Mixtures Effects

also see insects, birds , fungicides, mixture effects, digestive tract/microbiome, Bee Die-off, microbiota changes,  filed under organochlorines, health/low dose,  PFAs p.2

Synergistic Effects Documented for Multiple Pesticide Exposure on Honey Bee Health   (Beyond Pesticides, July 24, 2026) A study published in the Journal of Hazardous Materials finds that the cumulative impact of the pyrethroid insecticide flumethrin and the triazole fungicide hexaconazole “induced an acute synergistic effect” in honey bees (Apis mellifera L.). Flumethrin is used in pest strip in hives to control mites. Hexaconazole was used in Canada as seed treatment.

• Flumethrin was obviously more acutely toxic to honeybees than hexaconazole.
• Flumethrin in combination with hexaconazole induced acute synergistic effect.
• SOD activity was distinctly changed in the mixture groups relative to individuals. (SOD is an important antioxidant defense in nearly all living cells exposed to oxygen) 
• Expression levels of 4 genes in mixtures exhibited greater changes than individual chemicals. .

SNAP Comment: There are 0 (from 3) hexaconazole and 2 (from 2) flumethrin pesticide products currently registered in Canada

Literature Review Highlights Synergies Between Microplastics and Numerous Stressors, Including Pesticides    (Beyond Pesticides, July 29, 2026)    In a literature review published in Chemosphere, researchers at UTRGV - The University of Texas Rio Grande Valley identified thousands of studies published since 2012 that unpack how four environmental stressors (heatwaves, pesticides, pharmaceuticals, and pathogenic diseases) interact with microplastics in real-world conditions, adversely affecting ecosystems   “Most current research focuses on experiments with one or two stressors, leaving multi-stressor interactions poorly understood,” write the coauthors. “Future studies should emphasize multi-stressor experiments conducted under realistic environmental conditions to better reflect natural systems.”     The issue of microplastic contamination in organic food systems is a critical issue to Beyond Pesticides, including through advocacy in the Spring 2026 National Organic Standards Board (NOSB) meeting.  #environment #stressors #pesticides #microplastics #realworld #interactions #dailynews

Literature Review Captures Science on Need to Assess and Regulate Pesticide Mixtures for Adverse Effects   (Beyond Pesticides, August 5, 2026) In a review of over 60 experimental and epidemiological studies related to chronic, low-dose exposure to pesticide mixtures, a team of international researchers finds unreasonable adverse health effects that are not adequately captured in regulatory processes.   Published in the Journal of Environmental Protection, the authors note that the focus on single compounds in conventional risk assessments ignores mixture toxicity and subsequent synergistic effects.  Through mechanisms of “oxidative stress, mitochondrial dysfunction, endocrine and immune dysregulation, DNA damage, and persistent epigenetic reprogramming,” the research documents how exposure to mixtures of pesticides can induce a wide range of health implications in humans.      Chemical exposure does not occur in isolation but rather as simultaneous exposure to a “toxic soup” of environmental contaminants. Many pesticide products also contain more than one active ingredient, while risk assessments analyze these compounds individually.     These results highlight current regulatory deficiencies that fail to incorporate mixture toxicity in cumulative risk assessments, further strengthening the need for sustainable agricultural and land management practices that protect public and environmental health.  #pesticides #mixtures #toxicity #synergies #publichealth #dailynews

Literature Review Documents Enhanced Toxicity of Chemical Mixtures in Aquatic Organisms with PFAS Exposure   (Beyond Pesticides, May 13, 2026) Published in Toxics, a review finds that per- and polyfluoroalkyl substances (PFAS) can heighten the risks to exposed organisms from environmental contaminants. Mixtures of these compounds can negatively impact the nervous, cardiovascular, immune, and reproductive systems, particularly in aquatic organisms, and threaten overall biodiversity. The review highlights synergistic effects (greater in combination) observed in mixtures, such as PFAS with pesticides and microplastics, that can cause enhanced oxidative stress, neurotoxicity, developmental defects, and reproductive dysfunction, among others.  PFAS in agriculture represents a large source, as PFAS can be pesticide active ingredients, used in the plastic containers that pesticides are stored in, and as surfactants in pesticide products. 

Synergistic Effects from Glyphosate and Urea Fertilizer Magnify Earthworm Poisoning   (Beyond Pesticides, November 4, 2025) A study of earthworms published in Environmental Science & Technology highlights how chemical mixtures can have both synergistic and species-specific effects, threatening the soil microbiome and overall soil health. In exposing two species, Eisenia fetida and Metaphire guillelmi, to the weed killer glyphosate alone and in combination with urea, a form of synthetic nitrogen fertilizer, the researchers find enhanced toxicity with co-exposure as well as varying health effects between the two species.  .......exposed to soils treated with environmentally relevant concentrations of glyphosate, urea, or a combination of both for 28 days.    The species-specific results highlight the importance of studying a wide range of nontarget organism.

Research Finds Heightened Toxicity to Aquatic Organisms from Microplastic–Pesticide Interactions      (Beyond Pesticides, July 25, 2025) The scientific literature shows that microplastics (MPs) and pesticides, both ubiquitous throughout the environment, have synergistic effects that threaten aquatic organisms. This means the combined toxicity of the two substances is greater than the sum of two individual exposures. The most recent study to demonstrate this, published in Ecotoxicology, focuses on the impacts of MP in bodies of water come from various sources including wastewater effluents..    As a result, no mortality is observed to MP only treatments while MPs preconditioned with CPF (MP^CPF) show acute effects. Chronic exposure also shows reduced survival and reproductive output in both cladoceran species, with C. cornuta as more vulnerable than E. triserialis.     Cladocerans play an important role in the aquatic food web, helping to transfer carbon and nutrients from lower to higher trophic levels. In documenting impacts to cladoceran species, this represents threats to other aquatic organisms and overall biodiversity.    “Studies have shown that wastewater treatment plants discharge around 160–300 million MP per day into aquatic habitats,” the researchers note. MPs that are smaller than 2 mm can be easily ingested by cladocerans and other zooplankton. and chlorpyrifos (CPF), a widely used organophosphate insecticide, on cladocerans, a group of microcrustaceans.

Exposure to a mix of pesticides raises risk of pregnancy complications, study suggests  'Research looks at health impacts of being exposed to multiple pesticides versus just one substance  (The Guardian, 19 July 2025)    The new study checked for pesticides in the urine of nearly 90 pregnant women in Santa Fe, Argentina, a heavily agricultural region, and monitored their pregnancy outcomes. About 40 different pesticides were detected.     At least one pesticide was found in the urine of 81% of women, and 64% showed multiple pesticides. Of those, 34% had pregnancy complications.      But about 70% of women in rural settings showed multiple pesticides, compared to 55% of women in urban settings, highlighting a greater risk among the former.     Rural participants were over twice as likely to have pregnancy-related complications compared to urban, in part because they are more frequently exposed to mixtures.         The findings may also point to dangers in the type of pesticide to which women are exposed, the authors wrote. Those who had complications showed higher levels of triazole fungicides, a pesticide class that is widely used on crops like corn, soybeans and wheat.     Though not all the same pesticides are used in the US or other countries as in Argentina, the use of triazole fungicides increased four-fold in the US between 2006 and 2016, especially in the southeast and midwest. Still, it has drawn little regulatory scrutiny.    Exposure to mixtures of pesticides in general “is the rule, not the exception”,'     The study, which bio-monitored pregnant women in a heavily agricultural state in Argentina, adds to recent-but-limited evidence pointing to heightened dangers in mixtures of pesticides. SNAP Comment: There are currently 293 triazole fungicide formulations registered as pesticides in Canada.

Study of Chemical Mixtures at Low Concentrations Again Finds Adverse Health Effects   (Beyond Pesticides, April 10, 2024) Researchers in a 2024 Chemosphere study find synergistic relationships in certain chemical mixtures, particularly heptachlor and triallate and trifluralin and lindane at lower concentrations, respectively.... “According to a Centers for Disease Control (CDC) assessment, more than 50 pesticides are detected in blood or urine samples from the US population,” Researchers point to a cause for concern.... Researchers “used the exposure data from a complex operating site with legacy pesticide pollution.... “Only volatile COPCs... in soil and groundwater were included in this study (triallate, trifluralin, lindane, heptachlor, dieldrin, and aldrin,” the researchers indicate in the Methods section. Quantitative risk assessment for pesticide exposure was rooted on oral exposure... which demands a higher dose to induce an identifiable adverse effect relative to inhalation exposure. In other words, using an oral reference dose may underestimate the potential risk....  Researchers did find values suggesting “significant health concerns” to toddlers, infants, teenagers, and adults in “commercial and industrial land use.”... “Nine of the 15 tested binary mixtures of pesticides synergistically reduced cell viability. Seven mixtures (Trifluralin/Heptachlor, Trifluralin/Aldrin, Lindane/Heptachlor, Lindane/Aldrin, Heptachlor/Dieldrin, Heptachlor/Aldrin and Dieldrin/Aldrin) were synergistic at higher concentrations. However, two mixtures of herbicides and OCPs (organochlorine pesticides) (Trifluralin/Lindane and Triallate/Heptachlor) interacted synergistically at lower concentrations'.    SNAP Comment: All the pesticides listed were historically registered in Canada except dieldrin and two still are:trifluralin and triallate. 'There are 23,078 federal sites listed in the FCSI maintained by the Treasury Board of Canada Secretariat, including 5,337 active contaminated sites and 2,355 suspected sites. 15,386 are listed as closed because remediation is complete or because no action was necessary following assessment.' Inventory of federal contaminated sites.    'Research shows adverse health effects most likely occur within a 1.8 mile boundary around a Superfund site.' Millions of Americans Live Near Toxic Waste Sites. How Does This Affect Their Health?(February 16, 2022)

Neonicotinoids Combined with Other Pesticides Elevate Hazards to Honey Bee  (Beyond Pesticides, February 22, 2023)   'Among the eight pesticides tested, honey bee toxicity was as follows from most to least toxic: the neonicotinoid insecticide thiamethoxam, the organophosphate insecticide dimethoate, the carbamate insecticide methomyl, the synthetic pyrethroid insecticides permethrin, and then cypermethrin, the triazole fungicide tetraconazole, and the synthetic pyrethroids cyfluthrin and then esfenvalerate. These results did change based on different treatment lengths, yet thiamethoxam was found to remain the most toxic throughout all studies.  In the study, scientists evaluate a total of 98 different mixtures, from binary combinations of two different chemicals to octonary combinations of all eight different pesticides. Within these tests, approximately 30% of these were found to be synergistic to honey bees, exhibiting toxicity greater than each individual material in the mixture.  Perhaps the most concerning interaction came from combinations that included thiamethoxam and the fungicide tetraconazole. Any variation of pesticide combinations that include these two chemicals have a roughly 55% chance of exhibiting synergistic toxicity to honey bees.'

Pesticide Mixtures Reduce Life Span of Honey Bees, Damage Gut Microbiome    (Beyond Pesticides, November 1, 2022) Study done with field relevant concentrations. 'Honey bees exposed to a combination of multiple pesticides suffer a reduced lifespan and experience adverse changes to their gut microbiome, increasing susceptibility to pathogens and disease. This finding comes from a study published recently in Science of the Total Environment, which examines the interactions between the insecticides flupyradifurone and sulfoxaflor and the fungicide azoxystrobin on honey bee health.   As the present study reveals, pesticide risk assessments do not inadequately capture the range of harm that can result when pesticides are combined, necessitating a shift toward safer, alternative, and regenerative organic farming systems that do not use these dangerous chemicals.For the initial experiment on individual bees, those exposed to flupyradifurone fared the worst, experiencing significantly reduced survival (50% reduction). The addition of azoxystrobin did not significantly add to this effect. However, with sulfoxaflor, it did. Bees subjected to sulfoxaflor and azoxystrobin in combination experienced significantly reduced survival when compared to a sole sulfoxaflor exposure.'     All experimental groups 'show significantly increased abundance of Serratia spp. This rod-shaped bacteria can serious harm honey bee fitness. “These bacteria are pathogenic and harmful to bees’ health,” said Dr. Al Naggar. “They can make it harder for the insects to fight off infection, leading to premature death.” 

Ingestion of Real-World Pesticide Residues in Grain Threatens Bird Offspring More than Parents    (Beyond Pesticides, September 8, 2022) A study published in Environmental Pollution finds parental exposure to real-world, sublethal concentrations of pesticide residues on grains is a major contributor to unfavorable offspring development among foraging birds. Parents’ ingestion of grains with conventional pesticide residues, whether from contaminated or pesticide-treated seeds, results in chronic exposure that adversely affects offspring health, even at low doses.    However, researchers find that ingestion of low pesticide residues in grain has consequences on reproduction and offspring quality without altering mortality. Chicks whose parents consume grains with pesticide residues are more petite in size, lack proper skeletal growth, and have lower red blood cell counts with increasing body mass index as a trade-off.

Direct pesticide exposure of insects in nature conservation areas in Germany  (Carsten A. Brühl et al; Scientific Reports,16 December 2021)    In total, residues of 47 current use pesticides were detected, and insect samples were on average contaminated with 16.7 pesticides. Residues of the herbicides metolachlor-S, prosulfocarb and terbuthylazine, and the fungicides azoxystrobin and fluopyram were recorded at all sites. The neonicotinoid thiacloprid was detected in 16 of 21 nature conservation areas, most likely due to final use before an EU-wide ban. The individual chemicals reflect sales volume of each.  A change in residue mixture composition was noticeable due to higher herbicide use in spring and increasing fungicide applications in summer. The number of substances of recorded residues is related to the proportion of agricultural production area in a radius of 2000 m. Therefore, a drastic pesticide reduction in large buffers around nature conservation areas is necessary to avoid contamination of their insect fauna.   see also Insects in Nature Preserves Contaminated with Over a Dozen Pesticides (Beyond Pesticides, January 13, 2022)   SNAP Comment: As mentioned in the article, the higher chemical detection reflects volume of sales so a similarly designed study in other locations would have to reflect pesticide use and persistence in the area. There are currently 32 PMRA registered pesticide products containing metolachlor in Canada, 0 present or historical containing prosulfocarb, 0 present or historical containing terbuthylazine,  44 (down from 49) containing azoxystrobin, 18 containing fluopyram and 4 containing the neonicotinoid thiacloprid.