Effects of the herbicides linuron and S-metolachlor on Perez's frog embryos

Strategies for mitigation of pesticides from the environment through alternative approaches: A review of recent developments and future prospects

Chemical-based peticides are having negative impacts on both the healths of human beings and plants as well. The World Health Organisation (WHO), reported that each year, >25 million individuals in poor nations are having acute pesticide poisoning cases along with 20,000 fatal injuries at global level. Normally, only ∼0.1% of the pesticide reaches to the intended targets, and rest amount is expected to come into the food chain/environment for a longer period of time. Therefore, it is crucial to reduce the amounts of pesticides present in the soil. Physical or chemical treatments are either expensive or incapable to do so. Hence, pesticide detoxification can be achieved through bioremediation/biotechnologies, including nano-based methodologies, integrated approaches etc. These are relatively affordable, efficient and environmentally sound methods. Therefore, alternate strategies like as advanced biotechnological tools like as CRISPR Cas system, RNAi and genetic engineering for development of insects and pest resistant plants which are directly involved in the development of disease- and pest-resistant plants and indirectly reduce the use of pesticides. Omics tools and multi omics approaches like metagenomics, genomics, transcriptomics, proteomics, and metabolomics for the efficient functional gene mining and their validation for bioremediation of pesticides also discussed from the literatures. Overall, the review focuses on the most recent advancements in bioremediation methods to lessen the effects of pesticides along with the role of microorganisms in pesticides elimination. Further, pesticide detection is also a big challenge which can be done by using HPLC, GC, SERS, and LSPR ELISA etc. which have also been described in this review.

Reproductive toxicity due to herbicide exposure in freshwater organisms

Excessively used pesticides in agricultural areas are spilled into aquatic environments, wherein they are suspended or sedimented. Owing to climate change, herbicides are the fastest growing sector of the pesticide industry and are detected in surface water, groundwater, and sediments near agricultural areas. In freshwater, organisms, including mussels, snails, frogs, and fish, are exposed to various types and concentrations of herbicides. Invertebrates are sensitive to herbicide exposure because their defense systems are incomplete. At the top of the food chain in freshwater ecosystems, fish show high bioaccumulation of herbicides. Herbicide exposure causes reproductive toxicity and population declines in freshwater organisms and further contamination of fish used for consumption poses a risk to human health. In addition, it is important to understand how environmental factors are physiologically processed and assess their impacts on reproductive parameters, such as gonadosomatic index and steroid hormone levels. Zebrafish is a good model for examining the effects of herbicides such as atrazine and glyphosate on embryonic development in freshwater fish. This review describes the occurrence and role of herbicides in freshwater environments and their potential implications for the reproduction and embryonic development of freshwater organisms.

Embryotoxic effects of Rovral® for early chicken (Gallus gallus) development

Rovral® is a fungicide used to control pests that affect various crops and little is known regarding its effects on embryonic development of amniotes. Thus, this study aimed to determine the influence of Rovral® during chicken organogenesis using acute in ovo contamination. Fertilized eggs were inoculated with different concentrations of Rovral® (100, 300, 500 or 750 µl/ml), injected into the egg's air chamber. After 7 days, embryos were examined for possible malformations, staging, weight and mortality. Subsequently, head, trunk, limbs and eyes were measured for morphometry and asymmetry. For blood analysis, eggs were treated with 300 µl/ml Rovral® and glucose, presence of micronuclei and erythrocyte nuclei abnormalities determined. Treatments with Rovral® affected the mortality rate in a concentration-dependent manner. LC₅₀ value was found to be 596 µl/ml which represents 397-fold higher than the recommended concentration for use. Rovral® produced several malformations including hemorrhagic, ocular and cephalic abnormalities. No significant changes were observed in body weight, staging, body measurements, symmetry and glucose levels of live embryos, which indicates this fungicide presents low toxicity under the analyzed conditions. Changes in erythrocyte nuclei were noted; however significant difference was observed only for presence of binucleated erythrocytes. It is important to point out that possibly more significant changes may have occurred at lower concentrations through chronic contamination. Therefore, caution is needed in the use of this fungicide, since it presents teratogenic and mutagenic potential.

Testing for population differences in evolutionary responses to pesticide pollution in brown trout (Salmo trutta)

Pesticides are often toxic to nontarget organisms, especially to those living in rivers that drain agricultural land. The brown trout (Salmo trutta) is a keystone species in many such rivers, and natural populations have hence been chronically exposed to pesticides over multiple generations. The introduction of pesticides decades ago could have induced evolutionary responses within these populations. Such a response would be predicted to reduce the toxicity over time but also deplete any additive genetic variance for the tolerance to the pesticides. If so, populations are now expected to differ in their susceptibility and in the variance for the tolerance depending on the pesticides they have been exposed to. We sampled breeders from seven natural populations that differ in their habitats and that show significant genetic differentiation. We stripped them for their gametes and produced 118 families by in vitro fertilization. We then raised 20 embryos per family singly in experimentally controlled conditions and exposed them to one of two ecologically relevant concentrations of either the herbicide S-metolachlor or the insecticide diazinon. Both pesticides affected embryo and larval development at all concentrations. We found no statistically significant additive genetic variance for tolerance to these stressors within or between populations. Tolerance to the pesticides could also not be linked to variation in carotenoid content of the eggs. However, pesticide tolerance was linked to egg size, with smaller eggs being more tolerant to the pesticides than larger eggs. We conclude that an evolutionary response to these pesticides is currently unlikely and that (a) continuous selection in the past has either depleted genetic variance in all the populations we studied or (b) that exposure to the pesticides never induced an evolutionary response. The observed toxicity selects against large eggs that are typically spawned by larger and older females.

The agrochemical S-metolachlor disrupts molecular mediators and morphology of the swim bladder: Implications for locomotor activity in zebrafish (Danio rerio)

Metolachlor herbicides are derived from the chloroacetamide chemical family of which there are the S- and R-metolachlor isomers. S-metolachlor is a selective herbicide that inhibits cell division and mitosis via enzyme interference. The herbicide is used globally in agriculture and studies report adverse effects in aquatic organisms; however, there are no studies investigating sub-lethal effects of S-metolachlor on swim bladder formation, mitochondrial ATP production, nor light-dark preference behaviors in fish. These endpoints are relevant for larval locomotor activity and metabolism. To address these knowledge gaps, we exposed zebrafish embryos/larvae to various concentrations of S-metolachlor (0.5-50 µM) over early development. S-metolachlor affected survival, hatching percentage, and increased developmental deformities at concentrations of 50 µM and above. Exposure levels as high as 200 µM for 24 and 48 h did not alter oxygen consumption rates in zebrafish, and there were no changes detected in endpoints related to mitochondrial oxidative phosphorylation. We observed impairment of swim bladder inflation at 50 µM in 6 dpf larvae. To elucidate mechanisms related to this, we measured relative transcript abundance for genes associated with the swim bladder (smooth muscle alpha (α)-2 actin, annexin A5, pre-B-cell leukemia homeobox 1a). Smooth muscle alpha (α)-2 actin mRNA levels were reduced in fish exposed to 50 µM while annexin A5 mRNA levels were increased in abundance, corresponding to reduced swim bladder size in larvae. A visual motor response test revealed that larval zebrafish exhibited some hyperactivity in the light with exposure to the herbicide and only the highest dose tested (50 µM) resulted in hypoactivity in the dark cycle. Regression analysis indicated that there was a positive relationship between surface area of the swim bladder and distance traveled, and the size of the swim bladder explained ~10-14% in the variation for total distance moved. Lastly, we tested larvae in a light dark preference test, and we did not detect any altered behavioral response to any concentration tested. Here we present new data on sublethal endpoints associated with exposure to the herbicide S-metolachlor and demonstrate that this chemical may disrupt transcripts associated with swim bladder formation and morphology, which could ultimately affect larval zebrafish activity. These data are expected to contribute to further risk assessment guidelines for S-metolachlor in aquatic ecosystems.

Exposure of the alga Pseudokirchneriella subcapitata to environmentally relevant concentrations of the herbicide metolachlor: Impact on the redox homeostasis

This study investigated the effect of the herbicide metolachlor (MET) on the redox homeostasis of the freshwater green alga Pseudokirchneriella subcapitata. At low MET concentrations (≤40 μg L^-1), no effects on algal cells were detected. The exposure of P. subcapitata to 45-235 μg L^-1 MET induced a significant increase of reactive oxygen species (ROS). The intracellular levels of ROS were particularly increased at high (115 and 235 μg L^-1) but environmentally relevant MET concentrations. The exposure of algal cells to 115 and 235 μg L^-1 MET originated a decrease in the levels of antioxidants molecules (reduced glutathione and carotenoids) as well as a reduction of the activity of scavenging enzymes (superoxide dismutase and catalase). These results suggest that antioxidant (non-enzymatic and enzymatic) defenses were affected by the excess of MET. As consequence of this imbalance (ROS overproduction and decline of the antioxidant system), ROS inflicted oxidative injury with lipid peroxidation and damage of cell membrane integrity. The results provide further insights about the toxic modes of action of MET on a non-target organism and emphasize the relevance of toxicological studies in the assessment of the impact of herbicides in freshwater environments.

Environmentally relevant mixture of S-metolachlor and its two metabolites affects thyroid metabolism in zebrafish embryos

Herbicides and their metabolites are often detected in water bodies where they may cause adverse effects to non-target organisms. Their effects at environmentally relevant concentrations are often unclear, especially concerning mixtures of pesticides. This study thus investigated the impacts of one of the most used herbicides: S-metolachlor and its two metabolites, metolachlor oxanilic acid (MOA) and metolachlor ethanesulfonic acid (MESA) on the development of zebrafish embryos (Danio rerio). Embryos were exposed to the individual substances and their environmentally relevant mixture until 120 hpf (hours post-fertilization). The focus was set on sublethal endpoints such as malformations, hatching success, length of fish larvae, spontaneous movements, heart rate and locomotion. Moreover, expression levels of eight genes linked to the thyroid system disruption, oxidative stress defense, mitochondrial metabolism, regulation of cell cycle and retinoic acid (RA) signaling pathway were analyzed. Exposure to S-metolachlor (1 μg/L) and the pesticide mixture (1 μg/L of each substance) significantly reduced spontaneous tail movements of 21 hpf embryos. Few rare developmental malformations were observed, but only in larvae exposed to more than 100 μg/L of individual substances (craniofacial deformation, non-inflated gas bladder, yolk sac malabsorption) and to 30 μg/L of each substance in the pesticide mixture (spine deformation). No effect on hatching success, length of larvae, heart rate or larvae locomotion were found. Strong responses were detected at the molecular level including induction of p53 gene regulating the cell cycle (the pesticide mixture - 1 μg/L of each substance; MESA 30 μg/L; and MOA 100 μg/L), as induction of cyp26a1 gene encoding cytochrome P450 (pesticide mixture - 1 μg/L of each substance). Genes implicated in the thyroid system regulation (dio2, thra, thrb) were all overexpressed by the environmentally relevant concentrations of the pesticide mixture (1 μg/L of each substance) and MESA metabolite (1 μg/L). Zebrafish thyroid system disruption was revealed by the overexpressed genes, as well as by some related developmental malformations (mainly gas bladder and yolk sac abnormalities), and reduced spontaneous tail movements. Thus, the thyroid system disruption represents a likely hypothesis behind the effects caused by the low environmental concentrations of S-metolachlor, its two metabolites and their mixture.

Effects of pollution on freshwater aquatic organisms

This paper presents the reviews of scientific papers published in 2018 issues on the effects of anthropogenic pollution on the aquatic organisms dwelling in freshwater ecosystem at global scale. The first part of the study provides the summary of relevant literature reviews followed by field and survey based studies. The second part is based on categories of different classes/sources of pollutants which affect freshwater organism. This is composed of several sections including metals and metalloids, wastewater and effluents, sediments, nutrients, pharmaceuticals, polycyclic aromatic hydrocarbons, flame retardants, persistent organic pollutants, pharmaceuticals and illicit drugs, emerging contaminants, pesticides, herbicides, and endocrine disruptors. The final part of the study highlights the reviews of published research work on new pollutants such as microplastics and engineered nanoparticles which affect the freshwater organisms. PRACTITIONER POINTS: Heavy metals concentrations should be assessed at nano-scale in aquatic environment. Air pollutants could have long-term effects on freshwater ecosystem. Future studies should focus on bioremediations of freshwater pollution.

Effects of S-metolachlor and its degradation product metolachlor OA on marbled crayfish (Procambarus virginalis)

Increasing production of energy crops in Europe, mainly maize and rapeseed, has altered patterns of pesticide use in recent decades. The long-term effects of S-metolachlor (S-M) and of its metabolite metolachlor OA (M-OA) at the environmentally relevant concentration of 4.2 μg L^-1 and at 42 μg L^-1 (ten-fold concentration) on marbled crayfish (Procambarus virginalis) were evaluated in a 28-day exposure and after a subsequent 28-day recovery period. Indicators assessed were behaviour; biochemical haemolymph profile; oxidative and antioxidant parameters of gill, hepatopancreas, and muscle; and histology of hepatopancreas and gill. Results showed biochemical haemolymph profile (lactate, alanine aminotransferase, aspartate aminotransferase, inorganic phosphate), lipid peroxidation in hepatopancreas, and antioxidant parameters (catalase, reduced glutathione, glutathione S-transferase) of hepatopancreas and gill of crayfish exposed to S-M and M-OA to significantly differ from controls (P < 0.01). Antioxidant biomarker levels remained different from controls after a 28-day recovery period. Differences in behaviour including speed of movement and velocity, and histopathological damage to gill and hepatopancreas were associated with S-M and M-OA exposure and persisted after 28 days in S-M- and M-OA-free water. Results suggest harmful effects of low concentrations of S-M and its metabolite M-OA on non-target organisms and provide information for assessing their effects at environmentally relevant concentrations.

An ecotoxicological view on neurotoxicity assessment

The numbers of potential neurotoxicants in the environment are raising and pose a great risk for humans and the environment. Currently neurotoxicity assessment is mostly performed to predict and prevent harm to human populations. Despite all the efforts invested in the last years in developing novel in vitro or in silico test systems, in vivo tests with rodents are still the only accepted test for neurotoxicity risk assessment in Europe. Despite an increasing number of reports of species showing altered behaviour, neurotoxicity assessment for species in the environment is not required and therefore mostly not performed. Considering the increasing numbers of environmental contaminants with potential neurotoxic potential, eco-neurotoxicity should be also considered in risk assessment. In order to do so novel test systems are needed that can cope with species differences within ecosystems. In the field, online-biomonitoring systems using behavioural information could be used to detect neurotoxic effects and effect-directed analyses could be applied to identify the neurotoxicants causing the effect. Additionally, toxic pressure calculations in combination with mixture modelling could use environmental chemical monitoring data to predict adverse effects and prioritize pollutants for laboratory testing. Cheminformatics based on computational toxicological data from in vitro and in vivo studies could help to identify potential neurotoxicants. An array of in vitro assays covering different modes of action could be applied to screen compounds for neurotoxicity. The selection of in vitro assays could be guided by AOPs relevant for eco-neurotoxicity. In order to be able to perform risk assessment for eco-neurotoxicity, methods need to focus on the most sensitive species in an ecosystem. A test battery using species from different trophic levels might be the best approach. To implement eco-neurotoxicity assessment into European risk assessment, cheminformatics and in vitro screening tests could be used as first approach to identify eco-neurotoxic pollutants. In a second step, a small species test battery could be applied to assess the risks of ecosystems.