Toxicity analysis of leachates from hazardous wastes via microtox anddaphnia magna

Tertiary treatment of a mixture of composting and landfill leachates using electrochemical processes

The study investigated the treatment efficiency of coupled electrocoagulation (EC) and electrooxidation (EO) processes for landfill leachate treatment in batch and continuous mode. The EC process (iron anode and graphite cathode) at 18.2 mA/cm² for 2.5 min resulted in COD, turbidity, total phosphorus, total coliforms and fecal coliforms removal of 58.1, 72.9, 98.5, 97.9, and 97.2% respectively. Under the same operating conditions, the coupled EC/EO (Ti-Pt anode, bipolar iron electrode, and graphite cathode) processes showed that the COD, turbidity, total phosphorus, total coliforms, and fecal coliforms removal of 56.5%, 78.3%, 96.3%, 97.2% and fecal coliforms 72.7%, respectively. The energy costs associated with the EC and EC/EO were 0.11 and 0.25 $/m³, respectively. Compared to the batch configuration, the continuous configuration of EC resulted in similar processing performance. However, the EC/EO process resulted in the production of chlorates, perchlorates, and trihalomethanes as by-products. Moreover, the continuous process slightly increases the pH and ammonia concentration of the leachate and also resulted in the metallic sludge production with an average dryness of 4.2%. The toxicity tests determined that the treated effluent was not toxic to Rainbow trout and Daphnia.

Evaluation of toxicity and mutagenicity of a synthetic effluent containing azo dye after Advanced Oxidation Process treatment

Approximately 20% industrial water pollution comes from textile dyeing process, with Azo dyes being a major problem in this scenario and requiring new forms of efficient treatment. Effluent treatments using the Advanced Oxidation Processes (AOP) are justified by the potential of application in the dyed effluent treatments once they can change the Azo dye chemical structure. Thus, this study aimed to evaluate the toxicity and mutagenic capacity of a synthetic effluent containing Amido Black 10B (AB10B) azo dye before treatment with AOP, named Gross Synthetic Effluent (GSE), and after the AOP, named Treated Synthetic Effluent (TSE). Daphnia magna and Allium cepa tests were used to evaluate acute toxicity effects and chromosomal mutagenesis, respectively. The Salmonella/microsome assay was performed to evaluate gene mutations. In silico assays were also performed aiming to identify the mutagenic and carcinogenic potential of the degradation byproducts of AB10B. There was 100% immobility to D. magna after 24 h and 48 h of treatments with TSE, showing EC₅₀ values around 5%, whereas GSE did not show acute toxicity. However, GSE induced chromosomal mutations in A. cepa test. Both GSE and TSE were not able to induce gene mutations in S. typhimurium strains. These effects can be associated with two byproducts generated with the cleavage of the azo bonds of AB10B, 4-nitroaniline and -2-7-triamino-8-hydroxy-3-6-naphthalinedisulfate (TAHNDS). In conclusion, AOP is an efficient method to reduce the mutagenicity of synthetic effluent containing AB10B and additional methods should be applied aiming to reduce the toxicity.

Evaluation of the acute effects of chemical additives on the toxicity of a synthetic oilfield produced water

This study evaluated the acute effects of nine different production chemicals typically employed in oil exploration on the toxicity of a synthetic produced water (PW). Bioassays with the Microtox® System were performed to monitor changes in the level of light emission of the marine luminescent bacteria Vibrio fischeri during exposure to the samples. The results show that synthetic PW is moderately toxic to these organisms, and the addition of oilfield chemicals significantly increases its toxicity. For most of the additives tested, the toxicity of the aqueous phase following partitioning against crude oil was not strongly altered by the presence of these chemicals. Synergistic effects occurred in the three different mixtures investigated. Among the additives studied, biocide, corrosion inhibitor, H₂S scavenger, and surfactant were the most toxic for V. fischeri. Furthermore, the surfactant has been identified as the possible source of the acute toxicity observed.

Treatment of Produced Water with Photocatalysis: Recent Advances, Affecting Factors and Future Research Prospects

Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated to be effective at degrading recalcitrant organic contaminants, however, there is limited understanding about its application to treating produced water that has a complex and highly variable water composition. Therefore, the determination of the appropriate photocatalysis technique and the operating parameters are critical to achieve the maximum removal of recalcitrant compounds at the lowest cost. The objective of this review is to examine the feasibility of photocatalysis-involved treatment for the removal of contaminants in produced water. Recent studies revealed that photocatalysis was effective at decomposing recalcitrant organic compounds but not for mineralization. The factors affecting decontamination and strategies to improve photocatalysis efficiency are discussed. Further, recent developments and future research prospects on photocatalysis-derived systems for produced water treatment are addressed. Photocatalysis is proposed to be combined with other treatment processes, such as biological treatments, to partially reduce total organic carbon, break down macromolecular organic compounds, increase biodegradability, and reduce the toxicity of produced water.

Microplastics but not natural particles induce multigenerational effects in Daphnia magna

Several studies have investigated the effects of nano- and microplastics on daphnids as key freshwater species. However, while information is abundant on the acute toxicity of plastic beads, little is known regarding the multigenerational effects of irregular microplastics. In addition, a comparison of microplastics to naturally occurring particles is missing. Therefore, we investigated the effects of irregular, secondary polystyrene microplastics (<63 μm) and kaolin as natural reference particle on the survival, reproduction, and growth of Daphnia magna over four generations under food-limited conditions. Additionally, we tested the sensitivity of the neonates in each generation to a reference compound as a proxy for offspring fitness. Exposure to high concentrations of microplastics (10,000 and 2000 particles mL^-1) reduced daphnid survival, resulting in extinction within one and four generations, respectively. Microplastics also affected reproduction and growth. Importantly, an exposure to kaolin at similar concentrations did not induce negative effects. The sensitivity of neonates to potassium dichromate was not affected by maternal exposure to particles. Taken together, our study demonstrates that irregular PS particles are more toxic than natural kaolin in daphnids exposed over multiple generations under food limitation. Thus, our work builds towards more realistic exposure scenarios needed to better understand the impacts of microplastics on zooplankton.

Produced water treatment by advanced oxidation processes

Different Advanced Oxidation Processes (AOPs) such as photocatalysis, Fenton-based processes and ozonation were studied to include one of these technologies within an integrated solution for produced water (PW) polishing. Synthetic PW was prepared adding toluene, xylene, naphthalene, phenol, acetic and malonic acids to a seawater matrix. Despite that in all AOPs studied in this work BTEX and naphthalene were removed, the efficiency (in terms of TOC removal) of each treatment varied largely. Among these techniques, photocatalysis was found to be the less effective for the treatment of PW, as TOC removals lower than 20% were obtained for the best scenario after 4 h treatment. In the contrary, best results were obtained by ozonation combined with H₂O₂, where all the organic components were removed, including a high percentage of acetic acid, which was not abated by the rest of the AOPs studied. The optimum conditions for ozonation were 4 g h^-1 O₃ and 1500 mg L^-1 H₂O₂ at pH 10, where after 2 h a 74% of TOC removal was achieved and the acetic acid elimination was 78%. This condition enabled that ozonation process accounted for the lowest electric energy consumption per order of target compound destruction regarding total organic carbon (TOC).

Effect of low-purity Fenton reagents on toxicity of textile dyeing effluent to Daphnia magna

This study aimed to identify the source of toxicity in textile dyeing effluent collected from February to July 2016, using Daphnia magna as a test organism. Toxicity identification evaluation (TIE) procedures were used to identify the toxicants in textile dyeing effluent, and Jar testing to simulate the Fenton process was conducted to identify the source of toxicants. Textile dyeing effluent was acutely toxic to D. magna [from 1.5 to 9.7 toxic units (TU)] during the study period. TIE results showed that Zn derived from the Fenton process was a key toxicant in textile dyeing effluent. Additionally, Jar testing revealed that low-purity Fenton reagents (FeCl₂ and FeSO₄), which contained large amounts of Zn (89 838 and 610 mg L^-1, respectively), were the source of toxicity. Although we were unable to conclusively identify the residual toxicity (approx. 1.4 TU of 9.71 TU) attributable to unknown toxicants in textile dyeing effluent, the findings of this study suggest that careful operation of the Fenton treatment process could contribute to eliminating its unintended toxic effects on aquatic organisms.

Use of solar advanced oxidation processes for wastewater treatment: Follow-up on degradation products, acute toxicity, genotoxicity and estrogenicity

Wastewater tertiary treatment by advanced oxidation processes is thought to produce a treated effluent with lower toxicity than the initial influent. Here we performed tertiary treatment of a secondary effluent collected from a Waste Water Treatment Plant via homogeneous (solar/HSO5(-)/Fe(2+)) and heterogeneous (solar/TiO2) solar advanced oxidation aiming at the assessment of their effectiveness in terms of contaminants' and toxicity abatement in a plain solar reactor. A total of 53 organic contaminants were qualitatively identified by liquid chromatography coupled to high-resolution mass spectrometry after solid phase extraction. Solar advanced oxidation totally or partially removed the major part of contaminants detected within 4.5 h. Standard toxicity tests were performed using Vibrio fischeri, Daphnia magna, Pseudokirchneriella subcapitata and Brachionus calyciflorus organisms to evaluate acute and chronic toxicity in the secondary or tertiary effluents, and the EC50% was calculated. Estrogenic and genotoxic tests were carried out in an attempt to obtain an even sharper evaluation of potential hazardous effects due to micropollutants or their degradation by-products in wastewater. Genotoxic effects were not detected in effluent before or after treatment. However, we observed relevant estrogenic activity due to the high sensitivity of the HELN ERα cell line.

Toxicity assessment of dye containing industrial effluents by acute toxicity test using Daphnia magna

Toxicity of dye containing effluent of tannery, textile, dyes and pulp-paper industries was evaluated in an acute toxicity test using Daphnia magna. The 48-hour EC(50) values were 4.33% and 19.5% for tannery effluents (Tn1 and Tn2). Textile effluents (Tx1-Tx7) had 48-hour EC(50) values; >100%, >100%, 62.9%, 63.0%, 40.3%, >100% and >100%, respectively. Dye industries (D1-D7) had 48-hour EC(50) values; 14.1%, 15.5%, 24.5%, 29.7%, 23.2%, >100% and >100%, respectively. Similarly pulp-paper effluents (P1-P5) showed acute toxicity as 100%, 77.87%, 46.44%, 69.55% and 82.84%, respectively. These results showed linear relationship with high degree of confidence (r(2) ≥ 0.84-0.99) between immobility and test concentrations. Toxicity classification criteria showed that out of five effluents from pulp-paper mill, four were minor acutely toxic having 48-hour EC(50) value in between >46%-100%. Out of seven textile effluents, four were not acutely toxic (48-hour EC(50) value >100%) and three were minor acutely toxic (48-hour EC( 50) value in the range of 40.3%-63.0%). Similarly, out of seven dye industrial effluents, two were not acutely toxic and five minor acutely toxic. One of the two tanneries was moderately acutely toxic and another one was minor acutely toxic. Classification based on toxic unit revealed that four out of five pulp-paper effluent, three out of seven textile effluents, five out of seven dye effluents and both the tannery effluents were toxic. Overall, 66.67% effluents were found toxic and 33.33% as non-toxic. In general, tannery and dyes effluents showed more toxicity than textile and paper mill effluents.

Acute toxicity assessment of textile dyes and textile and dye industrial effluents using Daphnia magna bioassay

Aquatic toxicity of textile dyes and textile and dye industrial effluents were evaluated in an acute toxicity study using Daphnia magna as an aquatic experimental animal model. The 48-h EC50 value for the azo dyes, Remazol Parrot Green was 55.32 mg/L and for Remazol Golden Yellow was 46.84 mg/L. Whereas 48-h EC50 values for three dye industrial effluents (D1, D2, and D3) were 14.12%, 15.52%, and 29.69%, respectively. Similarly, EC50 value for three textile mill effluents (T1, T2, and T3) were >100%, 62.97%, and 63.04%, respectively. These results also showed linear relationship with high degree of confidence ( r2 = >0.84 to >0.99) between immobility and test concentrations. The ratio of 24 to 48-h EC50 remains to be in between 1.1 and 1.2. The general criteria of toxicity classification showed that both dyes were minor acutely toxic having 48-h EC50 in between 10 and 100 mg/L. Of the six textile and dye industrial effluents tested, one was not acutely toxic (48-h EC50 > 100%) and five were minor acutely toxic (48-h EC50 > 14.12–29.69%). The toxicity classification of effluent based on toxic unit (TU) showed that of the six effluents tested five were found toxic (TU = >1) and one was non-toxic (TU = <1). Thus, dye effluents showed highest toxicity and textile effluents lowest toxicity. The study also suggested that the assay with D. magna was an excellent method for evaluation of aquatic toxicity of dyes and dyes containing industrial effluents.

Ecotoxicological assessment of effluents in the Basque country (Northern Spain) by acute and chronic toxicity tests using Daphnia magna straus

Acute pass/fail, multi-concentration tests, and 3-brood chronic toxicity tests with Daphnia magna Straus (Cladocera, Crustacea) were used to characterise industrial and municipal effluents from various sources. The effluents that "passed" the pass/fail tests had 48-h EC50 values >100% and reproduction No Observed Effect Concentration (NOECs) > or =100%, except for one effluent that had a reproduction NOEC of 31.6%. The acute multi-concentration toxicity tests allowed a rapid classification of effluents from Very Toxic (48-h EC50 < 25%), to Non-Toxic (48-h EC50 >100%). The acute-to-chronic ratio (ACR: 48-h EC50 divided by the NOEC for reproduction) in the studied effluents ranged from 5 to about 100. From these results, we propose a step-wise protocol for assessing effluent toxicity. First, effluent is evaluated by means of simple and rapid pass/fail acute toxicity tests, to discriminate Non-Toxic from potentially Toxic effluents, thus facilitating the establishment of priority actions. Second, 48-h ECx is estimated to classify effluents on a toxicity scale from Non-Toxic to Very Toxic. Third, chronic multi-concentration tests are used to calculate reproduction NOECs. These parameters combined with data on effluent chemical composition, chemical and hydrological characteristics of receiving waters, and biological quality criteria can be jointly used for more rational regulatory practices and risk assessment of effluents.

Bioremediation of municipal sludge by vermitechnology and toxicity assessment by Allium cepa

The aim of this study was to evaluate municipal sludge (MS) for its toxic potential by Allium cepa and also to understand the effect of vermicomposting on the reduction of toxicity, if any. Municipal sludge (MS) and vermicomposted sludge (VS) were evaluated. Elemental analysis of MS showed the presence of heavy metals. Morphological studies of A. cepa roots indicated coiled and wavy roots on exposure to MS but no root abnormality was reported in VS. Under genotoxic studies, inhibition in mitotic index was concentration dependent and the control values of 11.76 gradually reduced to 5.40 at 10% MS leachate whereas mitotic index was increased to 9.48 at 10% VS leachate. Exposure of leachate induced chromosomal aberrations, micronucleus formation and binucleate cells in a dose dependent manner. However, mitotic aberrations were observed significant at 10% MS leachate but they were insignificant at 10% VS leachate. The wet and dry weight of roots, root elongation and chlorophyll contents were reduced as the concentration of leachate increased but VS leachate did not produce considerable reduction. The wet and dry weight of A. cepa roots were 20.312 g and 3.250 g respectively and they were reduced to 10.82 g and 1.68 g respectively at 10% MS leachate but VS leachate showed an increase to 18.127 g and 2.53 g respectively. Total chlorophyll in control, 10% MS leachate and 10% VS leachate were 0.245 g, 0.162 g and 0.214 g respectively. It could be concluded that the MS was toxic to a remarkable extent but vermicomposting of sludge might be beneficial for bioremediation and recommended before land filling.

Cytogenetic effects of leachates from tannery solid waste on the somatic cells of Vicia faba

The contamination of surface- and groundwater by the leaching of solid wastes generated by industrial activities as a result of water runoff and rainfall is a matter of great concern. The leachates from tannery solid waste (TSW), a major environmental pollutant, were examined for their possible genotoxic effects on the somatic cells of Vicia faba. Leachates were prepared from solid wastes procured from leather-tanning industrial sites, and V. faba seedlings were exposed to three test concentrations, 2.5%, 5%, and 10%, through soil and aqueous media for 5 days. The root tips examined for cytogenetic damage revealed that leachate of TSW significantly inhibited the mitotic index and induced significantly frequent chromosomal and mitotic aberrations (CA/MA) in a dose-dependent manner. The chemical analysis of TSW samples revealed that the chief constituents were chromium and nickel, which may cause genetic abnormalities. The frequency of aberrations was found to be higher in the root meristematic cells of Vicia faba exposed through the aqueous medium than those exposed through the soil medium. The results of the present study indicated that contamination of potable water bodies by leachates of TSW may cause genotoxicity. For the biomonitoring of complex mixtures of toxicants with the V. faba bioassay, the use of the aqueous medium seems to be a more promising method than the use of the soil medium.