Search

AbstractThe fast-increasing use of chemicals led to large numbers of chemical compounds entering the aquatic environment, raising concerns about their potential effects on ecosystems. Therefore, assessment of the ecotoxicological features of organic compounds on aquatic organisms is very important. Daphnia magna and Fathead minnow are two aquatic species that are commonly tested as standard test organisms for aquatic risk assessment and are typically chosen as the biological model for the ecotoxicology investigations of chemical pollutants. Herein, global quantitative structure–toxicity relationship (QSTR) models have been developed to predict the toxicity (pEC(LC)50) of a large dataset comprising 2106 chemicals toward Daphnia magna and Fathead minnow. The optimal descriptor of correlation weights (DCWs) is calculated using the notation of simplified molecular input line entry system (SMILES) and is used to construct QSTR models. Three target functions, TF1, TF2, and TF3 are utilized to generate 12 QSTR models from four splits, and their statistical characteristics are also compared. The designed QSTR models are validated using both internal and external validation criteria and are found to be reliable, robust, and excellently predictive. Among the models, those generated using the TF3 demonstrate the best statistical quality with R2 values ranging from 0.9467 to 0.9607, Q2 values ranging from 0.9462 to 0.9603 and RMSE values ranging from 0.3764 to 0.4413 for the validation set. The applicability domain and the mechanistic interpretations of generated models were also discussed. [ABSTRACT FROM AUTHOR]

Ecotoxicological safety assessment of chemicals requires toxicity data on multiple species, despite the general desire of minimizing animal testing. Predictive models, specifically machine learning (ML) methods, are one of the tools capable of solving this apparent contradiction as they allow to generalize toxicity patterns across chemicals and species. However, despite the availability of large public toxicity datasets, the data is highly sparse, complicating model development. The aim of this study is to provide insights into how ML can predict toxicity using a large but sparse dataset. We developed models to predict LC50-values, based on experimental LC50-data covering 2431 organic chemicals and 1506 aquatic species from the ECOTOX-database. Several well-known ML techniques were evaluated and a new ML model was developed, inspired by recommender systems. This new model involves a simple linear model that learns low-rank interactions between species and chemicals using factorization machines. We evaluated the predictive performances of the developed models based on two validation settings: 1) predicting unseen chemical-species pairs, and 2) predicting unseen chemicals. The results of this study show that ML models can accurately predict LC50-values in both validation settings. Moreover, we show that the novel factorization machine approach can match well-tuned, complex, ML approaches. [ABSTRACT FROM AUTHOR]

Initially, density approximations and generalised gradient approximations (GGA) functional of DFT were executed to determine the electronic structure where the non-local functionals of GGA obtained more close value of reference value, so that GGA method was used to calculate the band structures, DOS, PDOS and optical properties of ZrO2, Zr0.93Si0.07O2 and Zr0.86Si0.14O2 using the Perdew–Burke–Ernzerhof (PBE), Revised Perdew–Burke–Ernzerhof (RPBE), Perdew Wang (PW91), and Wu-Cohen. The transferability of electrons is completely related to PseudoPotential (PP), where four methods, such as OTFG ultra-soft, OTFG norm-conserving, ultra-soft, and norm-conserving, were used in this study. Finally, the norm-conserving PP has been selected as the most accurate method for determination of electronic structure. In addition, to assess the nature of orbital, the DOS and PDOS were additionally simulated and even the optical properties of crystals were calculated. Furthermore, the chemical reactivity, such as HOMO and LUMO, quantum properties, is justified where doping can have a vast effect as well as the open circuit voltage (Voc) is increased after doping. Finally, the toxicity data from in silico study refers to us that these are non-toxic or non-carcinogenic materials with not readily biodegradable status. [ABSTRACT FROM AUTHOR]

The present study examined the histopathological changes and some parameters of oxidative stress in the testes of the freshwater leech Limnatis nilotica, following their exposure to 50 µg l−1 of cadmium (Cd). The protective effects of salicylic acid (SA) in mitigating Cd-induced oxidative and histopathological injury were also investigated. We found that Cd exposure caused several histopathological changes in leech testes, such as vacuolisation of spermatogenic cysts which were strongly destroyed and disorganised. Biochemical study showed oxidative stress damage marked by a substantial increase in malondialdehyde and hydrogen peroxidase levels as well as disturbance in the activity of the leech antioxidant system. Interestingly, the testes from the Cd and SA leech-exposed group exhibited increased enzymatic and nonenzymatic antioxidant mechanism defenses, including superoxide dismutase, catalase, glutathione peroxidase, glutathione, oxidized glutathione, thiols, and ascorbic acid, in comparison with the testes of leeches exposed to Cd alone. Thus, SA supplementation considerably attenuated the histopathological lesions induced by Cd exposure, thereby restoring the normal appearance of the testes. In summary, the findings of this study indicate that SA treatment ameliorated the testicular histopathological and oxidative stress-induced damages caused by exposure to Cd through enhancing the antioxidant defense system. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of Cd on the ovaries of the freshwater leech Limnatis nilotica and the ability of salicylic acid (SA) treatment to alleviate the Cd harmful effects. Our results showed that Cd treatment increased the level of oxidative stress leading to severe alterations in histopathological and biochemical indexes. Cd exposure was found to induce a substantial increase in malondialdehyde (MDA) and hydrogen peroxidase (H2O2) contents as well as an impairment in catalase (CAT) and Glutathione peroxidase (GPx) activities. These findings are thoroughly supported by histopathological evidence which showed several modifications in the ovary cord organization. However, SA addition reduced the toxic effect of Cd-exposure through decreasing MDA and H2O2 levels, the regulation of enzymatic and nonenzymatic antioxidant mechanism pathways leading to the alleviation of the histopathological lesions. These results suggest that SA can prevent damage under Cd toxicity in the leech ovaries. [ABSTRACT FROM AUTHOR]

The quantitative structure–activity relationship (QSAR) modelling of mixtures is not as simple as that for individual chemicals, and it needs additional care to avoid overestimation of the performance. In this research, we have developed a 2D-QSAR model using only 2D interpretable and reproducible descriptors to predict the aquatic toxicity of mixtures of polar and non-polar narcotic substances present in the environment. Partial least squares (PLS) regression has been used to model the response variable (log 1/EC50 against Photobacterium phosphoreum) and the structural features of 84 binary mixtures of polar and nonpolar narcotic toxicants complying with the Organization of Economic Co-operation and Development (OECD) protocols. The model was cross-validated by mixtures-out and compounds-out cross-validation to nullify the developmental bias. The reliability of prediction of the model has been judged by the Prediction Reliability Indicator (PRI) tool using a newly designed set. The new model is robust, reproducible, extremely predictive, easily interpretable, and can be used for reliable prediction of aquatic toxicity of any untested chemical mixtures within the applicability domain. We have additionally used a machine learning-based chemical read-across algorithm in this study to improve the quality of predictions for the toxicity of the mixtures with the modelled descriptors. [ABSTRACT FROM AUTHOR]

Dimethyl sulfoxide (DMSO) is widely used as a vehicle solvent in ecotoxicity bioassays.Despite its frequent use, it could be toxic for organisms at some concentrations. Hence, this study aims to investigate the effects of DMSO on the model organisms: microalgae Raphidocelis subcapitata, microcrustacean Daphnia magna, and rotifer Brachionus calyciflorus. DMSO was applied to the organisms in concentrations ranging from 0.031% to 4%. For R. subcapitata the lowest observed effect concentration (LOEC) after 72 h of exposure was 0.125% DMSO. The 50% effective concentration (EC50) was 2.138 ± 0.372%. In D. magna, significant differences in the mobility after 24 h or 48 h of exposure were observed for 1% DMSO being 1.712 ± 0.207% and 1.167 ± 0.220% DMSO the EC50 observed for 24 h and 48 h exposure, respectively. For B. calyciflorus, it was not possible to validate the tests performed, as there were insufficient animals alive in the control conditions at the end of the exposure period. Therefore, we recommended avoiding DMSO as a vehicle in assays using B. calyciflorus, and to use final DMSO concentrations in an experimental solution not exceeding 0.125% for R. subcapitata and 0.5% for D. magna. Finally, using a maximum of 0.01% DMSO is safe for the organisms tested. The effects of the vehicle solvent dimethyl sulfoxide (DMSO) were investigated in three aquatic model organisms, the microalgae Raphidocelis subcapitata, the microcrustacean Daphnia magna and the rotifer Brachionus calyciflorus. As a result, negative effects on growth rate for the algae population, immobilisation of daphnids and inhibition of rotifer reproduction was observed obtaining EC50 close to 1% of DMSO for all these cases. [ABSTRACT FROM AUTHOR]

Reviewing the toxicological literature for over the past decades, the key elements of QSAR modelling have been the mechanisms of toxic action and chemical classes. As a result, it is often hard to design an acceptable single model for a particular endpoint without clustering compounds. The main aim here was to develop a Pass-Pass Quantitative Structure-Activity-Activity Relationship (PP QSAAR) model for direct prediction of the toxicity of a larger set of compounds, combing the application of an already predicted model for another species, and molecular descriptors. We investigated a large acute toxicity data set of five aquatic organisms, fish, Daphnia magna, and algae from the VEGA-Hub, as well as Tetrahymena pyriformis and Vibrio fischeri. The statistical quality of the models encouraged us to consider this alternative for the prediction of toxicity using interspecies extrapolation QSAAR models without regard to the toxicity mechanism or chemical class. In the case of algae, the use of activity values from a second species did not improve the models. This can be attributed to the weak interspecies relationships, due to different aquatic toxicity mechanisms in species. [ABSTRACT FROM AUTHOR]

Ractopamine, a β-adrenergic receptor agonist, is commonly used as a repartitioning agent and growth promotor in animal agriculture. There is evidence that ractopamine can enter natural water sources from livestock wastes, at concentrations in the low ng/L range. Currently, aquatic toxicity data for ractopamine is scarce. Therefore, in two separate experiments Xenopus laevis tadpoles were exposed to ractopamine in tank water at concentrations ranging from 2 ng/L to 2.2 mg/L for up to 14 d utilizing FETAX methodology. No overt signs of toxicity were identified in measured endpoints including survival, growth, malformation, and developmental stage. Oral ractopamine exposure in mammals and fish is associated with cardiotoxicity, increased mortality, and physiological alterations; however, this study suggests that aqueous ractopamine is not a developmental toxicant or overtly toxic to amphibians at environmentally relevant concentrations. [ABSTRACT FROM AUTHOR]

Owing to their widespread use in wooden products, industrial products, cosmetics, and personal care products, biocides are frequently detected in wastewater and surface water. In this study, I examined the acute toxicities of 10 commonly used biocides, namely methylisothiazolinone, benzisothiazolinone, octylisothiazolinone, dichlorooctylisothiazolinone, iodopropynyl butylcarbamate, triclosan, azoxystrobin, pyraclostrobin, climbazole, and clotrimazole, in the water flea (Daphnia similis), freshwater planarians (Dugesia japonica) and green neon shrimp (Neocaridina denticulata). Among the 10 tested biocides, dichlorooctylisothiazolinone was the most toxic to both D. similis and N. denticulata, whereas pracolstrobin was the most toxic to Du. japonica. By contrast, the least toxic biocides for D. similis, Du. japonica, and N. denticulata were climbazole, iodopropynyl butylcarbamate, and methylisothiazolinone, respectively. The 48-h nominal LC50 values of all the biocides, except for benzisothiazolinone and climbazole, in D. similis were mostly less than 1 mg/L. In addition, the 96-h nominal LC50 values of all the biocides, except for methylisothiazolinone and iodopropynyl butylcarbamate, in Du. japonica was less than 1 mg/L. These results indicate the biocides with low LC50 values are relatively toxic to freshwater organisms. [ABSTRACT FROM AUTHOR]

Gas-to-liquid (GTL) products are synthetic hydrocarbons produced from natural gas using a catalytic process known as the Fischer-Tropsch process. This process yields a synthetic crude oil that consists of saturated hydrocarbons which can subsequently be refined to a range of products analogous to those obtained from petroleum refining. However, in contrast to their petroleum-derived analogs, GTL products are essentially free of unsaturated or aromatic compounds and do not contain any sulfur-, oxygen-, or nitrogen-containing compounds. Under new chemical substance notification requirements, an extensive testing program covering the entire portfolio of GTL products has been undertaken to assess their hazardous properties to human health and environment. The results of these studies have been summarized in a two-part review. Part 1 provides an overview of the mammalian toxicity hazardous properties of the various GTL products. This second part of the review focuses on the aquatic, sediment, terrestrial, and avian toxicity studies which assess the ecotoxicological hazard profile of the GTL products. Many challenges were encountered during these tests relating to dosing, analysis and interpretation of results. These are discussed with the intent to share experiences to help inform and shape future regulatory mandates for testing of poorly soluble complex substances. As was the case with the mammalian toxicology review, there were a few cases where adverse effects were found, but overall the GTL products were found to exert minimal adverse ecotoxicological effects and these were less severe than effects observed with their conventional, petroleum-derived analogs. [ABSTRACT FROM AUTHOR]

As integration of nanoparticles (NPs) into products becomes more common, the need to address the paucity of chronic hazard information for aquatic environments required to determine risk potential increases. This study generated acute and chronic toxicity reference values forCeriodaphnia dubiaexposed to 20 and 100 nm silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) to generate and evaluate potential differences in acute-to-chronic ratios (ACR) using two different feeding methods. A modified feeding procedure was employed alongside the standard procedures to investigate the influence of food on organism exposure. An 8-h period before food was added allowed direct organism exposure to NP dispersions (and associated ions) without food-to-NP interactions. The AgNPs [chronic lethal median concentrations (LC50) between 18.7 and 31.9 µg/L] were substantially more toxic than AuNPs (LC50 = 21 507 to >26 384 µg/L). The modified chronic testing method resulted in greater sensitivity in AgNPs exposures. However, the modified feeding ration had less of an effect in exposures to the larger (100 nm) AgNPs compared to smaller particles (20 nm). The ACRs for AgNPs using the standard feeding ration were 1.6 and 3.5 for 20 nm and 100 nm, respectively. The ACRs for AgNPs using the modified feeding ration were 3.4 and 7.6 for 20 nm and 100 nm NPs, respectively. This supports that the addition of the standard feeding ration decreasesC. dubiachronic sensitivity to AgNPs, although it must also be recognized organisms may be sensitized due to less access to food. The ACRs for 20 nm and 100 nm AuNPs (standard ration only) were 4.0 and 3.0, respectively. It is important to also consider that dissolved Ag+ions are more toxic than AgNPs, based on both acute toxicity values in the cited literature and chronic toxicity thresholds generated in this study that support existing thresholds that Ag+are likely protective of AgNPs effects. [ABSTRACT FROM AUTHOR]

The potential adverse effects of CuO nanoparticles (NPs) have increasingly attracted attention. Combining electron microscopic and toxicological investigations, we determined the adhesion, uptake, and toxicity of CuO NPs to eukaryotic algaChlorella pyrenoidosa. CuO NPs were toxic toC. pyrenoidosa, with a 72 h EC50of 45.7 mg/L. Scanning electron microscopy showed that CuO NPs were attached onto the surface of the algal cells and interacted with extracellular polymeric substances (EPS) excreted by the organisms. Transmission electron microscopy (TEM) showed that EPS layer of algae was thickened by nearly 4-fold after CuO NPs exposure, suggesting a possible protective mechanism. In spite of the thickening of EPS layer, CuO NPs were still internalized by endocytosis and were stored in algal vacuoles. TEM and electron diffraction analysis confirmed that the internalized CuO NPs were transformed to Cu2O NPs (d-spacing, ∼0.213 nm) with an average size approximately 5 nm. The toxicity investigation demonstrated that severe membrane damage was observed after attachment of CuO NPs with algae. Reactive oxygen species generation and mitochondrial depolarization were also noted upon exposure to CuO NPs. This work provides useful information on understanding the role of NPs–algae physical interactions in nanotoxicity. [ABSTRACT FROM AUTHOR]

VolSurf+in silicophysicochemical descriptors for both the cationic and the anionic counterparts of ionic liquids (ILs) have been derived. These descriptors, suitable for molecular modelling of IL structures which, due to their amphiphilic nature, interact strongly with biological matrices, can be related to aquatic toxicity by means of a partial least squares statistical model. This model gives an insight into the relationships between structural physicochemical properties and aquatic toxicity as well as a satisfactory quantitative structure–property correlation, allowing prediction of aquatic toxicity scores of ILs. [ABSTRACT FROM AUTHOR]

The objective of this study was to identify and to apply appropriate biotests having the advantages of being highly sensitive, easy to run, relatively inexpensive and able to substitute fish toxicity tests due to ethical reasons of animal welfare. To perform an ecotoxicological assessment of industrial wastewaters, different microbiotests were conducted to substitute the fish toxicity test withLebistes reticulatusthroughVibrio fischeri, Thamnocephalus platyurus, Daphnia magna,Lemna minorandLepidium sativumrepresenting different trophic levels in the aquatic and terrestrial ecosystems. Also, Algaltox FTMwithPseudokirchneriella subcapitataand Protox FTMwithTetrahymena thermophilatests were carried out. However, they could not be applied successfully for the wastewater samples. Wastewater samples from seven different industrial zones comprising different industries were subjected to characterization through measuring their physical–chemical parameters and their toxicity versus the above-mentioned organisms.T. platyurus,D. magnaandL. reticulatuswere the most sensitive test organisms investigated for the wastewaters. Considering toxic unit values, generally wastewater samples were toxic according to Thamnotox FTM, Daphtox FTMand fish toxicity tests. As an important outcome, it was concluded that Daphtox FTMand Thamnotox FTMcould be a good alternative for the fish toxicity test, which is so far the sole toxicity test accepted by the Turkish Water Pollution Control Regulation. [ABSTRACT FROM AUTHOR]

In addition to molecular structure profiles, descriptors based on physicochemical properties are useful for explaining the eco-toxicities of chemicals. In a previous study we reported that a criterion based on the difference between the partition coefficient (logPOW) and distribution coefficient (logD) values of chemicals enabled us to identify aromatic amines and phenols for which interspecies relationships with strong correlations could be developed for fish–daphnid and algal–daphnid toxicities. The chemicals that met the logD-based criterion were expected to have similar toxicity mechanisms (related to membrane penetration). Here, we investigated the applicability of logD-based criteria to the eco-toxicity of other kinds of chemicals, including aliphatic compounds. At pH 10, use of a logPOW– logD> 0 criterion and omission of outliers resulted in the selection of more than 100 chemicals whose acute fish toxicities or algal growth inhibition toxicities were almost equal to their acute daphnid toxicities. The advantage of logD-based criteria is that they allow for simple, rapid screening and prioritizing of chemicals. However, inorganic molecules and chemicals containing certain structural elements cannot be evaluated, because calculated logDvalues are unavailable. [ABSTRACT FROM AUTHOR]

The neonicotinoid insecticide imidacloprid is among the pesticides that most frequently exceed current water quality standards in Dutch surface waters. Recent research shows that effects of imidacloprid on water organisms occur at concentrations below these standards. Mayflies appear to be particularly sensitive with chronic No Observed Effect Concentrations in the nanogram per liter range. The aim of this study was to derive updated water quality standards in accordance with the methodology of the European Water Framework Directive by evaluating the available recent literature on acute and chronic ecotoxicity of imidacloprid to aquatic organisms in laboratory and semi-field experiments. It is concluded that the standard for long-term exposure should be lowered to 8.3 nanograms per liter; the standard for short-term concentration peaks can be maintained at the current value of 0.2 micrograms per liter. The European Commission set restrictions to the use of imidacloprid-based products to reduce the risks for bees and the Dutch national authorities issued emission reduction measures to protect aquatic life. Future monitoring data will ultimately reveal if these measures are sufficient to meet the newly proposed standards. [ABSTRACT FROM PUBLISHER]

Surfactant formulations used in chemical dispersing agents are derived from the same functional components used in numerous household products such as dishwashing soaps and laundry detergents. During theDeep Water Horizon(DWH) oil spill response, a significant volume of chemical dispersant was deployed, causing members of the public and the media to question the role of chemical dispersant (Corexit 9500) usage in mitigating oil spill effects. Consequently, laboratory tests were conducted by regulatory agencies to further evaluate and substantiate the existing aquatic toxicity of Corexit dispersants. To help put dispersant toxicity in context, two independent accredited labs were commissioned to conduct parallel studies that compared the acute toxicity of Corexit 9500 to common household cleaning agents. The results indicate that the acute toxicity of Corexit 9500 to marine aquatic organism is either within the median range or less toxic than the household cleaning agents tested. The median LC50 value for Corexit 9500 exposures toAmericamysis bahiawas 42.5 mg/L (four products were less toxic and four products were more toxic); whereas, the median LC50 value for Corexit 9500 exposures toMenidiaberyllinawas 73.1 mg/L (one product was less toxic and seven products were more toxic). [ABSTRACT FROM PUBLISHER]

The ability to estimate aquatic toxicity is a critical need for ecological risk assessment and chemical regulation. The consensus in the literature is that mode of action (MOA) based toxicity models yield the most toxicologically meaningful and, theoretically, the most accurate results. In this study, a two-step prediction methodology was developed to estimate acute aquatic toxicity from molecular structure. In the first step, one-against-the-rest linear discriminant analysis (LDA) models were used to predict the MOA. The LDA models were able to predict the MOA with 85.8–88.8% accuracy for broad and specific MOAs, respectively. In the second step, a multiple linear regression (MLR) model corresponding to the predicted MOA was used to predict the acute aquatic toxicity value. The MOA-based approach was found to yield similar external prediction accuracy (r2= 0.529–0.632) to a single global MLR model (r2= 0.551–0.562) fit to the entire training set. Overall, the global hierarchical clustering approach yielded a higher combination of accuracy and prediction coverage (r2= 0.572, coverage = 99.3%) than the other approaches. Utilizing multiple two-dimensional chemical descriptors in MLR models yielded comparable results to using only the octanol–water partition coefficient (logKow). [ABSTRACT FROM AUTHOR]

REACH regulation demands information about acute toxicity of chemicals towards fish and supports the use of QSAR models, provided compliance with OECD principles. Existing models present some drawbacks that may limit their regulatory application. In this study, a dataset of 908 chemicals was used to develop a QSAR model to predict the LC5096 hours for the fathead minnow. Genetic algorithms combined withknearest neighbour method were applied on the training set (726 chemicals) and resulted in a model based on six molecular descriptors. An automated assessment of the applicability domain (AD) was carried out by comparing the average distance of each molecule from the nearest neighbours with a fixed threshold. The model had good and balanced performance in internal and external validation (182 test molecules), at the expense of a percentage of molecules outside the AD. Principal Component Analysis showed apparent correlations between model descriptors and toxicity. [ABSTRACT FROM AUTHOR]

Significant advances were made in the development of quantitative structure–activity relationships (QSARs) relating molecular structure to aquatic toxicity by three studies over 30 years ago by Ferguson in 1939, Konemann in 1981, and Veith and colleagues in 1983. We revisit the original concepts and data from these studies and review these contributions from the bases of current perspectives on the hypothesized mechanism of baseline narcotic toxicity and the underlying thermodynamic and kinetic aspects. The relationships between LC50, octanol–water partition coefficient, aqueous solubility, chemical activity and chemical volume fraction in lipid phases are outlined including kinetic influences on measured toxicities. These relationships provide a compelling and plausible explanation of the success of these and other QSARs for aquatic toxicity. Suggestions are made for further advances in these QSARs to improve assessments of toxicity by baseline narcotic toxicity and selective modes of action, especially using emerging quantum chemical computational capabilities. [ABSTRACT FROM PUBLISHER]

Many chemicals commonly occurring in surface water are found to be hormonally active. Fourteen compounds including four sex hormones, three synthetic hormones, one non-steroidal anti-androgen, and six industrial endocrine-disrupting chemicals were selected to examine their acute toxicities on the freshwater planarian,Dugesia japonica. Among all test chemicals, diethylstilbestrol had the highest toxicity. Relatively, the toxicities of the synthetic hormones were higher than the natural ones. Among the six industrial endocrine-disrupting chemicals tested, bisphenol A was the most toxic, with a 48-h LC50of 8.3 mg L−1. Overall, the natural or synthetic hormones, other than estrone and estriol, were more acutely toxic to planarians than the industrial endocrine disruptors tested. The acute toxicities of the test chemicals toDugesia japonicawere in the same order of magnitude as those toDaphnia magnabased on available published data. Despite this study used non-environmentally relevant levels, such kinds of chemicals do not exist singly in the aquatic environment, but typically act in synergistic and/or additive ways in the complex environmental mixtures, and the total estrogen equivalents are much higher than a single chemical. This study stands as a starting point for other acute and chronic assays, namely using mixtures. [ABSTRACT FROM AUTHOR]

Because of their global distribution, environmental persistence, and potential risk to human beings and ecosystems, poly- and perfluorinated compounds (PFCs) are of particular concern to scientific and regulatory communities. Despite this concern, data about the physicochemical properties and aquatic toxicity of PFCs are still limited, and there are big debates regarding the actual values of some properties investigated. In order to have a clear overview of the data available, the authors summarize the data available for the physicochemical properties and aquatic toxicity of PFCs. [ABSTRACT FROM AUTHOR]

Agrochemicals have the potential to cause deleterious effects on living organisms and therefore they must be subjected to various (eco)toxicological studies and monitoring programs in order to protect human health and the environment. The aim of this study was to assess the ecotoxicity of a new natural formicide with a battery of three classical and three ecotox-kit tests. The former tests were performed with Aliivibrio fischeri bacteria (Lumistox test), the cladoceran Daphnia magna and Pseudokirchneriella subcapitata algae, and the latter with Thamnotoxkit FTM (Thamnocephalus platyurus), Ostracodtoxkit F® (Heterocypris incongruens) and LuminoTox (photosynthetic enzyme complexes). In the range of formicide concentrations tested (from 0.06 to 2.0 g L−1), the measurement endpoint values varied from 0.79 g L−1 for the algal test to > 2 g L−1 for the LuminoTox and Ostracodtoxkit F® tests. Hierarchical sensitivity ranking based on the no-observed effect concentration (NOEC) values established to assess the formicide ecotoxicity was as follows: algal growth inhibition test ≈ daphnid immobilization test ≈ bacterial luminescence inhibition test > Thamnotoxkit FTM > LuminoTox > Ostracodtoxkit F®. Overall, results from the battery of bioassays showed that this formicide preparation presents low ecotoxicity as compared to the aquatic ecotoxicity of presently commercialized formicides. In conclusion, classical aquatic bioassays are more sensitive than ecotox-kit tests in the assessment and monitoring of the new natural formicide. [ABSTRACT FROM AUTHOR]

Fourteen benzophenone-type UV filters and four paraben preservatives were selected to examine their acute toxicities on Dugesia japonica. The 48-h LC50 values for planarians exposed to benzophenone-type UV filters can be ranked as oxybenzone > mexenone > 5-chloro-2-hydroxybenzophenone > 2,4-dihydroxybenzophenone > 2-hydroxybenzophenone > dioxybenzone > benzophenone > 2,2′,4,4′-tetrahydroxybenzophenone > 4-hydroxybenzophenone > 3-hydroxybenzophenone > 4,4′-dihydroxybenzophenone > 2,2′-dihydroxy-4,4′-dimethoxybenzophenone > 2,3,4-trihydroxybenzophenone > sulisobenzone with a range from 0.9 to 145 mg L−1 with a similar sequence for the 96 h LC50 values, ranging from 0.5 to 77 mg L−1. The 48 and 96 LC50 values for planarians exposed to paraben preservatives can be ranked as butylparaben > propylparaben > ethylparaben > methylparaben. Among all the tested chemicals, oxybenzone was the most toxic and sulisobenzone the least toxic chemical to planarian at each exposure period. Most benzophenone-type UV filters are toxic to aquatic animals with 48 h LC50 values less than 10 mg L−1, except for 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,3,4-trihydroxybenzophenone, and sulisobenzone. Because of their common occurrence in aquatic environment, more studies on aquatic toxicities of benzophenone-type UV filters and paraben preservativs are needed to provide important information to adequately assess their ecological risk. [ABSTRACT FROM AUTHOR]

The use of nanoparticles—particles with size ∼1-100 nm is increasing worldwide. This is particularly the case for applications of titanium dioxide nanoparticles (nano-TiO2) in consumer products, which have expanded at a fast rate in the last decade. The properties of nano-TiO2 differ significantly from bulk-TiO2 of the same composition because of an increase in surface area. A release of nano-TiO2 from application sources to the aquatic environment may pose possible risks due to their bioavailability and toxicity. The aggregation of nano-TiO2 plays an important role in the environmental effects of nanoparticles because the size and shape of nanoparticles will determine the magnitude of any potentially toxic effect. Aggregation is affected by pH, ionic strength, and ionic identity (inorganic and organic) of aqueous suspensions and is reviewed in this paper. The current information on the evaluation of ecotoxicological hazards of nano-TiO2 to bacteria, algae, invertebrates, nematodes, and rainbow trout is also given. [ABSTRACT FROM AUTHOR]

Aquatic toxicity tests using spore germination and gametophyte growth of the green alga, Ulva pertusa Kjellman, were developed and evaluated by assessing the toxicity of different organic and inorganic chemicals and elutriates of sewage or waste sludge. The toxic ranking of three metals was: Cu (EC50 of 0.017 mg l-1) > Zn (0.378 mg l-1) > Cd (0.789 mg l-1) for spore germination and Cu (0.023-0.027 mg l-1) > Cd (0.189-0.200 mg l-1) > Zn (0.307-0.317 mg l-1) for gametophyte growth. Spore germination (EC50 of 3.95 mg l-1) was more sensitive to formalin than gametophyte growth (6.92-7.18 mg l-1). The EC50 for tributyltin oxide differed between the endpoints, with values of 0.586 mg l-1 for germination and 0.391-0.396 mg l-1 for growth responses. After exposure to three different sludge elutriates the greatest and least toxic effects were found for urban sewage (7.6-8.3%) and filtration bed (>61%), respectively. The bioassays are simple, inexpensive, eco-relevant and have a potential application worldwide. [ABSTRACT FROM AUTHOR]

This research evaluated the toxicity of TiO2 nanoparticles to freshwater aquatic organisms and the effects of organic and inorganic material on TiO2 toxicity. The fathead minnow was much less acutely sensitive to TiO2 (LC50 500 mg/l and higher) than Ceriodaphnia dubia and Daphnia pulex (mean LC50 values 7.6 and 9.2 mg/l, respectively). Total organic carbon levels of 1.5 mg/l decreased TiO2 acute toxicity to C. dubia (LC50 > 100 mg/l), but kaolinite clay decreased TiO2 toxicity to a lesser extent. In chronic toxicity tests, the green algae Pseudokirchneriella subcapitata was more sensitive to TiO2 (IC25 1-2 mg/l) than C. dubia (IC25 9.4-26.4 mg/l) and the fathead minnow (IC25 values over 340 mg/l). Study results indicate that the specific organisms exposed and the effects of water quality parameters on TiO2 toxicity should be considered in hazard evaluations of this nanoparticle. [ABSTRACT FROM AUTHOR]

The acute and chronic toxicity of monocrotophos (MCP), the binary joint toxicity of MCP and bifenthrin (BF), and sodium dodecyl benzene sulfonate (SDBS) to Daphnia magna (D. magna) was evaluated. The 24 h-median effective concentration (24 h-EC50) and 48 h-median lethal concentration (48 h-LC50) of MCP towards D. magna were 161 and 388 μ g/L, respectively. In addition, the lowest-observed effective concentration (LOEC) and non-observed effective concentration (NOEC) of MCP to D. magna were 10 and 5 μ g/L, respectively. Furthermore, the chronic value (ChV) of MCP against D. magna was 7 μ g/L and the acute chronic ratio (ACR) was 55. The number of offspring per female and the intrinsic rate of natural increase (r) were identified as the parameters that were most sensitive to MCP. In addition, toxic unit (TU) analysis was employed to evaluate the joint toxicities. The calculated TUmix values of binary equitoxic mixtures of MCP + BF and MCP + SDBS were 1.47 and 1.63, respectively, which suggests that both equitoxic mixtures exert a limited antagonistic effect. The results of this study revealed that the toxic threshold of MCP towards D. magna is higher than its reported highest residue (4 μ g/L) in the ordinary aquatic environment, and that concurrent exposure to BF or SDBS may exert a slight antagonistic effect. [ABSTRACT FROM AUTHOR]

The pesticides originally designed to kill target organisms are dangerous for many other wild species. Since they are applied directly to the environment, they can easily reach the water basins and the topsoil. A dataset of 125 aromatic pesticides with well-expressed aquatic toxicity towards trout was subjected to quantitative structure activity relationships (QSAR) analysis aimed to establish the relationship between their molecular structure and biological activity. A literature data for LC50 concentration killing 50% of fish was used. In addition to the standard 2D-QSAR analysis, a comparative molecular field analysis (CoMFA) analysis considering the electrostatic and steric properties of the molecules was also performed. The CoMFA analysis helped the recognition of the steric interactions as playing an important role for aquatic toxicity. In addition, the transport properties and the stability of the compounds studied were also identified as important for their biological activity. [ABSTRACT FROM AUTHOR]

The toxicity of 11 polyquaterniums used in cosmetic applications, and polydimethyldiallylammonium chloride (poly(DADMAC)) were studied for toxicity of the polyquaternium alone, and of a polyquaternium/anionic surfactant complex as occurs in some cosmetic formulations. The surfactant used in the study was sodium dodecyl sulfate (SDS), which is used in cosmetic formulations under its International Nomenclature of Cosmetic Ingredients (INCI) name Sodium Laurel Sulfate. In fish immobilization studies with Gambusia holbrooki, the EC50 of the polyquaternium/surfactant complex was found to be the same as or similar to the EC50 for the polyquaternium alone. The toxicity of the polyquaterniums investigated was similar to the published values for other cationic polyelectrolytes and cationic surfactants, in the range from < 1.0 to 10 mg/L, with the exception of low charge density cellulosic polyquaterniums. The anionic surfactant alone was not toxic to fish in the concentration range tested. Results thus showed the toxicity of the polyquaternium was not mitigated by the presence of the anionic surfactant. [ABSTRACT FROM AUTHOR]

Cartap and cypermethrin, which are among the most widely used pesticides in many countries, are considered safe because of their low mammalian toxicity and their low persistence in the environment. However, recent findings of endocrine-disrupting effects and developmental neurotoxicity have raised concerns about the potential ecological impacts of these pesticides. We evaluated the aquatic toxicity of cartap [S,S'-(2-dimethylaminotrimethylene) bis(thiocarbamate), unspecified hydrochloride] and cypermethrin [(RS)-alpha-cyano-3-phenoxybenzyl-(1RS,3RS,1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate], both individually and combined, on different life stages of the freshwater cladoceran Daphnia magna and a freshwater teleost, Japanese medaka (Oryzias latipes). The 96-hr Daphnia median effective concentrations (EC50s) for cartap and cypermethrin were 91.0 μ g/L and 0.00061 μ g/L, respectively. Rapid recovery of Daphnia was observed after short-term pulsed exposure to cartap and cypermethrin; there were no adverse effects on reproduction or survival 20 d after a 24 hr exposure to cartap up to 1240 μ g/L and cypermethrin up to 1.9 μ g/L. Chronic continuous exposure (for 21 d) of 7-d-old Daphnia to cypermethrin significantly reduced the intrinsic population growth rate in a concentration-dependent manner. However, because the intrinsic population growth rates were all above zero, populations did not decrease even at the highest experimental concentration of 200 ng/L. Exposure of Daphnia neonates (< 24 hr old) to cypermethrin for 21 d caused significant, sub-lethal reproduction-related problems, such as increased time to first brood, reduced brood size, and reduced total brood number, at 0.0002, 0.002, and 0.2 ng/L cypermethrin, but the intrinsic population growth rate was not significantly affected. Oryzias latipes was relatively more resistant to both pesticides. In particular, embryos appeared to be more resistant than juveniles or adults, which may be partly due to the protective role of the chorion. The incidence of larval fish deformity was significantly higher after a 96 hr exposure to as low as 250 μ g/L of cartap or 40 μ g/L of cypermethrin. The mixture of both compounds showed no synergistic toxicity. The extremely high acute-to-chronic ratio suggests that the standard acute lethal toxicity assessment might not reflect the true environmental hazards of these frequently used pesticides. Ecological hazard assessments of long-term low dose or pulsed exposures to cartap and cypermethrin may reveal more realistic consequences of these compounds in surface water. [ABSTRACT FROM AUTHOR]

In the present study, a quantitative structure – activity relationship (QSAR) model has been developed for predicting acute toxicity to the fathead minnow ( Pimephales promelas ), the aim being to demonstrate how statistical validation and domain definition are both required to establish model validity and to provide reliable predictions. A dataset of 408 heterogeneous chemicals was modelled by a diverse set of theoretical molecular descriptors by using multivariate linear regression (MLR) and Genetic Algorithm – Variable Subset Selection (GA-VSS). This QSAR model was developed to generate reliable predictions of toxicity for organic chemicals not yet tested, so particular emphasis was given to statistical validity and applicability domain. External validation was performed by using OECD Screening Information Data Set (SIDS) data for 177 High Production Volume (HPV) chemicals, and a good predictivity was obtained (&ThickSpace;=&ThickSpace;72.1). The model was evaluated according to the OECD principles for QSAR validation, and compliance with all five principles was established. The model could therefore be useful for the regulatory assessment of chemicals. For example, it could be used to fill data gaps within its chemical domain and contribute to the prioritization of chemicals for aquatic toxicity testing. [ABSTRACT FROM AUTHOR]

The environmental fate and the loss of toxicity of two important antifouling actives, zinc pyrithione (ZnPT) and copper pyrithione (CuPT), were investigated using a bioassay study and an outdoor microcosm study. The bioassay used inhibition of the growth of a marine diatom ( Amphora coffeaeformis ) to measure the toxicity of ZnPT and CuPT over time in sterile, natural, and sediment-supplemented seawater. In natural seawater and sediment-supplemented seawater in the dark and in sterile seawater exposed to light, growth inhibition was reduced at rates corresponding to the rapid degradation rates for ZnPT and CuPT measured in previous aquatic metabolism, die-away, and photolysis studies. Similarly, the bioassay results from sterile seawater in the dark were consistent with the slower degradation rates measured in abiotic hydrolysis studies. In addition to corroborating the rapid degradation of pyrithione upon exposure to light or sediment, the loss of toxicity indicated that the degradation products were not toxic at the concentrations produced from the dose, which was much higher than predicted environmental concentrations. To supplement environmental fate studies designed to elucidate single-pathway transformations, a microcosm study was conducted to integrate all of the degradation pathways. The study used two sediment and water systems, one of which was dosed during the day and the other at night. The pyrithione degraded rapidly in the water phase, with very little accumulation in the sediment. 2-Pyridine sulfonic acid (PSA) and carbon dioxide were the only detectable degradation products 30 d after dosing. Aquatic toxicity studies with PSA showed no observable effect at concentrations at least three orders of magnitude higher than those for either ZnPT or CuPT. As a result, the worst-case environmental concentration of PSA is expected to be far below the no observable effect concentration. [ABSTRACT FROM AUTHOR]

The paper and pulp industry have been the main pollutant of Finnish water bodies, but extensive investments have been made into improvinginternal and external purification. Activated sludge plants have been the most common waste water treatment method, but they are sensitive to shock loading and toxicity and their capacity to remove poorly biodegradable or toxic substances is limited. In this study pre-ozonation was investigated in order to prevent process failure, to improve the purification efficiency and to increase the removal rate of aquatic toxicity of the waste water. The ozonation of the most toxic paperand pulp mill effluent stream, bleaching effluent with the ozone dose, 0.4 MgO3 mg CODCr-1, increased the biodegradability measured as BOD/COD ratio by converting COD to BOD. This resulted in an increase in overall treatment efficiencies of up to 91% BOD removal, 85% COD removal, compared to 22-60% BOD and 47-62 % COD without preozonation. Pre-ozonation also helped to prevent process failure caused by bulking of sludge. Pre-ozonation combined with biological treatment was effective in the removal of acute aquatic toxicity measured by luminescent bacteria or water flea which had not been removed by biological or chemical treatment alone. [ABSTRACT FROM AUTHOR]