Pesticide Contamination of Important Microorganism Communities Moves through Environment to Protected Areas

(Beyond Pesticides, March 19, 2026) A study of water contamination in Protected Areas (PAs) in Brazil, published in Science of The Total Environment, highlights the pervasiveness of pesticides. “Our objective was to evaluate the effectiveness of these PAs in mitigating pesticide contamination in watercourses and to investigate how land use patterns influence the presence of pesticide residues,” the authors state. “We found pesticide compounds in biofilms [mutually beneficial community of microorganisms] both inside and outside PAs’ streams, with no buffer effect of these protected lands against herbicides, insecticides and fungicides, contrary to our expectations.” In analyzing epilithic biofilms, which are communities of microorganisms that adhere to submerged rocks and surfaces in aquatic ecosystems, the researchers find residues of 14 pesticide compounds and one metabolite across the 19 sampling sites, threatening aquatic organisms and ecosystem functioning. The authors say, “[M]onitoring epilithic biofilms in PAs provides valuable information by detecting pesticide compounds that analysis of surface water and sediments might miss.”

Through various routes, such as runoff to waterways, leaching into groundwater, and aerial drift, pesticides are ubiquitous in the environment, even in remote and protected areas. As the testing of the freshwater epilithic biofilms in this study reveals 15 pesticide residues both in protected and non-protected areas, this shows the widespread nature of pesticide contamination in waterways that has deleterious impacts on biodiversity. PAs, as documented here, do not adequately safeguard this biodiversity, despite conservation strategies trying to protect natural areas with buffer zones, particularly near agricultural areas.

“In this study, we hypothesized that PAs are an efficient way to mitigate pesticide contamination, given the strict regulations of land use and land cover inside these areas, resulting in lower accumulation of these compounds in epilithic biofilm samples from streams inside their borders than those outside,” the researchers note. This hypothesis, however, was proven wrong as pesticides residues “were found in almost 95% of the sampling sites,” both in and around the protected areas. Higher concentrations of certain pesticides are also shown within the PAs when compared to levels in the surrounding non-protected areas.

Importance and Background
PAs act as crucial refuges for many organisms and provide vital ecosystem services, including water purification and soil conservation. Protecting natural areas is increasingly important, as habitat destruction, environmental contaminants, and the ongoing biodiversity and climate change crises continue to threaten wildlife and ecological systems. Within PAs, many human activities are restricted, which allows “natural regeneration and recovery of ecosystems, enabling the maintenance, survival, and recovery of natural and/or threatened species.”

As the authors say, PAs are: “one of the main refuges for biodiversity, especially for the functioning of forests located close to high anthropogenic activities, as these can result in environmental chemical changes that propagate through trophic levels and influence important ecosystem processes. Their role is essential and, in several countries, they represent the only land specifically designed to preserve natural habitats.”

In Brazil, where the study was conducted, there are multiple types of PAs, all with boundaries defined by law designed to decrease human impact and protect the environment. “Together, they preserve 19% of the Brazilian terrestrial land, encompassing different biomes,” the researchers write. They continue: “Considering only the Atlantic Forest biome, a biodiversity hotspot and one of the most threatened in the world, where this study was carried out, the proportion of the biome that is protected is reduced to approximately 10%. Brazil is one of the world leaders in land protection, but it is also one of the leaders in crop production, and PAs surrounded by agricultural and other economic activities (such as cattle raising) suffer from the indirect impacts of these types of land use.”

Even with many terrestrial PAs surrounding waterways that are meant to provide protection, the biodiversity of freshwater ecosystems continues to decline. “Based on the index used by the World Wildlife Fund (WWF) since 1970, the populations of freshwater aquatic organisms have declined by 83%, more than twice the rate of marine and terrestrial species,” the authors point out. One of the main factors adversely impacting biodiversity is the contamination of pesticides in these aquatic ecosystems. Once pesticide residues reach these environments, they can bioaccumulate and biomagnify within the food web, causing adverse effects to a multitude of organisms.

“Among these organisms, there are the epilithic biofilms–complex communities of bacteria, fungi, and algae embedded in extracellular polymeric substances (EPS) on rock surfaces–that act as long-term pollutant accumulators,” the researchers describe. These organisms provide key services, such as nutrient cycling, primary production, and decomposition of organic matter, in aquatic environments, in addition to being able to act as bioindicators of health. “Because biofilms can accumulate pollutants over time, allowing for the detection of long-term and seasonal contamination patterns, they supply a fingerprint of pesticide usage in the catchment,” the authors add.

Study Methodology
The study was conducted in five PAs throughout southern Brazil within the Atlantic Forest Biome, including São Joaquim National Park (SJNP), Aparados da Serra National Park (ASNP), Serra Geral National Park (SGNP), São Francisco de Paula National Forest (SFPNF), and the Private Natural Heritage Reserve Portal das Nascentes (PNHR). At each of these sites and surrounding areas, 20 rocks were randomly selected for epilithic biofilm sample collection. Pesticide residue detection in these samples was then conducted at the Pesticides Laboratory of the Instituto Nacional de Tecnología Agropecuaria (INTA) in Balcarce, Argentina.

Analysis of 46 pesticides and metabolites was performed, finding concentrations of herbicides, insecticides, and fungicides in the majority of samples. The pesticide residues tested for include glyphosate and its metabolite aminomethylphosphonic-acid (AMPA), 2,4-D, 2,4-DB, acetochlor, alachlor, allethrin, ametrine, atrazine, atrazine-desethyl, atrazine desisopropyl, atrazine-OH, carbaryl, chlorimuron-ethyl, chlorpyrifos, chlorpyrifos methyl, kresoxim-methyl, diazinon, dicamba, diclosulam, dimethoate, epoxiconazole, fipronil, flumethrin, flurochloridone, fomesafen, flumioxazin, imazapic, imazapyr, imazethapyr, imidacloprid, metalaxyl, metconazole, metribuzin, metsulfuron-methyl, parathion-methyl, pendimethalin, piperonyl butoxide, pirimicarb, pirimiphos-methyl, simazine, tebuconazole, tetramethrin, and triticonazole.

Results
Of the 46 compounds tested for, 15 were present in both PAs and non-protected areas. Of note, insecticide and fungicide concentrations are higher inside PAs, and there is a correlation between fungicide presence and nearby forest plantations. In looking at the concentrations of herbicides, fungicides, and insecticides both inside and outside the PAs, there are no statistically significant differences in the mean concentrations, despite the researchers’ prediction that there would be less pesticide residue present in the protected areas.

The residues identified in the samples include seven herbicides (glyphosate and AMPA, picloram, metsulfuron-methyl, metribuzin, acetochlor, and pendimethalin), five insecticides (allethrin, imidacloprid, carbaryl, chlorpyrifos, and tetramethrin), and three fungicides (epoxiconazole, triticonazole, and tebuconazole). Nine of these pesticides are present within the PAs (three herbicides, three insecticides, and three fungicides) and all sampling sites are “contaminated by at least one compound, even in pristine and protected regions, except site 12, where no compound was detected.”

Additional noteworthy results include:

• Aside from site 12, at least one fungicide compound is detected in each sampling site.
• The fungicide triticonazole is present in 15 of the 19 sampling sites.
• The herbicide pendimethalin is detected most frequently in seven sites, five of which are inside PAs.
• “[S]ite 15 (SGNP) had the highest number of pesticides recorded within PAs, five in total: imidacloprid, carbaryl, triticonazole, tebuconazole, and pendimethalin.”
• “[S]ite 14 (SGNP) had the highest pesticide concentration registered, comprising four compounds – the herbicides picloram and pendimethalin; and the fungicides tebuconazole and triticonazole.”
• While only present in a few sites, glyphosate and its metabolite AMPA show the highest overall concentrations.
• Higher insecticide concentrations are documented inside PAs, with allethrin having the most significant results being detected in four sampling sites (three within PAs and one outside).
• “[A] significant positive correlation between fungicides and silviculture is observed, in which an increase in the land covered by planted forest resulted in a higher fungicide concentration.”
• Fungicides from the class known as azoles have a “notable presence along our sampling sites, being recorded in 18 of the 19 sites. We highlight triticonazole, present in eight PAs, which is widely used in cereal crops in order to control different fungal diseases and seems to be one of the least toxic fungicides for biodiversity. We also detected tebuconazole, a fungicide banned in Europe, in nine sites, five within PAs.”

These results indicate that PAs do not act as effective buffers against pesticide contamination in freshwater, with the aquatic environments in PAs, and all organisms within them, vulnerable to the adverse effects of pesticide residues. In summary, the researchers state: “[T]he conservation of freshwater ecosystems faces a challenge with pesticides, as more and more of these compounds are found in the most varied types of environments, regardless of the degree of anthropization in their surroundings, where even pristine environments can be affected, as observed in PAs. The ideals of sustainable development must be considered when balancing food production worldwide with biodiversity conservation.”

Previous Research

There is a long history of pesticide contamination in waterways, with scientific literature documenting risks to not only aquatic organisms as a result, but also to terrestrial wildlife and humans. In a Daily News post from 2024, entitled Pesticide-Contaminated Algae Found to Jeopardize Ecosystems and Human Well-Being [Study], research on pesticide-contaminated algae finds that the disruption of algal communities has a devastating effect on the health of the aquatic food web. The study findings show that contact with pesticides can result in changes to “algal physiology, causing tissue injury, developmental delay, genotoxicity, procreative disruption, and tissue biomagnification” that alter the dominance of algae species in the environment. This, in turn, “can impact higher trophic levels and have a domino effect on the aquatic food web. It is possible for biodiversity to disappear, reducing ecosystem stability and resistance to environmental alterations,” the study authors state.

The persistence of pesticides in the environment leads to bioaccumulation in “algal tissues, which could result in biomagnification as the toxins climb the food chain and endanger higher trophic levels.” The direct contact with these chemicals can cause “rapid physiological stress that impairs photosynthesis growth rates and, in extreme situations, results in death,” while the indirect contact with other organisms through the food web leads to negative impacts on the biological balance of entire marine ecosystems. The pesticide-laden algae pass their contamination to organisms that consume them, and the contamination continues to increase through trophic transfer. As the National Oceanic and Atmospheric Administration (NOAA) explains, “Phytoplankton and algae form the bases of aquatic food webs. They are eaten by primary consumers like zooplankton, small fish, and crustaceans. Primary consumers are then eaten by fish, small sharks, corals, and baleen whales. Top ocean predators include large sharks, billfish, dolphins, toothed whales, and large seals. Humans consume aquatic life from every section of this food web.” For more information on water contamination and the threats to biodiversity, see here, here, and here.

The Organic Solution
To remove pesticide residues within both protected and non-protected areas that threaten all life and ecosystem stability, the elimination of all petrochemical pesticides and synthetic fertilizers from agricultural and land management practices is necessary. Organically managed systems focus on soil health, building a healthy foundation that makes the use of chemical-intensive practices obsolete. Taking into consideration all of the adverse effects of pesticide exposure and the ubiquitous nature of pesticide residues within the environment, as well as all of the effects that have yet to be fully studied, the path forward must incorporate a widespread transition to fully organic practices.

Learn more about the health and environmental benefits of organic methods, as widely documented and supported by science (see here, here, and here), and take action to advance the organic movement.

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

Source:

Mollmann, V. et al. (2026) Epilithic biofilms as bioindicators of water contamination by pesticides in Protected Areas from Atlantic Forest, Science of The Total Environment. Available at: https://www.sciencedirect.com/science/article/pii/S0048969726003177.