07
May
Meta-Review: Pesticides Kill or Harm Soil Invertebrates Essential to Soil Health
(Beyond Pesticides, May 7, 2021) Soil health is one of the linchpins on which the food production that sustains human life — as well as biodiversity, pollinator health, and carbon sequestration — depend. A recent meta-review of nearly 400 studies finds that, in 71% of the cases reviewed, pesticides kill or otherwise harm soil invertebrates that contribute mightily to soil health. In their paper, “Pesticides and Soil Invertebrates: A Hazard Assessment,” published in Frontiers in Environmental Science in early May, the researchers write, “A wide variety of soil-dwelling invertebrates display sensitivity to pesticides of all types . . . [These results] support the need for pesticide regulatory agencies to account for the risks that pesticides pose to soil invertebrates and soil ecosystems.” Beyond Pesticides, which has long reported on impacts of pesticides on soil health, concurs with that conclusion, and adds that the real solutions to noxious pesticide impacts lie in the adoption of regenerative organic approaches to all land management because they obviate any need for petroleum-based toxic chemical controls.
The term “pesticide” can refer to myriad kinds of chemical treatments — including antimicrobials, disinfectants, rodenticides, and others — but in the agricultural and land management realms, primarily means insecticides, herbicides, and fungicides. These are used intensively in conventional, chemical-intensive (i.e., non-organic) agriculture to kill off insect pests, weeds, and fungal infestations, respectively. As the study paper notes, pesticides enter soils when they are applied to flora or to soils themselves (as sprays or drenches, or in granular form), but they also contaminate soil in the form of seed coatings. In addition, soils can be contaminated by pesticide runoff from treated fields, and through drift of aerially applied compounds to non-target areas. Beyond Pesticides recently wrote about the extent of pesticide contamination of U.S. farmland, including how residues of these compounds can persist in soils, even after transition to organic management, for decades.
The researchers’ broad conclusions include: (1) insecticides have greater negative impacts on invertebrates in soil than do herbicides or fungicides; and (2) nevertheless, herbicides and fungicides do have many negative effects, but show more variance across different pesticide classes and studied taxa than do insecticides. The study also notes that research studies on pesticide impacts often “use a narrow range of surrogate species that are easy to rear, identify, or study, while smaller and more cryptic organisms are rarely analyzed. In some cases, the organisms that are the most extensively studied are known to be less sensitive to pesticides than other organisms, suggesting that we have limited knowledge of the extent of harm caused by pesticides.”
Healthy, living soils contain a universe of organisms, including many invertebrates, that provide critical services: they decompose biomass and cycle nutrients, maintain soil structure, hold carbon, and support ecosystem equilibrium by controlling pests and diseases, and making nutrients available to biota. Such organisms include earthworms, ground-nesting bees, beetles, ants, springtails, termites, millipedes, and others. The declines in such terrestrial invertebrate populations have been attributed in large part to agrichemical (synthetic pesticide and fertilizer) pollution and habitat loss. Invertebrates that are harmed, or killed, by pesticides are thus compromised in their ability to deliver those soil and ecosystem services. Such extreme loss of these organisms is also devastating to biodiversity.
In a recent Daily News Blog, Beyond Pesticides covered research that showed that the pivot in agriculture from “older generation” pesticides (e.g., organochlorines, organophosphates, and carbamates) to newer compounds, such as pyrethroids and neonicotinoids, is significantly responsible for invertebrate (and plant) population declines. The blog entry noted, “Invertebrates and plants are vital for ecosystem function, offering various services, from decomposition to supporting the food web. Furthermore, invertebrates and plants can act as indicator species . . . that scientists can observe for the presence and impact of environmental changes and stressors. Therefore, reductions in invertebrate and plant life have implications for ecosystem health that can put human well-being at risk.”
This subject study (“Pesticides and Soil Invertebrates: A Hazard Assessment”) was conducted by researchers from the Center for Biological Diversity (CBD), Friends of the Earth, and the Department of Entomology at the University of Maryland, College Park. This is the first comprehensive review of the impacts of pesticides on soil invertebrates; it focuses on invertebrates that spend at least some stage of their development in soil and are not target species of pesticide applications. The study evaluated 275 different taxa (or combined taxa) of such organisms, and 284 discrete pesticide active ingredients (or unique mixtures thereof). In doing so, it used data related to nine different endpoints: mortality, biochemical biomarkers, behavior, reproduction, growth, structural changes, richness and diversity, abundance, and biomass. This methodology meant that the study ultimately analyzed 2,842 separate “tested parameters, measured as a change in a specific endpoint following exposure of a specific organism to a specific pesticide.”
As mentioned, research results indicate that 71% of the tested parameters showed negative effects from pesticide exposure; 28% showed no significant impacts, and the remaining 1% showed positive impacts. Sorted by pesticide type, 75% of parameters were negatively affected by insecticides, 63% by herbicides, 71% by fungicides, and 56% by pesticide mixtures. Impacts of such mixtures yielded varying results based on type: of the 49 mixtures evaluated, insecticide mixtures negatively affected tested parameters 84% of the time, herbicide mixes 62%, fungicide mixes 39%, and cross-category pesticide mixes 50% of the time.
Among the more concerning specific results of the research are those for earthworms: 84–90% of tested parameters in them were negatively affected by the most-studied classes of insecticides, and some herbicides and fungicides (amide/anilide herbicides and benzimidazole fungicide) were especially harmful. This is disturbing because earthworms are a keystone species. They play a huge role in soil health: they increase aeration of soil, boost water infiltration and retention, reduce soil compaction, stimulate microbial activity, transform decaying material and minerals into usable forms and cycle nutrients, increasing soil fertility. In addition, they are an important menu item and part of the food chain for birds, frogs, snails, moles, foxes, snakes, and turtles, among others.
Study co-author and Senior Researcher at CBD, Nathan Donley, PhD, commented, “Beetles and springtails have enormous impacts on the porosity of soil and are really getting hammered, and earthworms are definitely getting hit as well. A lot of people don’t know that most bees nest in the soil, so that’s a major pathway of exposure for them. It’s not just one or two pesticides that are causing harm, the results are really very consistent across the whole class of chemical poisons.” He added, “The level of harm we’re seeing is much greater than I thought it would be. Soils are incredibly important. But how pesticides can harm soil invertebrates gets a lot less coverage than pollinators, mammals and birds — it’s incredibly important that changes.”
The researchers conclude that pesticide use is a serious threat to soil invertebrates and the essential ecosystem services they provide. They assert that soil organisms ought to be included in any risk assessment for a pesticide that could potentially contaminate soils, and that mitigation of such risk must be done in a way that “will specifically reduce harm to the soil organisms that sustain important ecosystem services. The United States Environmental Protection Agency [EPA] does not have sufficient testing requirements or tools in place to quantify risk to soil dwelling organisms. The European honeybee is the only terrestrial invertebrate included in mandatory ecotoxicological testing of pesticides. The practice of using the honeybee as a surrogate underestimates harm to many taxa and often results in narrow efforts to mitigate pesticide impacts solely to honeybees and other pollinators, not soil organisms.”
Nathan Donley, PhD commented: “It’s crazy to have a single species that may never come into contact with soil in its entire life as a proxy for every terrestrial invertebrate out there. You might as well use a fish.” Matt Shardlow, head of the conservation group Buglife, commented: “The answer is clear here — the distribution of outcomes in published studies is massively weighted on the negative side. The high level of negative effects on reproduction across the board is one of the most concerning results [the researchers] highlight. We all want fertile agricultural soils, but this shows that the pesticides we are applying are assaulting the fertility of the animals that live in the soil. If we want to protect healthy soils, we do need to take soil organisms into consideration when deciding if a pesticide is safe to use.”
An important sidebar: Dr. Donley will be a speaker at Beyond Pesticides’ 2021 National Pesticide Forum, Cultivating Healthy Communities: Confronting Health Threats, Climate Disasters, and Biodiversity Collapse with a Toxic-Free Future. Co-author of this subject study, he is also a former cancer researcher at the Oregon Health and Science University, and is a current senior scientist with the Center for Biological Diversity, where his work focuses on U.S. pesticide policy and regulation.
Beyond Pesticides would readily argue that, given the myriad harms they cause, including the harm to invertebrates demonstrated in this research, pesticides are incompatible with healthy soil ecosystems — yet EPA is failing to attend to the dire impacts of pesticides on the soil organisms that ensure that health. We recently wrote: “To prevent a future void of vital invertebrate and plant species critical to biodiversity and food production, global leaders must examine the necessity of pesticide use. More than ever, individuals must connect with their local, state, and federal elected officials to demand that we protect insect populations. . . . Solutions like regenerative organic agriculture and organic land management curtail the need for toxic pesticide use.”
The public has an important role to play in reducing pesticide harms. Learn about what to do as an individual and with the community to support biodiversity, eliminate pesticides in lawn and garden maintenance, create pollinator-friendly landscapes, use pollinator-friendly seeds, and support the growth of organic agriculture. Beyond individual, it is critical to contact elected officials at every level — local, state, and federal — to insist on more-protective regulation of pesticides. Contact us for help with advocacy on this, and any pesticide-related issue.
Sources: https://www.frontiersin.org/articles/10.3389/fenvs.2021.643847/full and https://www.theguardian.com/environment/2021/may/04/vital-soil-organisms-being-harmed-by-pesticides-study-shows
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
