Strobilurins are popular fungicides used in agriculture on a global scale. Due to their widespread use as agrochemicals, they can enter aquatic environments at concentrations that can elicit adverse effects in organisms. This review synthesizes the current state of knowledge regarding the toxic effects of strobilurin fungicides on aquatic species, including algal species, Daphnia magna, and fish species, to determine risk to aquatic organisms and ecosystems. Data show that the toxicities of strobilurins vary widely across aquatic species. Strobilurins bind cytochrome bc1 in mitochondrial complex III in fungi, and as such, research in aquatic species has focused on mitochondria-related endpoints following exposures to strobilurins. In fish, studies into the activities of mitochondrial complexes and the expression of genes involved in the electron transfer chain have been conducted, converging on the theme that mitochondrial complexes and their enzymes are impaired by strobilurins. In general, the order of toxicity of strobilurins for fish species are pyraoxystrobin > pyraclostrobin ≈ trifloxystrobin > picoxystrobin > kresoxim-methyl > fluoxastrobin > azoxystrobin. In addition to mitochondrial toxicity, studies also report genotoxicity, immunotoxicity, cardiotoxicity, neurotoxicity, and endocrine disruption, and each of these events can potentially impact whole organism-level processes such as development, reproduction, and behavior. Screening data from the US Environmental Protection Agency ToxCast database supports the hypothesis that these fungicides may act as endocrine disruptors, and high throughput data suggest estrogen receptor alpha and thyroid hormone receptor beta can be activated by some strobilurins. It is recommended that studies investigate the potential for endocrine disruption by strobilurins more thoroughly in aquatic species. Based on molecular, physiological, and developmental outcomes, a proposed adverse outcome pathway is presented with complex III inhibition in the electron transfer chain as a molecular initiating event. This review comprehensively addresses sub-lethal toxicity mechanisms of strobilurin fungicides, important as the detection of strobilurins in aquatic environments suggests exposure risks in wildlife.

South Africa is the largest agrochemical user in sub-Saharan Africa, with over 3000 registered pesticide products. Although they reduce crop losses, these chemicals reach non-target aquatic environments via leaching, spray drift or run-off. In this review, attention is paid to legacy and current-use pesticides reported in literature for the freshwater environment of South Africa and to the extent these are linked to endocrine disruption. Although banned, residues of many legacy organochlorine pesticides (endosulfan and dichlorodiphenyltrichloroethane (DDT)) are still detected in South African watercourses and wildlife. Several current-use pesticides (triazine herbicides, glyphosate-based herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and chlorpyrifos) have also been reported. Agrochemicals can interfere with normal hormone function of non-target organism leading to various endocrine disrupting (ED) effects: intersex, reduced spermatogenesis, asymmetric urogenital papillae, testicular lesions and infertile eggs. Although studies investigating the occurrence of agrochemicals and/or ED effects in freshwater aquatic environments in South Africa have increased, few studies determined both the levels of agricultural pesticides present and associated ED effects. The majority of studies conducted are either laboratory-based employing in vitro or in vivo bioassays to determine ED effects of agrochemicals or studies that investigate environmental concentrations of pesticides. However, a combined approach of bioassays and chemical screening will provide a more comprehensive overview of agrochemical pollution of water systems in South Africa and the risks associated with long-term chronic exposure.

Growing applications of nanoagrichemicals have resulted in their increasing accumulation in agricultural soils, which could modify soil properties and affect soil health. A greenhouse pot trial was conducted to determine the effects of three metallic nanoagrichemicals on several fundamental chemical properties of a rice paddy soil, including zinc oxide nanoparticles (ZnO NPs) and copper oxide nanoparticles (CuO NPs) at 100 mg/kg, and silicon oxide nanoparticles (SiO₂ NPs) at 500 mg/kg, as well as their bulk and ionic counterparts. The investigated soil amendments displayed significant and distinctive impact on the examined soil chemical properties relevant to agricultural production, including soil pH, redox potential, soil organic carbon (SOC), cation exchange capacity (CEC), and plant available As. For example, all amendments increased the bulk soil pH at day 47 to some extent, but the increase was substantially higher for SiO₃²⁻ (37.7%) than other amendments (5.8%–13.7%). Soil Eh was elevated markedly at day 47 after the addition of soil amendments in both the bulk soil (45.9%–74.4%) and rice rhizosphere soil (20.3%–68.9%). CuO NPs and Cu²⁺ generally exhibited greater impact on soil chemical properties than other agrichemicals. Significantly different responses to soil amendments were observed between bulk and rhizosphere soils, suggesting the essential role of plants in affecting soil properties and their responses to environmental disturbance. Overall, our results confirmed that the tested amendments could have remarkable impacts on the fundamental chemical properties of rice paddy soils.

Aquatic pollution from emerging organic contaminants (EOCs) is of key environmental importance in India and globally, particularly due to concerns of antimicrobial resistance, ecotoxicity and drinking water supply vulnerability. Here, using a broad screening approach, we characterize the composition and distribution of EOCs in groundwater in the Gangetic Plain around Patna (Bihar), as an exemplar of a rapidly developing urban area in northern India. A total of 73 EOCs were detected in 51 samples, typically at ng.L⁻¹ to low μg.L⁻¹ concentrations, relating to medical and veterinary, agrochemical, industrial and lifestyle usage. Concentrations were often dominated by the lifestyle chemical and artificial sweetener sucralose. Seventeen identified EOCs are flagged as priority compounds by the European Commission, World Health Organisation and/or World Organisation for Animal Health: namely, herbicides diuron and atrazine; insecticides imidacloprid, thiamethoxam, clothianidin and acetamiprid; the surfactant perfluorooctane sulfonate (and related perfluorobutane sulfonate, perfluorohexane sulfonate, perfluorooctanoic acid and perfluoropentane sulfonate); and medical/veterinary compounds sulfamethoxazole, sulfanilamide, dapson, sulfathiazole, sulfamethazine and diclofenac. The spatial distribution of EOCs varies widely, with concentrations declining with depth, consistent with a strong dominant vertical flow control. Groundwater EOC concentrations in Patna were found to peak within ∼10 km distance from the River Ganges, indicating mainly urban inputs with some local pollution hotspots. A heterogeneous relationship between EOCs and population density likely reflects confounding factors including varying input types and controls (e.g. spatial, temporal), wastewater treatment infrastructure and groundwater abstraction. Strong seasonal agreement in EOC concentrations was observed. Co-existence of limited transformation products with associated parent compounds indicate active microbial degradation processes. This study characterizes key controls on the distribution of groundwater EOCs across the urban to rural transition near Patna, as a rapidly developing Indian city, and contributes to the wider understanding of the vulnerability of shallow groundwater to surface-derived contamination in similar environments.

As agriculture expands to provide food and wellbeing to the world’s growing population, there is a simultaneous increasing concern about the use of agrochemicals, which can harm non-target organisms, mainly in the aquatic environment. The fungicide Mancozeb (MZ) has been used on a large-scale and is a potent inducer of oxidative stress. Therefore, there is an urgent need for the development of more sensitive biomarkers designed to earlier biomonitoring of this compound. Here we tested the hypothesis that behavioral changes induced by sublethal MZ concentrations would occur first as compared to biochemical oxidative stress markers. Embryos at 4 h post-fertilization (hpf) were exposed to Mancozeb at 5, 10 and 20 μg/L. Controls were kept in embryo water only. Behavioral and biochemical parameters were evaluated at 24, 28, 72, and 168 hpf after MZ exposure. The results showed that MZ significantly altered spontaneous movement, escape responses, swimming capacity, and exploratory behavior at all exposure times. However, changes in ROS steady-stead levels and the activity of antioxidant enzymes were observable only at 72 and 168 hpf. In conclusion, behavioral changes occurred earlier than biochemical alterations in zebrafish embryos exposed to MZ, highlighting the potential of behavioral biomarkers as sensitive tools for biomonitoring programs.

Nuclear abnormality (NA) assay in fish has been widely applied for toxicity risk assessment under field and laboratory conditions. The zebrafish (Danio rerio) has become a suitable model system for assessing the NA induced by pollutants. Thus, the current study aimed to summarize and discuss the literature concerning micronucleus (MN) and other NA in zebrafish and its applications in toxicity screening and environmental risk assessment. The data concerning the publication year, pollutant type, experimental design, and type of NA induced by pollutants were summarized. Also, molecular mechanisms that cause NA in zebrafish were discussed. Revised data showed that the MN test in zebrafish has been applied since 1996. The MN was the most frequently NA, but 15 other nuclear alterations were reported in zebrafish, such as notched nuclei, blebbed nuclei, binucleated cell, buds, lobed nuclei, bridges, and kidney-shaped. Several pollutants can induce NA in zebrafish, mainly effluents (mixture of pollutants), agrochemicals, and microplastics. The pollutant-induced NA in zebrafish depends on experimental design (i.e., exposure time, concentration, and exposure condition), developmental stages, cell/tissue type, and the type of pollutant. Besides, research gaps and recommendations for future studies are indicated. Overall, the current study showed that zebrafish is a suitable model to assess pollutant-induced mutagenicity.

Cavity nesting bees are proficient and important pollinators that can augment or replace honey bee pollination services for some crops. Relatively little is known about specific pesticide concentrations present in cavity nesting insect reed matrices and associated potential risks to cavity nesting bees. Nesting substrates (Phragmites australis reeds in bundles) were deployed in an agriculturally intensive landscape to evaluate colonization and agrochemical exposure among cavity nesting pollinators over two consecutive field seasons. Composition of insect species colonizing reeds within nest bundles varied considerably; those placed near beef cattle feed yards were dominated by wasps (93% of the total number of individuals occupying reed nest bundles), whereas nest bundles deployed in cropland-dominated landscapes were colonized primarily by leaf cutter bees (71%). All nesting/brood matrices in reeds (mud, leaves, brood, pollen) contained agrochemicals. Mud used in brood chamber construction at feed yard sites contained 21 of 23 agrochemicals included in analysis and >70% of leaf substrate stored in reeds contained at least one agrochemical. Moxidectin was most frequently detected across all reed matrices from feed yard sites, and moxidectin concentrations in nonviable larvae were more than four times higher than those quantified in viable larvae. Agrochemical concentrations in leaf material and pollen were also quantified at levels that may have induced toxic effects among developing larvae. To our knowledge, this is the first study to characterize agrochemical concentrations in multiple reed matrices provisioned by cavity-nesting insects. Use of nest bundles revealed that cavity nesting pollinators in agriculturally intensive regions are exposed to agrochemicals during all life stages, at relatively high frequencies, and at potentially lethal concentrations. These results demonstrate the utility of nest bundles for characterizing risks to cavity nesting insects inhabiting agriculturally intensive regions.

Pyraclostrobin is a widely used and highly efficient fungicide that also has high toxicity to aquatic organisms, especially fish. Although some research has reported the toxic effects of pyraclostrobin on fish, the main toxic pathways of pyraclostrobin in fish remain unclear. The present study has integrated histopathological, biochemical and hematological techniques to reveal the main toxic pathways and mechanisms of pyraclostrobin under different exposure routes. Our results indicated that pyraclostrobin entered fish mainly through the gills. The highest accumulation of pyraclostrobin was observed in the gills and heart compared with accumulation in other tissues and gill tissue showed the most severe damage. Hypoxia symptoms (water jacking, tummy turning and cartwheel formation) in fish were observed throughout the experiment. Taken together, our results suggested that the gills are important target organs. The high pyraclostrobin toxicity to gills might be associated with oxidative damage to the gills, inducing alterations in ventilation frequency, oxygen-carrying substances in blood and disorders of energy metabolism. Our research facilitates a better understanding of the toxic mechanisms of pyraclostrobin in fish, which can promote the ecotoxicological research of agrochemicals on aquatic organisms.

Commercial beekeepers in many locations are experiencing increased annual colony losses of honey bees (Apis mellifera), but the causes, including the role of agrochemicals in colony losses, remain unclear. In this study, we investigated the effects of chronic consumption of pollen containing a widely-used fungicide (Pristine®), known to inhibit bee mitochondria in vitro, which has recently been shown to reduce honey bee worker lifespan when field-colonies are provided with pollen containing field-realistic levels of Pristine®. We fed field colonies pollen with a field-realistic concentration of Pristine® (2.3 ppm) and a concentration two orders of magnitude higher (230 ppm). To challenge flight behavior and elicit near-maximal metabolic rate, we measured flight quality and metabolic rates of bees in two lower-than-normal air densities. Chronic consumption of 230 but not 2.3 ppm Pristine® reduced maximal flight performance and metabolic rates, suggesting that the observed decrease in lifespans of workers reared on field-realistic doses of Pristine®-laced pollen is not due to inhibition of flight muscle mitochondria. However, consumption of either the 230 or 2.3 ppm dose reduced thorax mass (but not body mass), providing the first evidence of morphological effects of Pristine®, and supporting the hypothesis that Pristine® reduces forager longevity by negatively impacting digestive or nutritional processes.