Purified Pyropia yezoensis Pigment Extract-Based Tandem Dye Synthesis.

Red phycoerythrin (R-PE) is a highly valuable protein found in an edible seaweed, Pyropia yezoensis. It is used extensively in biotechnological applications due to its strong fluorescence and stability in diverse environments. However, the current methods for extracting and purifying R-PE are costly and unsustainable. The aim of the present study was to enhance the financial viability of the process by improving the extraction and purification of R-PE from dried P. yezoensis and to further enhance R-PE value by incorporating it into a tandem dye for molecular biology applications. A combination of ultrafiltration, ion exchange chromatography, and gel filtration yielded concentrated (1 mg·mL-1) R-PE at 99% purity. Using purified PE and Cyanine5 (Cy5), an organic tandem dye, phycoerythrin-Cy5 (PE-Cy5), was subsequently established. In comparison to a commercially available tandem dye, PE-Cy5 exhibited 202.3% stronger fluorescence, rendering it suitable for imaging and analyzes that require high sensitivity, enhanced signal-to-noise ratio, broad dynamic range, or shorter exposure times to minimize potential damage to samples. The techno-economic analysis confirmed the financial feasibility of the innovative technique for the extraction and purification of R-PE and PE-Cy5 production.

Interactive Effects of Blue Light and Water Turbulence on the Growth of the Green Macroalga Ulva australis (Chlorophyta).

Macroalgal growth and yield are key to sustainable aquaculture. Although light and water turbulence are two important factors that affect algal productivity, research on their interaction is limited. Therefore, in this study, we investigated the effects of different wavelengths of light and the presence or absence of water turbulence on the growth of the green macroalga Ulva australis. Water turbulence was found to enhance the growth of U. australis irrespective of photosynthetic performance, but only in blue light cultures. The quantum dose of blue light required to induce 50% growth promotion was 1.02 mol m-2, which is comparable to the reported values for cryptochrome-mediated effects in other macroalgae. The combined effect of blue light and water turbulence led to the accumulation of photosynthesis-related proteins that support plastid differentiation and facilitate efficient photosynthesis and growth. Our findings thus highlight the potential of harnessing blue light and water turbulence to maximise macroalgal cultivation for sustainable and profitable algal aquaculture.

Assessing industrial wastewater effluent toxicity using boosting algorithms in machine learning: A case study on ecotoxicity prediction and control strategy development.

Trace heavy metals have a tendency to persist in the effluent of industrial wastewater treatment facilities, leading to toxic effects on downstream water bodies. Traditional assessment methods relied on animal testing, but ethical concerns have rendered them unacceptable. An alternative solution is to evaluate wastewater toxicity using trophic-level aquatic organisms as bioassays. However, these bioassay methods involve costly and time-consuming chemical and biological analytical experiments. In this study, an artificial intelligence-powered water quality assessment (AiWA) approach is proposed for predicting industrial effluent ecotoxicity to further enhance the quick and cost-effective ecotoxicity assessment process. Initially, 99 samples were collected from industrial wastewater treatment plants representing 21 different industries in the Republic of Korea. Fourteen parameters were measured, encompassing both physicochemical and ecotoxicological aspects. Boosting algorithms, especially extreme gradient boosting (XGBoost) and adaptive boosting (AdaBoost), were employed for model development. XGBoost outperformed AdaBoost in terms of model performance. Feature selection analysis revealed that conductivity, copper, lead, selenium, pH, and zinc concentrations were the most suitable inputs for training the boosting model. The innovated XGBoost-based AiWA model demonstrated significantly higher performance (i.e., up to 80%) compared to conventional models with an R2 value of exceeding 0.94 and root mean square error of 3.5 toxicity unit for predicting the integrated toxicity unit (ITU). Additionally, pH and conductivity emerged as crucial indicators for reflecting ecotoxicity levels. Specially, this case study indicated that non-toxic/directly dischargeable levels (TU ≤ 1) were achieved when the pH ranged from 6.8 to 8.4 and the conductivity remained below 1651 µS/cm. These findings are expected to facilitate rapid and cost-effective detection of heavy metal ecotoxicity in industrial wastewater effluents, aiding decision-making in wastewater management.

Giant Duckweed (Spirodela polyrhiza) Root Growth as a Simple and Sensitive Indicator of Copper and Chromium Contamination.

Aquatic environment are often contaminated with heavy metals from various industrial sources. However, physicochemical techniques for pollutant detection are limited, thus prompting the need for additional bioassays. We investigated the use of greater duckweed (Spirodela polyrhiza) as a bioindicator of metal pollution. We exposed S. polyrhiza to four pollutants (namely, silver, cadmium, copper, and chromium) and assessed metal toxicity by measuring its frond area and the length of its regrown roots. The plant displayed significant differences in both frond size and root growth in response to the four metals. Silver was the most toxic (EC50 = 23 µg L-1) while copper the least (EC50 = 365-607 µg L-1). Direct comparisons of metal sensitivity and the reliability of the two endpoint assays showed that root growth was more sensitive (lower in terms of 50% effective concentration) to chromium, cadmium, and copper, and was more reliable (lower in terms of coefficient of variation) than those for frond area. Compared to conventional Lemna-based tests, the S. polyrhiza test is easier to perform (requiring only one 24-well plate, 3 mL of medium and a 72-h exposure). Moreover, it does not require livestock cultivation/maintenance, making it more suitable for repeated measurements. Measurements of S. polyrhiza root length may be suitable for assessment when copper and chromium in municipal and industrial wastewater exceed the environmentally permissible levels.

Metal Toxicity across Different Thallus Sections of the Green Macroalga, Ulva australis.

We aimed to identify functional differences between different sections of the thallus of Ulva australis and develop tissue-endpoint combinations to assess the toxicity of six metals (i.e., Ag, As, Cd, Cr, Cu, and Ni). EC50 values for these metals in three sections of the thallus of Ulva were obtained for multiple endpoints: relative growth rate (RGR), chlorophyll a fluorescence, pigment contents, and the expression of the photosynthesis-related gene, rbcL. The responses of the endpoints varied across the respective thallus sections; overall, the most toxic metals were Ag and Cu. These endpoints were the best for evaluating metal toxicity: ETRmax of the middle thallus sections for Ag toxicity; RGR of the middle thallus section for As and Cd; ETRmax of the marginal thallus section for Cr; Chl b contents of the marginal thallus section for Cu; RGR of the basal thallus section for Ni. The EC50 values for the inhibition of ETRmax in middle (0.06 mg∙L-1) and Chl b in the marginal thallus sections (0.06 mg∙L-1) were all lower than those of the quality standard for wastewater discharge values of Ag and Cu in Republic of Korea and the US, pointing to the suitability of U. australis-based endpoints for risk assessment.

Qualitative and quantitative assessment of diatom deformities and protoplasmic condition under metal and metalloid stress.

Metals and metalloids are toxic, persistent, and non-biodegradable and can be biomagnified (e.g., Hg), and therefore pose a serious threat to the algal flora of aquatic ecosystems. This laboratory study tested the effects of metals (Zn, Fe, and Hg) and a metalloid (As) on the cell wall morphology and protoplasmic content of living cells of six widespread diatom genera over 28 days. Diatoms exposed to Zn and Fe had a higher frequency of deformed diatom frustules (> 1%) compared to the As, Hg, and control treatments (< 1%). Deformities in the valve outline and striae were found in all treatments, including the control, whereas deformed raphes and more than one type of deformity were more prevalent under Zn and Hg stress. The order of toxicity is as follows: Zn > Fe > Hg≈As. Deformities were more frequent in Achnanthes and Diploneis (adnate forms) than in the motile genera of Nitzschia and Navicula. The correlation between the % healthy diatoms and % deformities in all six genera showed a negative relationship with the integrity of protoplasmic content (i.e., greater alteration in protoplasmic content was associated with greater frustule deformation). We conclude that diatom deformities can be a good indicator of metal and metalloid stress in waterbodies and are very useful in the rapid biomonitoring of aquatic ecosystems.

Evaluating ecotoxicological assays for comprehensive risk assessment of toxic metals present in industrial wastewaters in the Republic of Korea.

Toxicity tests represent a rapid, user-friendly and cost-effective means to assess the impact of wastewater quality on aquatic ecosystems. There are not many cases where wastewater management standards are set based on various bio-based ecotoxicity values. Here, we tested a novel multitaxon approach to compare standard water quality indices to toxicity metrics obtained from ecotoxicity tests, conducted using aquatic organisms representing several trophic levels (Aliivibrio, Ulva, Daphnia, and Lemna), for 99 industrial wastewater samples from South Korea. For five wastewater samples, the concentrations of Se, Zn, or Ni exceeded the permissible limits (1, 5, and 3 mg L-1, respectively). All the four physiochemical water quality indices tested were positively correlated with Se and Pb concentrations. The toxicity unit (TU) scores indicated a declining sensitivity to pollutants, in the order Lemna (2.87) >Daphnia (2.24) >Aliivibrio (1.78) >Ulva (1.42). Significant correlations were observed between (1) Cd and Ni, and Aliivibrio, (2) Cu and Daphnia, (3) Cd, Cu, Zn, and Cr and Lemna, and (4) Cu, Zn, and Ni and Ulva. Daphnia-Lemna and Lemna-Ulva were found to be good indicators of ecologically harmful Se and Ni contents in wastewater, respectively. We suggest that regulatory thresholds based on these bioassays should be set at TU = 1 for all the species or at TU = 1 for Aliivibrio and Ulva and TU = 2 for Daphnia and Lemna, if the number of companies whose wastewater discharge exceeds the allowable TU levels is <1 % or 5 % of the total number of industries, respectively. Taken together, these findings could help in establishing a rapid, ecologically relevant wastewater quality assessment system that would be useful for developing strategies to protect aquatic ecosystems.

A Ten-Minute Bioassay to Test Metal Toxicity with the Freshwater Flagellate Euglena agilis.

A chemical analysis of water quality cannot detect some toxicants due to time constraints, high costs, and limited interactions for detection. Bioassays would offer a complementary means to assess pollution levels in water. Euglena is a flagellate green alga and an excellent system for toxicity testing thanks to its ease of culture, rapid growth, and quick response to environmental stresses. Herein, we examined the sensitivity of E. agilis to seven heavy metals by analyzing six end-point parameters: motility, velocity, cell compactness, upward swimming, r-value, and alignment. Notably, the velocity of E. agilis was most sensitive to cadmium (96.28 mg·L-1), copper (6.51 mg·L-1), manganese (103.28 mg·L-1), lead (78.04 mg·L-1), and zinc (101.90 mg·L-1), while r-values were most sensitive to arsenic (12.84 mg·L-1) and mercury (4.26 mg·L-1). In this study, velocity and r-values are presented as useful biomarkers for the assessment of metal toxicity in Euglena. The metals As, Cd, Cu, and Pb were suitable for this test. The advantages of the ecotoxicity test are its rapidity: It takes 10 min to obtain results, as opposed to the typical 3-4 d of exposure time with intensive labor. Moreover, this test can be performed at room temperature under dark conditions.

Commercial Potential of the Cyanobacterium Arthrospira maxima: Physiological and Biochemical Traits and the Purification of Phycocyanin.

Arthrospira maxima is a natural source of fine chemicals for multiple biotechnological applications. We determined the optimal environmental conditions for A. maxima by measuring its relative growth rate (RGR), pigment yield, and photosynthetic performance under different pH and temperature conditions. RGR was highest at pH 7-9 and 30 °C. Chlorophyll a, phycocyanin, maximal quantum yield (Fv/Fm), relative maximal electron transport rate (rETRmax), and effective quantum yield (ΦPSII) were highest at pH 7-8 and 25 °C. Interestingly, phycoerythrin and allophycocyanin content was highest at 15 °C, which may be the lowest optimum temperature reported for phycobiliprotein production in the Arthrospira species. A threestep purification of phycocyanin (PC) by ultrafiltration, ion-exchange chromatography, and gel filtration resulted in a 97.6% purity of PC.

Assessment of Various Toxicity Endpoints in Duckweed (Lemna minor) at the Physiological, Biochemical, and Molecular Levels as a Measure of Diuron Stress.

The common, broad-spectrum herbicide diuron poses some risks to the environment due to its long persistence and high toxicity. Therefore, the effective monitoring of diuron residues will inform efforts to assess its impacts on ecosystems. In this study, we evaluated the toxicity targets of diuron in the model aquatic macrophyte Lemna minor at the physiological (growth and photosynthetic efficiency), biochemical (pigment biosynthesis and reactive oxygen species (ROS) levels), and molecular (rbcL transcript) levels. The toxicity of diuron was detectable after 48 h of exposure and the order of sensitivity of toxicity endpoints was gene transcription > maximum electron transport rate (ETRmax) > non-photochemical quenching (NPQ) > maximum quantum yield (Fv/Fm) > ROS > fresh weight > chlorophyll b > chlorophyll a > total frond area > carotenoids. Under diuron stress, pigment, ROS, and gene transcript levels increased while frond area, fresh weight, and photosynthesis (Fv/Fm and ETRmax) gradually decreased with the increasing duration of exposure. Notably, ROS levels, Fv/Fm, frond area, and fresh weight were highly correlated with diuron concentration. The growth endpoints (frond area and fresh weight) showed a strong negative correlation with ROS levels and a positive correlation with Fv/Fm and ETRmax. These findings shed light on the relative sensitivity of different endpoints for the assessment of diuron toxicity.

Solution-Based One-Step Preparation of Three-Dimensional Self-Assembled Octadecyl Silica Nanosquare Plate and Microlamella Structures for Superhydrophobic and Icephobic Surfaces.

Icephobic surfaces have gained immense attention owing to their significant roles in decreasing the energy consumption of refrigerators and in improving safety issues by preventing the formation of ice on them. Superhydrophobic surfaces incorporating micro- or nanoscale roughness and hydrophobic functional groups have been shown to prevent ice accumulation. Herein, we report a simple, low-cost, and solution-based one-step process for the production of superhydrophobic surfaces with three-dimensional (3D) self-assembled structures. The controlled hydrolysis and polycondensation of n-octadecyltrichlorosilane (OTS-Cl) in an acetone solution produced a highly uniform superhydrophobic surface on various substrates such as glass, metals, and polymers without the limitation of the surface curvature structure. The as-prepared 3D self-assembled surface exhibited a very high contact angle of 161.7° and a low contact hysteresis of 1.47°. The solvent type, H2O content in acetone, and carbon chain length of the silane compound were critical in the formation of self-assembled nanostructures. The thickness of the superhydrophobic 3D self-assembled structure could be varied by controlling the surface properties of the glass substrate. In addition, a novel octadecyl silica nanosquare plate structure was formed as an intermediate for the microlamella structure. The water drop impact experiments on the 3D self-assembled superhydrophobic glass substrates at low temperatures (T < -25 °C) showed that the as-prepared superhydrophobic glass possessed a high impalement threshold for water contact, resulting in excellent and stable icephobic properties. The preparation method proposed in this study is scalable and can be used on a flat glass surface or in a glass vial inside a glass tube. Moreover, it can be applied to various substrates such as metals and polyurethane surfaces with curvature. Therefore, the solution-based self-assembly method proposed in this study is a promising approach to produce superhydrophobic and icephobic surfaces on a wide range of substrates regardless of their structure and properties.

Interlaboratory Validation of Toxicity Testing Using the Duckweed Lemna minor Root-Regrowth Test.

The common duckweed (Lemna minor), a freshwater monocot that floats on the surfaces of slow-moving streams and ponds, is commonly used in toxicity testing. The novel Lemna root- regrowth test is a toxicity test performed in replicate test vessels (24-well plates), each containing 3 mL test solution and a 2-3 frond colony. Prior to exposure, roots are excised from the plant, and newly developed roots are measured after 3 days of regrowth. Compared to the three internationally standardized methods, this bioassay is faster (72 h), simpler, more convenient (requiring only a 3-mL) and cheaper. The sensitivity of root regrowth to 3,5-dichlorophenol was statistically the same as using the conventional ISO test method. The results of interlaboratory comparison tests conducted by 10 international institutes showed 21.3% repeatability and 27.2% reproducibility for CuSO4 and 21.28% repeatability and 18.6% reproducibility for wastewater. These validity criteria are well within the generally accepted levels of <30% to 40%, confirming that this test method is acceptable as a standardized biological test and can be used as a regulatory tool. The Lemna root regrowth test complements the lengthier conventional protocols and is suitable for rapid screening of wastewater and priority substances spikes in natural waters.

Diatoms as indicators of environmental health on Korean islands.

Diatoms are highly sensitive to perturbations in their environment and are thus useful as bioindicators for anthropogenic impacts such as pollution. However, there is no consensus about what aspects of diatom populations to measure (e.g., diversity, physiology, or morphology) and efficient and reliable survey protocols are lacking. Here, we evaluated the ecological status of diatom communities using both traditional and relatively novel methods on two islands (Deokjeok island and Daeijak island) affected by anthropogenic activities due to extensive agricultural practices and exploitation and that are under consideration for representative touristic sites in South Korea. Dissolved concentrations of metals and metalloid (As, Cu, Cr, Cd, Ni, Hg, Pb, and Zn) were below the ecological screening and toxicity reference values in water fractions but were above these values for sediment, particularly at one island, Deokjeok. The tested methods were generally consistent in finding little evidence for disruption of diatom communities, with dominance by Navicula and Gyrosigma, relatively high diversity, and typical abundance of lipid bodies and morphological deformities. However, analysis of lipid bodies and morphological deformities suggested greater potential anthropogenic disturbance at one site in Deokjeok. Future planning is required to ensure the maintenance of the near-pristine environments present on these islands.

Assessment of five live-cell characteristics in periphytic diatoms as a measure of copper stress.

Metal pollution of fluvial systems remains a major problem and biomonitoring can be a useful tool for assessing the metal contamination. To assess their potential as new bioindicators of copper stress, we treated a field-collected live periphytic diatom community (dominated by Amphora, Navicula, and Nitzschia) with dissolved Cu under optimal growth conditions. We studied the effects of Cu on five live-cell attributes: motility, protoplasmic content, lipid body number and biovolume, and frustule morphology. In all three genera, motility and protoplasmic content decreased, whereas the LB number, biovolume and deformity increased when Cu and exposure time increased. The sensitivity to Cu was highest for % MF, % CPC and % BCLB in Navicula and the LB number and deformity in Nitzschia. Amphora appeared to be more tolerant to Cu in comparison with other genera. The five cell attributes were inter-related. A heatmap showed that a recommended indicator for rapid screening of Cu toxicity was % BCLB for Amphora and % MF for Navicula and Nitzschia. % MF might be the most common representative indicator that can be applied to all three genera to evaluate the lethal effects of Cu stress if only one of the five cell attributes must be selected.

Rapid toxicity assessment of six antifouling booster biocides using a microplate-based chlorophyll fluorescence in Undaria pinnatifida gametophytes.

Biocides of antifouling agents can cause problems in marine ecosystems by damaging to non-target algal species. Aquatic bioassays are important means of assessing the quality of water containing mixtures of contaminants and of providing a safety standard for water management in an ecological context. In this study, a rapid, sensitive and inexpensive test method was developed using free-living male and female gametophytes of the brown macroalga Undaria pinnatifida. A conventional fluorometer was employed to evaluate the acute (48 h) toxic effects of six antifouling biocides: 4,5-Dichloro-2-octyl-isothiazolone (DCOIT), diuron, irgarol, medetomidine, tolylfluanid, zinc pyrithione (ZnPT). The decreasing toxicity in male and female gametophytes as estimated by EC50 (effective concentration at which 50% inhibition occurs) values was: diuron (0.037 and 0.128 mg l-1, respectively) > irgarol (0.096 and 0.172 mg l-1, respectively) > tolylfluanid (0.238 and 1.028 mg l-1, respectively) > DCOIT (1.015 and 0.890 mg l-1, respectively) > medetomidine (12.032 and 12.763 mg l-1, respectively). For ZnPT, 50% fluorescence inhibition of U. pinnatifida gametophytes occurred at concentrations above 0.4 mg l-1. The Undaria method is rapid, simple, practical, and cost-effective for the detection of photosynthesis-inhibiting biocides, thus making a useful tool for testing the toxicity of antifouling agents in marine environments.

Application of a programmed semi-automated Ulva pertusa bioassay for testing single toxicants and stream water quality.

A toxicity test based on inhibition of reproduction in the green macroalga Ulva pertusa involves quantifying the change in thallus color as reproduction progresses. However, interpretation of this color change is reliant on the skill level of the examiner. This study aimed to validate a new toxicity test based on inhibition of reproduction in the green macroalga U. pertusa using a vital stain and programmed semi-automated analysis (using Image J) of the change in thallus color. The toxicity rank by inverse EC50 values was: irgarol (0.048 mg L-1) > Ag (0.132 mg L-1) > As (0.172 mg L-1) > simazine (0.378 mg L-1) > formaldehyde (0.442 mg L-1) > DCOIT (0.783 mg L-1) > ZnPT (3.556 mg L-1) > medetomidine (11.600 mg L-1) > phenol (29.316 mg L-1) > methanol (2,736 mg L-1) > ethanol (3,306 mg L-1). The sensitivity of the U. pertusa test to stream waters was similar to or lower than those of the commonly-used Lemna minor and Daphnia magna bioassays. The U. pertusa bioassay is sensitive to, and suitable for, testing various toxicants including metals, volatile organic compounds, herbicide, antifouling agents and phenol and can also be applied to testing freshwater quality after salinity adjustment.

Reappraisal of the toxicity test method using the green alga Ulva pertusa Kjellman (Chlorophyta).

This study was aimed to develop an objective way of quantifying the reproductive status of the green macroalga, Ulva pertusa using a vital stain and programmed automated analysis (by Image J program). The EC50 values (with 95% CI), the concentrations of toxicants inducing a reduction of 50% in sporulation after 96 h exposure, from the newly developed method were similar to those obtained by the conventional method: 0.651 (0.598-0.705) mg l-1 for Cd, 0.144 (0.110-0.162) mg l-1 for Cu, 0.180 (0.165-0.195) mg l-1 for atrazine, 0.076 (0.049-0.094) mg l-1 for diuron and 30.6 (26.5-34.4) ml l-1 for DMSO, respectively. When the EC50 values from this study were compared to that those from literatures, the sensitivity for some toxicants was similar or higher than that of U. fasciata (1.930 mg l-1 for germination for Cd), U. armoricana (0.250 mg l-1 for Fv/Fm for Cu), U. reticulata (0.126-1.585 mg l-1 for growth for Cu), and U. intestinalis (0.650 mg l-1 for Fv/Fm for atrazine). The subjective views of the experimental performers can be eliminated using the newly developed method. The Ulva method gave consistent responses to Cu and Cd of internationally allowable ranges for effluents, implying that the method is a useful tool for monitoring industrial wastewaters containing these metals.

Towards a multi-bioassay-based index for toxicity assessment of fluvial waters.

Despite their proven reliability for revealing 'acceptable' degrees of toxicity in waste- and reclaimed waters, bioassays are rarely used to assess the toxicity of hazardous contaminants present in natural waters. In this study, we used organisms from different trophic levels to assess the toxicity of water samples collected from four different South Korean rivers. The main objective was to develop a multi-descriptor index of toxicity for undiluted river water. The responses of six test organisms (Aliivibrio fischeri, Pseudokirchneriella subcapitata, Heterocypris incongruens, Moina macrocopa, Danio rerio and Lemna minor) after laboratory exposure to water samples were considered for this index, as well as the frequency of teratologies in diatom assemblages. Each individual test was attributed a toxicity class and score (three levels; no toxicity = 0, low toxicity = 1, confirmed toxicity = 2) based on the organism's response after exposure and a total score was calculated. The proposed index also considers the number of test organisms that received the highest toxicity score (value = 2). An overall toxicity category was then attributed to the water sample based on those two metrics: A = no toxicity, B = slight toxicity, C = moderate toxicity; D = toxicity and E = high toxicity. The susceptibility of the test organisms varied greatly and the sensitivity of their response also differed among bioassays. The combined responses of organisms from different trophic levels and with different life strategies provided multi-level diagnostic information about the intensity and the nature of contamination.

Assessment of metal contamination in water and sediments from major rivers in South Korea from 2008 to 2015.

This study is the first report to evaluate (8 years data) the contamination degree and distribution characteristics of metals in the surface water and sediments of four Korean rivers (Nakdong, Yeongsan, Geum, and Han). Eight years of data were evaluated, and metal concentrations in the river water were found to be below permissible limits but high enough to cause detrimental effects (under chronic exposure) to aquatic organisms. The analysis of metals in the river sediments showed the following trend: Zn > Cu > Cd > Pb > Ni > As > Cr > Hg. The concentrations of metals in sediments (especially in the Geum and Han rivers) were above the permissible limits reported by international agencies. Concentrations of Cu, Ni, and Zn were high enough to pose risks to aquatic communities. In sediments, metals pollution was also evaluated using different indices, such as enrichment factor (EF), geoaccumulation index (Igeo), contamination factor (CF), degree of contamination (Cd), modified degree of contamination (mCd), and pollution load index (PLI). The CF, EF, and Igeo indices demonstrated that most of the river sediment samples were moderately to heavily contaminated by Cd, Cu, Pb, and Zn. The PLI values were above one in the Geum and Han river sediments, which indicated polluted conditions. Similarly, Cd indicated a considerable to very high degree of contamination, while mCd indicated a low to moderate degree of contamination in all four river sediments. Finally, it was found that the extent of metals pollution in the Korean rivers reached a critical condition, which could be detrimental to the biota of the rivers, as well as to humans in the long term.

Testing the toxicity of metals, phenol, effluents, and receiving waters by root elongation in Lactuca sativa L.

Phytotoxicity tests using higher plants are among the most simple, sensitive, and cost-effective of the methods available for ecotoxicity testing. In the present study, a hydroponic-based phytotoxicity test using seeds of Lactuca sativa was used to evaluate the water quality of receiving waters and effluents near two industrial sites (Soyo and Daejon) in Korea with respect to the toxicity of 10 metals (As, Cd, Cr, Cu, Fe, Pb, Mn, Hg, Ni, Zn) and phenol, and of the receiving waters and effluents themselves. First, the L. sativa hydroponic bioassay was used to determine whether the receiving water or effluents were toxic; then, the responsible toxicant was identified. The results obtained with the L. sativa bioassay ranked the EC50 toxicities of the investigated metal ions and phenol as: Cd > Ni > Cu > Zn > Hg > phenol > As > Mn > Cr > Pb > Fe. We found that Zn was the toxicant principally responsible for toxicity in Daejeon effluents. The Daejeon field effluent had a higher Zn concentration than permitted by the effluent discharge criteria of the Ministry of Environment of Korea. Our conclusion on the importance of Zn toxicity was supported by the results of the L. sativa hydroponic assay, which showed that the concentration of Zn required to inhibit root elongation in L. sativa by 50% (EC50) was higher in the Daejeon field effluent than that of pure Zn. More importantly, we proved that the L. sativa hydroponic test method can be applied not only as an alternative tool for determining whether a given waste is acceptable for discharge into public water bodies, but also as an alternative method for measuring the safety of aquatic environments using EC20 values, with respect to the water pollutants investigated (i.e., Cd, Cr, Cu, Pb, Mn, Hg, Ni, Zn, and phenol).