Temporal variation of imidacloprid concentration and risk in waterways discharging to the Great Barrier Reef and potential causes

Exposure and combined risk of pesticide mixtures in tropical wetland waters, Australia

Located within the Great Barrier Reef Catchment Area (GBRCA), the Herbert River Floodplain is designated as an area of nationally important wetlands. Furthermore, these wetlands provide a range of critical ecosystem services which protect the Great Barrier Reef World Heritage area ecosystem from land-based effects including agricultural runoff. The surrounding intensive agricultural land use puts these wetlands at risk of excessive loading of pesticides, which may result in species decline, loss of value and reduced function of ecosystem services. The aim of this study is to investigate the combined risk from the co-occurrence of pesticides in wetlands of the Herbert River Floodplain. Waters of five freshwater wetlands were monitored for 55 pesticides using a combination of grab and passive sampling techniques between February 2021 and March 2023. The combined mixture toxicity for up to 19 commonly detected pesticide active ingredients (PAIs) was estimated using the pesticide risk metric (PRM) model, calculated as the combined percentage of species affected (PAF). Thirty-six pesticides were detected in waters across five wetlands, eight of which exceeded regulatory guidelines at least once. Site-specific species protection goals were exceeded at least once at four of the five studied wetlands. Average monthly PAF (from passive sampling) was found to be increased during the wet season, though no increase in instantaneous PAF (from grab sampling) was detected in the wet season. Our findings indicate wetlands of the broader GBRCA are likely to be at risk due to pesticide exposure, and that this risk occurs during both wet and dry seasons. Risk periods in wetlands are not consistent with those previously observed in nearby rivers and creeks and should be monitored accordingly.

The Temporal Response Surface: A Novel Method for the Assessment of Delayed and Time-Cumulative Aquatic Ecosystem Risk

In Australia, pesticide risk assessments in aquatic environments typically compare measured water concentrations to relevant ecosystem protection guidelines based on species sensitivity distributions (SSDs). These guidelines estimate concentrations that are protective against long-term (chronic) exposure but do not consider extended exposure to chemicals with cumulative toxicity, such as neonicotinoid insecticides. The Australian and New Zealand Guidelines caution against the application of default acute to chronic ratios (ACRs) for such chemicals but lack suitable alternatives. Addressing this gap, we introduce the Temporal Response Surface (TRS) method that incorporates exposure duration into SSDs via taxa-specific regression relationships. The TRS considers both toxicity and exposure duration, setting meaningful guidelines for aquatic ecosystem protection and facilitating probabilistic risk assessments. Applied to imidacloprid, concentrations that are protective of 99, 95, 90, and 80% of the ecosystem (PC99, PC95, PC90, and PC80, respectively) drop quickly within the first 30 days of continuous exposure, then progressively decline over longer exposure periods. This suggests that previous risk assessments may have underestimated the toxic effects of prolonged or repeated imidacloprid exposure. The TRS method offers a holistic solution, addressing policy and risk assessment gaps for chemicals with delayed or cumulative toxicity, further enhancing aquatic ecosystem protection in Australia and internationally.

Advancing aquatic ecological risk assessment of imidacloprid in global surface water with mesocosm-based thresholds

Aquatic ecological risk posed by neonicotinoids has become a growing concern due to their widespread use and documented environmental impacts. However, current risk assessments predominantly rely on laboratory-based toxicity data, which often lack ecological relevance and may introduce substantial biases. In this study, we addressed a critical knowledge gap in neonicotinoid risk assessment by establishing the first global-scale comparison between traditional laboratory-based and ecologically realistic mesocosm-derived toxicity thresholds. Analysis of literature-reported concentrations revealed significant regional variations in imidacloprid pollution at a global scale, with the highest median concentrations detected in Oceania, followed by Asia, Africa, America, and Europe, although extreme concentrations were observed in America. The mesocosm-based hazard concentration for 5 % of species (HC5) was determined to be 0.013 μg/L, which was significantly lower than the laboratory-based HC5 of 0.086 μg/L. Risk assessment using the laboratory-based threshold identified 1.2 % of the 1378 freshwater samples as high risk (risk quotient, RQ>10) and 7.1 % as medium risk (1 Collapse

Key Words

• Land use
• Mesocosm
• Neonicotinoids
• Regional distribution
• Regulatory thresholds
• Species sensitivity distribution

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Affiliation(s)

Huizhen Li Guangdong Key Laboratory of Environmental Pollution and Health, College of Environment and Climate, Jinan University, Guangzhou 511443, China
Lingzhi Xie Guangdong Key Laboratory of Environmental Pollution and Health, College of Environment and Climate, Jinan University, Guangzhou 511443, China
Zewei Xu Guangdong Key Laboratory of Environmental Pollution and Health, College of Environment and Climate, Jinan University, Guangzhou 511443, China
Fei Cheng State Key Laboratory of Advanced Environmental Technology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Jing You Guangdong Key Laboratory of Environmental Pollution and Health, College of Environment and Climate, Jinan University, Guangzhou 511443, China.

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Impacts of neonicotinoids on biodiversity: a critical review

Neonicotinoids are the most widely used class of insecticides in the world, but they have raised numerous concerns regarding their effects on biodiversity. Thus, the objective of this work was to do a critical review of the contamination of the environment (soil, water, air, biota) by neonicotinoids (acetamiprid, clothianidin, imidacloprid, thiacloprid, thiamethoxam) and of their impacts on terrestrial and aquatic biodiversity. Neonicotinoids are very frequently detected in soils and in freshwater, and they are also found in the air. They have only been recently monitored in coastal and marine environments, but some studies already reported the presence of imidacloprid and thiamethoxam in transitional or semi-enclosed ecosystems (lagoons, bays, and estuaries). The contamination of the environment leads to the exposure and to the contamination of non-target organisms and to negative effects on biodiversity. Direct impacts of neonicotinoids are mainly reported on terrestrial invertebrates (e.g., pollinators, natural enemies, earthworms) and vertebrates (e.g., birds) and on aquatic invertebrates (e.g., arthropods). Impacts on aquatic vertebrate populations and communities, as well as on microorganisms, are less documented. In addition to their toxicity to directly exposed organisms, neonicotinoid induce indirect effects via trophic cascades as demonstrated in several species (terrestrial and aquatic invertebrates). However, more data are needed to reach firmer conclusions and to get a clearer picture of such indirect effects. Finally, we identified specific knowledge gaps that need to be filled to better understand the effects of neonicotinoids on terrestrial, freshwater, and marine organisms, as well as on ecosystem services associated with these biotas.

Aquatic hazard and risk posed by four pesticides detected in waterways discharging to the Great Barrier Reef, Australia: Part 2. Hazard and risk assessment

Pesticide active ingredients (PAIs) are regularly detected in the rivers, creeks, wetlands, and inshore waterways that discharge to the Great Barrier Reef (GBR) lagoon. Pesticide active ingredients detected above ecologically protective concentrations may pose a hazard and risk to aquatic species. The ability to assess this hazard and risk is reliant on the availability of water quality guidelines, which are only available for a limited number of PAIs detected in GBR catchment waterways. Unendorsed guideline values, known as ecotoxicity threshold values (ETVs) were developed in part one of this study for active ingredients in two fungicides (4-hydroxychlorothalonil (fungicide degradate) and carbendazim) and two insecticides (dimethoate and methoxyfenozide) that are commonly detected in GBR catchment waterways. In the current study, the hazard and risk posed by these PAIs was assessed by comparing the ETVs to environmental monitoring data from the Great Barrier Reef Catchment Loads Monitoring Program. Exceedances of the concentrations that should protect 99 % of aquatic species (i.e., PC99) were observed for all four pesticides. Detected concentrations of 4-hydroxychlorothalonil, carbendazim and methoxyfenozide exceeded the PC95 ETV, however no exceedances of the PC95 were observed for dimethoate. The hazard quotient (HQ) method was used to identify high hazard sites across the GBR catchment area. In total, six sites were identified as having concentrations that exceeded the PC95 ETVs. For 4-hydroxychlorothalonil, the risk to aquatic species based on the 95th percentile concentrations ranged from 3 to 13 %, 1 to 8 % for carbendazim and 2 to 8 % for methoxyfenozide. Detected concentrations of carbendazim were two orders of magnitude higher than concentrations that are reported to induce behavioural effects in some fish species. Considering that detected concentrations of three of the four PAIs individually pose a potential risk to aquatic species, their contributions to pesticide mixture toxicity should be further assessed.

Pesticides in the Great Barrier Reef catchment area: Plausible risks to fish populations

Waterways that drain the Great Barrier Reef catchment area (GBRCA) transport pollutants to marine habitats, provide a critical corridor between freshwater and marine habitats for migratory fish species, and are of high socioecological value. Some of these waterways contain concentrations of pesticide active ingredients (PAIs) that exceed Australian ecotoxicity threshold values (ETVs) for ecosystem protection. In this article, we use a "pathway to harm" model with five key criteria to assess whether the available information supports the hypothesis that PAIs are or could have harmful effects on fish and arthropod populations. Strong evidence of the first three criteria and circumstantial weaker evidence of the fourth and fifth criteria are presented. Specifically, we demonstrate that exceedances of Australian and New Zealand ETVs for ecosystem protection are widespread in the GBRCA, that the PAI contaminated water occurs (spatially and temporally) in important habitats for fisheries, and that there are clear direct and indirect mechanisms by which PAIs could cause harmful effects. The evidence of individuals and populations of fish and arthropods being adversely affected species is more circumstantial but consistent with PAIs causing harmful effects in the freshwater ecosystems of Great Barrier Reef waterways. We advocate strengthening the links between PAI concentrations and fish health because of the cultural values placed on the freshwater ecosystems by relevant stakeholders and Traditional Owners, with the aim that stronger links between elevated PAI concentrations and changes in recreationally and culturally important fish species will inspire improvements in water quality. Integr Environ Assess Manag 2024;20:1256-1279. © 2023 Commonwealth of Australia and The Commonwealth Scientific and Industrial Research Organisation. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Environmental DNA highlights the influence of salinity and agricultural run-off on coastal fish assemblages in the Great Barrier Reef region

Agricultural run-off in Australia's Mackay-Whitsunday region is a major source of nutrient and pesticide pollution to coastal and inshore ecosystems of the Great Barrier Reef. While the effects of run-off are well documented for the region's coral and seagrass habitats, the ecological impacts on estuaries, the direct recipients of run-off, are less known. This is particularly true for fish communities, which are shaped by the physico-chemical properties of coastal waterways that vary greatly in tropical regions. To address this knowledge gap, we used environmental DNA (eDNA) metabarcoding to examine fish assemblages at four locations (three estuaries and a harbour) subjected to varying levels of agricultural run-off during a wet and dry season. Pesticide and nutrient concentrations were markedly elevated during the sampled wet season with the influx of freshwater and agricultural run-off. Fish taxa richness significantly decreased in all three estuaries (F = 164.73, P = <0.001), along with pronounced changes in community composition (F = 46.68, P = 0.001) associated with environmental variables (largely salinity: 27.48% contribution to total variance). In contrast, the nearby Mackay Harbour exhibited a far more stable community structure, with no marked changes in fish assemblages observed between the sampled seasons. Among the four sampled locations, variation in fish community composition was more pronounced within the wet season (F = 2.5, P = 0.001). Notably, variation in the wet season was significantly correlated with agricultural contaminants (phosphorus: 6.25%, pesticides: 5.22%) alongside environmental variables (salinity: 5.61%, DOC: 5.57%). Historically contaminated and relatively unimpacted estuaries each demonstrated distinct fish communities, reflecting their associated catchment use. Our findings emphasise that while seasonal effects play a key role in shaping the community structure of fish in this region, agricultural contaminants are also important contributors in estuarine systems.

Application of passive sampling device for exploring the occurrence, distribution, and risk of pharmaceuticals and pesticides in surface water

Pharmaceuticals and pesticides are compounds of high concern in surface waters around the world. However, few studies have used passive sampling methods to screen and detect these compounds in natural waters. In this study, a self-developed passive sampler was employed to measure pharmaceuticals and pesticides in the rivers of Nanjing, China. A total of 41 pharmaceuticals and 11 pesticides were detected, among which antibiotic and insecticide were the predominant classes, respectively. Valproic acid, caffeine and triclosan from the pharmaceuticals, and isoprocarb and imidacloprid from the pesticides were found frequently with high concentrations. At most sampling sites, the concentration ratios of caffeine versus carbamazepine exceeded 10, and even above 50, indicating relatively poor efficiency of wastewater treatment, or possibly the direct discharge of raw sewage, or other unknown source of pollution. It was found that the concentrations and ecological risks in the northern area of Yangtze River were higher than those in the southern area of Yangtze River, implying that economic development and population density were not the main contributors to the discovered pollution. The total concentration of pharmaceuticals and pesticides in Qinhuai River increased gradually with the direction of water flow, demonstrating the success of water diversion project in flushing and scouring pollutants.

Occurrence, spatial variation, seasonal difference, and risk assessment of neonicotinoid insecticides, selected agriculture fungicides, and their transformation products in the Yangtze River, China: From the upper to lower reaches

Neonicotinoid insecticides (NNIs) and agricultural fungicides (including strobilurin, azole, and morpholine fungicides) are widely used, while data on their contamination in the Yangtze River of China and the risks posed by them are limited. The occurrence and distribution of ten NNIs, twenty-one transformation products (TPs) of them, seventeen agricultural fungicides, and six TPs of them were investigated in the main stream of the Yangtze River. Surface water samples (n = 144) were obtained from 72 sampling points in dry season and wet season. Among the NNIs, the detection frequencies (DFs) of acetamiprid (ACE), clothianidin, dinotefuran, flonicamid, imidacloprid (IMI), thiacloprid (THCP), and thiamethoxam (THM) were higher than 85%, with the median concentrations ranged from 0.06 ng/L (THCP) to 3.63 ng/L (IMI). The DFs of the TPs descyano-acetamiprid, desmethyl-acetamiprid (DM-ACE), N-[(6-Chloropyridin-3-yl) methyl] methylamine, desnitro-clothianidin, desnitro-imidacloprid, desnitro-thiamethoxam, imidacloprid-urea, and thiamethoxam-urea (THM-urea) were higher than 80%, with the median concentrations ranged from 0.25 ng/L for DM-ACE to 2.41 ng/L for THM-urea. Some agricultural parent fungicides, including azoxystrobin (AZS), carbendazim (CBDZ), difenoconazole, dimethomorph, propiconazole, pyraclostrobin, and tebuconazole (TBCZ), were detected in all the samples; others were also detected in more than 80% of the samples except for fluoxastrobin (12.5%). The median concentrations of the frequently detected fungicides ranged from 0.02 ng/L (trifloxystrobin) to 26.8 ng/L (CBDZ). The DFs of the fungicide TPs azoxystrobin acid (AZS acid), difenoconazole-alcohol, tebuconazole-tert-butylhydroxy (TBCZ-OH), and 5-hydroxymethyl-tricyclazole were higher than 75%, with the median concentrations ranged from 0.09 ng/L (TBCZ-OH) to 1.80 ng/L (AZS acid). The summed concentrations of the NNIs and their TPs at the sampling points varied between 0.23 and 418 ng/L, and the summed concentrations of the selected fungicides and their TPs varied from 0.29 to 1160 ng/L. The spatial distribution of most target analytes revealed an increasing trend in their concentrations from the upstream to downstream Yangtze River (250 times increase in their cumulative concentration). Most target pesticides in this study had significantly higher concentrations during wet season than those during dry season. Furthermore, ecological risk assessment suggested that ACE, IMI, THM, CBDZ, TBCZ, and thifluzamide in some samples (n = 1, 11, 1, 1, 1, and 6, respectively) posed high risks to the ecosystem (risk quotient > 1). Priority attention should be paid to the ecological risk posed by these pesticides. Thirty-seven samples had concentrations of individual target analytes over 100 ng/L and four samples had cumulative concentrations of the target analytes over 500 ng/L, exceeding the European Commission guideline values. Taken together, our findings demonstrate a widespread occurrence of the NNIs, agricultural fungicides, and their TPs in the mainstream of the Yangtze River and potential ecological risks posed by some of them.

Sex-specific alterations in adaptive responses of Chironomus columbiensis triggered by imidacloprid chronic and acute sublethal exposures

The use of imidacloprid is a common pest control practice in the Neotropical region. However, the imidacloprid unintended sublethal effects on Neotropical aquatic non-target arthropods and undesirable consequences for aquatic environments remain unclear. Here, we assessed the susceptibility of Chironomus columbiensis (Diptera: Chironomidae) larvae to the neonicotinoid imidacloprid and evaluated whether sublethal exposure types would trigger sex-dependent adaptive responses (e.g., emergence, body mass, reproduction, wing morphology). We conducted a concentration-mortality curve (96 h of exposure) and established chronic and acute sublethal exposure bioassays. While chronic sublethal exposures consisted of exposing individuals during their entire larval and pupal stages, the acute sublethal exposures represented a single short duration (24 h) exposure episode during either the first or fourth larval instar. Our results revealed that chronic sublethal exposure reduced the body mass of males, while acute sublethal exposures during the first instar resulted in heavier males than those that were not exposed to imidacloprid. Chronic exposure also reduced the reproduction of males and females, while the acute sublethal exposure only affected the reproduction of individuals that were imidacloprid-exposed on their later larval instar. Chronic and acute sublethal exposures did differentially affect the wing properties of C. columbiensis males (e.g., increased size when chronically exposed and highly asymmetric wings when acutely exposed in early larval phase) and females (e.g., highly asymmetric wings when chronically and acutely exposed). Collectively, our findings demonstrated that imidacloprid can cause unintended sublethal effects on C. columbiensis, and those effects are dependent on sex, exposure type, and developmental stage.

Neonicotinoid insecticides in global agricultural surface waters - Exposure, risks and regulatory challenges

Neonicotinoids are the most widely used insecticides worldwide. However, the widespread usage of neonicotinoids has sparked concerns over their effects on non-target ecosystems including surface waters. We present here a comprehensive meta-analysis of 173 peer-reviewed studies (1998-2022) reporting measured insecticide concentrations (MICs; n = 3983) for neonicotinoids in global surface waters resulting from agricultural nonpoint source pollution. We used compound-specific regulatory threshold levels for water (RTL_SW) and sediment (RTL_SED) defined for pesticide authorization in Canada, the EU and the US, and multispecies endpoints (MSE_SW) to assess acute and chronic risks of global neonicotinoid water-phase (MIC_SW; n = 3790) and sediment (MIC_SED; n = 193) concentrations. Results show a complete lack of exposure information for surface waters in >90 % of agricultural areas globally. However, available data indicates for MIC_SW overall acute risks to be low (6.7 % RTL_{SW_acute} exceedances), but chronic risks to be of concern (20.7 % RTL_{SW_chronic} exceedances); exceedance frequencies were particularly high for chronic MSE_SW (63.3 %). We found RTL_SW exceedances to be highest for imidacloprid and in less regulated countries. Linear model analysis revealed risks for global agricultural surface waters to decrease significantly over time, potentially biased by the lack of sensitive analytical methods in early years of neonicotinoid monitoring. The Canadian, EU and US RTL_SW differ considerably (up to factors of 223 for RTL_{SW_acute} and 13,889 for RTL_{SW_chronic}) for individual neonicotinoids, indicating large uncertainties and regulatory challenges in defining robust and protective RTLs. We conclude that protective threshold levels, in concert with increasing monitoring efforts targeting agricultural surface waters worldwide, are essential to further assess the ecological consequences from anticipated increases of agricultural neonicotinoid uses.

Cascading effects of climate change on recreational marine flats fishes and fisheries

Tropical and subtropical coastal flats are shallow regions of the marine environment at the intersection of land and sea. These regions provide myriad ecological goods and services, including recreational fisheries focused on flats-inhabiting fishes such as bonefish, tarpon, and permit. The cascading effects of climate change have the potential to negatively impact coastal flats around the globe and to reduce their ecological and economic value. In this paper, we consider how the combined effects of climate change, including extremes in temperature and precipitation regimes, sea level rise, and changes in nutrient dynamics, are causing rapid and potentially permanent changes to the structure and function of tropical and subtropical flats ecosystems. We then apply the available science on recreationally targeted fishes to reveal how these changes can cascade through layers of biological organization-from individuals, to populations, to communities-and ultimately impact the coastal systems that depend on them. We identify critical gaps in knowledge related to the extent and severity of these effects, and how such gaps influence the effectiveness of conservation, management, policy, and grassroots stewardship efforts.