The sensitivity of an hydroponic lettuce root elongation bioassay to metals, phenol and wastewaters

Stabilization of residual mercury from gold mining as metacinnabar and cinnabar in ball mills on a pilot scale

Waste liquid mercury generated as a by-product of the Merrill-Crowe process in gold mining and recovered from mercury-containing waste must be stabilized for secure storage or disposal. This study developed a procedure for mercury stabilization. A ball mill with a 0.5 m3 capacity and a rotational speed of 43 rpm was used to stabilize the residual mercury with sulfur. The treatments were conducted for 30, 60, and 90 min at mercury: sulfur molar ratios of 1.0, 0.8, and 0.67. The ball loading ratio was 7.0 with residual mercury, and the temperature was below 40 °C. The treatment efficiency was evaluated by measuring the concentrations of mercury and other metals using the Toxicity Characteristic Leaching Procedure (TCLP), examining the stabilized residual mercury by X-ray diffraction, and conducting bioassays on Daphnia magna and Lactuca sativa. Principal component analysis (PCA) was performed on the aforementioned variables. The 90-min treatment, with a mercury-to-sulfur molar ratio of 0.67, stabilized mercury mainly as cinnabar compared with the other treatments and presented leachate mercury values below the detection limit <0.003. The leachate from the treatments also showed values of 21.28-38.44 toxic units, classified as very toxic, and generated toxicity, particularly for D. magna, because of the presence of other metals such as Al, Ba, B, Ca, Cu, Cr, Fe, Mn, Ni, and Zn. The variability of the residues in the PCA analysis was explained by the treatment effect and the presence of other metals in the residual mercury. The stabilized residual mercury obtained was classified as non-hazardous and could be stored or disposed of as ordinary waste in a security landfill.

Biodegradation and Detoxification of Low-Density Polyethylene (LDPE) by Stenotrophomonas sp. and Alcaligenaceae bacterium

Every year, human activities introduce large amounts of synthetic plastics into the environment. Decomposition of the plastic derivatives is very difficult and time consuming, so it is essential to eliminate these pollutants using different methods. Bioremediation, is suitable option, because of the low cost and environmentally safe. In this research, degradation of low-density polyethylene (LDPE) was investigated by two strains, isolated from Hamadan province (Iran) landfill soil. After identification by 16sr DNA primers, their abilities of polyethylene biodegradation were examined by Fourier transform infrared (FTIR), SEM and Gas Chromatography-Mass Spectrometry (GC-MS). Using media contain polyethylene) after and before addition of bacteria), toxicity test was conducted by measuring the germination index, root and hypocotyl length of Lactuca sativa seed. After three months, 10.15% ± 1.04 weight loss of LDPE achieved through strain Stenotrophomonas sp. degradation. Both strains had high biofilm formation capacity, confirmed by Electron microscope images and FTIR analysis. GC-MS confirmed the presence of the end-product of LDPE degradation (Pentacosane, Hexacosane, and Octadecane). Both, Stenotrophomonas sp. and Alcaligenaceae bacterium had significant detoxification ability. In media contain LDPE (without bacteria), decrease in the germination of lettuce seeds was observed.

Phytotoxicity of coal waste elutriates (Douro Coalfield, North Portugal) in Lactuca sativa

One of the most important mining areas in the Douro Carboniferous Basin is the Pejão Coalfield. In the summer of 2017, a wildfire promoted the ignition and self-burning some of the coal waste piles in the area and caused important environmental changes, promoting a new heterogenic pedological zonation. This study aims to assess the ecotoxicological effects of 25 soil elutriates from these different soil types in seed germination and individual (emergence, growth, and morphologic alterations) and subindividual parameters in Lactuca sativa. The different evaluated endpoints were differently affected regarding the soil elutriate revealing the high heterogeneity of soil characteristics. The presence of different potentially toxic elements (e.g., Cd, Cr, Pb, Zn) in soil elutriates, even in low concentrations, caused effects on L. sativa development. Unburned coal wastes and downhill soil elutriates were able to inhibit the germination of L. sativa and affect them individually and sub-individually (decrease in size, biomass, and presence of morphological alterations). Additionally, it was observed that all soil elutriates induce a decrease in root size. The results highlight the importance of using elutriate samples in phytotoxicity studies of coal mining waste, since the tailings lixiviate may reduce plant establishment and growth, affecting the terrestrial ecosystems. The integrated use of seed germination assays with the analysis of morphological and biochemical alterations in plants proved to be sensitive parameters to evaluate the phytotoxicity of coal mining wastes.

Morphoanatomical, Physiological, and Biochemical Indicators in Lactuca sativa L. Germination and Growth in Response to Fluoride

Fluoride is one of the main phytotoxic environmental pollutants, and high concentrations (10-30 mg L^-1) are commonly detected in surface and groundwater. Little, however, is known about the effects of this pollutant on crops that require irrigation during their development, which, in addition to phytotoxicity, may cause negative human health effects. Thus, the aim of this study was to characterize the effects of potassium fluoride (KF) on the germination of lettuce seeds and identify the physiological and anatomical markers of this pollutant's action on plants exposed to it during growth. Initially, lettuce seeds were sown in gerboxes and soaked in solutions containing 0 mg L^-1, 10 mg L^-1, 20 mg L^-1, and 30 mg L^-1 KF. Plants grown in a greenhouse were treated daily with KF irrigation at the same KF concentrations for 40 days. KF exposure reduced the germination rate and germination speed index of lettuce seeds at 20 mg L^-1 and 30 mg L^-1, resulting in compromised root development at the highest KF concentration. Lettuce plants displayed a slight photosynthesis reduction and a significant photochemical efficiency decrease after exposures to all KF concentrations. Lower chlorophyll contents and nitrogen balance indices were observed in plants exposed to 30 mg L^-1 KF. On the other hand, increases in phenolic compounds and malondialdehyde were noted with increasing KF concentrations. Lettuce plants can, therefore, accumulate fluoride in leaves when irrigated with KF-rich water. The investigated physiological and biochemical variables were proven to be adequate fluoride action biomarkers in lettuce plants and may become an important tool in the study of olericulture contaminants.

In Vitro Potential of Clary Sage and Coriander Essential Oils as Crop Protection and Post-Harvest Decay Control Products

Owing to their various application fields and biological properties, natural products and essential oils (EO) in particular are nowadays attracting more attention as alternative methods to control plant pathogens and pests, weeds, and for post-harvest applications. Additionally, to overcome EO stability issues and low persistence of effects, EO encapsulation in β-cyclodextrin (β-CD) could represent a promising avenue. Thus, in this work, the EO distilled from two aromatic plants (Salvia sclarea L. and Coriandrum sativum L.) have been evaluated in vitro for their antifungal, herbicidal and insecticidal activities, against major plant pathogens and pests of agronomical importance. Both plants were grown on unpolluted and trace-element-polluted soils, so as to investigate the effect of the soil pollution on the EO compositions and biological effects. These EO are rich in oxygenated monoterpenes (clary sage and coriander seeds EO), or aliphatic aldehydes (coriander aerial parts EO), and were unaltered by the soil pollution. The tested EO successfully inhibited the growth of two phytopathogenic fungi, Zymoseptoria tritici and Fusarium culmorum, displaying IC₅₀ ranging from 0.46 to 2.08 g L⁻¹, while also exerting anti-germinative, herbicidal, repellent and fumigant effects. However, no improvement of the EO biological effects was observed in the presence of β-CD, under these in vitro experimental conditions. Among the tested EO, the one from aerial parts of coriander displayed the most significant antifungal and herbicidal effects, while the three of them exerted valuable broad-range insecticidal effects. As a whole, these findings suggest that EO produced on polluted areas can be of great interest to the agricultural area, given their faithful chemical compositions and valuable biological effects.

Bioassays to screen the toxicity in drinking water samples collected in Brazilian rural area

Agriculture activities have increased the concentration of pesticides and metals in the environment. The excessive use of pesticides can generate an environmental impact and contribute to the development of human diseases. This study aimed to determine the presence of pesticides and metals in water samples collected in the Brazilian rural area in two different periods (before and after pesticide application) and to evaluate the alternative bioassays Lactuca sativa, Allium cepa, and Caenorhabditis elegans to monitoring toxicity in human drinking water samples. Eight sites in the rural area were selected and water samples were collected in two different periods of the year (before and after pesticide application). The presence of the pesticides was determinated by ultra-high performance liquid chromatography-tandem mass spectrometry and metals by inductively coupled plasma mass spectrometry. The potential toxicity of the water samples was performed with three different alternatives in vivo models (L. sativa, A. cepa, and C. elegans). Fifty-seven pesticides were analyzed and, according to the results, the most found ones were clomazone, atrazine, tebuconazole, metconazole, pyrimethanil, and carbofuran-3-hydroxide, which is a metabolic degradation product of insecticide carbofuran. The most detected metals were Cu, Cr, Mg, Fe, and Mn. The assays with L. sativa and A. cepa showed alterations in the period after pesticide application, while C. elegans presented changes in both periods compared to the same collection sites. These results indicate that bioassays, especially C. elegans, could be complementary and useful tools for monitoring the toxicity in drinking water samples.

Application of two bioassays as potential indicators of phenol phytoremediation efficiency by tobacco hairy roots

Phenol is one of the contaminants most frequently found in the environment and it is considered a priority pollutant due to their toxic effects. Hairy roots (HR) constitute a good model tool for the removal of this contaminant. In this work, phenol removal using wild type (WT) and double transgenic (DT) Nicotiana tabacum HR was performed with high efficiency (60-80%, for 25-250 mg L-1 phenol solutions, respectively). After phytoremediation process, the toxicity of post removal solutions (PRS) was evaluated through two-toxicity test belonging to two trophic levels, Lactuca sativa test and Rhinella arenarum (AMPHITOX). Toxicity of PRS showed variable results since these solutions were less toxic to L. sativa seeds compared to R. arenarum embryos, which could be attributed to different sensitivities of the exposed organisms. Although PRS obtained using WT and DT HR reduced phenol phytotoxicity on L. sativa seeds, WT PRS were even less toxic than DT PRS according to this test. Regarding AMPHITOX, HR culture medium without phenol but incubated with HR and phenol PRS exerted a toxic effect on the embryos, which could be related to the presence of toxic products derived from HR metabolism. The results demonstrated that an efficient phenol removal is not always accompanied by a considerable reduction of the solution toxicity and therefore, the use of organisms from different trophic levels to evaluate the toxicity after the removal process gains importance.

Phytotoxicity, cytotoxicity, and in vivo antifungal efficacy of chitosan nanobiocomposites on prokaryotic and eukaryotic cells

Chitosan (CS) nanosystems have potential applications for the control of microorganisms in the medical, environmental, and agrifood fields. In vivo and in vitro assays of CS nanosystems have experienced increased activity due to improved physicochemical properties, biological activity, and reactivity. Hence, it is important to determine whether their application involves toxicological risks. The aim of this study was to evaluate the mutagenic, cytotoxic, phytotoxic, and in vivo antifungal activity of chitosan-pyrrole-2-carboxylic acid nanobiocomposites (CS-PCA). The CS-PCA nanoparticles were synthesized by means of the nanoprecipitation technique with a size and ζ-potential of 502 ± 72 nm and + 54.7 ± 15.0 mV, respectively. According to the Ames test, no evidence of mutagenic activity was observed in Salmonella typhimurium strains. The cytotoxic assay showed that the incorporation of PCA into the CS matrix increased the toxic effect on ARPE-19 cells. However, fluorescence microscopy of ARPE-19 cells did not reveal morphostructural changes allusive to cell injury. CS-PCA exhibited strong phytotoxicity on lettuce seeds and the complete inhibition of seed development. The antifungal assay demonstrated that the CS-PCA delayed Aspergillus niger infection in tomato fruit until day 3; however, its use for the pre-treatment of seeds might exert adverse effects on plant development.

Phytotoxicity indexes and removal of color, COD, phenols and ISA from pulp and paper mill wastewater post-treated by UV/H2O2 and photo-Fenton

Pulp and paper mill wastewater (PPMWW) contains high concentrations of recalcitrant compounds that cause toxicity to organisms. Advanced oxidation processes (AOPs) have the ability to degrade these compounds and reduce overall toxicity. Physicochemical characterization and Lactuca sativa toxicity test were conducted to compare the effectiveness of two post-treatments: UV/H₂O₂ and photo-Fenton. A comparison of four phytotoxicity indexes was carried out. PPMWW from a Brazilian treatment plant was characterized by high values of phenols, color, integrated spectral area (ISA), and chemical oxygen demand (COD), and caused significant inhibition to seedling development. The use of both post-treatments allowed the removal of over 75% of phenols, color, ISA, and COD. Although UV/H₂O₂ was more effective in removing phenols and ISA, photo-Fenton better reduced phytotoxicity. The most sensitive phytotoxicity indexes were RGIC_0.8 and GIC_80%, whereas SGC₀, REC_-0.25 and REC_-0.50 better showed the effectiveness of the post-treatments. We suggest the combined use of two phytotoxicity indexes: one that evaluates the effects on seed germination and, another, on root elongation, e.g., SGC₀ and RGIC_0.8. Additionally, we recommend the use of ISA for monitoring programs of wastewater treatments because it is a cost-effective approach that allows narrowing down the search and identification of compounds present in complex mixtures.

Impact assessment of bioaugmented tannery effluent discharge on the microbiota of water bodies

Effluents are commonly discharged into water bodies, and in order for the process to be as environmentally sound as possible, the potential effects on native water communities must be assessed alongside the quality parameters of the effluents themselves. In the present work, changes in the bacterial diversity of streamwater receiving a tannery effluent were monitored by high-throughput MiSeq sequencing. Physico-chemical and microbiological parameters and acute toxicity were also evaluated through different bioassays. After the discharge of treated effluents that had been either naturally attenuated or bioaugmented, bacterial diversity decreased immediately in the streamwater samples, as evidenced by the over-representation of taxa such as Brachymonas, Arcobacter, Marinobacterium, Myroides, Paludibacter and Acinetobacter, typically found in tannery effluents. However, there were no remarkable changes in diversity over time (after 1 day). In terms of the physico-chemical and microbiological parameters analyzed, chemical oxygen demand and total bacterial count increased in response to discharge of the treated effluents. No lethal effects were observed in Lactuca sativa L. seeds or Rhinella arenarum embryos exposed to the streamwater that had received the treated effluents. All of these results contribute to the growing knowledge about the environmental safety of effluent discharge procedures.

Antifungal and Phytotoxic Activities of Essential Oils: In Vitro Assays and Their Potential Use in Crop Protection

(1) Background: The use of natural products based on essential oils (EO) is nowadays arousing great interest as an alternative method to control plant pathogens and weeds. However, EO possess low bioavailability and are highly volatile, and their encapsulation in hydroxypropyl-ß-cyclodextrin (HP-β-CD) could be a means to enhance their stability and maintain their bioactivity. Thus, the current study aims at investigating, in the presence and the absence of HP-β-CD, the antifungal and phytotoxic activities of nine EO, distilled from plant species belonging to Alliaceae, Apiaceae, and Cupressaceae families, with considerations for their chemical composition. (2) Methods: EO antifungal activity was assessed by direct contact and volatility assays against Fusarium culmorum, a major phytopathogenic fungi, while phytotoxic effects were evaluated against lettuce (Lactuca sativa L.) and rye-grass (Lolium perenne L.), by seedling’s emergence and growth assays. (3) Results: These EO inhibit fungal growth in both direct contact and volatility assays, with half-maximal inhibitory concentrations (IC50) ranging from 0.01 to 4.2 g L−1, and from 0.08 up to 25.6 g L−1, respectively. Concerning phytotoxicity, these EO have shown great potential in inhibiting lettuce (IC50 ranging from 0.0008 up to 0.3 g L−1) and rye-grass (IC50 ranging from 0.01 to 0.8 g L−1) seedlings’ emergence and growth. However, the EO encapsulation in HP-β-CD has not shown a significant improvement in EO biological properties in our experimental conditions. (4) Conclusion: All tested EO present antifungal and phytotoxic activities, with diverse efficacy regarding their chemical composition, whilst no increase of their biological effects was observed with HP-β-CD.

Chemical Nature of Spent Coffee Grounds and Husks

Waste coffee husks and spent coffee grounds (SCGs) are produced in large qualities worldwide. Characterisation of these waste streams from Australian commercial outlets in terms of lipid, caffeine, and polyphenol content was undertaken giving values up to 10% lipids and 23mg g−1 phenols from SCGs, consistent with reports from other parts of the world. Husks generally gave lower values. Caffeine residues of 5 and 10mg g−1 (dry weight basis) were found in husks and SCGs respectively. Comparing air-dried and water-extracted solid SCGs and the resulting water extract in plant phytotoxicity studies indicated that pretreatment of the SCGs and plants exposed to the SCGs, are important factors when considering their use as a soil amendment.

Milli-channel array for direct and quick reading of root elongation bioassays

A novel platform to perform systematic analysis and direct reading of root elongation bioassays is presented. The device was designed to include multiplexed microenvironments for the germination and growth of individual seeds, which allows observation by the naked eye or by optical systems, notably cellphone cameras. Prototypes were fabricated by laser micromachining on a highly transparent material that is fully compatible with biological systems. The effectiveness of the milli-channel array was verified against the conventional system (Petri dish). Lactuca sativa was chosen as a model species and glyphosate as a typical toxic agent. All tests were run according to standardized procedures and data analysis was carried out through different statistical indicators such as the root elongation and germination indexes. Results attained in the milli-channel array were identical to those in Petri dish, with the remarkable benefit that several steps required in the conventional system were avoided, which enormously decreases the operation time and the possibility of experimental errors. Further advantages of the milli-channel array are also reported, such as the capability to achieve live imaging of plant organs growth through a simple experiment. The developed device has been proven to be effective, versatile, easy-to-use, and integrable to cellphones, which naturally provide facilities for data recording, analysis, and networking. These improvements open the route to novel applications of bioassays in the wide field of ecotoxicology and environmental studies.

Laboratory and field microcosms as useful experimental systems to study the bioaugmentation treatment of tannery effluents

Tannery effluents require effective treatment prior to their final disposal, and the use of native bacterial consortia could be an appropriate strategy for this purpose. In the present work, consortium SFC 500-1 was found to be highly tolerant to different metals, metalloids and aromatic compounds like phenols. It was also able to remove the black dye commonly used in tanneries. Moreover, it promoted a significant reduction in chemical oxygen demand and exhibited high capability for the simultaneous removal of Cr(VI) and phenol. However, the effectiveness of the remediation processes markedly varied from one experimental system (Erlenmeyer flasks) to another (field microcosm system), highlighting the importance of moving from a small-scale study system to one involving more realistic environmental scenarios. In addition, we found a decrease in the toxicity of the effluent treated with consortium SFC 500-1. Taken together, our results indicate that this consortium possesses great potential for the treatment of tannery effluents. We conclude that for the development of a bioremediation strategy, it is necessary to develop experiments at a larger scale under conditions similar to those of the original system, in order to complete the scenario first created by in vitro approaches.

Salicylic acid loaded chitosan microparticles applied to lettuce seedlings: Recycling shrimp fishing industry waste

Shrimp fishing industry wastes are still a main problem with high environmental impact worldwide. In this study, chitosan with ultra-high molecular weight and deacetylation degree ≥85% was obtained from shrimp fishing industry waste from Argentinean Patagonia. Chitosan based microparticles capable to entrap salicylic acid, a phytohormone known to play major role in the regulation of plant defense response against various pathogens, were prepared using TPP as crosslinker. Unloaded microparticles and microparticles loading several salicylic acid amount were fully characterized exhibiting a size between 1.57 μm and 2.45 μm. Furthermore, a good PDI, entrappment efficiencies from 59% to 98% and salicylic acid sustained release over 24 h were achieved. Chitosan based microparticles were non toxic in most of the doses applied in lettuce seedlings. Instead, microparticles can positively modulate plant growth and have the potential to improve plant defense responses. In particular salicylic acid loaded microparticles effect was very promising for its application as activators of salicylic acid dependent plant defense responses in lettuce as a model of horticultural plant species.

Hypoxia enhances lignification and affects the anatomical structure in hydroponic cultivation of carrot taproot

Hypoxia enhances lignification of carrot root. Hypoxia stress was thought to be one of the major abiotic stresses that inhibiting the growth and development of higher plants. The genes encoding the plant alcohol dehydrogenase (ADH-P) were induced when suffering hypoxia. To investigate the impact of hypoxia on the carrot root growth, carrot plants were cultivated in the hydroponics with or without aeration. Morphological characteristics, anatomical structure, lignin content, and the expression profiles of DcADH-P genes and lignin biosynthesis-related genes were measured. Six DcADH-P genes were identified from the carrot genome. The expression profiles of only three (DcADH-P1, DcADH-P2, and DcADH-P3) genes could be detected and the other three (DcADH-P4, DcADH-P5, and DcADH-P6) could not be detected when carrot cultivated in the solution without aeration. In addition, carrot roots had more lignin content, aerenchyma and less fresh weight when cultivated in the solution without aeration. These results suggested that hypoxia could enhance the lignification and affect anatomical structure of the carrot root. However, the expression levels of the genes related to lignin biosynthesis were down-regulated under the hypoxia. The enhancement of lignification may be the consequence of the structure changes in the carrot root. Our work was potentially helpful for studying the effect of hypoxia on carrot growth and may provide useful information for carrot hydroponics.

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).

Evaluation of toxic and genotoxic potential of a wet gas scrubber effluent obtained from wooden-based biomass furnaces: A case study in the red ceramic industry in southern Brazil

Red ceramic industry in southern Brazil commonly uses wood biomass as furnace fuel generating great amounts of gas emissions and ash. To avoid their impact on atmospheric environment, wet scrubbing is currently being applied in several plants. However, the water leachate formed could be potentially toxic and not managed as a common water-based effluent, since the resulting wastewater could carry many toxic compounds derived from wood pyrolysis. There is a lack of studies regarding this kind of effluent obtained specifically and strictly from wooden-based biomass furnaces. Therefore, we conducted an evaluation of toxic and genotoxic potentials of this particular type of wet gas scrubber effluent. Physical-chemical analysis showed high contents of several contaminants, including phenols, sulphates and ammoniacal nitrogen, as well as the total and suspended solids. The effluent cause significant toxicity towards microcrustacean Artemia sp. (LC50 = 34.4%) and Daphnia magna (Toxicity Factor = 6 on average) and to higher plants (Lactuca sativa L. and Allium cepa L.) with acute and sub-acute effects in several parameters. Besides, using plasmid DNA, significant damage was observed in concentrations 12.5% and higher. In cellular DNA, concentrations starting from 12.5% and 6.25% showed significant increase in Damage Index (DI) and Damage Frequency (DF), respectively. The results altogether suggest that the effluent components, such phenols, produced by wood combustion can be volatilized, water scrubbed, resulting in a toxic and genotoxic effluent which could contaminate the environment.