The research team, led by Alex da Silva de Freitas of the Universidade Federal Fluminense, set out to test a deceptively simple hypothesis: that rising human activity in the watershed would change both the identity and the concentration of contaminants settling into the lagoon’s sediments between the two sampling campaigns. To do this, they collected surface sediments from the top five centimeters at seven fixed stations during the dry seasons of 2021 and 2023, using a Van Veen grab sampler. Fixing the sampling locations across both years allowed direct comparisons in space and time, a design that many contaminant surveys lack.

The analytical strategy combined two complementary approaches. First, the team extracted contaminants from freeze-dried sediment using methanol, concentrated the extracts by solid-phase extraction, and identified and quantified the target compounds by gas chromatography–mass spectrometry after chemical derivatization to boost volatility and stability. Second, they assessed the biological punch of the extracts using the yeast estrogen screen, a bioassay in which a genetically engineered strain of Saccharomyces cerevisiae carries the human estrogen receptor wired to a reporter system. When estrogenic compounds activate the receptor, the yeast produces an enzyme that turns a colorless substrate red, allowing researchers to express the total estrogenic effect of a sample as 17β-estradiol equivalents.

The chemistry told a clear story. Nine of twelve target compounds were detected across the two campaigns. Bisphenol A, the plasticizer found in polycarbonate plastics and epoxy resins, was the most ubiquitous, appearing in nearly every sample at concentrations ranging from 0.10 to 0.99 nanograms per gram of sediment, with a marked increase between 2021 and 2023. The alkylphenols 4-octylphenol and 4-nonylphenol, byproducts of industrial surfactant degradation, ranged from 0.010 to 0.390 and 0.033 to 0.344 nanograms per gram respectively, signaling sustained or growing inputs. Steroid estrogens and pharmaceuticals showed patchier distributions, with estrone detected at a couple of stations and the lipid-lowering drug gemfibrozil, the painkiller diclofenac, and naproxen appearing in the 2023 campaign.

One station stood out dramatically. Site M7, sampled in 2023, contained nine of the twelve monitored compounds, including the full suite of steroid hormones: estrone, 17β-estradiol, the synthetic contraceptive estrogen ethinylestradiol, and estriol, alongside pharmaceuticals and alkylphenols. The researchers identify M7 as a localized hotspot of mixed contamination, most likely fed by urban wastewater inputs. The presence of ethinylestradiol is particularly notable because this synthetic estrogen, used in oral contraceptives, is among the most potent endocrine disruptors known, exhibiting greater estrogenic activity and toxicity than its natural counterparts even at vanishingly low concentrations.

The biological results, however, were more enigmatic. Estrogenic activity, ranging from 0.01 to 0.18 nanograms of estradiol equivalents per gram, was detected only in samples from station M4 in 2021 and M5 in 2023. Strikingly, the sample that contained both 17β-estradiol and ethinylestradiol showed no measurable estrogenic response in the yeast assay. Even more puzzling, one sample from station M5 in 2021 proved so cytotoxic that yeast cell viability collapsed to just five percent, effectively masking any estrogenic signal that might have been present. This mismatch between chemical detection and biological response is not a failure of the study but a window into the messy reality of environmental toxicology.

The authors attribute these discrepancies to several interacting factors. Compounds bound tightly to sediment organic matter may simply not be bioavailable to the yeast cells, limiting receptor access. Complex environmental mixtures can contain antagonistic substances that suppress estrogen receptor activation or interfere with downstream gene expression, producing non-additive effects that no single-compound analysis would predict. And co-extracted matrix components can inhibit yeast growth outright, as the dramatic cytotoxicity at M5 demonstrated. The lesson, the researchers argue, is that chemical presence alone does not translate into measurable biological activity, and neither chemistry nor bioassays alone can capture the full picture. Only by integrating targeted chemical analysis with effect-based screening can scientists realistically assess the risk posed by contaminant mixtures in sediments.

Sediment texture, surprisingly, offered little explanatory power. Although fine-grained sediments are typically expected to soak up hydrophobic contaminants, micropollutants turned up across samples with widely differing particle-size characteristics, and silt content shifted by more than twenty percentage points at some stations between the two years. Instead, the researchers point to hydrodynamics as the dominant force shaping contaminant distribution. Maricá Lagoon is shallow, averaging just one to two meters deep, and wind-driven waves approaching one meter in height regularly resuspend sediments and redistribute particle-bound pollutants. Silting of the Ponta Negra and Cordeirinho channels restricts tidal exchange with the ocean, lengthening water residence times and favoring the retention of both nutrients and contaminants. Inflows from the Mumbuca River and the Inoã Channel, both conduits for anthropogenic inputs, likely shuttle contaminants across the system and help create localized accumulation zones.

The temporal comparison between 2021 and 2023 reveals a system that is dynamic yet stubbornly contaminated. Compounds like bisphenol A, the alkylphenols, and diclofenac appeared in both campaigns, pointing to continuous inputs and long-term stability in the sedimentary archive rather than one-off pollution events. Meanwhile, the appearance of gemfibrozil and naproxen only in 2023 suggests shifting emission patterns or changing transport and deposition conditions. The persistence of endocrine-active compounds across both years indicates that the lagoon shows little sign of recovery, even as the exact mixture of chemicals continues to evolve with the watershed’s growing population, sand extraction, clay mining, livestock farming, and notoriously limited sewage treatment. According to Brazil’s National Sanitation Information System, only about 55 percent of the population has access to sewage treatment, a gap that is especially acute in the Rio de Janeiro metropolitan region.

Why should anyone beyond Rio de Janeiro care about nanogram-scale contamination in a shallow lagoon? Because sediments act as both sinks and secondary sources. Contaminants that settle into the mud can persist for years, then be remobilized by resuspension and taken up by benthic organisms, entering food webs where chronic exposure to even trace-level mixtures can impair reproduction, development, and physiology in fish and invertebrates. This study also marks the first report of pharmaceutical residues in Maricá Lagoon sediments, establishing a baseline for long-term monitoring. The broader message resonates far beyond Brazil: as urbanization accelerates around tropical coastlines worldwide, restricted-exchange lagoons are quietly archiving our pharmaceutical and industrial footprints. Detecting those archives, and understanding when they translate into real biological harm, will require exactly the kind of dual chemical-plus-bioassay approach this study champions, applied repeatedly over time in the places where people and water most intimately intersect.

Subject of Research: Temporal occurrence of emerging contaminants and estrogenic activity in sediments of a tropical coastal lagoon in Brazil

Article Title: Temporal variability of emerging contaminants and estrogenic activity in sediments of a tropical coastal lagoon

Article References: da Silva de Freitas, A., de Oliveira Santos, A. D., Sanson, A. L., Ferreira dos Santos, R., Teresa Lima do Nascimento, M., Gomes, G., dos Santos Argolo, A., da Cruz Félix, L., Bila, D. M., & Baptista Neto, J. A. (2026). Temporal variability of emerging contaminants and estrogenic activity in sediments of a tropical coastal lagoon. Environmental Monitoring and Assessment, 198(10), Article 1073. https://doi.org/10.1007/s10661-026-15919-5

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15919-5

Keywords: emerging contaminants, endocrine disruptors, bisphenol A, alkylphenols, steroid estrogens, pharmaceuticals, yeast estrogen screen, GC-MS, sediment contamination, coastal lagoon, Maricá Lagoon, Brazil