Consolidation of temperature-dependent toxicity and thermoregulatory behavior into risk assessments of insecticides under thermal scenarios: A prospective study on Eremias argus

Assessing the combined effects of elevated temperature and chlorpyrifos on meiobenthic community structure in intertidal and mangrove estuarine ecosystems

In the age of anthropocene, elevated temperatures and pesticide pollution represent critical environmental challenges with profound ecological implications. As crucial bio-indicator, meiobenthic organisms play a pivotal role to assess the impacts of these disturbances on ecosystem health. Despite their ecological significance, the combined impacts of these stressors on meiobenthic community structures remain unexplored. This study investigates the acute exposure of elevated temperature (34 °C) and chlorpyrifos contamination (at 3 μg L-1 and 4.5 μg L-1) on meiobenthic community structure from mangrove mudflat and intertidal sandflat. A 10-days acute benthocosm experiment unveiled significant declines in total meiobenthic abundance under high-stress conditions; 75 % and 73 % in mangrove mudflat and intertidal sandflat respectively. A 4-factor PERMANOVA revealed significant effects of temperature, pesticide, and exposure duration on meiobenthic abundance (p < 0.05). Sensitive taxa such as kinorhyncha, bivalvia, and ostracoda were eliminated from treated benthocosms. Nematode species composition also affected and shifted under stress, with opportunistic and stress tolerant species became dominant. Nematode abundance decreased by up to 65 % and 63 % in the mangrove mudflat and intertidal sandflat, correspondingly. Species diversity, richness, and Shannon-Wiener index (H') significantly declined, with changes in the Maturity Index (MI) and Index of Trophic Diversity (ITD). The effects of combined stressors were more pronounced than individual stressors and mangrove mudflat displayed slightly higher susceptibility than intertidal sandflat. According to Hierarchical Modelling of Species Communities (HMSC) a noticeable influence of habitat type, stressors levels and exposure duration on the sensitivity of nematode species has been observed.

Assessing Changes in Permethrin Toxicity to Juvenile Inland Silversides (Menidia beryllina) Under Different Temperature Scenarios

Aquatic systems are impacted by temperature fluctuations which can alter the toxicity of pesticides. Increased temperatures related to climate change have elevated pest activity, resulting in an escalation of pesticide use. One such pesticide class, pyrethroids, has replaced the use of several banned pesticides due to its low mammalian toxicity. The impacts of increased temperatures on the toxicity of a pyrethroid, permethrin, to fish is not yet known. In the current study, juvenile inland silversides (Menidia beryllina) were exposed to permethrin at three temperatures: 10 °C, 20 °C, and 30 °C. Inland silversides were chosen for this study because they are a species used in standardized USEPA whole effluent toxicity testing. Permethrin toxicity showed an inverse relationship with temperature. As temperatures fluctuate, fishes experience a change in respiration, biotransformation, and elimination rates, which can drive the noted difference in toxicity. Based on these findings, toxicity can be temperature-dependent and should be considered when assessing risk of exposure to pesticides in aquatic systems.

Reductive stress and cytotoxicity in the swollen river mussel (Unio tumidus) exposed to microplastics and salinomycin

Multistress effects lead to unpredicted consequences in aquatic ecotoxicology and are extremely concerning. The goal of this study was to trace how specific effects of the antibiotic salinomycin (Sal) and microplastics (MP) on the bivalve molluscs are manifested in the combined environmentally relevant exposures. Unio tumidus specimens were treated with Sal (0.6 μg L-1), MP (1 mg L-1, 2 μm size), and both at 18 °C (Mix) and 25 °C (MixT) for 14 days. The redox stress and apoptotic enzyme responses and the balance of Zn/Cu in the digestive gland were analyzed. The shared signs of stress included a decrease in NAD+/NADH and Zn/Cu ratios and lysosomal integrity and an increase in Zn-metallothioneins and cholinesterase levels. MP caused a decrease in the glutathione (GSH) concentration and redox state, total antioxidant capacity, and Zn levels. MP and Mix induced coordinated apoptotic/autophagy activities, increasing caspase-3 and cathepsin D (CtD) total and extralysosomal levels. Sal activated caspase-3 only and increased by five times Cu level in the tissue. Due to the discriminant analysis, the cumulative effect was evident in the combined exposure at 18 °C. However, under heating, the levels of NAD+, NADH, GSH, GSH/GSSG and metallothionein-related thiols were decreased, and coordination of the cytosolic and lysosomal death stimuli was distorted, confirming that heating and pollution could exert unexpected synergistic effects on aquatic life.

Changes in thermal sensitivity of Rhinella arenarum tadpoles (Anura: Bufonidae) exposed to sublethal concentrations of different pesticide fractions (Lorsban® 75WG)

The intensive use of agrochemicals and the rapid increase of global temperatures have modified the thermal conditions of aquatic environments, thus increasing amphibians' vulnerability to global warming and positioning them at great risk. Commercial formulations of chlorpyrifos (COM) are the pesticides most widely used in agricultural activities, with a high toxic potential on amphibians. However, little is known about the separate effects of the active ingredient (CPF) and adjuvants (AD). We studied the thermal sensitivity at different concentrations and pesticide fractions in Rhinella arenarum tadpoles, on thermal tolerance limits (CTmax = Critical thermal maximum and CTmin = Critical thermal minimum), swimming speed (Ss), Optimum temperature (Top), and Thermal breadth 50 (B50). Our results demonstrate that the pesticide active ingredient, the adjuvants, and the commercial formulation of chlorpyrifos differentially impair the thermal sensitivity of R. arenarum tadpoles. The pesticide fractions affected the heat and the cold tolerance (CTmax and CTmin), depending on the concentrations they were exposed to. The locomotor performance (Ss, Top, and B50) of tadpoles also varied among fractions, treatments, and environmental temperatures. In the context of climate change, the outcomes presented are particularly relevant, as mean temperatures are increasing at unprecedented rates, which suggests that tadpoles inhabiting warming and polluted ponds are currently experiencing deleterious conditions. Considering that larval stages of amphibians are the most susceptible to changing environmental conditions and the alarming predictions about environmental temperatures in the future, it is likely that the synergism between high temperatures and pesticide exposure raise the threat of population deletions in the coming years.