Research and Resources on the Negative Effects of Pesticide and Aerial Spray

Pesticide Applications are compromising to the health of the ecosystem to which they are applied, and residents have a right to protect themselves from dangerous industrial forestry practices such as aerial herbicide spraying. There is substantial evidence that long term exposure to even relatively low levels of herbicides can cause significant harm to farms, forests, water quality and inhabitants.

Any herbicide application is potentially dangerous, but the risk of drift and chemical trespass is greatly increased when applied from aircraft.  The toxins drift not only when they are sprayed but again when they rise on the mists of coastal fog and descend to unintended areas.  Phenoxy herbicides (including 2,4-D, triclopyr, MCPA, dicamba) are examples of chemicals which may volatilize on their own, especially in ester formulations (Hellman and Fult, 1999).  Herbicides have been documented to drift up to 8 miles from a target area, and even 0 mph wind conditions can be dangerous due to the potential of inversion which will cause the poisons to remain suspended longer and spread in the atmosphere before settling off-target (Davis, 2015).

Current regulations have proved inadequate to prevent herbicide drift. Herbicides aerially sprayed in accordance with Oregon Forest Practices Act regulations have drifted off target and caused harm.  A 2012 Oregon Health Authority study found logging industry herbicides in the urine of families in the Triangle Lake area, in Lane County, where residents have long complained that nearby spraying was allowing chemicals to drift onto their homes.  In October of 2013, one logging operation sprayed toxic chemicals on more than 40 people in the community of Cedar Valley, in Curry County, in what became a particularly notorious case of chemical trespass.  Some national forests have suspended their spraying programs in response to public pressure, but were responsible for dousing many acres with 2,4,5-T in years past, with disastrous results on pregnant women (Felicep, 2009).

State officials have long ignored concerns about the health and safety of aerial spraying.  They claim the herbicides sprayed are harmless, but multiple news outlets have alerted the public to the fact that rural residents exposed to these chemicals have experienced symptoms including severe headaches, rashes, respiratory problems, bleeding lungs, nosebleeds, and the death of pets and livestock exposed to spraying (Schick, 2014).  Medical professionals know that long-term exposure to chemicals like glyphosate, 2,4-D and atrazine-commonly used by the logging industry-can injure the liver and kidneys.  Scientific research continues to mount showing the hazardous side-effects of herbicides at various doses.

For example, the most applied desiccant, glyphosate, kills plants through disruption of a metabolic pathway called the shikimate pathway, which starves the plant of key nutrients.  It was supposed to be safe for animals and humans whose cells  were not thought to have this metabolic pathway.  However we now know that human gut bacteria, which are necessary for the synthesis of many nutrients, contain the shikimate pathway.  Human bodies actually contain several times more bacterial cells than human cells that all have the shikimate pathway and are essential for vital bodily functions.  Decades of research show that glyphosate interference with Cytochrome P450 enzymes acts synergistically with disruption of the biosynthesis of aromatic amino acids by gut bacteria, as well as impairment in serum sulfate transport (Samsel and Seneff, 2013).  The consequences are embodied by gastrointestinal disorders, obesity, diabetes, heart disease, depression, autism, infertility, cancer and Alzheimer’s disease (Samsel and Seneff, 2013).  Glyphosate is also known to cause liver damage at ultra low environmentally relevant levels (Mesnage, 2017) and is responsible for the four-fold increase in Celiac disease in the U.S. the past 50 years (Samsel and Seneff, 2013).  The World Health Organization has classified glyphosate as probably carcinogenic.

Potentially Harmful Synergistic effects: Analysis of USGS National Water-Quality Assessment Program monitoring data found that > 90% of water samples from urban, agricultural, and mixed-use streams contained two or more pesticides (Gilliom 2007).  The toxicologic effects of these mixtures on the health of humans and wildlife are largely unknown.  Research suggests that mixing chemicals can lead to synergistic effects.  Chemicals applied in a mix can interact, which may result in more harmful environmental effects than when applied individually (Laetz, 2009) (Hayes, 2009). In other words, the effects of synergistic doses cannot be predicted by the effects observed at single doses.  Impacts to people, fish and other organisms from these tank mixes are not clearly understood and therefore cannot be considered scientifically sound practice.  In a literature review published by the U.S. National Center for Biotechnology Information researchers suggest that chemicals that act as endocrine disrupters and carcinogens have long-term impacts via epigenetic mechanisms (Silins & Högberg, 2011).  The authors concluded, “solid evidence shows that these groups of chemicals can interact and even produce synergistic effects.”  Even lesser amounts of herbicides within a chemical mix may produce toxic impacts during sensitive windows of vulnerability, such as fetal development and early childhood.

Much like the synergistic effects of chemical tank mixes, the effects of individual adjuvants (supposedly inert ingredients added to the spray tank to improve herbicidal activity or application characteristics) and adjuvants mixed with active ingredients are largely unknown. Cox and Surgan (2006) summarize potential environmental health concerns, “Inert ingredients can increase the ability of pesticide formulations to affect significant toxicologic end points, including developmental neurotoxicity, genotoxicity, and disruption of hormone function. They can also increase exposure by increasing dermal absorption, decreasing the efficacy of protective clothing, and increasing environmental mobility and persistence.  Inert ingredients can increase the phytotoxicity of pesticide formulations as well as the toxicity to fish, amphibians, and microorganisms.”  Note that federal law does not require manufacturers to identify these “inerts” although inert ingredients are known to have toxic properties.

There are enormous shortcomings in current procedures to assess the hazards of pesticides.  Pesticide registration should require full assessment of formulations including inert ingredients, to enable independent research and risk assessment.  Evaluations of pesticides under the National Environmental Policy Act, the Endangered Species Act, and similar statutes should include impact assessment of mixed formulations.

Individual pesticides are known to be dangerous and their widespread use in the Coast Range is concerning.  More concerning is that pesticide applicators create tank mixes of chemicals that contain multiple active ingredients and adjuvant products, despite a lack of understanding about the synergistic effects of multiple chemicals combined and released into the environment.  It is not in accordance with label guidance to mix a pesticide with another pesticide or chemical unless the combination is listed on the label.  Permitting mixed chemical applications is not in accordance with Oregon statues and ODF policy, and these off-label applications should not be approved by the ODF office.

The harm caused by the aerial spraying of 2,4-D, glyphosate, atrazine and similar chemicals is unnecessary.  Fir trees will grow  absent of these toxic applications and choke out any underbrush in only a few years after planting.  Many timberland owners, National Forests, and tribes have stopped using herbicides altogether and their timber receipts continue to run in the black.  While manual removal of competing brush may cost slightly more than chemical applications these methods are effective, environmentally sound, and provide employment.

Citizens have little to no recourse.  Proving that pesticide trespass caused an injury is a difficult process, and the attorney fee provision of the “right to farm” law has an entirely chilling effect on neighboring property owners who feel they’ve been harmed.

The use of these chemicals continues to rise year after year while Oregon retains the weakest protections for such activity in the Western US.  State agencies, including ODF, should work to protect public health, wildlife, clean water, and private property, not shield politically influential industries from accountability.  We can no longer ignore all the science that has been available for years about the serious toxic damage that is being caused to our people, land and wildlife.  We have a right to clean air and clean water.


Arkin, L.  (2014). Poisoned Paradise: Stories from Cedar Valley.  Retrieved from

Bernstein, L., Arkin, L., and Lindberg, R. (2013).  Oregon’s Industrial Forests and Herbicide Use: A Case Study of Risk to People, Drinking Water and Salmon. Retrieved from

Cox, C. and Surgan, M. (2006). Unidentified inert ingredients in pesticides: implications for human and environmental health. Environmental Health Perspectives, 114(12):1803-6.

Davis, R. (2015, October 21). “Oregon agencies blew off complaints, red flags before helicopter sprayed weed killers on residents”.  Oregonian. Retrieved from

Felicep.  (2009, November 20). “The Pesticide Wars”.  High Country News. Retrieved from

Gilliom RJ. (2007). Pesticides in U.S. streams and groundwater. Environmental Science and Technology, 41(10):3407–3413.

Hayes, T. B., Anderson, L. L., Beasley, V. R., de Solla, S. R., Iguchi, T., Ingraham, H., et al. (2011). Demasculinization and feminization of male gonads by atrazine: consistent effects across vertebrate classes.  The Journal of Steroid Biochemistry and Molecular Biology.

Hellman, E. and Fults, J. (1999). Preventing Phenoxy Herbicide Damage to Grape Vineyards.  Oregon State University Extension Service. Retrieved from

Laetz, C. D. (2009). The synergistic toxicity of pesticide mixtures: implications for risk assessment and the conservation of endangered Pacific salmon. Environmental Health Perspectives, 117(3): 348-353.

Mesnage R, Renney G, Séralini G, Ward M. and Antoniou M. (2017). Multiomics reveal non-alcoholic fatty liver disease in rats following chronic exposure to an ultra-low dose of Roundup herbicide. Scientific Reports. Retrieved from

Samsel, A. and Seneff, S. (2013). Glyphosate’s suppression of cytochrome P450 enzymes and amino acid biosynthesis by the gut microbiome: Pathways to modern diseases. Entropy. 15:1416–1463.  Retrieved from

Samsel, A. and Seneff, S. (2013). Glyphosate, pathways to modern diseases II: Celiac sprue and gluten intolerance. Interdisciplinary Toxicology; 6(4): 159–184. Retrieved from

Schick, T. Follow (2014, April 23).  Southern Oregon Pesticide Case Highlights Gaps in State Oversight.  Oregon Public Broadcasting. Retrieved from

Silins I. and Högberg J. (2011). Combined toxic exposures and human health: biomarkers of exposure and effect. International Journal of Environmental Research and Public Health. 8(3):629-47.

Herbicides & Aquatic Species – Annotated Bibliography

Numerous studies have been conducted that show the negative impacts of herbicides on salmon and other aquatic species.  Here is a small sample of relevant research studies:

Health effects of pesticide mixtures: Unexpected insights from the salmon brain (Scholz, 2008), and Chemicals in our waters are affecting humans and aquatic life (SeaWeb, 2008)

Scientists from the American Association for the Advancement of Science (AAAS) report that pesticides that run off the land and mix in rivers and streams combine to have a greater than expected toxic effect on the salmon nervous system than the pesticides would have individually. The scientists concluded that “[c]urrent risk assessments based on a single chemical will likely underestimate impacts on wildlife in situations where that chemical interacts with other chemicals in the environment,” and that the findings may have relevance for human health because these toxins act on the nervous systems of salmon and humans in a similar way.  The Agency concluded that “Current risk assessments based on a single chemical will likely underestimate impacts on wildlife in situations where that chemical interacts with other chemicals in the environment.”  Scholz and his colleagues found that salmon died when exposed to combinations of pesticides that were not deadly when tested in individual trials.

A fish of many scales: extrapolating sublethal pesticide exposures to the productivity of wild salmon populations (Baldwin, 2009);jsessionid=4400FEF13DA1E3E89974E57BC9ACED77.f04t03  Results indicate that short-term (i.e., four-day) exposures that are representative of seasonal pesticide use may be sufficient to reduce the growth and size at ocean entry of juvenile chinook. The consequent reduction in individual survival over successive years reduces the intrinsic productivity (lambda) of a modeled oceantype chinook population. Overall, the study shows that exposures to common pesticides may place important constraints on the recovery of ESA-listed salmon species, and that simple models can be used to extrapolate toxicological impacts across several scales of biological complexity

Contaminant Exposure and Associated Biological Effects in Juvenile Chinook Salmon (Oncorhynchus tshawytscha) from Urban and Nonurban Estuaries of Puget Sound (Varanasi, et al., 1993)  A National Marine Fisheries Service study of juvenile fall Chinook salmon found that salmon accumulate significant concentrations of chemical contaminants even during relatively short residence times in estuaries, and that juvenile salmon from polluted environments “exhibit abnormalities ranging from subcellular effects to changes in immune function and growth. In many cases the effects alter physiological processes, such that the potential for survival is reduced.” Results demonstrate that chemical contaminant exposure in juvenile chinook salmon was sufficient to elicit responses at the chemical, biochemical, and biological level, and provides evidence of linkage between complex mixtures of chemical contaminants in the environment and effects on health and survival of fish.

Demasculinization and feminization of male gonads by atrazine: consistent effects across vertebrate classes (Hayes, et al., 2009)  Atrazine was shown to be an endocrine disrupter for amphibians. Reductions in androgen levels and the induction of estrogen synthesis – demonstrated in fish, amphibians, reptiles, and mammals – represent plausible and coherent mechanisms that explain these effects.

Potential endocrine disruption of sexual development in free ranging male northern leopard frogs (Rana pipiens) and green frogs (Rana clamitans) from areas of intensive row crop agriculture (McDaniel, et al., 2008)  The study assessed a suite of potential endocrine effects in amphibians, including the occurrence of testicular ovarian follicles in male frogs.  The proportion of testicular oocytes correlated with a mixture of pesticides and nutrients, particularly atrazine and nitrate, while the number of pesticides detected at each site was also important.