Fungi in a Toxic River Basin Reveal New Warning Signs for Urban Soil Health

Deep beneath one of the most polluted river basins on the planet, an invisible workforce of soil fungi is quietly recording the story of decades of industrial abuse. In the Matanza-Riachuelo river basin, which cuts through the sprawling metropolitan area of Buenos Aires and has long been ranked among the world’s worst toxic hotspots, researchers have now shown that the microscopic partners of plant roots can serve as sensitive gauges of environmental damage. A new study published in Environmental Science and Pollution Research suggests that two biological measurements tied to arbuscular mycorrhizal fungi, one rising and one falling with pollution, could become reliable tools for monitoring soil health in heavily disturbed urban landscapes.

The research team, led by Mailen Guerra Moreno and Roxana Paula Colombo of the University of Buenos Aires together with colleagues at the National University of Avellaneda and CONICET, sampled soils and plant roots at sites spanning the upper, middle, and lower sections of the basin. Their goal was to test whether three fungus-related variables, namely the richness of arbuscular mycorrhizal fungal species determined from spore morphology, the mycorrhizal status of the plants growing in each soil, and the concentration of glomalin-related soil proteins, could function as practical bioindicators of soil health. These biological measures were then compared against the chemical fingerprint of contamination at each site, particularly the burden of heavy metals and metalloids.

The Matanza-Riachuelo basin presents an unusually stark gradient of degradation. Tanneries, metalworking plants, chemical factories, and open dumps have discharged effluents into the river and its floodplain for more than a century, and millions of people live along its banks, many in informal settlements with direct exposure to contaminated soil and water. Previous studies have documented alarming concentrations of chromium, copper, lead, and other toxic elements in basin sediments and soils, along with groundwater quality problems that pose documented risks to human health. Yet, as the authors note, biological indicators of soil health have rarely been examined in urban basins of this kind, leaving a gap between chemical monitoring and the living condition of the soil itself.

The chemical results confirmed the severity of the problem and revealed a clear spatial pattern. The highest concentrations of heavy metal(loid)s were detected in the lower basin, the section closest to the Rio de la Plata, which receives a continuous influx of pollutants and endures intense anthropogenic pressure. The degree of contamination, expressed as a mean value across sampled sites, reached 44.55 in the lower basin, a figure that underscores how far this stretch of urban soil has drifted from any reference condition. By contrast, sites in the upper and middle basin, though still disturbed, carried lighter contaminant loads, allowing the researchers to evaluate how the fungal community responded along this gradient of toxicity.

What the fungi revealed was striking. Across all sampled sites, the family Glomeraceae dominated the arbuscular mycorrhizal community, accounting for 54.55 percent of the species recorded. Among the sixteen species of arbuscular mycorrhizal fungi described so far for the entire basin, eight appear here for the first time, making the survey a significant expansion of documented fungal diversity for the region. Only one species, Rhizoglomus intraradices, was detected at every sampled site, a finding that marks it as a remarkably tolerant generalist capable of persisting even in the most contaminated soils of the lower basin. The pattern echoes observations from other polluted environments worldwide, where a small set of hardy fungal generalists dominates while more sensitive species disappear.

The two candidate bioindicators behaved in opposite but complementary directions. Glomalin-related soil protein concentrations increased with soil toxicity, and the differences in protein levels were specifically associated with the lower basin and with elevated concentrations of copper and chromium. Glomalin is a glycoprotein produced on the walls of arbuscular mycorrhizal fungal hyphae, and it is known to bind metal ions and to help glue soil particles into stable aggregates. Its accumulation in the most toxic soils likely reflects both a stress response by the fungi and the sequestration of metals onto the protein itself, a mechanism documented in earlier laboratory and field studies of copper smelter sites, mangrove wetlands, and cadmium-contaminated fields.

Species richness, by contrast, moved in the opposite direction. The number of arbuscular mycorrhizal fungal species decreased as soil disturbance and contamination intensified, meaning that the most damaged sites hosted the simplest fungal communities. This loss of diversity matters because diverse mycorrhizal communities underpin resilient ecosystems, supporting plant nutrition, soil structure, and nutrient cycling. A community reduced to a handful of tolerant species may still function, but it represents a soil whose biological buffer capacity has been eroded. Together, the two measures form a paired signal: rising glomalin flags mounting metal stress, while shrinking species richness flags the loss of biological integrity.

The study also examined the mycorrhizal status of the plants themselves, asking which species growing across the basin were actually forming arbuscular mycorrhizal symbioses. This plant-level information complements the spore-based survey, since the presence of colonized roots confirms that the fungi found in the soil are actively engaged with the vegetation rather than merely persisting as dormant propagules. Riparian plants in the basin have been the focus of earlier restoration research, including work exploring lotus and other native species in symbiosis with mycorrhizal fungi as tools for rehabilitating degraded riverbanks, and the new findings give those efforts a diagnostic framework rooted in measurable soil biology.

The practical implications extend well beyond Buenos Aires. Chemical analyses of heavy metals are expensive and tell only part of the story, since they reveal what is present but not how the living soil is responding. A biological indicator that can be measured from a soil sample, such as a glomalin protein assay or a spore-based diversity count, offers regulators and restoration practitioners a way to track whether remediation efforts are actually restoring ecological function. The authors suggest that the variables they studied could serve as reliable biological indicators of soil health in future studies, and the paired directionality they observed, with one measure increasing and the other decreasing along the contamination gradient, is precisely the kind of sensitivity that makes a bioindicator useful.

There are, of course, caveats. The study relied on spore morphology to identify fungal species, a classical method that can underestimate diversity compared with DNA sequencing, and glomalin-related soil protein measurements capture a pool of related compounds rather than a single molecule. Seasonal variation, plant community composition, and soil physical properties such as pH and electrical conductivity are also known to shape mycorrhizal communities and would need to be accounted for in any long-term monitoring program. Nevertheless, the work represents the first systematic attempt to link arbuscular mycorrhizal variables to the contamination gradient of the Matanza-Riachuelo basin, and it adds a new chapter to the growing recognition that the smallest inhabitants of urban soils may be its most honest witnesses. In a basin where the damage has been measured in tons of discharged metal for generations, the fungi offer something chemical tests cannot: a living record of how much the soil has suffered, and a benchmark for how far it still has to recover.

Subject of Research: Arbuscular mycorrhizal fungi as bioindicators of heavy metal contamination and soil health in an urban river basin

Article Title: Sensitivity variations on soil health indicators related to arbuscular mycorrhizae in a highly disturbed urban basin of Buenos Aires, Argentina

Article References: Guerra Moreno, M., Silvani, V. A., Godeas, A. M., & Colombo, R. P. (2026). Sensitivity variations on soil health indicators related to arbuscular mycorrhizae in a highly disturbed urban basin of Buenos Aires, Argentina. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38298-3

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38298-3

Keywords: arbuscular mycorrhizal fungi, soil health, heavy metals, glomalin, bioindicators, Matanza-Riachuelo basin, urban pollution, Glomeraceae, Rhizoglomus intraradices, soil microbiology, Buenos Aires, environmental monitoring