Quantitative weight of evidence assessment of higher-tier studies on the toxicity and risks of neonicotinoid insecticides in honeybees 1: Methods

Individual and combined toxicity of imidacloprid and two seed dressing insecticides on collembolans Folsomia candida

The aim of this study was to examine the chronic toxicity of imidacloprid (IMI), clothianidin (CLO) and fipronil (FIP) as a single exposure, as well as binary mixtures of IMI with CLO or FIP toward collembolans Folsomia candida, which are fauna present in the soil. Chronic toxicity assays were performed following an ISO guideline in a Tropical Artificial Soil (TAS), and the influence on the number and growth of the juveniles produced were determined. The range of nominal concentrations used in the tests with the individual compounds was 0.08-1.28 mg/kg (IMI), 0.079-1.264 mg/kg (FIP) and 0.007-0.112 mg/kg (CLO), whereas the mixture assays were performed with half the value used in the tests with individual compounds. Based upon single exposures, IMI produced a similar impact of reducing reproduction by 50% (EC₅₀ ranging from 0.74 to 0.85 mg/kg) compared to FIP (EC₅₀ = 0.78 mg/kg), whereas CLO was the most toxic to F. candida (EC₅₀ = 0.08 mg/kg). Their mixtures generally resulted in a diminished effect on reproduction, as evidenced by the higher EC₅₀ values. In contrast, in the case of the IMI+FIP combination at high concentrations at the EC₅₀ level, a synergistic effect on toxicity was observed. The single exposure to the three insecticides and the mixture of IMI-FIP also decreased the size of generated juveniles, which was evidenced by the reduction in the proportion of large juveniles and increased proportion of small juveniles. However, both binary mixtures (IMI-FIP and IMI-CLO) presented antagonistic effects as evidenced by less than expected reductions in growth. Data on the toxic effects of IMI in a mixture with other seed dressing insecticides to collembolans provides useful information to environmental risk assessors by diminishing the uncertainties on the ecological risk of exposure to pesticides, enabling soil management degradation by utilizing multiple insecticides.

Toxicity of the neonicotinoid insecticides thiamethoxam and imidacloprid to tadpoles of three species of South American amphibians and effects of thiamethoxam on the metamorphosis of Rhinella arenarum

The present study examined the acute and chronic toxicity of the neonicotinoid insecticides imidacloprid (IMI) and thiamethoxam (TIA) on the neotropical amphibian species Rhinella arenarum, Rhinella fernandezae and Scinax granulatus. The median lethal concentration after 96 hr exposure (96 hr-LC₅₀) ranged between 11.28 and >71.2 mg/L amongst all species and development stages tested, indicating that these pesticides are not likely to produce acute toxicity in the wild. The subchronic toxicity was also low, with 21 day-LC₅₀ values ranging between 27.15 and >71.2 mg/L. However, tadpoles of Rhinella arenarum exposed to thiamethoxam from stage 27 until completion of metamorphosis presented a significantly lower metamorphic success rate together with a smaller size at metamorphosis, starting from the lowest concentration tested. Although a number of studies previously examined the effects of neonicotinoids on amphibian tadpoles, these investigations focused on the time to metamorphosis and reported a variety of results including retardation, acceleration or lack of effect. Here, data demonstrated that thiamethoxam predominantly impacts metamorphosis through reduction of the transformation success and body weight, rather than by affecting the timings of metamorphosis. By closely monitoring progression of tadpoles through the different stages, impairment of metamorphosis was demonstrated to occur during the transition from stage 39 to 42, suggesting an effect on the thyroid system. An asymmetry in the length of the arms was also observed in metamorphs treated with thiamethoxam. Overall, these results indicate that thiamethoxam, and conceivably other neonicotinoids, have the potential to significantly impair metamorphosis of amphibians and diminish their performance and survival in the wild.

Open Science in regulatory environmental risk assessment

A possible way to alleviate the public skepticism toward regulatory science is to increase transparency by making all data and value judgments used in regulatory decision making accessible for public interpretation, ideally early on in the process, and following the concepts of Open Science. This paper discusses the opportunities and challenges in strengthening Open Science initiatives in regulatory environmental risk assessment (ERA). In this discussion paper, we argue that the benefits associated with Open Science in regulatory ERA far outweigh its perceived risks. All stakeholders involved in regulatory ERA (e.g., governmental regulatory authorities, private sector, academia, and nongovernmental organizations), as well as professional organizations like the Society of Environmental Toxicology and Chemistry, can play a key role in supporting the Open Science initiative, by promoting the use of recommended reporting criteria for reliability and relevance of data and tools used in ERA, and by developing a communication strategy for both professionals and nonprofessionals to transparently explain the socioeconomic value judgments and scientific principles underlying regulatory ERA. Integr Environ Assess Manag 2021;17:1229-1242. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Ecotoxicology of Glyphosate, Its Formulants, and Environmental Degradation Products

The chemical and biological properties of glyphosate are key to understanding its fate in the environment and potential risks to non-target organisms. Glyphosate is polar and water soluble and therefore does not bioaccumulate, biomagnify, or accumulate to high levels in the environment. It sorbs strongly to particles in soil and sediments and this reduces bioavailability so that exposures to non-target organisms in the environment are acute and decrease with half-lives in the order of hours to a few days. The target site for glyphosate is not known to be expressed in animals, which reduces the probability of toxicity and small risks. Technical glyphosate (acid or salts) is of low to moderate toxicity; however, when mixed with some formulants such as polyoxyethylene amines (POEAs), toxicity to aquatic animals increases about 15-fold on average. However, glyphosate and the formulants have different fates in the environment and they do not necessarily co-occur. Therefore, toxicity tests on formulated products in scenarios where they would not be used are unrealistic and of limited use for assessment of risk. Concentrations of glyphosate in surface water are generally low with minimal risk to aquatic organisms, including plants. Toxicity and risks to non-target terrestrial organisms other than plants treated directly are low and risks to terrestrial invertebrates and microbial processes in soil are very small. Formulations containing POEAs are not labeled for use over water but, because POEA rapidly partitions into sediment, risks to aquatic organisms from accidental over-sprays are reduced in shallow water bodies. We conclude that use of formulations of glyphosate under good agricultural practices presents a de minimis risk of direct and indirect adverse effects in non-target organisms.

Quantum Yields and N2O Formation from Photolysis of Solid Films of Neonicotinoids

Neonicotinoids (NN), first introduced in 1991, are found on environmental surfaces where they undergo photolytic degradation. Photolysis studies of thin films of NN were performed using two approaches: (1) transmission FTIR, in which solid films of NN and the gas-phase products were analyzed simultaneously, and (2) attenuated-total-reflectance FTIR combined with transmission FTIR, in which solid films of NN and the gas-phase products were probed in the same experiment but not at the same time. Photolysis quantum yields using broadband irradiation centered at 313 nm were (2.2 ± 0.9) × 10^-3 for clothianidin (CLD), (3.9 ± 0.3) × 10^-3 for thiamethoxam (TMX), and (3.3 ± 0.5) × 10^-3 for dinotefuran (DNF), with all errors being ±1 s. At 254 nm, which was used to gain insight into the wavelength dependence, quantum yields were in the range of (0.8-20) × 10^-3 for all NNs, including acetamiprid (ACM) and thiacloprid (TCD). Nitrous oxide (N₂O), a potent greenhouse gas, was the only gas-phase product detected for the photolysis of nitroguanidines, with yields of ΔN₂O/ΔNN > 0.5 in air at both 313 and 254 nm. The atmospheric lifetimes with respect to photolysis for CLD, TMX, and DNF, which absorb light in the actinic region, are estimated to be 15, 10, and 11 h, respectively, at a solar zenith angle of 35° and 12, 8, and 10 h at a solar zenith angle of 15°.

Response to Tennekes (2018) "The Resilience of the Beehive" Journal of Toxicology and Environmental Health B 20: 316-386

This paper is a response to a letter from Dr. H Tennekes ("The Resilience of the Beehive" Journal of Toxicology and Environmental Health B 20: 316-386). Here we emphasize that our quantitative weight of evidence analyses were focused on the level of the honeybee colony. These colony-level responses include redundancy and resiliency as well as a number of possible sublethal effects of pesticides on the colony. We also note that the literature has shown that binding of neonicotinoid insecticides to the nicotinic acetylcholine receptor is reversible. The comments in this letter do not provide reasons to change our conclusions, that, as currently used in good agricultural practices as seed-treatments, imidacloprid, clothianidin, and thiamethoxam do not present significant risks to honeybees at the level of the colony.