Abstract

Currently, only Apis mellifera is used in environmental regulation to evaluate the hazard of pesticides to pollinators. The low representativeness of pollinators and bee diversity in this approach may result in insufficient protection for the wild species. This scenario is intensified in tropical environments, where little is known about the effects of pesticides on solitary bees. We aimed to calculate the medium lethal dose (LD50) and medium lethal concentration (LC50) of the insecticide dimethoate in the Neotropical solitary bee Centris analis, a cavity-nesting, oil-collecting bee distributed from Brazil to Mexico. Males and females of C. analis were exposed orally to dimethoate for 48 h under laboratory conditions. Lethality was assessed every 24 h until 144 h after the beginning of the test. After the LD50 calculation, we compared the value with available LD50 values in the literature of other bee species using the species sensitivity distribution curve. In 48 h of exposure, males showed an LD50 value 1.33 times lower than females (32.78 and 43.84 ng active ingredient/bee, respectively). Centris analis was more sensitive to dimethoate than the model species A. mellifera and the solitary bee from temperate zones, Osmia lignaria. However, on a body weight basis, C. analis and A. mellifera had similar LD50 values. Ours is the first study that calculated an LD50 for a Neotropical solitary bee. Besides, the results are of crucial importance for a better understanding of the effects of pesticides on the tropical bee fauna and will help to improve the risk assessment of pesticides to bees under tropical conditions, giving attention to wild species, which are commonly neglected. Environ Toxicol Chem 2023;00:1–10. © 2023 SETAC

Abstract

Pollinator population declines are global phenomena with severe consequences for native flora and agriculture. Many factors have contributed to pollinator declines including habitat loss, climate change, disease and parasitism, reductions in abundance and diversity of foraging resources, and agrochemical exposure. Particulate matter (PM) serves as a carrier of toxic agrochemicals, and pollinator mortality can occur following exposure to agrochemical-contaminated PM. Therefore, laboratory-controlled experiments were conducted to evaluate impacts of individual PM-bound agrochemicals. Honeybees (Apis mellifera), blue orchard mason bees (Osmia lignaria), and painted lady butterfly (Vanessa cardui) larvae were exposed to bifenthrin, permethrin, clothianidin, imidacloprid, abamectin, and ivermectin via suspended, airborne PM. Agrochemical concentrations in PM to which pollinators were exposed were based on concentrations observed in fugitive beef cattle feedyard PM including a “mean” treatment and a “max” treatment reflective of reported mean and maximum PM-bound agrochemical concentrations, respectively. In general, pollinators in the mean and max treatments experienced significantly higher mortality compared with controls. Honeybees were most sensitive to pyrethroids, mason bees were most sensitive to neonicotinoids, and painted lady butterfly larvae were most sensitive to macrocyclic lactones. Overall, pollinator mortality was quite low relative to established toxic effect levels derived from traditional pollinator contact toxicity tests. Furthermore, pollinator mortality resulting from exposure to individual agrochemicals via PM was less than that reported to occur at beef cattle feedyards, highlighting the importance of mixture toxicity to native and managed pollinator survival and conservation. Environ Toxicol Chem 2023;00:1–9. © 2023 SETAC

Abstract

The effects assessment of metals is mainly based on data of single metals on single species, thereby not accounting for effects of metal mixtures or effects of species interactions. Both of these effects were tested in combination, thereby hypothesizing that the sensitivity of a community to synergistic mixture toxicity depends on the correlation of single-species sensitivities among the single metals. Single-metal and metal-mixture effects were tested in full concentration–response experiments (fixed ray of 1:1:3 and 5:1:13 mass ratio Ni:Cu:Zn) on eight single freshwater algal species and 14 algal communities of four species each. The mean correlation of single-species median effect concentrations among the single metals (Ni–Cu, Cu–Zn, and Zn–Ni) for all species in a community (r ̅ $\mathop{r}\limits^{̅}$) ranged from −0.4 to 0.9 among the communities; most of these (12/14) were positive. Functional endpoints (total biomass) were overall less sensitive than structural endpoints (Bray-Curtis similarity index) for communities with positively correlated single-species sensitivities among the single metals (r ̅ > 0.33 $\mathop{r}\limits^{̅}\gt 0.33$), suggesting that such correlations indicate functional redundancy under metal-mixture stress. Antagonistic metal-mixture interactions were predominantly found in single species, whereas metal-mixture interactions were antagonistic and surprisingly synergistic for the communities, irrespective of the reference mixture model used (concentration addition or independent action). The mixture interactions close to the carrying capacity (day 7) of communities gradually shifted from antagonism to more noninteractions with increasing correlation of single-species sensitivities among the single metals. Overall, this suggests that functional redundancy under mixed-metal stress comes at the cost of reduced biodiversity and that synergisms can emerge at the community level without any synergisms on the single-species level. Environ Toxicol Chem 2023;00:1–18. © 2023 SETAC.

ABSTRACT

Five metal mixture dose-response models are used to predict toxicity of porewater to young sturgeon at areas of interest in the Upper Columbia River and to evaluate these models as tools for risk assessments. Dose components of metal mixture models include exposure to free metal ion activities or metal accumulation by biotic ligands or humic acid, whereas links of dose to response use logistic equations, independent joint action equations, or additive toxicity functions. Laboratory bioassay studies of single metal exposures to juvenile sturgeon, porewater collected in-situ in the fast-flowing Upper Columbia River, and metal mixture models are used to evaluate toxicity.

The five metal mixture models are very similar in their predictions of adverse response of juvenile sturgeon and in identifying copper (Cu) as the metal responsible for the most toxic conditions. Although the modes of toxic action and EC20 values are different among the dose models, predictions of adverse response are consistent among models because all doses are tied to the same biological responses. All models indicate that 56+5% of 122 porewater samples are predicted to have <20% adverse response, 25+5% of samples are predicted to have 20-80% adverse response, and 20+4% are predicted to have >80% adverse response of juvenile sturgeon.

The approach of combining bioassay toxicity data, compositions of field porewater, and metal mixture models to predict lack of growth and survival of aquatic organisms due to metal toxicity is an important tool that can be integrated with other information (e.g., survey studies of organism populations, lifecycle and behavior characteristics, sediment geochemistry, and food sources) to assess risks to aquatic organisms in metal-enriched ecosystems.

ABSTRACT

The mechanisms of acute (96 h) and sub-chronic (28-d) toxicity of the waterborne trace metal thallium (Tl) to rainbow trout (Oncorhynchus mykiss) were investigated. Specifically, effects on branchial and renal ionoregulatory enzymes (sodium/potassium ATPase and proton ATPase) and hepatic oxidative stress endpoints (protein carbonylation, glutathione content and activities of catalase and glutathione peroxidase) were examined. Fish (19-55 g) were acutely exposed to 0 (control), 0.9 (regulatory limit), 2004 (half the acute median lethal concentration) or 4200 (acute median lethal concentration) µg Tl L^-1 or sub-chronically exposed to 0, 0.9 or 141 (an elevated environmental concentration) µg Tl L^-1. The only effect following acute exposure was a stimulation of renal H⁺-ATPase activity at the highest Tl exposure concentration. Similarly, the only significant effect of sub-chronic Tl exposure was an inhibition of branchial NKA activity at 141 µg Tl L^-1, an effect that may reflect the interaction of Tl with potassium ion handling. Despite significant literature evidence for effects of Tl on oxidative stress, there were no effects of Tl on any such endpoint in rainbow trout, regardless of exposure duration or exposure concentration. Elevated basal levels of antioxidant defences may explain this finding. These data suggest that ionoregulatory perturbance is a more likely mechanism of Tl toxicity than oxidative stress in rainbow trout, but is an endpoint of relevance only at elevated environmental Tl concentrations.