Algal Growth Inhibition Research Articles

Ecotoxicity profiling of a library of 24 l-phenylalanine derived surface-active ionic liquids (SAILs)

We evaluated the ecotoxicity of a library of 24 l-phenylalanine derived surface-active ionic liquids (SAILs) with various cationic head groups (pyridinium, Py; imidazolium, Imid and cholinium, Chol) and alkyl ester chains from C2 to C16. For toxicity evaluation we used 72-h algal growth inhibition assay (OECD 201) with Raphidocelis subcapitata and 24-h mortality test with aquatic crustaceans Thamnocephalus platyurus (ISO 14380:2011). The OECD 201 assay was applied to all 24 SAILs while the ISO 14380:2011 test was applied to a subset, specifically all eight pyridinium SAILs and C6 and C8 examples of the imidazolium and cholinium SAILs (total 12 SAILs). For the comparison, 30-min EC50 data (based on inhibition of bioluminescence) previously reported by this group for the 24 SAILs for marine bacteria Vibrio fischeri (ISO 21338:2010) were included and correlated to the algae and aquatic crustaceans data. According to the results of the multritrophic test battery only two studied SAILs - PyC2 and CholC2 – could be considered ‘low toxicity’, (i.e. were ranked not harmful, L(E)C50 > 100 mg/L by the most sensitive test - algal growth inhibition assay). T. platyurus proved about 100-times more tolerant to studied SAILs than algae. An alternative classification scale dependent on the average MW of the compound dataset (based on molar concentrations and not concentrations based on mg/L) was suggested to rank the compounds. When compared to the classification scale independent of the MW of the compound, a more accurate appraisal was achieved for suggesting the greener alternatives for certain commercial SAILs/surfactants.

Nitrogen Deficiency Maximizes the Production and Accumulation of Β-Carotene via Induction of Different Macromolecule Derivatives in Dunaliella salina (Dunal) Teodoresco

THIS STUDY aims at investigating the effects of nitrogen deficiency and NaCl stress on β-carotene production and growth of Dunaliella salina (Dunal) Teodoresco. D. salina was exposed to different levels of N: 2.5, 4.9, 7.4 and 9.9mM KNO3 or Na+: 1.3, 1.7, 2.6, 3.4 and 4.3M NaCl. β-carotene production and accumulation were significantly better in nitrogen deficiency-treated D. salina than that in NaCl-treated cells, with a maximum increase of 5.5mg g DW-1 at 2.5mM KNO3. Algal growth, in terms of cell number and the relative growth rate (RGR), was increased with the increase in the availability of nitrogen but decreased by NaCl stress. In contrast, the production of β-carotene by D. salina was enhanced under nitrogen deficiency and excessive salinity, suggesting the opposite effect of nitrogen availability and stressful NaCl on the production and accumulation of β-carotene concomitant with the inhibition of algal growth. GC analysis confirmed that nitrogen deficiency-treated D. salina accumulates β-carotene higher than untreated cells (control), suggesting the great potential of nitrogen deficiency-treated D. salina to produce different β-carotene macromolecule derivatives compared to those in the control. Such different hydrocarbons could be converted into safe β-carotene. Therefore, D. salina could be used as a reliable biological system for β-carotene production. The study recommended cultivating D. salina under low salinity to obtain D. salina cells, but high salinity to obtain their β-carotene.

Light-driven inactivation of harmful algae Microcystis aeruginosa and degradation of microcystin by oxygen-doped carbon nitride nanosheets

Oxygen-doped metal-free graphitic carbon nitride (g-C3N4) was synthesized, and this oxygen-carbon nitride (m-g-C3N4) effectively reduced algal growth under visible light. Membrane damage was a dominant mechanism for m-g-C3N4-induced cell destruction, and the extracellularly produced ·OH and O2·− were the main cause. Physical contact (13.6%) also contributed to the observed membrane damage. Oxygen doping enhanced visible light utilization and e−-h+ pair separation, which were responsible for the increased photocatalytic performance of m-g-C3N4. The released microcystin content did not increase during algal cell destruction due to the efficient degradation (82.4%) under sunlight irradiation. More importantly, algal growth inhibition by m-g-C3N4 was also effective in natural freshwater with abundant natural organic matter (~20 mg C/L). Algal inactivation by m-g-C3N4 could be further enhanced with increasing heating time (5–24 h) during synthesis, or under natural sunlight irradiation. Our results demonstrate that this metal-free m-g-C3N4 can be potentially applied in harmful algal control.

Utilization of immobilized horseradish peroxidase for facilitated detoxification of a benzidine based azo dye

Horseradish peroxidase (HRP) was immobilized on the poly(2-hydroxyethyl methacrylate-glycidyl methacrylate) [p(HEMA-GMA)] cryogel and used for the degradation of a benzidine containing azo dye (i.e., Direct Blue-6). The maximum amount of HRP loading was found to be 87.6 mg g−1 cryogel, and the retained immobilized HRP activity was 67% with respect to the same quantity of the free enzyme. Biochemical properties of the HRP preparations were also evaluated along with the stability studied under various denaturizing conditions. The toxicity of the Direct Blue-6 and its degradation products was tested using Daphnia magna. Decrease in the absorbance of the blue color of dye at 590 nm was observed during enzymatic degradation studies. Additionally, Chlorella vulgaris was used as a test organism in the algal growth inhibition studies. After 60 min reaction time, the Direct Blue-6 dye and its degradation product were enzymatically removed from the medium. Thus, after treatment with HRP approximately 60-min, the medium was non-toxic for both D. magna and C. vulgaris. The Direct Blue-6 dye and its degradation product toxicities were reduced after enzymatic treatment from 99.6 to 7.3%. It should be noted that the initial degradation products appeared to be extra toxic compared to the pristine dye.

Factors impacting the effectiveness of biological pretreatment for the alleviation of algal growth inhibition on anaerobic digestate

Algal growth is often inhibited in full-strength anaerobic digestate. The objective of this study was to investigate conditions under which digestate pretreatment using bacteria is effective in promoting algal growth, nutrient removal, and favorable changes in algal biomass composition. Batch culture experiments were carried out using low- and high-strength municipal sludge anaerobic digestate, two algae strains of varying sensitivity to digestate inhibitors, short and long pretreatment periods, and axenic vs. non-axenic algal cultures. Pretreatment of digestate increased algal growth up to 40%, N assimilation (up to 29%), and P removal (340%) by Chlorella sorokiniana (resilient algae) when grown on high-strength digestate. Pretreatment did not increase algal growth or nutrient assimilation when Chlorella sorokiniana was combined with low-strength digestate. The more sensitive strain, Auxenochlorella protothecoides, benefitted from pretreatment on both low- and high-strength digestate, even preventing complete cell death in the latter. Pretreatment increased starch content but not lipid content of algae.

Growth inhibition of Microcystis aeruginosa by sand-filter prevalent manganese-oxidizing bacterium

The utilization of algicidal bacteria is becoming an attractive method for the inhibition of algae growth. However, the previous research has mainly focused on the control of harmful blooms in eutrophic waters by the addition of algicidal bacteria. This study aims to investigate the growth of algal cells in the presence of a sand-filter prevalent manganese-oxidizing bacterium, which might alleviate the algae-induced clogging problem in sand filters via bioaugmented sand filtration. The manganese-oxidizing bacterium Pseudomonas sp. QJX-1 exhibited an inhibiting effect on algae growth. Compared with a control group, the chlorophyll a content of M. aeruginosa could be significantly decreased by 60% after exposure to 10% QJX-1 culture supernatant. The decrease in photosynthetic parameters demonstrated the damage to the photosynthetic system of algal cells exposed to QJX-1 cell-free supernatant. The results indicated that QJX-1 inhibited the growth of M. aeruginosa by excreting an algicidal compound, 2,4-di-tert-butylphenol (2,4-DTBP), without directly contacting algal cells. The photosynthetic system structure of algal cells could be damaged through 2,4-DTBP excretion by QJX-1, which could explain the weakened photosynthetic activity of algal cells exposed to QJX-1. Our findings highlight the algicidal effect of the manganese-oxidizing bacterium Pseudomonas sp. QJX-1 on M. aeruginosa via the excretion of 2,4-DTBP.

Growth properties and hydrogen yield in green microalga Parachlorella kessleri: Effects of low-intensity electromagnetic irradiation at the frequencies of 51.8 GHz and 53.0 GHz

The current research reports the effects of low-intensity extremely high frequency electromagnetic irradiation (EMI) of 51.8 GHz and 53.0 GHz on green microalga Parachlorella kessleri RA-002 isolated in Armenia. EMI demonstrated different effects on the growth properties of microalgae under various conditions. Under aerobic conditions a positive effect of EMI on the growth rate of P. kessleri and the content of photosynthetic pigments were observed. The data obtained indicates a significant role of O2, since the enhancing effect of EMI was determined only under aerobic conditions. Meanwhile under anaerobic conditions EMI with both frequencies caused inhibition of algal growth and a decrease in the amount of photosynthetic pigments. EMI also inhibited the yield of H2 production in P. kessleri, which was partially restored after 5-day cultivation due to the existence of protective mechanisms in this alga. The results might indicate membrane-bound mechanisms of EMI action on algae, which can be associated with the effects on photosynthetic pigments and membrane-associated enzymes responsible for H2 production. The results are useful for the development of algae biotechnology and the possibility of using EMI as a factor which regulates the production of biomass and biohydrogen by green microalgae.

Time-course effects of Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) on Chlorella pyrenoidosa: Growth inhibition and adaptability mechanisms

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP), a widely used chlorinated organophosphorus flame retardant, is an increasingly widespread contaminant of aquatic environment. In this study, time-dependent effect of TDCPP on the freshwater green-algae Chlorella pyrenoidosa was investigated and its underlying mechanisms were explored. We show that TDCPP lower than 10 ppm caused a reversible inhibition of algal growth, with complete inhibition occurring at 15 ppm. This inhibition was not caused by damage from reactive oxygen species, but rather resulted from the impairment of photosynthetic function, with PSII reaction center as the primary target, as indicated by Chl a fluorescence induction, QA− reoxidation, S-state distribution and immunoblot analysis. The reversal of damage caused by TDCPP concentrations under 10 ppm might be attributable to the repair of photosynthetic function by de novo protein biosynthesis in the chloroplast, with the most likely explanation being the replacement of the damaged PSII D1 protein. The results provide novel insights into mechanisms of TDCPP toxicity toward freshwater microalgae and better understanding of ecological consequences of TDCPP in the environment.

Influence of Size and Phase on the Biodegradation, Excretion, and Phytotoxicity Persistence of Single-Layer Molybdenum Disulfide.

The increasing applications of single-layer molybdenum disulfide (SLMoS2) pose great potential risks associated with environmental exposure. This study found that metallic-phase SLMoS2 with nanoscale (N-1T-SLMoS2, ∼400 nm) and microscale (M-1T-SLMoS2, ∼3.6 μm) diameters at 10-25 mg/L induced significant algal growth inhibition (maximum 72.7 and 74.6%, respectively), plasmolysis, and oxidative damage, but these alterations were recoverable. Nevertheless, membrane permeability, chloroplast damage, and chlorophyll biosynthesis reduction were persistent. By contrast, the growth inhibition (maximum 55.3%) and adverse effects of nano-sized semiconductive-phase SLMoS2 (N-2H-SLMoS2, ∼400 nm) were weak and easily alleviated after 96 h of recovery. N-1T-SLMoS2 (0.011 μg/h) and N-2H-SLMoS2 (0.008 μg/h) were quickly biodegraded to soluble Mo compared with M-1T-SLMoS2 (0.004 μg/h) and excreted by algae. Incomplete biodegradation of SLMoS2 (26.8-43.9%) did not significantly mitigate its toxicity. Proteomics and metabolomics indicated that the downregulation of proteins (50.7-99.2%) related to antioxidants and photosynthesis and inhibition of carbon fixation and carbohydrate metabolism contributed to the persistent phytotoxicity. These findings highlight the roles and mechanisms of the size and phase in the persistent phytotoxicity of SLMoS2, which has potential implications for risk assessment and environmental applications of nanomaterials.

Assessment and mechanisms of microalgae growth inhibition by phosphonates: Effects of intrinsic toxicity and complexation

The effects of phosphonates, the heavily-used antiscalants in reverse osmosis systems, on microalgae are controversial, although they are harmless to most aquatic organisms. Herein, we assessed the inhibitory effects of etidronic acid (HEDP) and diethylenetriamine penta(methylene phosphonic acid) (DTPMP) on algal growth and revealed the mechanisms involved in both intrinsic toxicity and complexation. The phosphonates showed weak influences on Scenedesmus sp. LX1 in the first 4 d of cultivation. In contrast, a significant growth inhibition was observed subsequently with half maximal effective concentrations of 57.6 and 35.7 mg/L for HEDP and DTPMP, respectively, at 10 d. The phosphonates had little effect on cellular energy transfer and oxidative stress, quantified by adenosine triphosphate level and superoxide dismutase activity, respectively, demonstrating weak intrinsic toxicities to algal cells. Phosphonates blocked the algal assimilation of iron ions through complexation. Severe iron deficiency limited photosynthetic activity and caused chlorophyll decline, resulting in a functional loss of the photosystem followed by complete algal growth inhibition at the late cultivation stage. Our findings point to a potential ecological impact wherein harmful algal blooms are induced by the natural degradation of phosphonates due to the release of both iron and phosphate ions that stimulate algal regrowth after disinhibition.

Micro- and Nanoplastic Exposure Effects in Microalgae: A Meta-Analysis of Standard Growth Inhibition Tests

Background: Ecological impacts of micro- and nanoplastics particles (MNP) are among the most discussed environmental concerns. In algae, MNP are commonly hypothesized to reduce growth, which is a standard ecotoxicological endpoint. However, the reported test outcomes vary, with both growth inhibition and stimulation being observed. Due to this conflict of information, a data synthesis for MNP potential to cause growth inhibition in toxicity testing is needed. Methods: We performed a meta-analysis study to assess the effect of MNP exposure on algal growth. Twenty studies published between 2010 and 2020 and representing 16 algal species and five polymer materials administered as particles in size range 0.04 to 3000 µm were included in this meta-analysis. A random-effect model was used to estimate the effect size in three datasets: (1) Low concentration range (< 100 mg/L), (2) High concentration range (≥ 100 mg/L), and (3) Full range model (0.004 to 1100 mg/L), which encompassed all studies using the combination of experimental settings (test species, MNP concentration, polymer material, and particle size) yielding the highest effect size within a study. Results: The exposure to MNP was not significantly associated with growth inhibition in any of the models tested. However, a high heterogeneity between the studies was found in all three models. Neither MNP concentration nor polymer material contributed significantly to the heterogeneity, whereas polymer density had a significant moderating effect, with a higher risk of growth inhibition at lower densities. We also identified a publication bias, with small studies that reported significant inhibition being overrepresented in our dataset. Conclusions: The meta-analysis found limited evidence for MNP effect on microalgal growth in the standard algal growth inhibition test. The heterogeneity and varying methodological quality of studies limited the interpretation and the confidence in the findings. For hazard assessment, standardization and controlled exposure are needed as well as more sensitive endpoints that can inform us about the effect mechanisms. Finally, using particle-free controls in such tests cannot account for the presence of inert particulates in the test system, and, hence, does not allow to attribute observed effects to the test polymers.

Effect of humic acids on the toxicity of pollutants to Chlamydomonas reinhardtii: Investigation by a microscale algal growth inhibition test.

Dissolved humic substances (DHSs) are the major components of organic matter in the aquatic environment. DHSs are well known to considerably affect the speciation, solubility, and toxicity of a wide variety of pollutants in the aquatic environment. In this study, the effects of the toxicity of heavy metals and hydrophobic organic pollutants (HOPs) on Chlamydomonas reinhardtii in the presence of humic acid (HA) were examined by a microscale algal growth inhibition (μ-AGI) test based on spectrophotometric detection. To clarify the relationship between the chemical properties of HAs and the toxicity change of pollutants, eight HAs from different sources were prepared and used. HAs were responsible for mitigating the toxicity of Hg, Cu, pesticides (γ-HCH, 2,4-D, and DDT), and polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (Nap), anthracene (Ant), and benzo[a]pyrene (BaP). In particular, an approximately 100-fold decrease in the toxicity of BaP was observed in the presence of 10 ppm HAs extracted from tropical peat. The results indicated that the carboxylic group content and the HA molecular weight are correlated to the changes in the heavy metal toxicity. For HOPs, the aromaticity and polarity of HAs are crucial for mitigating their toxicity. Furthermore, it was clearly shown that the lake water including a high concentration of DHSs collected from Central Kalimantan, Indonesia, reduced the toxicity of Hg and γ-HCH on Chlamydomonas reinhardtii. Graphical abstract.

Transcriptomic analysis of Raphidocelis subcapitata exposed to erythromycin: The role of DNA replication in hormesis and growth inhibition

The occurrence of hormesis in the algal growth inhibition test is a major challenge in the dose-response characterization, whereas the molecular mechanism remains unraveled. The aim of this study is therefore to investigate the changes in the molecular pathways in a model green alga Raphidocelis subcapitata treated with erythromycin (ERY; 4, 80, 120 μg L−1) by transcriptomic analysis. After 7 day exposure, ERY at 4 μg L−1 caused hormetic effects (21.9 %) on cell density, whereas 52.0 % and 65.4 % were inhibited in two higher exposures. By using adj p < 0.05 and absolute log2 fold change> 1 as a cutoff, we identified 218, 950, and 2896 differentially expressed genes in 4, 80, 120 μg L−1 treatment groups, respectively. In two higher ERY treated groups, genes involved in phases I, II & III metabolism processes and porphyrin and chlorophyll metabolism pathway were consistently suppressed. Interestingly, genes (e.g., pri2, mcm2, and mcm6) enriched in DNA replication process were up-regulated in 4 μg L−1 group, whereas these genes were all repressed in 120 μg L−1 group. Alteration trend in gene expression was consistent with algal growth. Taken together, our results unveiled the molecular mechanism of action in ERY- stimulated/ inhibited growth in green alga.

Physiological and morphological responses of green microalgae Chlorella vulgaris to silver nanoparticles

The toxic effects of silver nanoparticles (AgNPs) on the physiology and morphology of the green microalga Chlorella vulgaris were studied. AgNPs were characterized by particle size distribution, ζ potential measurement, and atomic force microscopy (AFM). Chlorella vulgaris was exposed to 90–1440 μg/L of AgNPs range in Bold's Basal Medium for 96 h. The inhibition of algae growth rate and changes in the concentrations of chlorophyll-a, chlorophyll-b, pheophytin, and carotenoids was determined at the beginning and end of the trial. Cell diameter and volume, carbohydrate, total lipids, and protein content were also determined. Our data strongly suggest that the toxic effects of the AgNPs resulted in concentration and time-dependent. AgNPs altered C. vulgaris growth kinetics and cell metabolism expressed in photosynthetic pigments and biochemical composition. Our study confirmed the cytotoxicity of AgNPs through the algal growth inhibition with an EC50 value of 110 μg/L. Also, changes of chlorophyll-a, chlorophyll-b, pheophytin, and carotenoids concentrations were observed associated with a color shift from green to pale brown of algae cultures exposed to AgNPs for 96 h. Furthermore, algae cell concentration, diameter, and volume, plus total lipid, protein, and carbohydrates contents in the presence of AgNPs, were significantly altered compared to untreated cells. In synthesis, this study highlighted AgNPs toxic effects on morphological and physiological traits of C. vulgaris and warns about possible impacts on energy flow and aquatic food web structure, and on the transfer efficiency of energy to higher trophic levels.

Effects of Selected Pharmaceuticals on Freshwater Algal Biofilms in Different Organic Loads

The growth pattern of different algal biofilms investigated in the presence of Ibuprofen and Benzoyl Metronidazole in batch reactors at varying organic loads. Study suggests that the inhibition of algal growth is correlated to organic loads in water rather than the concentrations of PhCs (Pharmaceuticals). Mortality of algae was recorded in BG11 media with binary mixtures of PhCs and no growth inhibition was monitored in the activated sludge with PhCs. These outcomes indicate that the presence of PhCs as pollutants in drinking water have severe effect on algal biofilms due to low organic load thus can alter the aquatic ecosystem. Additionally, PhCs might not adversely hinder the growth of microbes in WWTP (Wastewater Treatment Plants) or in waters with high organic loads. Nevertheless, inference of these results to a full-scale WWTP need more evidence through extensive studies using variable organic substrates and PhCs with numerous ranges of organic loads. These findings suggest that PhCs as water contaminant are able to shift microbial ecology in water bodies.

Effect of ozonation as pre-treatment and polishing step on removal of ecotoxicity and alkylphenol ethoxylates from tank truck cleaning wastewater

Wastewater originating from tank truck cleaning (TTC) industry is reputed for its large variability and may lead to emission of recalcitrant and ecotoxic substances in discharge waters. In this study, TTC wastewater was biologically treated in two lab-scale activated sludge sequencing batch reactors. Two strategies were used, (1) influent pre-treatment with ozone followed by activated sludge treatment and (2) activated sludge treatment followed by polishing with ozone. Effluent soluble chemical oxygen demand (sCOD), ecotoxicity and the 4-nonylphenol (NP) concentration were used to evaluate and compare both strategies. Experiments were conducted for two different TTC companies using the same set-up. For Company 1, a decrease in ecotoxicity of 80 % was observed for algal growth inhibition and 10 % for Daphnia immobilization when using effluent polishing compared to pre-treatment. Hereby the NP concentration decreased below discharge limits (0.3 ng.mL−1). For Company 2 the ecotoxic effect in the algal growth inhibition test increased to 100 % when conducting effluent polishing, while ecotoxicity for the original effluent and the effluent from the pre-treated system were similar. sCOD did not decrease significantly and the discharge limit of NP was only met for one sample. Extended (7 h) effluent ozone polishing tests were conducted at two pH setpoints to assess the impact of radical formation during ozone treatment. In general, it was observed that ozone as a pre-treatment step had no significant influence on ecotoxicity and COD removal. Effluent polishing can improve ecotoxicity and effluent characteristics, despite the dependence on wastewater composition, as toxic side products may be produced.

Growth inhibition of harmful algae using TiO2-embedded expanded polystyrene balls in the hypereutrophic stream

TiO2-embedded expanded polystyrene (TiO2EPS) balls were produced in large quantities using continuous manufacturing plants and four processes (i.e., fixing-coating-freeze drying-air drying). Two mesocosms [i.e., a photocatalytic zone (PZ) vs. a control zone (CZ)] and in-situ real-time monitoring device were installed to monitor the water quality within the hypereutrophic stream and to elucidate the long-term effect of TiO2EPS balls on the growth inhibition of harmful algae for two years (i.e., 2016–2017). The difference in the concentrations of both Chl-a and phycocyanin between CZ and PZ was temporally variable and was significant from August to October with higher solar irradiation levels. Although the effective depth of TiO2EPS balls varied as a complex function of the photocatalytic reactions of TiO2EPS balls and various environmental factors, the photooxidation effect of TiO2EPS balls decreased with the increase in water depth and the effective water depth for growth inhibition was less than 0.5 m. Compare to bimodal distributions in concentrations of both Chl-a and phycocyanin in CZ, both shifted and lowered peaks were mainly due to the photocatalytic degradation and irradiation shading under natural solar irradiation by applying TiO2EPS balls in hypereutrophic water body. Consequently, the TiO2EPS balls developed in this study can prevent both growth and reproduction of harmful algae in hypereutrophic water body, regardless of the environmental factors.

Ecological risk assessment of an antifouling biocide triphenyl (octadecylamine) boron in the Seto Inland Sea, Japan

In this study, we derived the predicted no-effect concentrations (PNEC) for triphenyl (octadecylamine) boron (TPB-18) and investigated the occurrence of triphenylboranes (TPBs), including TPB-18, for ecological risk assessment in the Seto Inland Sea, Japan. We tested algal growth inhibition, crustacean immobilization, and reproductive toxicity and performed toxicity tests in fish to assess acute and chronic toxicity and generate the PNEC for TPB-18. The minimum toxicity value was 0.30 μg/L, as determined by the 72-h no-observed-effect concentration (NOEC) for the alga Chaetoceros gracilis. The 5th-percentile of hazardous concentration (HC5), derived from NOECs using the species sensitivity distributions approach, was 0.059 μg/L, which indicated the PNEC of 0.0059 μg/L. In comparison, the highest concentration in seawater sampled from the Seto Inland Sea was 0.00034 μg/L, suggesting that the ecological risks posed by TPB-18 are currently low.

Toxicological effects of chlorophenols to green algae observed at various pH and concentration of humic acid

Humic acid (HA) is ubiquitous organic matter derived by microbial metabolisms. This polymeric substance has both hydrophilic and hydrophobic moieties, and it is known that they affect to bioavailability of environmental pollutants. Objective of this study is to investigate the toxicological effects of chlorophenols to green algae observed at various pH and concentration of HA. Toxicity was determined by algal growth inhibition rate and EC50 of green algae Chlorella vulgaris. As a result, toxicity of 2,4-dichlorophenol was mitigated with increase of the coexisting amount of HA and solution pH. In the case of coexisting 2.5 ppm HA, EC50 of 2,4-dichlorophenol was 12.2 ppm and approximately three times higher than the case of absence of HA at pH 7.5. Meanwhile, Toxicity of 2,4,6-trichlorophenol was enhanced with increase of the coexisting amount of HA. In the case of absence of HA, EC50 of 2,4,6-trichlorophenol was 13.1 ppm and approximately two times higher than the case of coexisting 2.5 ppm HA at pH 7.5. Results suggested that toxicity of chlorophenols is influenced by the electrostatic and hydrophobic interaction between HA and chlorophenols. The hypothesis of toxicity enhancement pathway was proposed in the case of equilibrium-state 2,4,6-trichlorophenol between anionic and nonionic states.

Phototransformation of roxithromycin in the presence of dissolved organic matter: Characteriazation of the degradation products and toxicity evaluation

Roxithromycin (ROX) is a widely used macrolide antibiotic and its environmental fate and ecotoxicity have attracted considerable attention. In this study, the phototransformation kinetics and products of ROX under the irradiation of simulated sunlight were investigated. The ecotoxicity of ROX before and after phototransformation were also examined using the bioluminescence bioassay and algae growth inhibition test. The results showed that ROX underwent direct photolysis and indirect photolysis in the presence of Suwannee River humic acid (SRHA) and Suwannee River natural organic matter (SRNOM). The kinetic rate constant of the photodegradation of ROX in the presence of 20 mg·L−1 SRHA and SRNOM were 4.0 and 3.6 times higher than direct photolysis in the absence of dissolved organic matter (DOM). A total of 20 phototransformation products (PTPs) formed as a result of the photodegradation of ROX by simulated solar irradiation were identified, and 10 of them were reported for the first time. The PTPs were generally formed through the N-demethylation, O-demethylation or direct cleavage of the side chain, desosamine or cladinose moiety from ROX. Solutions containing ROX and its PTPs showed an increased toxicity to Vibrio fischeri, demonstrating some PTPs were more toxic to V. fischeri. On the other hand, the toxicity of ROX after irradiation to Chlorella pyrenoidosa decreased, suggesting the phototransformation of ROX in the environment may be a positive outcome in the context of the growth of green algae.