Sublethal Toxicity Tests Research Articles

Sublethal Toxicity of 17 Per- and Polyfluoroalkyl Substances with Diverse Structures to Ceriodaphnia dubia, Hyalella azteca, and Chironomus dilutus.

Seven-day sublethal toxicity tests were performed with the freshwater invertebrates Ceriodaphnia dubia, Hyalella azteca, and Chironomus dilutus to determine the effects of per- or polyfluorinated alkyl substances (PFAS) of varying chain length within four classes: perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkyl sulfonic acids (PFSAs), perfluoroalkane sulfonamides, and fluorotelomer sulfonic acids. In general, toxicity increased with increasing chain length, but the slopes of these relationships varied markedly by species and chemical class. The toxicity of individual PFCAs was similar among species. The toxicity of PFSAs was similar to PFCAs for C. dubia and H. azteca, whereas PFSAs were much more toxic to C. dilutus, with median effect concentrations (EC50s) as low as 0.022 mg perfluorooctane sulfonate (PFOS)/L and 0.012 mg perfluorononane sulfonate (PFNS)/L. Despite the high sensitivity to PFOS and PFNS, C. dilutus was not very sensitive to structurally similar fluorotelomer sulfonates (6:2 and 8:2). Perfluoroalkane sulfonamides were the most toxic class tested among all species (e.g., EC50s of 0.011 and 0.017 mg perfluorooctane sulfonamide/L for C. dilutus and H. azteca, respectively). The differences in toxicity among species and chemical classes suggest that mechanisms of PFAS toxicity may differ as a function of both. Environ Toxicol Chem 2024;43:359-373. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Behavioural Response of Oreochromis niloticus Fingerlings Exposed to Sub-Lethal Concentrations of Imidacloprid

Imidacloprid, a neonicotinoid pesticide that was once thought to be a solution to environmental pollution caused by previous pesticides like organophosphates and organochlorines has raised global concern recently. The present study aimed at assessing the effect of Imidacloprid on the behaviour of a commercially important fish species, Oreochromis niloticus. The study involved a 48 h sub-lethal toxicity test which was carried out with 0, 5, 10, 20, and 40 ppm of Imidacloprid. Fingerlings of O. niloticus weighing between 18 and 32g were exposed to these concentrations in a static bioassay with continuous aeration. Regular observation of the clinical signs revealed that fish exposed to higher concentrations of Imidacloprid displayed behavioural abnormalities such as erratic behaviour, respiratory stress, and irregular nervousness. The findings of this study revealed that Imidacloprid is toxic and causes behavioural distress on O. niloticus fingerlings. Therefore, there is urgent need for further studies to determine safe limit of Imidacloprid and other pesticides in the environment. Unregulated disposal of toxic pesticides should be avoided, to ensure human safety and environmental sustainability.

Evaluation of the acute and sublethal toxicity of Mancozeb in Pacamã (Lophiosilurus alexandri).

The toxic potential of dithiocarbamates fungicides widely used in world agriculture is well known, among which Mancozeb is one of the most used. This study aimed to evaluate the toxicity of Mancozeb, determining the LC50% of the product and the behavioral and histological changes observed in fish of the Pacamã species through acute and sublethal toxicity tests. The first experiment was carried out on Pacamã fingerlings exposed to dosages of 0.5, 1, 2, 4, and 8mg/L of Mancozeb under the form ManzateWG®, for a total period of 96 hours in the acute experiment, and in the second experiment, fish were subjected to concentrations of 1/10 of those used in the acute experiment (0.05, 0.1, 0.2, 0.4 and 0.8mg/L, respectively), for 15 days in total. The 50% lethal concentration of ManzateWG® was calculated at the end of the acute experiment, presenting a value of 2.29mg/L at 96h for Pacamã fingerlings. A behavioral assessment was carried out through daily observation of the fish during both experiments, and an increase in mucus production was observed, as well as atypical social behavior in those exposed to the toxic agent. Histopathological evaluation was performed on livers collected after the end of the sublethal experiment, and the main hepatic alterations observed were cytoplasmic vacuolization, inflammatory infiltrate, and necrosis. Mancozeb has toxic potential and is capable of generating behavioral changes, as well as increasing the risk of liver damage in Pacamãs exposed to this compound.

Quantal Response and Histopathological Effects of Sub-lethal Concentrations of a Selected Oilfield Chemical on African Catfish (Clarias gariepinus)

The behavioural and histological effects of sublethal concentrations (0.0 ml/L, 12.8 ml/L, 25.59 ml/L, 38.39 ml/L, 51.19 ml/L, and 63.99 ml/L) of Xylene were evaluated in African Catfish (Clarias gariepinus) after 28 days of exposure. Physico-chemical parameters such as temperature, conductivity, hydrogen ion concentration (pH), total hardness, total dissolved solids, dissolved oxygen, total alkalinity, ammonia, and nitrate levels in the experiment were monitored using the standard method. Significant variations were observed in the different units except for the controlled unit. Behavioural changes were observed closely during the sublethal toxicity test using standard procedures. The bioassay experiments were repeated three times and the renewable test method was used. concentrations showed histopathological alterations in the gills and liver. Severely deformations were observed at 12.80ml/l, 38.39ml/l), 51.19ml/l, and 63.99ml/l. No form of abnormalities was observed in the fish gill and liver in the controlled unit. Progressive hyperventilation, faster operculum and tail beat movement, erratic movement, gulping of air, and spiralling. jumping, display of vigorous jerky movement suffocation, and loss of reflex were observed in C. gariepinus exposed to higher sublethal concentrations of Xylene. There was a significant dose-dependent variation in parameters in the experiment. In conclusion, xylene caused an alteration in the histopathological parameters and the behaviour of C. garienpinus. Therefore, we recommend the need for realistic regulatory measures and proper monitoring and sensitization on use to stakeholders.

Toxicopathic effects of lithium in mussels

The rising use of lithium (Li) in industrial processes, modern technology and medicine has generated concerns in the scientific community, in particular its potential impact on the environment. Unfortunately, there is only scarce information concerning the toxicity of lithium in marine organisms. The objective of this study is to determine the toxicity of Li using Mytilus galloprovincialis as model organism, based on acute and sublethal toxicity tests. In the first experiment, mussels were exposed for 9 days to a range of acute concentrations of Li (0, 2, 5, 13, 34, 89, 233 and 610 mg/L Li) in order to find the median lethal concentration. In the sublethal experiment, mussels were exposed to environmentally relevant concentrations of Li (0, 0.1, 1, 10 mg/L Li) for 21 days. Digestive gland and gonad samples were taken at day 0, 1, 7 and 21 for histopathological analysis. Samples of the whole mussels were taken for chemical analysis at day 0 and after 21 days. Results showed that M. galloprovincialis had a LC50 value of 153 mg/L Li after 9 days of exposure. Lower concentrations (environmentally relevant), led to Li bioaccumulation in a dose-dependent manner and histopathological effects in a time-dependent manner. Atrophy of the digestive alveoli epithelium and degeneration of the digestive gland were observed after 21 days of exposure. These findings open new perspectives for the understanding of the toxic effects of Li on marine organisms and evidence the need for further long-term research at different levels of biological organizations.

Dietary Effect of Probiotic and Prebiotic on Some Mucus Indices of Silver Carp (Hypophthalmichthys molitrix) Exposed to Silver Nanoparticles.

Prebiotic and probiotic supplements can directly activate fish primary defense mechanisms by acting on responsible receptors. This study aimed to investigate the effect of using Pediococcus acidilactici and Agaricus bisporus separately and in combination with silver carp's mucosal immune system indices and finally the possibility of reducing the toxicity of silver nanoparticles in silver carp. After calculating LC50, the sub-lethal toxicity test was performed to sub-lethal concentration of silver nanoparticles for 14 days. Fish skin mucus was collected in polyethylene bags containing 10 ml of 50 mM sodium chloride for future analysis. Results of skin mucosal indices activity showed significant changes in treatments fed with additives compared to the control treatment after exposure to silver nanoparticles on days 1, 7, and 14 in including lysozyme enzyme activity, total protein, and skin mucosal protein pattern. The addition of additives will improve the relative mucosal safety indices of silver carp. The results of statistical analysis showed that the addition of combination supplements, Pediococous acidilactici, and Agaricus bisporus powder could affect the skin mucosal safety indices. It is effective and ultimately improves the immune system function of silver carp skin in 14-day exposure to silver nanoparticles.

Hemato-biochemical responses and histopathological alterations in the gill and kidney tissues of Osteobrama belangeri (Valenciennes, 1844) exposed to different sub-lethal unionized ammonia

Ammonia is a factor restricting production in aquaculture systems, hindering fish production adversely. A detailed study was planned and conducted using a static water system to scrutinize the toxic effects of unionized ammonia (UIA) on patho-physiological responses of O. belangeri, an important aquaculture candidate for diversification of freshwater aquaculture and endangered species, when exposed to different sub-lethal concentrations of UIA. The 96-h LC50 value of UIA on O. belangeri was found to be 1.36 mg l−1. The sub-lethal toxicity test with three UIA concentrations, i.e., 0.27, 0.68, and 0.80 mg l−1 at different exposure period of 24, 48, 72, and 96-h revealed that exposure to UIA induced a significant reduction in hematological parameters, such as total erythrocyte count (TEC), total leukocyte count (TLC), hemoglobin (Hb), and hematocrit (Hct). Mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) also substantially declined due to UIA exposure. Among biochemical parameters, blood glucose, serum glutamate pyruvate transaminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT) and Na+ and K+ ion increased significantly. In contrast, serum protein, alkaline phosphatase (ALP) and serum albumin notably decreased due to ammonia exposure. Fish exposed to different UIA concentrations for 96-h displayed several histopathologic alterations in the gill and kidney tissues. Gill tissues showed several lamellar deformations, while kidney tissues showed significant changes at the level of the glomerulus and tubular epithelium. The NOEL or safe concentration of UIA for this particular fish species was found to be 0.07 mg l−1. The observed patho-physiological alterations in the present study establish the most detail insights of UIA stress in O. belangeri and will enhance the international literature on UIA toxicity.

Development of a Sublethal Chronic Toxicity Test for the Northern Trout Gudgeon, Mogurnda mogurnda, and Application to Uranium, Magnesium, and Manganese.

Many international guidance documents for deriving water quality guideline values recommend the use of chronic toxicity data. For the tropical fish northern trout gudgeon, Mogurnda mogurnda, 96-h acute and 28-d chronic toxicity tests have been developed, but both tests have drawbacks. The 96-h toxicity test is acute and has a lethal endpoint; hence it is not a preferred method for guideline value derivation. The 28-d method has a sublethal (growth) endpoint, but is highly resource intensive and is high risk in terms of not meeting quality control criteria. The present study aimed to determine the feasibility of a 7-d larval growth toxicity test as an alternative to the 96-h survival and 28-d growth tests. Once the method was successfully developed, derived toxicity estimates for uranium, magnesium, and manganese were compared with those for other endpoints and tests lengths within the literature. As a final validation of the 7-d method, the sensitivity of the 7-d growth endpoint was compared with those of 14-, 21-, and 28-d exposures. Fish growth rate, based on length, over 7 d was significantly more sensitive compared with existing acute toxicity endpoints for magnesium and manganese, and was similarly sensitive to existing chronic toxicity endpoints for uranium. For uranium, the sensitivity of the growth endpoint over the 4 exposure periods was similar, suggesting that 7 d as an exposure duration is sufficient to provide an indication of longer term chronic growth effects. The sensitivity of the 7-d method, across the 3 metals tested, highlights the benefit of utilizing the highly reliable short-term 7-d chronic toxicity test method in future toxicity testing using M. mogurnda. Environ Toxicol Chem 2021;40:1596-1605. © 2021 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2021 SETAC.

First insights into oxidative stress and theoretical environmental risk of Bronopol and Detarox® AP, two biocides claimed to be ecofriendly for a sustainable aquaculture

Bronopol and Detarox® AP are broad spectrum antimicrobial biocides of growing interest for the aquaculture sector. While their effectiveness against aquatic pathogens has been demonstrated, toxicity data on wild or farmed species are still lacking, as is information on their potential environmental risk for aquatic ecosystems. With this study, we assessed the acute and sublethal toxicity of Bronopol and Detarox® AP in the freshwater bivalve Sinanodonta woodiana and their theoretical risk for aquatic ecosystem. The 96-h median lethal concentration (LC50) was determined using the acute toxicity test, while for the sublethal toxicity test the bivalves were exposed to two concentrations for 14days of Bronopol (2.5 and 50mg/L) and Detarox® AP (1.11 and 22.26mg/L) followed by a 14-day withdrawal period. Biocide-mediated oxidative processes were investigated via a panel of oxidative stress biomarkers (malondialdehyde, superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase). Theoretical environmental risk assessment of both biocides, with predicted concentration of no effect (PNEC), expected theoretical concentration (TEC) in the environment, and risk quotient (RQ) was performed. TEC was calculated using a model based on the size of the aquaculture facility and the receiving basin, the estimated quantity of biocide dissolved in water, and published data on biocide stability in water. Although the LC50 was higher for Bronopol (2440mg/L) than for Detarox® AP (126mg/L), fluctuations in oxidative stress biomarkers levels indicated that both biocides exert a slight oxidative pressure on S. woodiana. Theoretical environmental risk assessment suggested a muted risk with Detarox® AP and greater eco-sustainability compared to Bronopol.

Comparative ecotoxicity of insecticides with different modes of action to Osmia excavata (Hymenoptera: Megachilidae)

Osmia excavata is an important pollinator in commercial fruit orchards. Little information has been published about ecotoxicity to O. excavata, especially the larvae. To clarify the risk of commonly used insecticides with different modes of action to the larvae of O. excavata, six insecticides (clothianidin, acetamiprid, sulfoxaflor, lambda-cyhalothrin, chlorfenapyr and abamectin) were selected for evaluation of their acute lethal toxicity and sublethal effects. Clothianidin and abamectin were the two most toxic insecticides to the larvae of O. excavata with LD50 values of 0.007 (0.006–0.008) and 0.0004 (0.0003–0.0006) μg active ingredient (a.i.) bee−1, respectively. And their ecological risks were high according to the hazard quotient values (HQ > 2500). Sulfoxaflor was identified as the only safe insecticide for O. excavata (HQ < 50) under field conditions. Sublethal toxicity tests showed that larval weight was significantly decreased by ingesting food treated with clothianidin, lambda-cyhalothrin and abamectin (less than the maximum field registered concentrations on fruit trees) due to interference with consumption per larva and reduction of the efficiency of conversion of ingested food. Additionally, above three insecticides significantly prolonged larval developmental duration before cocooning and decreased eclosion rate. Overall, there results suggested that clothianidin and abamectin should not be applied, especially during the flowering phase, the application frequency of lambda-cyhalothrin should be minimized for the purpose of conserving O. excavata. Our results provided important evidences for selecting appropriate insecticides for use in fruit orchards.

Toxic effects and potential mechanisms of Fluxapyroxad to zebrafish (Danio rerio) embryos

Fluxapyroxad is a broad-spectrum and high-efficiency succinate dehydrogenase inhibitor fungicide that can control plant fungal pathogens on many crops. However, fluxapyroxad can enter the aquatic environment when applied in the field, which has an impact on the aquatic environment. The potential threat and toxicological mechanisms of fluxapyroxad in aquatic organisms remain poorly understood. In this study, zebrafish embryos were exposed to fluxapyroxad to investigate the toxic effects and potential mechanisms of fluxapyroxad. In the acute toxicity test, the lethal sensitivity rank of the zebrafish during the three stages was larvae (0.699 mg/L) > adult fish (0.913 mg/L) > embryo (1.388 mg/L). Fluxapyroxad induced abnormal spontaneous movement, malformations and decreased heartbeat, hatching percentage, and body length of the embryos. In the sublethal toxicity test, succinate dehydrogenase activity was significantly increased in all treatment groups, while the activities of the electron transport chain complex II and ATPase were markedly inhibited in 0.347 and 0.694 mg/L fluxapyroxad groups compared to that of the control group. Exposure to fluxapyroxad resulted in significant increases in MDA production, and GPx activity was significantly reduced at 0.694 mg/L. Moreover, caspase-3 activity was significantly increased in the 0.694 mg/L group, and the expression of the genes related to growth (bmp4 and lox) was inhibited after fluxapyroxad exposure. These results indicated that oxidative stress, cell apoptosis and mitochondrial damage might be the potential mechanism underlying the toxic effects of fluxapyroxad on zebrafish embryos.

Antioxidative role of dietary ascorbic acid against arsenic induced haematological, biochemical and histomorphological alterations in Cyprinus carpio

The current study investigated the antioxidant potential of ascorbic acid to counteract arsenic induced toxic response in Cyprinus carpio. The 96 h LC50 of 107.05 mg L−1 was recorded through acute toxicity test and 1/5th and 1/10th LC50 of arsenic were chosen as sublethal concentrations for assessing toxicity induced through arsenic exposure in fish for a period of 28 days. There were six experimental groups for sublethal toxicity testing viz. negative control (basal feed), positive control (basal feed + 1 g kg−1 diet ascorbic acid), 1/5th LC50 Arsenic, 1/10th LC50 Arsenic, 1/5th LC50 Arsenic with ascorbic acid supplement, 1/10th LC50 Arsenic with ascorbic acid supplement. Following exposure, blood indices, antioxidant enzyme activity and histomorphology of gills, liver and kidney were examined. The results showed decreased total erythrocyte count, haemoglobin, haematocrit and an increased total leukocyte count upon arsenic exposure in fish with an improvement observed in the blood indices in arsenic with ascorbic acid supplementation. The study also analysed the antioxidant enzyme activity of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione-S-transferase which was found to decline in response to arsenic exposure with an increase in their activity recorded in arsenic with ascorbic acid supplemented fish. Furthermore, uptake of arsenic was also found to decrease on ascorbic acid supplementation with improvement in the histoarchitecture of gills, liver and kidney of fish. Collectively, the findings of the present study suggest the effectiveness of ascorbic acid as an ameliorating agent against the deleterious effects of arsenic in fish.

Chlorpyrifos mediated oxidative damage and histopathological alterations in freshwater fish Oncorhynchus mykiss in Northern Pakistan

The intensive applications of chlorpyrifos (CPF) in agricultural production have resulted in lethal effects on the environment, particularly on aquatic fauna. Thus, present study was aimed to assess the haematological responses, antioxidant enzymes (superoxide dismutase [SOD] and catalase [CAT]) activity, acetylcholinesterase enzyme (AChE) inhibition and histopathological alterations in liver and gill tissues of cold-water fish rainbow trout (Oncorhynchus mykiss) in their native habitat, when exposed to CPF. In total, 240 fingerlings were subjected to various CPF concentrations (0, 2, 4 and 6 μg/L) for acute and sub-lethal toxicity tests. Results revealed that increasing CPF concentration and exposure time have resulted in reduced erythrocyte count, haemoglobin concentration and haematocrit level; however, leucocyte count was increased. Additionally, decrease in AChE activity was also observed with increasing concentration. CPF concentrations at lowest exposure duration induced slight increase of SOD and CAT activity while the high exposure durations (14 and 21 days) exhausted the activity of antioxidant enzymes. Structural damages produced by CPF in liver tissues were hyperaemia, dilated central veins, sinusoids and degenerative changes, while the lesions observed in gill tissue were curling of secondary lamella, cell degeneration, cell necrosis, narrowing of water channels, hyperplasia, oedematous changes, fusion of secondary lamella and sloughing.

Application of a behavioural and biochemical endpoint in ecotoxicity testing with Exaiptasia pallida.

Exaiptasia pallida has been applied as a cnidarian model to assess the toxicity of various contaminants using endpoints related to growth, reproduction and mortality. However, increasingly accepted behavioural and biochemical endpoints are underrepresented in ecotoxicity testing with cnidarian species. The aim of this study was to assess the suitability of tentacle retraction and superoxide dismutase activity as behavioural and biochemical endpoints for ecotoxicity testing with E. pallida. A concentration-dependent, tentacle retraction response was found in sub-lethal toxicity testing for anemones exposed to 1–65 μg L−1 Cu and 2–630 μg L−1 Zn for 24 and 96 h. Semi-quantitative and quantitative approaches to tentacle retraction analysis showed a difference in response sensitivity, however, both methods resulted in similar 24- and 96-h EC50 values for Cu and Zn. Additionally, tentacle retraction analysis provided the benefit of identifying recovery in anemones previously exposed to 359 μg L−1 Zn following a 96-h recovery period. Conversely, no significant difference in superoxide dismutase activity was detected in anemones exposed to the Cu and Zn solutions compared with controls, after either 24- or 96-h exposures. These findings support the ease of application and sensitivity of tentacle retraction as an endpoint in ecotoxicity testing with E. pallida and recommend its suitability for use in acute, sub-lethal toxicity testing. Moreover, evidence of recovery in E. pallida following exposure suggests that recovery should be incorporated into future toxicity assessments.

Acute toxicity of the pesticide trichlorfon and inhibition of acetylcholinesterase in Colossoma macropomum (Characiformes: Serrasalmidae)

In Brazilian fish farms, trichlorfon has been widely used to control acanthocephalan infections in Colossoma macropomum. Toxicity tests were conducted to estimate the median lethal concentration (LC50–96 h) and evaluate the effects of trichlorfon on acetylcholinesterase (AChE) and glutathione S-transferase (GST) from different tissues of C. macropomum. The LC50–96 h of trichlorfon was estimated to be 0.87 mg L−1. In the sublethal toxicity tests, concentrations of 0.26 mg L−1 (30% of LC50–96 h) and 0.43 mg L−1 (50% of LC50–96 h) were used. AChE and GST activities were measured in the brain, muscle, intestine, and liver. In vitro studies were conducted to estimate the kinetic properties and half-maximal inhibitory concentration (IC50) values of AChE in the brain and muscle for trichlorfon. In the sublethal toxicity experiments, inhibition of more than 90% of AChE in the brain, muscle, and intestine was observed. However, the activity of GST did not vary in any of the tissues studied. This finding suggests that trichlorfon is not metabolised by this enzyme. The in vitro assay results suggest that trichlorfon tends to be a classic uncompetitive inhibitor of AChE in both the brain and muscle, since Km and Vmax values decrease, while the slope remains unchanged. The IC50 values ​of muscle AChE are lower than those of the brain. All these results show that C. macropomum has low tolerance to this pesticide and suggest that brain AChE can be used as a biochemical biomarker, while muscle AChE may be used as an indicator of mortality in toxicological studies.

Acute toxicity of lead in fresh water bivalves Lamellidens jenkinsianus obesa and Parreysia (Parreysia) corrugata with evaluation of sublethal effects on acetylcholinesterase and catalase activity, lipid peroxidation, and behavior.

The median lethal concentrations (LC50) of Pb at 96 h were 8.84, 192.14, and 3.22 mg L-1 for pre-reproductive and reproductive individuals of Lamellidens jenkinsianus obesa and reproductive individuals of Parreysia (Parreysia) corrugata, respectively. Thus, young L. j. obesa were much more sensitive to Pb than its adults, while P. (P.) corrugata was the most sensitive. However, all the three values were much higher than the Pb levels commonly found in natural waters, and indicative of the tolerance of these mollusks to acute, short-term Pb exposure. In contrary to these findings, acetylcholinesterase (AChE) and catalase (CAT) activities were affected and lipid peroxidation (LPO) elevated in young L. j. obesa and P. (P.) corrugata in 21-day sublethal toxicity tests at 26-68 ppb Pb concentrations, which might be considered environmentally realistic. Some behavioral patterns such as number of movement (Mov) and durations of foot mobilization together with siphon extensions (FSE) were reduced, and the durations of valves remaining completely closed without any extension of foot and siphons (VC) increased significantly at 25-69 ppb Pb as well. Thus, the study revealed significant interspecific differences as well as that between life stages of the same species, suggesting that apparently hardy species could be impacted by low Pb concentrations in their young stages. Further, a multi-biomarker approach involving biological effects, anti-oxidative enzyme activity and easy-to-measure behavioral elements could comprise a valuable tool in assessment of Pb-induced stress in freshwater bivalves.

English

Juveniles of Clarias gariepinus were exposed to different concentrations of cadmium chloride for 96 h under laboratory conditions using static bioassays with continuous aeration to determine its mean lethal concentration (LC50), biochemical alterations, bioaccumulation and histological pattern in a sub-lethal toxicity test. The median lethal concentration (LC50) at the end of the acute toxicity was 120.2 mgL-1. Also the toxicant led to significant (P&lt;0.05) changes in histotopathological parameters in the kidney, liver, gills and muscle as the toxicant concentration increased. The severity of these conditions was directly proportional to the toxicant concentration. Also, the biochemical studies showed that activities of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) ranged from (0.115 &plusmn; 0.15 to 1.634 &plusmn; 0.28) &micro;mol/min/mg protein, (2.354 &plusmn; 0.45 to 7.734 &plusmn; 0.08) &micro;mol/min/mg protein and (0.028 &plusmn; 0.05 to 0.21 &plusmn; 0.16) &micro;mol/min/mg protein respectively. These values increased significantly (p &lt; 0.05) with increase in concentration of cadmium chloride. The trend of bioaccumulation of cadmium in the tissues of the test organisms differs significantly (p&lt;0.05) and it followed the order, kidney &gt; liver &gt; gill &gt; muscle. The study concluded that cadmium is a potent pollutant that can cause severe damage in fish and hence man the final consumer. &nbsp; Key words: Clarias gariepinus, biochemical alterations, bioaccumulation, static bioassays, histopathology.

Single and combined effects of microplastics and roxithromycin on Daphnia magna.

There is a rising concern about the pollution of microplastics (plastic particles < 5mm) in water due to their physicochemical properties, especially their interaction with organic contaminants; however, such knowledge is still limited. The mass production and consumption of medication for the treatment of infectious diseases in human and animals have led to the ubiquity of antibiotics in the environment. We studied the single and joint effects of microplastics (1-μm and 10-μm polystyrene particles, PS) and roxithromycin (ROX) on Daphnia magna through the acute and sublethal toxicity tests. The 48-h median effective concentration (EC50) of 1-μm and 10-μm PS to D. magna was 66.97mg/L and 199.94mg/L, respectively, while the value of ROX was 20.28mg/L. Malondialdehyde (MDA) levels and the activities of four enzymatic biomarkers, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione S-transferase (GST), were further detected to assess the oxidative stress caused in D. magna caused. The results showed that 48-h exposure to PS (0.1mg/L) or ROX (0.01mg/L) alone activated the activities of CAT and GST and MDA levels. When compared with the ROX alone, the responses of GPx and MDA in D. magna co-exposed to 1-μm PS were significantly decreased, while co-exposure to 10-μm PS significantly decreased the responses of GST and MDA. Furthermore, the integrated biomarker response version 2 (IBRv2) analysis revealed that co-exposure to 1-μm PS and ROX led to the strongest biological responses in D. magna. Our findings underlined that microplastics should be a concern when they interact with the co-existence of pollutants in the aquatic environment.

Energy budget in Alona guttata (Chydoridae: Aloninae) and toxicant-induced alterations

Although chydorids are the most diverse cladocerans in the world, there is still little information available related to their biology and even less with respect to their susceptibility to toxicants. Therefore, this work aimed to implement protocols with Alona guttata for acute, chronic, and sublethal toxicity tests, using the environmental concern toxicants deltamethrin (DM) and lead (Pb2+), which are commonly used due to agriculture and vector control or for the automotive industry, respectively. Once the results of LC50 (0.1160 ± 0.0107 μg/L for DM and 1.5797 ± 0.1605 mg/L for Pb2+) were obtained, sublethal concentrations (0.01 to 0.2 LC50) were used for the evaluation of biomarkers and chronic toxicity. Concentrations as low as 0.01 LC50 reduced Alona's survival and fecundity, negatively affecting demographic parameters, and decreased the energy reserves. A significant correlation was found between the natural rate of population increase and the caloric content, which demonstrates the suitability of these biomarkers as endpoints of early warning that allow inferring alterations at higher biological levels. Subsequently, this work could constitute the first report on the evaluation of the energy budget in a non-daphnid species, its alterations due to exposure to toxic substances and the correlation with demographic responses.

Insecticide pyriproxyfen (Dragón®) damage biotransformation, thyroid hormones, heart rate, and swimming performance of Odontophrynus americanus tadpoles

Odontoprynus americanus tadpoles were used to determine the safety concentration of pyriproxyfen (PPF) insecticide by acute and sublethal toxicity tests (nominal range tested 0.01 to 10 [± 15%] PPF mg/L). Median lethal concentration (LC50) and no, and lowest-observed-effect concentrations (NOEC and LOEC, respectively) were calculated. We also assessed the effect on the activities of glutathione S-transferse (GST), acetylcholinesterase (AChE), and carboxylesterase (CbE) and compared to control (CO) tadpoles. Based on the 48-h NOEC value, two sublethal concentrations of PPF (0.01 and 0.1 mg/L) were assayed to detect effects on enzymes activities (GST and CbE), thyroid hormone's levels (triiodothyronine; T3 and thyroxine; T4), heart function, and tadpoles swimming behaviour. The results showed that the LC50 values of O. americanus tadpoles were 3.73 PPF mg/L and 2.51 PPF mg/L at 24-h and 48-h, respectively (NOEC = 0.1 mg/L; LOEC = 1 mg/L, for both times). PPF concentrations at 48 h, induced enzymatic activities such as GST (212.98%–242.94%), AChE (142.15%–165.08%), and CbE (141.86%–87.14%) significantly respect to COs. During the 22 days of chronic PPF exposure, GST (0.01 mg/L 88%–153% NOEC), AChE (177.82% NOEC), and T4 (70% NOEC) also significantly increased respect to COs. Similarly, heart rate (fH) and ventricular cycle length (VV interval) in CO tadpoles were significantly higher than PPF treated. Finally, at NOEC tadpoles exhibited significant effects on the behavioral endpoint (swimming distance, mean speed, and global activity; P < 0.05).