25
Oct
Study Shows Climate Change Exacerbates Synergistic Effects of Synthetic Pyrethroid on Biodiversity
(Beyond Pesticides, October 25, 2024) To better understand synergistic interactions between multiple stressors, researchers from the Helmholtz Centre for Environmental Research in Leipzig, Germany, analyze exposure to the pyrethroid insecticide esfenvalerate with two nonchemical environmental factors: elevated temperature and food limitation. In their recent publication in Environmental Pollution, the authors find the greatest synergistic effects when Daphnia magna (D. magna) are subjected to esfenvalerate under conditions experienced with climate change including lower food availability and increased temperature.
D. magna, also known as daphnids or water fleas, are small planktonic crustaceans that represent an essential part of the food web in lakes and ponds. Impacts on populations of daphnids can lead to effects throughout multiple trophic levels that impact overall biodiversity. As the researchers state, “Global biodiversity is declining at an unprecedented rate in response to multiple environmental stressors… A key challenge is understanding synergistic interactions between multiple stressors and predicting their combined effects.â€
To study this, a Stress Addition Model (SAM), which predicts the cumulative effects of interacting stressors, was utilized and compared to laboratory data using 24-hour-old neonates of D. magna. The organisms were subjected to various conditions, singularly and in combination, including increased temperature, lower quantities of food, and different concentrations of esfenvalerate. The study encompasses “eight esfenvalerate concentrations (0, 0.001, 0.01, 0.0316, 0.1, 0.316, 1.0 and 3.16 μg/L) × two temperature levels (20 and 25 °C) × two food conditions (high and low food), resulting in 32 treatments. In each treatment, we used 15 replicates, and the experiment was repeated 3 times,†the authors note. Â
The low food treatments received 100 times less food, and the increase to 25 °C was chosen as it represents the upper threshold of D. magna’s thermal tolerance. Both of these conditions represent a stress that the researchers hypothesized would exacerbate the effects of pesticide exposure. “We selected esfenvalerate because it has frequently been detected in agricultural streams and is allowed for agricultural practices in the EU [European Union] until May 2026,†the researchers share. The varying concentrations reflect those commonly found in the field and represent real-life exposure levels for aquatic organisms.
Esfenvalerate is a suspected endocrine disruptor and has documented effects of neurotoxicity, irritation, and kidney/liver damage, as well as reported toxicity to fish/aquatic organisms and bees. See more on the health effects of esfenvalerate and pyrethroids here and here.
The test groups in this study are used to predict “the combined effects of (i) elevated temperature and food limitation, (ii) elevated temperature and esfenvalerate, (iii) esfenvalerate and food limitation, and (iv) all stressors together.†In assessing the nonchemical environmental stressors, the authors find, “[E]levated temperature alone caused 12% mortality, while starvation alone caused 20% mortality. However, when both stressors were combined, the mortality rate increased to approximately 29%, indicating the additive effects of both stressors.â€
When factoring in exposure to esfenvalerate under each of these conditions individually, stronger interactions are observed with food stress. The results demonstrate that limitation of food decreases the tolerance of D. magna to esfenvalerate and causes synergism. When analyzing all three stressors together, the interactions between esfenvalerate and food limitation show even stronger effects at elevated temperatures. The researchers report, “[T]he synergistic interaction between food limitation and esfenvalerate at elevated temperature (25 °C) was 3.6-fold stronger as compared to synergism at reference temperature (20 °C).”
The increased effects of pesticide exposure under food limitation “can be attributed to metabolic depression resulting in limited energy budget for physiological defences against stress,†the authors say. When organisms experience starvation, their metabolic activity is lowered as a strategy to survive until food is available. Additional studies reveal that food limitation increases the toxicity of pesticides in invertebrates. (See here and here.)
When temperatures are elevated, it increases metabolic rates within organisms that creates greater energy demands, and compromises the organism’s ability to detoxify chemicals. With the depletion of energy that comes with limited food availability, this leaves the organisms particularly vulnerable. “Additionally, temperature stress might weaken the immune system, making daphnids more vulnerable to toxicant exposure. Thus, cumulative effects likely disrupt homeostasis, leading to synergistic rather than additive response… Each stressor diminished the general stress capacity of individuals, thereby increasing synergism with increasing total general stress,†the researchers state.
To summarize the study data, the authors say, “Our results indicate that, compared to high food and reference temperature, the combination of food limitation and elevated temperature substantially increased the sensitivity of D. magna to esfenvalerate.†With the current crises of climate change and biodiversity, food scarcity and warming are already individually impacting organisms. In finding that these stressors have a greater cumulative impact, without even factoring in chemical exposure, places a huge threat over the stability of aquatic and terrestrial food webs. Adding in the harmful effects of pesticides, which are further exacerbated under these environmental conditions, puts the entire ecosystem at risk.
Synergistic effects of pesticides have been well documented by Beyond Pesticides (see here, here, and here) and highlight the heightened risks of chemicals with additional stressors. The interaction of multiple stressors and pesticides is overlooked in ecological risk assessments. When pesticides are reviewed by the U.S. Environmental Protection Agency (EPA) to determine if they create unreasonable adverse effects on human health and the environment, the toxicity of the individual compounds is assessed without factoring in the real-life scenarios of pesticide mixtures and environmental stressors that create synergy.
Current regulatory review protocols do not adequately capture the complex interactions that occur in nature with pesticide exposure, which threatens the health of all organisms and the environment. As the researchers note, “[T]he combined impacts of climate change, chemical pollution, and other physical stressors are reshaping ecosystems by altering the composition of natural communities and affecting ecosystem services.â€
As Beyond Pesticides previously reported on biodiversity, the mix of diverse and intricate relationships of organisms in nature are essential for sustaining life. Pesticide use is a major cause of declining biodiversity, which is manifested in extinctions, endangered species, and species vulnerable to environmental disturbances—including climate change, habitat fragmentation, and toxic chemicals. Biodiversity is critical for many goods and services essential to life on earth, supports human and societal needs, influences human health and well-being, and protects against exposure to zoonotic diseases. Biodiversity loss harms our health and threatens the ecological cycles that support life.
The entire food web, including both aquatic and terrestrial organisms, relies on balance. When stressors, such as climate change and pollution, threaten that balance, all organisms including humans are at risk. D. magna represents an important foundation in the aquatic ecosystem, and its effects on these organisms highlight the wider threat to all wildlife. “Maintaining biodiversity of surface water ecosystems is paramount for providing essential ecosystem services,†the authors conclude. “However, these ecosystems are increasingly subjected to multiple anthropogenic stressors that compromise their ecological status.â€
Protecting biodiversity through the elimination of harmful chemicals is the path forward. By adopting organic land management practices, the effects on human health and the environment, as well as climate change, can be mitigated. Organic agriculture focuses on soil health, which leads to improved health of all organisms and the environment.
A study in the Journal of Environmental Science and Public Health, as previously reported by Beyond Pesticides, shares that, “The three most important environmental problems affecting the globe now are pollution, climate change, and biodiversity loss.†Based on the science, petrochemical pesticides, and synthetic fertilizers, central to conventional chemical-intensive systems, are contributors to these problems. There is an abundance of scientific, peer-reviewed evidence that shows these chemicals disrupt ecosystems that support and sustain life in addition to negatively influencing human health both directly and indirectly as well as acutely and chronically.
To solve the existential crises of climate change, biodiversity loss, and human disease, it is critical that we transition away from this reliance on chemicals and adopt organic agriculture as a standard. Take action to tell Congress to ensure that organic programs, and their funding, do not lapse this fall and encourage your community to transition to organic with the Parks for a Sustainable Future program. Add your voice to the urgent movement to help Beyond Pesticides accomplish the mission of eliminating fossil fuel-based pesticide use by 2032 by joining as a member today.
On the necessity, viability, productivity, and profitability of organic land management, attend the 41st National Forum: Imperatives for a Sustainable Future—Reversing the existential crises of pesticide-induced illness, biodiversity collapse, and the climate emergency.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Shahid, N., Siddique, A. and Liess, M. (2024) Synergistic interaction between a toxicant and food stress is further exacerbated by temperature, Environmental Pollution. Available at: https://www.sciencedirect.com/science/article/pii/S0269749124018268.
