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Daily News Blog

08
Apr

Invertebrates and Plants Face Increasing Threat from Pesticide Use, Despite Declining Chemical Use Patterns

Pesticide use threatens aquatic and terrestrial invertebrates and plants more than ever, despite declining chemical use and implementation of genetically engineered (GE) crops in the U.S., according to a University Koblenz-Landau, Germany study. Since the publication of Rachel Carson’s Silent Spring (1962), many environmental agencies have banned the use of pesticides like organochlorines, organophosphates, and carbamates for their devastating toxic—sometimes lethal—effects, particularly on vertebrates, including humans. However, this ban created a pathway for a new generation of pesticides (e.g., neonicotinoids, pyrethroids) to take hold. Although these pesticides are more target-specific, requiring lower chemical concentrations for effectiveness, they have over double the toxic effects on invertebrates, like pollinators. 

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 (bioindicators) 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. Study lead author Ralf Schulz, PH.D., notes, “[This study] challenge[s] the claims of decreasing environmental impact of chemical pesticides in both conventional and GM [genetically modified or genetically engineered (GE)] crops and call for action to reduce the pesticide toxicity applied in agriculture worldwide.”

Study researchers used data from the U.S. Geological Survey to determine national pesticides use by U.S. farmers over 25 years (1992 to 2016). To assess pesticide toxicity, researchers used U.S. Environmental Protection Agency (EPA) data on species-specific toxicology thresholds. Lastly, researchers compared the species-specific toxicology threshold data, a calculation for the point at which a substance might harm vegetation or wildlife, to the amount of real-world pesticide concentration on farms.

The study results find a decrease in total pesticide amounts by volume on U.S. farms by 40 percent over the last 25 years. Although bird and mammal toxicity decreases with a reduction in pesticide use (95 percent), invertebrates experience higher toxicity levels. Pyrethroid insecticides cause toxicity to double among aquatic invertebrates. Neonicotinoid insecticides present double the risk to terrestrial invertebrates. Overall, pesticide toxicity for terrestrial plants is highest regardless of whether fields are conventional, non-GE, or GE.

Pesticide residues readily contaminate all ecosystems and are prevalent in soils, water (solid and liquid), and the surrounding air. Scientific literature demonstrates pesticides’ long history of adverse effects to the environment, including wildlifebiodiversity, and human health effects. However, many of these chemicals are older classifications that are more stable and promptly accumulate in the environment and animal tissue. Organophosphates and carbamates impact immune and metabolic function among vertebrates as their mode of action inhibits acetylcholinesterase enzyme activation. Organochlorines induce similar effects on vertebrates’ immune and metabolic systems, but their mechanisms driving mode of action are poorly understood. These pesticides can bioaccumulate and produce severe toxicity outcomes among vertebrates. Therefore, many of these chemicals are phasing out from both commercial and industrial use. However, there is a misconception that the “newer generation” of chemicals, including pyrethroids, sulfoxaflor, fipronil, and neonicotinoids (neonics), are safer. These insecticides are fast-acting, with quick breakdown times, thus less likely to readily accumulate. However, studies find lower concentrations of these chemicals are more toxic than their older counterparts, requiring several kilograms less. These pesticides can promote higher sublethal toxicity levels, which can cause chronic effects on species abundance and biodiversity.

Some invertebrates are the victims of global insect apocalypse or population decline, wiping out roughly a quarter of the population since 1990. Much research attributes the recent population reduction to several factors, including pesticide exposureBroad-spectrum pesticides indiscriminately kill pests and nontarget organisms alike. Because many nontarget invertebrates and plants share the same physiological features as pests that insecticides and herbicides target, exposure can be disastrous. The sublethal effects of insecticides on non-target organisms are evident. Research shows long-term neonic exposure on some social insects (e.g., bees, butterflies) impacts foraging behavior, learning, orientation, memory abilities, immune functions, growth and developmentsleepcolony growth, and reproductionSulfoxaflor acts similarity to neonic toxicity. Pyrethroids are widely detectable in bee pollen and impair bee learning and foraging, bee fecundity, butterfly larvae, and bee developmental rate. Fipronil is highly toxic to most, if not all, insects and can reduce behavioral function and learning performances in honey bees. Considering EPA recognizes that pesticides are a risk to pollinators, preventing exposure is essential in avoiding the consequences of insect decline.

A majority of studies detailing the sublethal effects of pesticides focus on pollinators due to their economic and environmental importance. However, pesticides adversely impact the health and nutritional quality of other beneficial terrestrial and aquatic organisms. A University of Bern, Switzerland study finds that long-term exposure to sublethal (low-level) concentrations of the neonics in soil negatively affects the health and behavioral development of black garden ants colonies. Furthermore, other studies find pesticides also adversely affect the health of earthworms that provide essential ecosystem services by aerating the soil, cycling nutrients, and increasing microbial activity. Although insecticides are best known for their hazardous impacts on terrestrial invertebrate populations, it is becoming increasingly clear that the entire food chain is at risk from continuous use. Reports regularly detect pesticides in the nation’s waterways, and some concentrations exceed acute and chronic toxicity values for sensitive organisms. Imidacloprid exposure (a neonic) can adversely impact the health of shrimp, oysters, and other benthic invertebrates, resulting in population decline. Exposure to low levels of bifenthrin (a pyrethroid) can impact future generations of major commercial fish, despite future generations having no direct exposure to the chemicals. Moreover, pesticides can interact with chemicals in water from other sources, such as road salts, working together or synergizing to produce a more severe combined effect. Synergism is a common issue among pesticide mixtures and a failure to account for this can result in an underestimation of the toxic impacts on human, animal, and environmental health. As a result of risks to aquatic organisms, the Canadian pesticide regulatory agency has recommended banning imidacloprid which EPA is hesitant to implement.  

This study demonstrates that reducing the number of pesticides in the ecosystem does not indicate that an ecosystem is improving. The study results find a pivot toward pyrethroid and neonicotinoid use is responsible for invertebrate and plant population decline. However, this does not mean older chemicals do not affect invertebrates. Organophosphates are still widely available for use, especially for mosquito control and in agriculture and lawn care. Organophosphates commonly used in mosquito control programs, like malathion and naled, put bee health at risk. Both are highly toxic to bees, and other nontarget organisms, with reports of bee kills from Ultra-low volume (ULV) mosquito spraying. Furthermore, organophosphates can also impact aquatic communities, inducing toxicity among benthic organisms, like zooplankton, that are foundational to the food web structure.

Toxicity from herbicides is now double what it was in 2004, according to the study. Glyphosate is the main contributor to plant toxicity. The chemical’s use has been increasing since the inception of crops genetically modified to tolerate glyphosate. Genetically engineered crops pose an issue for pesticide use and species health and abundance. Resistance to pesticides is growing at similar rates among GE and non-GE conventionally grown crops. This increase in resistance is evident among herbicide-tolerant GE crops or GE crops containing plant-incorporated protectant (PIP) like Bacillus thuringiensis (Bt). Although one purpose of GE crops is to reduce pesticide use, an increase in resistance can result in additional pesticide use to compensate. However, overuse escalates toxic exposure to organisms that frequent or remain in these habitats, as well as nearby wild plants.

Although this study finds birds and mammals are experiencing less toxicity from current pesticide use, they are not safe from chemical consequences. Pesticide exposure patterns, including dietary exposure, co-exposure, and cumulative effects, put these species at risk. Pyrethroids are highly toxic to cats whose liver cannot process these chemicals, triggering seizures, tremors, muscle spasms that can lead to death. EPA’s preliminary ecological (non-pollinator) assessments for the neonicotinoids find that these pesticides pose both acute and chronic risks to aquatic life and birds. Furthermore, exposure to neonics can disrupt the energy-intensive metabolism of hummingbirds, even for a short period.

Just as residues from foliar spray adversely impact species health, so do pesticide-treated seeds. Most corn, soybeans, and other food crop seeds are pesticides-treated. These seeds have implications for birds who consume coated seeds. Compounds from neonic-coated grain accumulate in birds and reduce their chances of survival in the wild through sublethal impacts (weight reduction, travel delays, and a reduction in reproductive success). EPA finds that 1-5 seeds of treated corn cause acute to chronic levels of harm to large and small birds alike. EPA states, “Dietary exposures from clothianidin treated seeds are noted to result in the highest acute and chronic risks from the terrestrial risk assessment to birds and mammals.”

Furthermore, some common-use pesticides (e.g., neonics) are systemic, meaning plant roots and leaves uptake the chemical. With every type of use, the chemicals work their way into plants, pollen, nectar, and guttation droplets. Both vertebrates (e.g., birds, bats) and invertebrates (e.g., bees, butterflies) encounter indiscriminate exposure during foraging. However, these pesticides do not stay contained to plants, as chemicals can invade soil and surrounding waterways, causing indiscriminate poisoning and contamination.

As a result of this study, scientists outside this research study, including John Tooker, Ph.D. entomologist at Penn State, caution against continuous pesticide use. Dr. Tooker concludes, “The patterns in the US pesticide use and toxicity data should be a cautionary tale for the rest of the world, much of which seems to be leaning more heavily on pesticide use rather than ecological interactions for pest control.”

Chemical contamination is ubiquitous in terrestrial and marine environments, causing severe adverse effects to all species, especially invertebrates, that can span generationsMonarchs are near extinction, and beekeepers continue to experience declines that are putting them out of business. We continue to lose mayflies and fireflies, the foundation of so many food chains. Reducing the number of pesticides in our environment can safeguard insects, human, animal, and ecosystem health alike.

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. Now, grassroots advocacy groups in Connecticut, and Maryland, in addition to dozens of local groups, collaborate to create lasting positive changes to pollinator protection policies. Solutions like regenerative organic agriculture and organic land management curtail the need for toxic pesticide use as these practices warrant similar or better results than chemical-intensive ones. Learn more about the science and resources behind pesticides’ pollinator impact and take action against the use of pesticides. To find out more about what you can do to protect insects, check out information on pollinator-friendly landscapespollinator-friendly seeds. For more information on the insect apocalypse, see Beyond Pesticides article in our Pesticides and You newsletter, Tracking Biodiversity: Study Cites Insect Extinction and Ecological Collapse. Furthermore, learn more about the dangers pesticides pose to most wildlife on Beyond Pesticides’ Wildlife page.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Source: Eurasia Review, ScienceMag, Science

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2 Responses to “Invertebrates and Plants Face Increasing Threat from Pesticide Use, Despite Declining Chemical Use Patterns”

  1. 1
    Ahmad Mahdavi Says:

    Thanks for the good information, as I have been worry and mentioned many times here and elsewhere I am concerned about regulations and particularly enforcement issues in most developing countries and so the big damage that is going to people, environment and wildlife in these countries mostly in the MENA, we hope that REACH extends its activities in this region like what happened in East Asian countries.

  2. 2
    Judy M Lamana Says:

    You folks rock. I was just reading the Science article on the Schulz etc. al. study in the 2 April 21 print edition of Science.

    I had no idea we were ignorant of these impacts.

    I live in Fauquier County, VA.

    Will check out your drop-down menus regarding action, etc.

    I love science and facts. I am not consciously an idealogue.

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