5 (hazardous concentration for 5% of species) values for MEK were estimated as 53.04 and 2.593 mg MEK/kg dry soil, respectively. This is the first study to conduct battery testing for MEK; it specifies hazardous concentrations, warns of the need for accident preparedness, and points to serious potential hazards of MEK at various levels of the soil ecosystem which can translate into greater environmental damage with implications for human health. The specific sensitivity levels determined may serve as a benchmark for establishing soil standards and strategies for ecosystem protection in the face of accidental contamination.

Comparative study of the sensitivity of Daphnia galeata and Daphnia magna to heavy metals.

Daphnia galeata and Daphnia magna belong to the family Daphniidae. Daphnia galeata has a smaller body size and longer helmet than D. magna. Although D. galeata is widely distributed in the northern hemisphere, it is not as commonly used in aquatic ecotoxicity tests as D. magna. There have been only few ecotoxicological studies on the toxicity of heavy metals, organic matter, and nanomaterials in D. galeata. Thus, there is a need to discover new test species and expand the number of currently known test species to elucidate species sensitivity to aquatic pollutants. We carried out a comparative study on the sensitivity of D. magna (which represents the test water flea species) and D. galeata to heavy metal toxicity. The acute toxicity values (EC50 and LC50) of 11 heavy metal species, including silver (Ag+), arsenite (As3+), cadmium (Cd2+), chromate (Cr6+), cupric (Cu2+), ferrous (Fe2+), mercury (Hg2+), manganese (Mn2+), nickel (Ni2+), lead (Pb2+), and zinc (Zn2+), in D. galeata and D. magna were compared by conducting acute toxicity assays and comparing the data with the available data. The age of the tested Daphnia individuals and the type of exposure medium were considered for more reliable comparison of species sensitivity. We observed that D. galeata was more sensitive to Ag+, As3+, Cr6+, Fe2+, Ni2+, and Pb2+ than D. magna. The sensitivity to Cu2+, Cd2+, and Zn2+ was similar for D. magna and D. galeata. This study presents important aquatic toxicity and sensitivity data on D. galeata, which is not a widely used species in aquatic ecotoxicology studies. Our results recommend D. galeata as a suitable species for aquatic ecotoxicity tests because of its higher sensitivity.

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.