Microplastic ingestion in aquatic and soil biota: A comprehensive review of laboratory studies on edible size and intake pattern.

Microplastic contamination is ubiquitous and can be transferred through the food chain to humans. However, studies on microplastic size have mainly focused on large animals with a body length >20 mm. To address this gap, we conducted a comprehensive review of 169 laboratory studies to determine the edible size of microplastics for macrofauna and flora in aquatic and soil biota. Our findings indicate that microplastics with a size of <300 µm and 1 µm, respectively, are edible for these organisms, which are positioned at the base of the food chain. We also analyzed intake and depuration patterns and identified factors affecting microplastic ingestion. Our study fills an important knowledge gap by identifying the range of microplastic sizes that can enter the food chain and be transferred to humans. The study findings have strong implications for the ecological risk assessment of microplastics and suggest a starting point for mitigating this threat.

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.

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.

Assessing the risks of silver nanoparticle-concentrated matrix application in agricultural soil: Implications for plant and soil enzymes.

The practice of reusing biosolids may be an effective strategy for addressing nutrient reuse and soil shortages. However, the accumulation of silver nanoparticles (AgNPs) in biosolids poses a major ecological hazard to organisms. In this study, we evaluated the effects of AgNPs on plant and soil enzymes in terrestrial ecosystems by exposing soybean Glycine max, as well as soil, to varying concentrations of AgNPs embedded either on the surface soil layer or throughout the soil matrix. We found that exposing the plants to 20 mg AgNPs/kg soil that was embedded throughout the soil matrix had a significant impact. Conversely, soil enzymes (dehydrogenase, urease, and fluorescein diacetate hydrolase) were affected by exposure to 20 and 80 mg AgNPs/kg of soil embedded on the surface soil layer or throughout the soil matrix at 20 mg AgNPs/kg soil. The toxic effects of AgNPs were induced by different receptor habitats. The presence of AgNPs in soil led to developmental retardation, inhibited root growth, reduced photosynthetic activity, and decreased transpiration rates in leaves. These plants also produced fewer fruits compared to soybean plants grown in regular soil without AgNPs. Moreover, most of the AgNPs soil groups demonstrated a decrease in soil enzyme activity in the surface soil; therefore, soil-capping patterns involving embedded stressors should be considered. These findings provide valuable insights that will contribute substantially to advancements in the field of biosolids for land applications.

The potential of Euglena species as a bioindicator for soil ecotoxicity assessment.

Currently, there are no standard international test methods for assessing aquatic and soil toxicity, with aquatic toxicity tests based on limited Euglena species. Here, we proposed Euglena species as extended test species, especially as new soil test species for a paper-disc soil method, considering its ecologically important roles in providing highly bioavailable in-vivo nutrients to upper trophic level organisms. We conducted experiments to identify the optimal exposure duration for two Euglena species (Euglena viridis and Euglena geniculata). We demonstrated the toxic effects of nickel (model contaminant) on their photosynthetic parameters and growth in freshwater. The growth and photosynthetic activity of three Euglena species were significantly inhibited in nickel-contaminated soil during paper-disc soil tests, especially the test species adsorbed onto paper-disc soil. Euglena gracilis was more sensitive to nickel than E. viridis and E. geniculata in freshwater and soil. Thus, E. viridis and E. geniculata have potential as additional test species for improving test species diversity, while all three species have potential as new soil test species for soil toxicity assessment. Thus, results these species may be suitable for routine aquatic toxicity testing and new soil toxicity testing, addressing the current paucity of test species in freshwater and soil toxicity assessment.

Understanding hazardous concentrations of microplastics in fresh water using non-traditional toxicity data.

Microplastic pollution has become a major environmental problem, indicating the need to implement quantitative governance standards in combination with reducing or banning single-use plastic. Previous studies have predicted no-effect concentrations for limited microplastic-based toxicity data but have not considered environmentally relevant sizes, shapes, or polymers. To provide high quantity and quality data for microplastics of different sizes, shapes, or polymer compositions, non-traditional and traditional toxicity data may need to be considered in combination. In this study, we reviewed toxicity data for microplastics in freshwaters from 2018 to 2022 and analyzed the toxicity data using traditional and non-traditional methods. Based on 166 chronic traditional toxicity data points, the hazard concentration (HC) values calculated from non-traditional toxicity endpoints or all toxicity endpoints were lower than those calculated from traditional toxicity endpoints. Based on 398 chronic traditional plus non-traditional toxicity data points, the HC values calculated from traditional plus non-traditional values were higher than those calculated from traditional toxicity values. With these results, we developed a new framework for deriving microplastic-specific hazardous concentrations, one that especially considers non-traditional toxicity endpoints and values for microplastics. Overall, this study offers a basis for future management strategies and associated frameworks for mitigating microplastic toxicity.

Soil algae as a potential carrier for nanoplastics: Adsorption and internalization of nanoplastics in algal cells.

Although plastics are widely distributed in soil environments, few studies have assessed their effects on different test species. In this study, the responses (adsorption or internalization) of two green algal species (Chlorococcum infusionum and Chlamydomonas reinhardtii) to nanoplastics in soil were evaluated via microscopic analysis for nine weeks; additionally, the effects of polystyrene (PS) nanoplastics on their photosynthetic activity and growth were assessed. The results showed that PS nanoplastics and C. infusionum or C. reinhardtii cells were aggregated with the formation of palmelloid colonies; additionally, internalization of PS nanoplastics to C. reinhardtii cells was verified. However, no significant effects of PS nanoplastics on photosynthetic activity and growth of soil algae were observed. Algae were more likely to be threatened by plastic aggregation in the soil environment than in the aquatic environment due to the formation of a mucilaginous sheath on their cell. Our results highlighted that soil algae are a potential carrier of nanoplastics to other organisms in the food chain due to plastic aggregation through adsorption or internalization. This study will enhance our understanding of nanoplastic distribution in soil algae.

Validation of the paper-disc soil method using soil alga Chlorococcum infusionum to quantitatively determine the toxicity of heavy metals.

The paper-disc soil method is a soil algal bioassay used to assess soil water transfer in polluted soils. Although this ecotoxicological method was first established in 2016 to assess soil pollution, quantitative toxicity assessments of Cu- or Ni-treated soil and in situ or ex situ soils polluted with other heavy metals (HMs) have not been widely conducted. In this study, the paper-disc soil method was validated under different test conditions. The validated paper-disc soil method was used to quantitatively investigate the toxicity of four HMs (As, Cd, Cr, and Zn). Based on the results, the test species, initial inoculation concentration in the algal-dispersed solution, water content, light intensity, and exposure duration were proposed as Chlorococcum infusionum, 3 × 106 cells/mL in Bold's basal medium, 80% water-holding capacity, 4000 ± 500 lx, and 6 days, respectively. The toxicity of HMs was quantified using the validated paper-disc soil method, and the half-maximal effective concentration values for biomass were calculated as 22.49 (21.26-23.78) mg Cr/kg dry weight (dw) soil, 42.72 (38.64-47.24) mg Cd/kg dw soil, 57.79 (55.46-60.21) mg As/kg dw soil, and 183.06 (175.38-191.06) mg Zn/kg dw soil. The paper-disc soil method using the soil alga C. infusionum was validated by quantitatively evaluating the test conditions and toxicity of HMs. Our results provide important quantitative toxicity data for soil algae exposed to HMs and a basis for standardizing the paper-disc soil method using soil algae.

Towards understanding the impact of plastics on freshwater and marine microalgae: A review of the mechanisms and toxicity endpoints.

Plastics are ubiquitous and persistent in aquatic environments, threatening environmental and human health. This review focused on the effects of plastics (single toxicity) and associated chemicals (combined or leachate toxicities) on freshwater and marine microalgae. Forty-seven publications from 2010 to 2020 were used in this review. Based on their topic of focus, we classified the publications among the following categories: single plastic toxicity, combined toxicity of plastics and other chemicals, and toxicity of leachates released from plastics. The test species Chlorophyta and Ochrophyta were generally used to assess the impacts of plastics on aquatic microalgae. This study identified the inhibition of algal growth and photosynthesis due to single toxicity through the physical adsorption of plastics, showing that leachates released from plastics contained non-specific chemicals which could potentially affect microalgae. Production of malondialdehyde or reactive oxygen species presented significant effects on algae independent of the experimental conditions. This review could improve our understanding of the effects of plastic pollution on microalgae in freshwater and marine environments. It has implications for further research in this field and associated water management in light of the global ubiquity of plastic pollution.

Perspectives on microalgae as model organisms toward the standardization of soil algal toxicity test methods.

When considering test species for soil ecotoxicity, the development of new model organisms is often suggested to increase the reliability of ecological risk assessments. Ubiquitous soil algae could offer potential test species for assessing various soil pollution levels. Currently, there are few reviews offering comprehensive perspectives on stressors-based toxicological studies using microalgae in soil media, with the majority of scholarly attention paid to the toxicological effects of freshwater algae or marine algae in aquatic ecosystems. In this review, we focus on current toxicological studies of microalgae assessed in soil-related media and suggest considerations for using microalgae in soil toxicity tests based on 22 publications (1998-2021). In addition, we analyzed characteristics of soil algae based on criteria for selecting test species and suggest that future research should be directed toward the standardization of soil algal toxicity test methods. This review discusses a promising method using soil algae as new test species for soil toxicity assessment as cost-effective and environmentally sound soil quality bioindicators. The review also addresses the lack of understanding behind how soil algae can serve as important test species for soil ecotoxicity.

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.

Potential environmental risk of solar cells: Current knowledge and future challenges.

Photovoltaic (PV) technology such as solar cells and devices convert solar energy directly into electricity. Compared to fossil fuels, solar energy is considered a key form of renewable energy in terms of reducing energy-related greenhouse gas emissions and mitigating climate change. To date, the development and improvement of PV technologies has received substantial attention; however, their potential environmental risks remain unknown. Therefore, this review focuses on the potential risks of leachates derived from solar cell devices. We collect scientific literature on toxicity and leaching potential, tabulate the existing data, and discuss related challenges. Insufficient toxicity and environmental risk information currently exists. However, it is known that lead (PbI2), tin (SnI2), cadmium, silicon, and copper, which are major ingredients in solar cells, are harmful to the ecosystem and human health if discharged from broken products in landfills or after environmental disasters. Several research directions and policy initiatives for minimizing the environmental risks of PV technology are suggested. This review contributes to both solar energy and environmental science research.

Quantitative assessment of photosynthetic activity of Chlorella (Class Trebouxiophyceae) adsorbed onto soil by using fluorescence imaging.

In the present study, we evaluate our previously developed non-destructive soil algal toxicity method using species from a different class of algae; Class Trebouxiophyceae (Chlorella vulgaris and Chlorella sorokiniana), and directly measure the photosynthetic activity of these species adsorbed onto the soil as a new toxicity endpoint. This study shows that non-destructive soil algal toxicity method is applicable to non-specific test species, including those of Class Trebouxiophyceae as well as Class Chlorophyceae (Chlorococcum infusionum and Chlamydomonas reinhardtii). Furthermore, by performing photosynthesis image analysis, we verify that it is possible to measure the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soils without the need to extract algal cells from the soil. We propose that the non-destructive soil algal toxicity method represents a novel technique for 1) evaluating pollutants in soil using non-specific algae and 2) conveniently and rapidly assessing the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soil as a new toxicity endpoint.

Comparative study of feminine hygiene product regulations in Korea, the European Union, and the United States.

Recently, Korean consumers have experienced public health issues as a result of problematic feminine hygiene products. Consumers and local civic groups have urged manufacturers and the Korean government to provide clear information based on comprehensive studies and strengthen related policies. In this study, we collected and compiled information on the relevant regulations and organizations in Korea, the European Union, and the United States to compare the management systems and legal status of feminine hygiene products around the world. We confirmed that the definition of feminine hygiene products is similar for Korea, the EU, and the US; however, they are categorized as quasi-drugs in Korea, general products in the EU, and medical devices in US according to various regulations. Although we cannot completely prevent human exposure to chemicals in modern society, it is vital to establish a management system for the safe use and production of feminine hygiene products in a scientifically and legally sound manner. This research can contribute to the regulatory toxicology and risk assessment fields of feminine hygiene product research.

Soil algae pipe assay: ex situ method for the evaluation of soil quality based on soil algae and its application to the pot test.

We aimed to develop an ex situ method for evaluating soil quality using soil algae. The soil algae pipe assay involves application and sampling of algae and flow cytometry. As it can be performed in a greenhouse, the assay was effective for pot tests and conducive for soil quality assessment. This novel assay will enable broader toxicity testing.

Changes in soil properties after remediation influence the performance and survival of soil algae and earthworm.

Previous research on soil remediation focused on soil properties and not on its effects on soil ecosystems. The present study investigated the adverse effects of soil physicochemical changes due to remediation on the biological indicators Chlorococcum infusionum and Chlamydomonas reinhardtii (algae) and Eisenia andrei (earthworm). Soil physicochemical properties, concentrations of total, bioavailable, and water-soluble heavy metals in soil were measured before and after remediation. Changes in soil pH, electrical conductivity, total nitrogen, and total phosphorous immediately after soil remediation were the primary causes of the biomass and photosynthetic activity inhibition observed in C. infusionum and C. reinhardtii, and the survival, normality, and burrowing behavior decrease observed in E. andrei in remediated soils showing dramatic changes in those properties. These findings suggest that remediated soils need some time to recover before restoring their functions, although heavy metals are no longer contaminating the soil.

Size- and shape-dependent toxicity of silver nanomaterials in green alga Chlorococcum infusionum.

Silver nanomaterials (AgNMs) of different shapes and sizes are potentially toxic to aquatic organisms. However, studies on the toxicity of AgNMs and on their shape-dependent effects on algae are scarce. The present study evaluated the effects of three AgNMs (silver nanospheres, AgNPs; silver nanowires, AgNWs; silver nanoplates, AgPLs) with different shapes coated with polyvinylpyrrolidone on the growth and photosynthetic performance of an alga, Chlorococcum infusionum. We used growth measurements and determined the photosynthetic parameters based on chlorophyll fluorescence transients in the algal cells exposed to different concentrations of the three AgNMs. The effective concentrations at 50% (EC50) of AgNPs, AgNWs, and AgPLs were calculated to be 0.1, 0.045, and 0.021 mg/L, respectively. The results showed that the toxicity of AgNMs in C. infusionum was in the order, AgPLs (40 nm diameter) > AgNWs (21,000 nm length × 42 nm diameter) > AgNPs (57 nm diameter), based on the decrease in growth and three photosynthetic activities. We propose that the toxic potential of AgNMs is primarily dependent on their diameter and secondarily on their shape. Overall, this study provides, for the first time, a comparison of the growth and photosynthetic activities of C. infusionum exposed to AgNMs of three different shapes.

Assessing applicability of the paper-disc method used in combination with flow cytometry to evaluate algal toxicity.

Soil algal bioassays have been limited by their inability to evaluate several toxic endpoints because it is difficult to collect pure soil algae growing on and beneath the soil surface. This study describes the extension of a previously developed paper-disc method for analyzing soil toxicity to algae. The method can be used in conjunction with flow cytometric analysis and facilitates the assessment of previously proposed toxicity endpoints, such as the growth zone, biomass, and photosynthetic activity. We assessed the applicability of this paper-disc soil method using the green algae Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata exposed to nickel-contaminated soil; examined cell sizes, cell granularity, enzyme activity, and oxidative stress as new toxicity endpoints using flow cytometry; and identified morphological changes in green algae assayed. The results showed that, used in conjunction with flow cytometry, the extended paper-disc soil method is sufficiently sensitive to detect decreases in cell granularity in C. reinhardtii and esterase activity in P. subcapitata. The method also revealed decreases in growth zone, biomass, and electron transfer from the reaction center to the quinone pool. Collectively, the results of this study indicate that soil algal bioassays using nonspecific algae can be used to assess soil quality, to derive several toxicity endpoints for individual cells, and to evaluate previously established flow cytometric toxicity endpoints.

Quantification of silver nanoparticle toxicity to algae in soil via photosynthetic and flow-cytometric analyses.

Soil algae, which have received attention for their use in a novel bioassay to evaluate soil toxicity, expand the range of terrestrial test species. However, there is no information regarding the toxicity of nanomaterials to soil algae. Thus, we evaluated the effects of silver nanoparticles (0-50 mg AgNPs/kg dry weight soil) on the soil alga Chlamydomonas reinhardtii after six days, and assessed changes in biomass, photosynthetic activity, cellular morphology, membrane permeability, esterase activity, and oxidative stress. The parameters measured were markedly affected by AgNP-induced stress at 50 mg AgNPs/kg dry weight soil, where soil algal biomass, three measures of photosynthetic activity (area, reaction center per absorption flux, and reaction center per trapped energy flux), and esterase activity decreased. AgNPs also induced increases in both cell size and membrane permeability at 50 mg AgNPs/kg dry weight soil. In addition to the increase in cell size observed via microscopy, a mucilaginous sheath formed as a protective barrier against AgNPs. Thus, the toxicity of AgNPs can be effectively quantified based on the physiological, biochemical, and morphological responses of soil algae, where quantifying the level of toxicity of AgNPs to soil algae could prove to be a useful method in terrestrial ecotoxicology.

Water quality standards for the protection of human health and aquatic ecosystems in Korea: current state and future perspective.

Since the Korean Ministry of the Environment established the Master Plan for Water Environment (2006-2015), the need to revise the water quality standards (WQSs) has driven government projects to expand the standards for the protection of human health and aquatic ecosystems. This study aimed to provide an historical overview of how these WQSs were established, amended, and expanded over the past 10 years in Korea. Here, major projects related to national monitoring in rivers and the amendment of WQSs were intensely reviewed, including projects on the categorization of hazardous chemicals potentially discharged into surface water, the chemical ranking and scoring methodology for surface water (CRAFT, Chemical RAnking of surFace water polluTants), whole effluent toxicity (WET) management systems, the 4th, 5th, and 6th revisions of the water quality standards for the protection of human health, and efforts toward developing the 7th revision. In this review, we assimilated the past and current status as well as future perspectives of Korean surface WQSs. This research provides information that aids our understanding of how surface WQSs have been expanded, and how scientific approaches to ensure water quality have been applied at each step of the process in Korea.