Prometryn belongs to the triazine family of herbicides, a chemical class that includes the widely discussed atrazine. Like its relatives, prometryn works by blocking photosystem II in plants, halting the light-driven reactions that weeds need to survive. It is used against broadleaf and grassy weeds in crops such as maize, vegetables, and citrus, and it is registered in Argentina under several commercial names, Prometrex FW among them. The formulation tested in the study contains 50 percent active ingredient, with the remainder made up of so-called inert adjuvants, substances added to help the product mix, spread, and stick to foliage. Those adjuvants, recent research suggests, can contribute their own toxicity, which is one reason ecotoxicologists increasingly test the full commercial product rather than the pure active compound alone.

The Argentine Pampas is one of the most intensively cultivated regions in South America, and agricultural intensification has steadily raised the burden of pesticides entering its waterways. Amphibians are considered particularly vulnerable sentinels in this landscape. Their permeable skin, aquatic eggs, and free-swimming larvae place them in direct and prolonged contact with whatever runs off the surrounding fields. Rhinella arenarum, the common South American toad, is broadly distributed and relatively easy to rear in the laboratory, which has made it a standard model for ecotoxicology in the region for decades. Yet despite the long history of testing other herbicides on this species, no one had previously examined how a prometryn-based product affects its larvae.

To fill that gap, the research team exposed premetamorphic tadpoles to three concentrations of Prometrex FW: 0.0015, 0.015, and 15 milligrams of active ingredient per liter. The lowest dose was chosen to reflect concentrations that could plausibly be found in the environment, while the highest, although dramatically lower than the manufacturer’s recommended application rate, was included to probe the upper range of acute sublethal exposure. Larvae were kept in the solutions for two exposure periods, 48 hours and 96 hours, under controlled laboratory conditions and in accordance with internationally recognized guidelines for acute toxicity testing with amphibians. The experimental protocol was reviewed and approved by the institutional animal care committee at the National University of La Plata.

The most striking result came from the alkaline comet assay, a technique that detects strand breaks in the DNA of individual cells. Cells are embedded in a gel, subjected to electrophoresis, and stained so that damaged DNA migrates away from the nucleus, forming the comet-like tail that gives the method its name. In the treated tadpoles, the genetic damage index rose significantly at every concentration tested, including the lowest, environmentally relevant dose. In other words, there was no observable threshold below which the herbicide formulation stopped harming DNA within the range examined. Because unrepaired DNA damage can propagate as mutations, interfere with cell division, and undermine development, this result carries weight well beyond the laboratory dish.

The biochemical assays told a consistent story. The researchers measured the activity of catalase, an enzyme that decomposes hydrogen peroxide, and glutathione S-transferase, a family of enzymes that conjugate toxic compounds to the cellular antioxidant glutathione so they can be excreted. They also quantified the total glutathione content of the larvae. All three biomarkers were significantly elevated in exposed animals, a pattern the authors interpret as evidence of oxidative stress. When herbicides or their breakdown products enter cells, they can generate reactive oxygen species faster than the normal antioxidant defenses can neutralize them. The tadpoles’ systems responded by ramping up production of catalase and GST and by mobilizing glutathione, effectively fighting a biochemical fire on two fronts. Sustained oxidative stress of this kind is linked in the broader literature to lipid peroxidation, protein damage, and the activation of apoptotic cell death pathways.

Growth told its own grim tale. Across all treatments and both exposure durations, larval growth was significantly inhibited compared with controls. For a tadpole, growth is not merely a matter of getting bigger; it is a race against pond drying, predation, and the physiological demands of metamorphosis. Larvae that fall behind face longer windows of vulnerability in the water, and population-level consequences can follow if enough individuals fail to reach metamorphosis in time. The combination of DNA damage, oxidative stress, and stunted development in the same animals suggests that the formulation attacks larval health at several levels simultaneously, from the molecular to the whole organism.

The study does not stand in isolation. Earlier work has documented prometryn’s capacity to disrupt aquatic life in other species. In zebrafish, prometryn exposure has been associated with mitochondrial dysfunction, oxidative stress, and failed organogenesis during early development, while in marine medaka it induces developmental toxicity at environmentally relevant concentrations. In crustaceans such as the Chinese mitten crab, the compound provokes oxidative damage and apoptosis in the hepatopancreas. Fish studies, including work on common carp and goldfish exposed to prometryn-containing products, have reported disturbances of antioxidant defenses and blood parameters. The new findings extend this picture to a Neotropical amphibian and, crucially, to a complete commercial formulation rather than the purified active ingredient.

Why does the distinction between active ingredient and formulation matter so much? Adjuvants and solvents in commercial products can enhance the penetration of the active compound through biological membranes, including the skin of amphibians, and some adjuvants are themselves toxic. Screening studies using molecular dynamics simulation and machine learning have begun to catalog the environmental hazards posed by pesticide adjuvants, an area historically exempt from the rigorous testing applied to active ingredients. By testing Prometrex FW as sold and sprayed, the Argentine team captured the real-world chemical mixture to which pond-dwelling larvae would actually be exposed after agricultural application, rather than an idealized single molecule.

The authors are careful about the scope of their conclusions. The work was conducted under laboratory conditions with acute exposures, and the researchers note that data supporting the findings are available from the corresponding author upon request. Nevertheless, the convergence of effects at low concentrations, including one chosen for its environmental relevance, leads them to flag a potential ecological risk to non-target species. In the Pampas, where drainage canals, temporary ponds, and crop fields interpenetrate, the boundary between treated land and amphibian habitat is thin. The study, funded by the National University of La Plata, CONICET, and Argentina’s National Agency of Scientific and Technological Promotion, adds prometryn-based formulations to the growing list of agricultural chemicals that can injure native wildlife at doses regulators and applicators may assume are harmless, and it underscores the case for monitoring surface waters in farming regions with the same urgency applied to the crops themselves.

Subject of Research: Sublethal genotoxic and oxidative effects of a prometryn-based herbicide formulation on Rhinella arenarum tadpoles

Article Title: Biochemical and morphological alterations in Rhinella arenarum larvae exposed to the prometryn-based formulation Prometrex FW®

Article References: Ruiz de Arcaute, C., Laborde, M. R. R., Cardascia, F., & Soloneski, S. (2026). Biochemical and morphological alterations in Rhinella arenarum larvae exposed to the prometryn-based formulation Prometrex FW®. Environmental Science and Pollution Research, 33(28), 14590-14604. https://doi.org/10.1007/s11356-026-38194-w

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38194-w

Keywords: prometryn, Rhinella arenarum, amphibian toxicology, comet assay, DNA damage, oxidative stress, catalase, glutathione S-transferase, herbicide formulation, ecotoxicology, Argentine Pampas, tadpole growth

The stakes are considerable. Grassland ecosystems once covered roughly 30 to 40 percent of the ice-free land surface, but temperate grasslands have been among the most heavily transformed habitats on Earth, with most of what remains now used for livestock production. The Río de la Plata Grasslands, spanning central Argentina, Uruguay and southern Brazil, form one of the largest Neotropical grassland systems at approximately 700,000 square kilometers, yet protected areas cover less than 3 percent of the Argentine Pampas. That means most surviving grassland habitat sits on private ranches, where decisions about stocking rates, paddock rotation and herbicide use effectively function as conservation policy. The regional avifauna includes 109 species classified as Southeastern South America grassland birds—species that depend extensively, or entirely, on the original native grassland physiognomy.

These birds fall into three broad habitat categories, and the study’s findings hinge on those distinctions. Short-grass species include migratory shorebirds such as the Buff-breasted Sandpiper (Calidris subruficollis) and the American Golden-plover (Pluvialis dominica), which favor closely cropped, homogeneous turf. Tall-grass species, some of them of conservation concern, include the Bay-capped Wren-spinetail (Spartonoica maluroides), a secretive bird that nests and forages among dense tussocks. Broad species, such as the Great Pampa-finch (Embernagra platensis) and the Brown-and-yellow Marshbird (Pseudoleistes virescens), use both short and tall grass. Because each group responds to different vegetation structures, a single grazing prescription cannot serve them all—a tension that lies at the heart of grassland conservation in the region.

The two management systems the researchers compared represent fundamentally different philosophies. Continuous grazing management, the traditional practice in the Flooding Pampas, keeps cattle in the same paddocks throughout the year, which tends to produce spatially homogeneous grasslands with short vegetation and has been linked to negative impacts on birds dependent on tall grass. Ecological process-based management, by contrast, encompasses rotational and controlled grazing designed to achieve more efficient forage use across seasons and to improve grassland composition by regulating resting periods, allowing cool-season grasses to seed and establish. Previous work has shown that input-based practices such as herbicide application and the establishment of introduced pastures can intensify grassland degradation and displace grassland birds in favor of generalists, whereas ecological process-based approaches have been associated with greater vegetation heterogeneity and more diverse avian communities.

To quantify these effects, the team surveyed birds and vegetation during a single breeding season in October and November of 2016, on five ranches under each management type, evenly distributed across the subregion. At each ranch, 25 to 30 count points were systematically placed—one per paddock, separated by at least 150 meters and kept away from fences, drainages and floodplains to avoid edge effects. Observers recorded all birds seen or heard within a 50-meter radius during five-minute counts conducted in the three hours after dawn and the three hours before sunset, yielding 288 count points and a total sampling effort of 1,440 minutes. The surveys documented 3,800 individuals of 41 grassland bird species under continuous grazing and 3,719 individuals of 39 species under ecological process-based management. After each count, observers visually estimated vegetation height, cover and dominant plant species, classifying vegetation into seven height strata and noting the presence or absence of tussock-forming species such as Paspalum quadrifarium, Juncus acutus, Spartina species and Cortaderia selloana.

The statistical analysis, built on generalized linear mixed models with ranch as a random effect, revealed that overall grassland bird abundance was 8 percent higher under ecological process-based management—26.5 versus 24.5 individuals per count point—than under continuous grazing. More striking was the interaction involving tussocks. Broad species, the group driving the overall difference, reached roughly 9.7 individuals per point in tussock-free paddocks under continuous grazing, but nearly doubled to 17.7 individuals where tussocks were present under the same management, and rose to 18.4 and 20.3 individuals per point under ecological process-based management with and without tussocks respectively. In other words, rotational grazing appeared to create conditions suitable for broad species even where tussocks were absent, while traditional continuous grazing only supported comparable numbers where tussock clumps persisted. Tall-grass species, meanwhile, did not respond directly to management type but were almost ten times more abundant in the presence of tussocks—0.4 versus 0.04 individuals per point—an emphatic signal of how much these plants matter for the most habitat-specialized birds.

Short-grass species told a different story entirely: their abundance varied neither with management practice nor with tussock presence. Seven species accounted for 75 percent of total abundance across the study, and none were tall-grass birds; the dominant assemblage included the Southern Lapwing (Vanellus chilensis, 20 percent of individuals), the Grassland Yellow-Finch (Sicalis luteola, 19 percent), the American Golden-plover (11 percent) and the Correndera Pipit (Anthus correndera, 11 percent). Species richness showed no significant association with management practice and only a marginal one with tussocks, averaging 6 species per point with tussocks against 5.4 without. A canonical correspondence analysis then mapped the 37 most frequently detected species against six vegetation variables, revealing a significant association between bird communities and vegetation structure. The first ordination axis separated species along gradients of heterogeneity and height, while the second axis primarily reflected grassland height, tussock presence and lowland occurrence.

The ordination carried important conservation messages. The Bay-capped Wren-spinetail and the Warbling Doradito (Pseudocolopteryx flaviventris) anchored the tall-grass, tussock-associated end of the gradient, while the Buff-breasted Sandpiper and American Golden-plover sat at the opposite extreme, tied to short, homogeneous grass shorter than 10 centimeters—likely because low swards improve both arthropod detection and visibility of avian predators. The threatened Hudson’s Canastero (Asthenes hudsoni), a broad species that nests in tall grasslands but feeds in heterogeneous ones, was associated with tussocks and high structural diversity. Notably, the Bay-capped Wren-spinetail was recorded at fewer than 5 percent of count points, underscoring how rare suitable habitat has become even on semi-natural ranches. The researchers also observed that ranches under continuous grazing happened to hold higher tussock and lowland occupancy in this sample, and that ranch identity explained a substantial share of the variance in bird abundance—suggesting that land-use history, paddock size, stocking rate, topography and fire all shape the conservation value of individual properties.

The practical implications reach beyond Argentina. Studies in the temperate grasslands of the United States Great Plains have found that grazing systems alone often do not significantly affect bird communities, making the Pampas results a reminder that context matters: where tussock-forming plants persist or can be restored, they act as keystone structural features for threatened birds. Because cow-calf production is the predominant activity of the Flooding Pampas, meaningful change must happen at that stage, and ecological process-based management is already available and has been shown to increase production while reducing certain environmental and biodiversity impacts. Yet adoption barriers remain, including lack of knowledge and economic constraints, and different ranching systems face different obstacles. Crucially, the authors caution that rotational grazing does not automatically preserve tussock-dominated grasslands of Paspalum quadrifarium, which serve as refuges for native wildlife and still resemble the original physiognomy of the Pampas. The study’s central lesson is therefore twofold: grazing systems that promote heterogeneity can deliver productive, economic and conservation goals simultaneously, but deliberate preservation of tussock-forming plants within livestock systems is indispensable for safeguarding the region’s most specialized and threatened grassland birds.

Subject of Research: Effects of grazing management and tussock-forming plants on grassland bird communities in the Argentine Flooding Pampas

Article Title: The role of grazing management practices and tussock-forming plants on grassland birds in the Argentine Pampas

Article References: Niklison, F., Bilenca, D., & Codesido, M. (2025). The role of grazing management practices and tussock-forming plants on grassland birds in the Argentine Pampas. Discover Conservation, 2(1), Article 44. https://doi.org/10.1007/s44353-025-00066-8

Image Credits: AI Generated

DOI: 10.1007/s44353-025-00066-8

Keywords: grassland birds, Argentine Pampas, grazing management, tussock grasses, rotational grazing, Flooding Pampas, bird conservation, vegetation structure, Bay-capped Wren-spinetail, livestock production, Neotropical grasslands, habitat heterogeneity