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).

Clothianidin interferes with recognition of a previous encounter in rusty crayfish (Faxonius rusticus) due to a chemosensory impairment

Clothianidin, a neonicotinoid insecticide that binds to arthropod nicotinic acetylcholine receptors, is widely used to protect plants against a wide variety of agricultural pests. Little is known about how this insecticide affects non-target invertebrate species in aquatic environments. In this study, we explored the effects of aqueous exposures of clothianidin on locomotion, chemosensory-based responses, and agonistic encounters of rusty crayfish (Faxonius rusticus). Clothianidin exposures at a concentration of 1.0 μg/L (i.e., 1.0 ppb) did not alter initiations and retreats, but did increase the amount of time the crayfish interacted per interaction. In a subsequent food cue experiment with crayfish exposed to clothianidin concentrations of 0.4 μg/L and 1.0 μg/L, the test organisms demonstrated chemosensory dysfunction, but no decrease in locomotory movement. As chemosensation is essential for recognizing previous rivals in crayfish, the loss of this sense likely resulted in the exposed crayfish being unable to detect cues used to recognize a previous competitor. An inability to recognize a previous competitor (and who won or lost the previous interaction) could result in crayfish spending more time fighting and less time on foraging and reproduction. This study demonstrates that exposures of crayfish to clothianidin at concentrations found in the environment affects the behavioural ecology of these aquatic invertebrates.

Disentangling Mechanisms Behind Chronic Lethality through Toxicokinetic-Toxicodynamic Modeling

Ecotoxicological profiles of the 3 insecticides imidacloprid, thiacloprid, and flupyradifurone in terms of acute and chronic effects were analyzed in Chironomus riparius. Toxicokinetic-toxicodynamic modeling revealed that chironomids would die from starvation as a result of prolonged feeding inhibition under chronic exposures. The starvation effect is an indirect cause for mortality, which, for the neonicotinoids, adds to the direct/acute mortality, although the results suggests that this additional effect is not relevant for flupyradifurone. Environ Toxicol Chem 2021;40:1706-1712. © 2021 Bayer Inc. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Neonicotinoid Insecticides from a Marine Perspective: Acute and Chronic Copepod Testing and Derivation of Environmental Quality Standards

Neonicotinoid insecticides have become of global concern for the aquatic environment. Harpacticoid copepods are among the organisms most sensitive to neonicotinoids. We exposed the brackish copepod Nitocra spinipes to 4 neonicotinoid insecticides (clothianidin, imidacloprid, thiacloprid, and thiamethoxam) to investigate acute toxicity on adults (96-h exposure) and effects on larval development (7-d exposure). We used these results in combination with publicly available ecotoxicity data to derive environmental quality standards (EQS). These EQS were ultimately used in a single-substance and mixture risk assessment for the Belgian part of the North Sea. Acute toxicity testing revealed that immobilization is a more sensitive endpoint than mortality, with 96-h median effect concentration (EC50) values of 6.9, 7.2, 25, and 120 µg L^-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. In addition, the larval development tests resulted in 7-d no-observed-effect concentrations (NOECs) of 2.5, 2.7, 4.2, and >99 µg L^-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. The derived saltwater annual average (AA-)EQS were 0.05, 0.0048, 0.002, and 0.016 µg L^-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. Finally, the risk characterization revealed some exceedances of the AA-EQS in Belgian harbors for imidacloprid (number of exceedances, n = 2/4), for thiacloprid (n = 1/4), for thiamethoxam (n = 1/4), and for the mixture of the 4 neonicotinoids (n = 4/4), but not at the open sea. At the open sea site, the toxic unit sums relative to the AA-EQS were 0.72 and 0.22, suggesting no mixture risk, albeit with a relatively small margin of safety. Including short-term EC10 (96-h) values of N. spinipes for the AA-EQS derivation led to a refinement of the AA-EQS for clothianidin and thiamethoxam, suggesting their use for the AA-EQS derivation because one of the overarching goals of the definition of EQS is to protect species at the population level. Environ Toxicol Chem 2021;40:1353-1367. © 2021 SETAC.

Non-target toxicity of novel insecticides

Humans have used insecticides since ancient times. The spectrum and potency of available insecticidal substances has greatly expanded since the industrial revolution, resulting in widespread use and unforeseen levels of synthetic chemicals in the environment. Concerns about the toxic effects of these new chemicals on non-target species became public soon after their appearance, which eventually led to the restrictions of use. At the same time, new, more environmentally-friendly insecticides have been developed, based on naturally occurring chemicals, such as pyrethroids (derivatives of pyrethrin), neonicotinoids (derivatives of nicotine), and insecticides based on the neem tree vegetable oil (Azadirachta indica), predominantly azadirachtin. Although these new substances are more selective toward pest insects, they can still target other organisms. Neonicotinoids, for example, have been implicated in the decline of the bee population worldwide. This review summarises recent literature published on non-target toxicity of neonicotinoids, pyrethroids, and neem-based insecticidal substances, with a special emphasis on neonicotinoid toxicity in honeybees. We also touch upon the effects of pesticide combinations and documented human exposure to these substances.