The current study investigates the dissipation kinetics of two imidacloprid (IMI) nanoformulations (entitled: Nano-IMI and Nano-IMI/TiO2) on common bean (Phaseolus vulgaris) seeds under field conditions and compares them with 35% Suspension Concentrate (SC) commercial formulation. To do so, it sprays P. vulgaris plants at 30 and 60 g/ha within green bean stage, sampling them during the 14-day period after the treatment. Following extraction and quantification of IMI residues, dissipation data have been fitted to simple-first order kinetic model (SFOK) and to first-order double-exponential decay (FODED) models, with 50% and 90% dissipation times (DT50 and DT90, respectively) assessed along the pre-harvest interval (PHI). With the exception of Nano-IMI at 60 g/ha, other decline curves are best fitted to the FODED model. In general, dissipation is faster for Nano-IMI (at 30 g/ha: DT50 = 1.09 days, DT90 = 4.30 days, PHI = 1.23 days; at 60 g/ha: DT50 = 1.29 days, DT90 = 4.29 days, PHI = 2.95 days) and Nano-IMI/TiO2 (at 30 g/ha: DT50 = 1.15 days, DT90 = 4.40 days, PHI = 1.08 days; at 60 g/ha: DT50 = 0.86 days, DT90 = 4.92 days, PHI = 3.02 days), compared to 35% SC (at 30 g/ha: DT50 = 1.58, DT90 = 6.45, PHI = 1.93; at 60 g/ha: DT50 = 1.58 days, DT90 = 14.50 days, PHI = 5.37 days). These results suggest the suitability of Nano-IMI and Nano-IMI/TiO2 application at both rates in terms of their residues on P. vulgaris seeds.

There is currently a lack of ecotoxicity tests adapted to earthworm species of higher ecological relevance and whose endpoints could be directly related to their ecological role in the soil. We propose a new and relatively simple ecotoxicity test based on the estimation of cast production (CP) by Lumbricus terrestris under laboratory conditions. CP was found to be linearly correlated to earthworm biomass and to be greatly influenced by soil water content. Azinphos-methyl had no effect on CP at all the concentrations tested. Significant decreases were observed at the normal application rate for other pesticides with (imidacloprid, carbaryl, methomyl) or without (ethyl-parathion and chlorpyrifos-ethyl) a clear concentration–effect response. For the highest concentration tested, reduction in CP varied between 35 and 67%. CP is straightforward and rapidly measured and ecologically meaningful. We thus believe it to be of great use as an endpoint in ecotoxicity testing.

Due to technical limitations, there have been minimal studies performed on thermal preferences and thermotactic behaviors of aquatic ectotherm species commonly used in ecotoxicity testing. In this work, we demonstrate an innovative, purpose-built and miniaturized electrothermal array for rapid thermal preference behavioral tests. We applied the novel platform to define thermal preferences in multiple invertebrate and vertebrate species. Specifically, Dugesia notogaea (freshwater planarians), Chironomus tepperi (nonbiting midge larvae), Ostracoda (seed shrimp), Artemia franciscana (brine shrimp), Daphnia carinata (water flea), Austrochiltonia subtenuis (freshwater amphipod), Physa acuta (freshwater snail), Potamopyrgus antipodarum (New Zealand mud snail) and larval stage of Danio rerio (zebrafish) were tested. The Australian freshwater water fleas, amphipods, snail Physa acuta as well as zebrafish exhibited the most consistent preference to cool zones and clear avoidance of zones >27 °C out of nine species tested. Our results indicate the larval stage of zebrafish as the most responsive species highly suitable for prospective development of multidimensional behavioral test batteries. We also showcase preliminary data that environmentally relevant concentrations of pharmaceutical pollutants such as non-steroidal anti-inflammatory drug (NSAID) ibuprofen (9800 ng/L) and insecticide imidacloprid (4600 ng/L) but not anti-depressant venlafaxine (2200 ng/L) and (iv) anticonvulsant medications gabapentin (400 ng/L) can perturb thermal preference behavior of larval zebrafish. Collectively our results demonstrate the utility of simple and inexpensive thermoelectric technology in rapid exploration of thermal preference in diverse species of aquatic animals. We postulate that more broadly such technologies can also have added value in ecotoxicity testing of emerging contaminants.

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.

Novel stressors introduced by human activities increasingly threaten freshwater ecosystems. The annual application of more than 2.3 billion kg of pesticide active ingredient and 22 billion kg of road salt has led to the contamination of temperate waterways. While pesticides and road salt are known to cause direct and indirect effects in aquatic communities, their possible interactive effects remain widely unknown. Using outdoor mesocosms, we created wetland communities consisting of zooplankton, phytoplankton, periphyton, and leopard frog (Rana pipiens) tadpoles. We evaluated the toxic effects of six broad-spectrum insecticides from three families (neonicotinoids: thiamethoxam, imidacloprid; organophosphates: chlorpyrifos, malathion; pyrethroids: cypermethrin, permethrin), as well as the potentially interactive effects of four of these insecticides with three concentrations of road salt (NaCl; 44, 160, 1600 Cl⁻ mg/L). Organophosphate exposure decreased zooplankton abundance, elevated phytoplankton biomass, and reduced tadpole mass whereas exposure to neonicotinoids and pyrethroids decreased zooplankton abundance but had no significant effect on phytoplankton abundance or tadpole mass. While organophosphates decreased zooplankton abundance at all salt concentrations, effects on phytoplankton abundance and tadpole mass were dependent upon salt concentration. In contrast, while pyrethroids had no effects in the absence of salt, they decreased zooplankton and phytoplankton density under increased salt concentrations. Our results highlight the importance of multiple-stressor research under natural conditions. As human activities continue to imperil freshwater systems, it is vital to move beyond single-stressor experiments that exclude potentially interactive effects of chemical contaminants.

Sulfur, an essential macronutrient, plays important roles in plant development and stress mitigation. Sulfur deficiency, a common problem in agricultural soils, may disturb plant stress resistance and xenobiotic detoxification. In the present study, the function and mechanism of limited sulfur nutrition on the residues and phtotoxicity of imidacloprid were investigated in lettuce plants. Sulfur deficiency significantly increased imidacloprid accumulation in lettuce tissues, exacerbated imidacloprid biological toxicity by enhancing the accumulation of toxic metabolites, like imidacloprid-olefin. Simultaneously, imidacloprid-induced detoxification enzymes including cytochromes P450, glutathione S-transferases (GSTs) and glycosyltransferases were inhibited under limited sulfur supply. On the other hand, sulfur deficiency further enhanced the generation of reactive oxygen species and exacerbated lipid peroxidation in lettuce tissues. Sulfur deficiency mainly reduced the abundance of thiol groups, which are essential redox modulators as well as xenobiotic conjugators, and significantly inhibited GSTs expression. These results clearly suggested that sulfur deficiency inhibited the synthesis of sulfur-containing compounds, leading to increased accumulation of pesticide residues and toxic metabolites as well as reduced detoxification capacity, consequently leading to oxidative damage to plants. Therefore, moderate sulfur supply in regions where neonicotinoid insecticides are intensively and indiscriminately used may be an efficient strategy to reduce pesticide residues and the potential risk to ecosystem.

Neonicotinoid insecticides (NIIs) are extensively used worldwide and frequently detected in the environment. The human and ecological risks associated with the occurrence of NIIs in agricultural zones are of high importance. The present study highlights the regional occurrence and human exposure risks of NIIs in agricultural soil within the Pearl River Delta (PRD), South China. Six neonicotinoids, i.e., imidacloprid, clothianidin, acetamiprid, imidaclothiz, dinotefuran, and flonicamid, were measured in 351 soil samples from Zengcheng, a typical agricultural zone. The soil samples were categorized into three groups based on cultivated plants: vegetables, rice, and fruits. At least one of these neonicotinoid insecticides was detected in 95% of the soil samples. The levels of ∑₆NII (range (median)) were 0.26–390 (23), 0.26–280 (6.1), and 0.26–120 (5.0) ng g⁻¹ dry weight in soil samples from vegetable farms, rice paddies, and fruit farms, respectively. Neonicotinoids were detected more frequently and at statistically higher concentrations in vegetable farms than in both rice paddies and fruit farms. This is likely ascribed to higher application frequencies of NIIs in vegetable farms due to higher planting frequencies. The hazard index values for human exposure to NIIs in the agricultural soils were all below 1, suggesting negligible non-cancer risks. The current residual levels of NIIs in the soils could however pose sub-lethal or acute effects to non-target terrestrial organisms such as earthworms. The present study suggests that more information is needed regarding NIIs contamination in soils from agricultural regions of South China to ensure that human and ecological risk from exposure to these compounds can be fully addressed.

The on-going and extensive use of neonicotinoids occur in orchards. However, it is still unknown whether and how orchard management affects soil properties, especially the contents and structure of soil organic matter during orchard development, and their further influences on neonicotinoid persistence. Here, surface soil samples were collected from the citrus orchards with different cultivation ages (1, 10, 14, and 20 years), and their physicochemical properties were determined. Changes in the chemical structure of soil organic matter (SOM) were furtherly examined using solid-state CP/TOSS ¹³C NMR. Then, the sorption isotherms of imidacloprid in these soils were investigated. The sorption coefficient (Kd) of imidacloprid at Cₑ of 0.05 mg/L in the orchard soils increased by 19.4–23.3%, along a 20-year chronosequence of cultivation, which should be mainly ascribed to the increase of SOM. However, the organic carbon-normalized sorption coefficient (Kₒc, sorption per unit mass of OM) of imidacloprid declined with increasing cultivation ages. Moreover, the polar and aliphatic domains of SOM had a significantly positive relation to the Kₒc of imidacloprid, suggesting its key role in governing imidacloprid sorption. The results highlighted that reasonable management measures could be adopted to control the occurrence and fate of neonicotinoids in soils, mainly by affecting the content and quality of SOM.

Neonicotinoid insecticides have posed a great threat to non-target organisms, yet the mechanisms underlying their toxicity are not well characterized. Major modes of action (MoAs) of imidacloprid were analyzed in an aquatic insect Chironomus dilutus. Lethal and sublethal outcomes were assessed in the midges after 96-h exposure to imidacloprid. Global transcriptomic profiles were determined using de novo RNA-sequencing to more holistically identify toxicity pathways. Transcriptional 10% biological potency values derived from ranked KEGG pathways and GO terms were 0.02 (0.01–0.08) (mean (95% confidence interval) and 0.05 (0.04–0.06) μg L⁻¹, respectively, which were more sensitive than those from phenotypic traits (10% lethal concentration: 0.44 (0.23–0.79) μg L⁻¹; 10% burrowing behavior concentration: 0.30 (0.22–0.43) μg L⁻¹). Major MoAs of imidacloprid in aquatic species were identified as follows: the activation of nicotinic acetylcholine receptors (nAChRs) induced by imidacloprid impaired organisms’ nerve system through calcium ion homeostasis imbalance and mitochondrial dysfunction, which posed oxidative stress and DNA damage and eventually caused death of organisms. The current investigation highlighted that imidacloprid affected C. dilutus at environmentally relevant concentrations, and elucidated toxicity pathways derived from gene alteration to individual outcomes, calling for more attention to toxicity of neonicotinoids to aquatic organisms.

Organisms and ecosystems are generally exposed to mixtures of chemicals rather than to individual chemicals, but there have been relatively few detailed analyses of the mixtures of pesticides that occur in surface waters. This study examined over 2600 water samples, analysed for between 21 and 47 pesticides, from 15 waterways that discharge to the lagoon of the Great Barrier Reef in Queensland, Australia between July 1, 2011 and June 30, 2015. Essentially all the samples (99.8%) contained detectable concentrations (>limit of detection) of pesticides and pesticide mixtures. Approximately, 10% of the samples contained no quantifiable (>limit of reporting) pesticides, 10% contained one quantifiable pesticide and 80% contained quantifiable mixtures of 2–20 pesticides. Approximately 82% of samples that contained quantifiable mixtures had more than two modes of action (MoAs), but only approximately 6% had five or more MoAs. The mode, average and median number of quantifiable pesticides in all the samples were 2, 5.1 and 4, respectively. The most commonly detected compounds both individually and in mixtures were the pesticides atrazine, diuron, imidacloprid, hexazinone, 2,4-D, and the degradation product desethylatrazine. The number of pesticides and modes of action of pesticides in mixtures differed spatially and were affected by land use. Waterways draining catchments where sugar cane was a major land use had mixtures with the most pesticides.