The study, published in Environmental Monitoring and Assessment, arrives at a moment when the legacy of the 2019 spill remains uncertain. Tar balls chemically linked to that disaster continued to reach Brazilian beaches years afterward, echoing the pattern seen after the Prestige spill off Spain, where polycyclic aromatic hydrocarbons persisted in coastal ecosystems long after the acute emergency ended. PAHs are among the most worrying compounds released in oil spills because they are persistent, they bioaccumulate in fatty tissues, and several members of the family carry mutagenic and carcinogenic potential. Humans encounter them continuously through airborne particles, polluted water, and contaminated food, which makes reliable monitoring of seafood a genuine public health concern rather than an abstract environmental exercise.

Guanabara Bay is arguably the most challenging possible proving ground for such a method. The estuary, the second-largest bay on the Brazilian coast at roughly 384 square kilometers, is ringed by a metropolitan region of more than 16 million people and hosts a dense concentration of petrochemical infrastructure, including refineries and oil-storage terminals in its northwestern sector. Its sediments carry PAH burdens reflecting both chronic petrogenic inputs from oil handling and pyrogenic inputs from urban and vehicular combustion. Yet the bay also sustains artisanal mussel fisheries that provide an important protein source for local communities, creating an urgent need for affordable, routine contamination surveillance in exactly the kind of resource-limited setting where sophisticated analytical infrastructure is often unavailable.

Mussels are ideal sentinels for this task. As filter feeders, they ingest contaminants suspended in the water column and accumulate lipophilic pollutants in their tissues, and they tolerate a broad range of environmental conditions. Their track record in Guanabara Bay is well documented: after a fuel oil spill in 2000, PAH burdens in mussels collected from the pillars of the Rio-Niterói Bridge rose two to fivefold, tracking changes in the surrounding water closely. But extracting PAHs from lipid- and protein-rich mussel tissue has always been analytically awkward. Conventional approaches such as matrix solid-phase dispersion, accelerated solvent extraction with gel-permeation clean-up, or supercritical fluid extraction work, but they demand expensive equipment, large volumes of hazardous solvent, and considerable time per sample.

The new method borrows a trick from food safety chemistry. The QuEChERS approach, whose name stands for Quick, Easy, Cheap, Effective, Rugged and Safe, was originally devised in 2003 for extracting pesticide residues from produce. It relies on simple salting-out chemistry: homogenized tissue is vortexed with a mixture of acetonitrile and dichloromethane, then magnesium sulfate and sodium chloride are added to drive analytes into the organic layer. The researchers adapted this for mussel tissue and added a solid-phase extraction clean-up step using Florisil, silica gel, and alumina columns to strip out co-extracted lipids before instrumental analysis. The combination proved remarkably effective at minimizing the matrix interference that normally plagues PAH analysis in fatty biological samples.

The analytical team collected 210 mussels from four artisanal fishing communities around the bay, including Itaipu, Copacabana, Barra da Tijuca, and Recreio dos Bandeirantes, across four seasonal campaigns between September 2021 and June 2022, roughly two to three years after the spill. Each pooled sample of about twenty individuals was homogenized and analyzed in triplicate. The validated method achieved strong linearity, with coefficients of determination exceeding 0.995 for most compounds, and acceptable recoveries between 51.1 and 109.0 percent for 15 of the 18 target PAHs. Detection limits ranged from 0.009 nanograms per gram for naphthalene to just over one nanogram per gram for the most problematic analytes, figures comparable to those reported for far more expensive tandem mass spectrometry setups.

Not every target compound cooperated. Benzo(j)fluoranthene and benzo(k)fluoranthene share an identical retention time of 40.944 minutes on the DB-5MS capillary column used, a documented limitation of five-percent phenyl methylpolysiloxane phases that even laboratories running triple quadrupole instruments encounter. Both isomers were excluded from quantitative interpretation, a decision the authors note does not disadvantage the dataset because regulatory indices such as the EFSA-endorsed PAH4 already omit benzo(j)fluoranthene. Indeno(1,2,3-cd)pyrene yielded no quantifiable signal at any fortification level and was likewise excluded. Benzo(a)pyrene, the single most notorious carcinogenic PAH, showed precision marginally above the 20 percent threshold but was retained for reporting given its environmental significance. This transparent accounting of limitations, the researchers argue, is what makes the method genuinely useful for future monitoring programs.

The environmental findings were as instructive as the analytical ones. Only five PAHs were quantified above the limit of quantification across all 210 samples: naphthalene, phenanthrene, 5-methylchrysene, benzo(a)anthracene, and benzo(a)pyrene. Concentrations were low and statistically homogeneous across sites and seasons, with benzo(a)pyrene reaching the highest mean at just 0.308 nanograms per gram, far below the European Union maximum of 5 nanograms per gram for bivalve molluscs. Crucially, the compositional pattern told a story: the total PAH burden of 4.27 nanograms per gram was dominated almost entirely by high-molecular-weight, combustion-derived compounds rather than the light petrogenic compounds, such as naphthalene and phenanthrene, that would signal lingering petroleum from the spill. The contamination signature points instead to diffuse, continuous pyrogenic inputs from vehicle emissions, industrial combustion, and atmospheric deposition.

That counterintuitive result carries a sobering implication. Benzo(a)pyrene is classified by the International Agency for Research on Cancer as a Group 1 confirmed human carcinogen, acting through reactive diol-epoxide metabolites that form covalent DNA adducts, while benzo(a)anthracene and 5-methylchrysene are Group 2B possible carcinogens. None of these genotoxic compounds has a recognized safe exposure threshold, and mussels remain a staple protein for the fishing communities surrounding the bay. The authors caution that without pre-spill baseline data or an uncontaminated reference site, low burdens cannot be read as recovery from the 2019 disaster, nor can the spill be disentangled from chronic urban-industrial pollution. What the study does establish is that the threat to these communities comes less from dramatic spill events than from the quiet, ceaseless combustion chemistry of a megacity.

The broader significance of the work lies in accessibility. Compared with pressurized solvent extraction, QuEChERS-based workflows have been shown to cut per-sample costs roughly fivefold while increasing throughput tenfold, and other studies report cost reductions approaching 97 percent relative to Soxhlet extraction. Because the new method uses matrix-matched calibration rather than costly isotope-dilution standards and relies on a single quadrupole mass spectrometer, it can be adopted by laboratories that could never afford tandem instrumentation. For oil-impacted tropical estuaries worldwide, from Jakarta Bay to the Gulf of Guinea, the message is that meaningful PAH biomonitoring no longer requires a flagship budget, only mussels, modest solvents, and a well-validated protocol.

Subject of Research: Development and validation of a QuEChERS-SPE-GC-MS method for PAH biomonitoring in Perna perna mussels from an oil-impacted tropical estuary

Article Title: Development of a short and sensitive QuEChERS-SPE-GC-MS method for polycyclic aromatic hydrocarbon (PAH) biomonitoring in Perna perna (Linnaeus, 1758) mussels from an oil-impacted tropical estuary

Article References: de Pinho, J. V., Tessaro, L., Silva Melo, P. T., de Andrade, J. C., Celano, M. R., de Almeida Rodrigues, P., Castro Cardoso de Almeida, A. E., Hauser-Davis, R. A., & Conte-Junior, C. A. (2026). Development of a short and sensitive QuEChERS-SPE-GC-MS method for polycyclic aromatic hydrocarbon (PAH) biomonitoring in Perna perna (Linnaeus, 1758) mussels from an oil-impacted tropical estuary. Environmental Monitoring and Assessment, 198(11), Article 1184. https://doi.org/10.1007/s10661-026-15980-0

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15980-0

Keywords: polycyclic aromatic hydrocarbons, QuEChERS, GC-MS, Perna perna, Guanabara Bay, biomonitoring, oil spill, mussels, benzo(a)pyrene, pyrogenic contamination, solid-phase extraction, environmental monitoring

The story begins with biofouling, the relentless settlement of organisms on any submerged surface. On commercial vessels, fouling can increase fuel consumption by up to 40 percent, accelerate hull corrosion, and hitchhike invasive species across the globe along shipping routes. To fight it, the shipping industry turned to antifouling paints, first based on copper and zinc oxides, then on organotin compounds such as tributyltin. TBT was devastatingly effective but also devastatingly toxic, inducing imposex in gastropods and wreaking hormonal havoc in ship traffic zones, which led the International Maritime Organization to ban it. The replacements, a new generation of so-called booster biocides including Irgarol, Diuron, DCOIT, chlorothalonil, and dichlofluanid, were assumed to be safer. Whether that assumption holds for tropical ecosystems has remained largely untested.

Dichlofluanid, formally N-dichlorofluoromethythio-N′,N′-dimethyl-N-phenylsulfamide, is a non-metallic organochlorine compound with low water solubility and a strong tendency to associate with particles, reflected in its octanol-water partition coefficient of 3.7. It is also used as a fungicide and has previously been linked to mutagenic and carcinogenic effects in non-target marine invertebrates. Because it degrades rapidly in water, with a half-life of just a few hours and by-products including DMSA and dichloromethane aniline, organisms in ports and marinas are exposed to a shifting cocktail of the parent compound and its transformation products. Yet toxicity data for tropical species, which may be more sensitive to contaminants than their temperate counterparts, have been scarce.

To fill that gap, a team led by Ana Carolina Feitosa Cruz of São Paulo State University designed a two-pronged experiment. In the water-based arm, brown mussels Perna perna, a classic sentinel species sourced from an aquaculture farm at Cocanha Beach, were exposed for 96 hours to five nominal dichlofluanid concentrations ranging from 0.01 to 100 micrograms per liter, a span that brackets measured environmental levels of up to 3.37 micrograms per liter in seawater. Solutions were renewed every 24 hours to mimic the dynamic exposure that rapid degradation creates in nature. In the sediment arm, clams Anomalocardia flexuosa, collected from the Cananéia region, spent 21 days in sediments spiked with 1 to 10,000 nanograms per gram of the biocide. Crucially, the researchers used two sediment types from the protected Cananéia-Iguape Peruíbe Estuarine Complex: one with roughly 4 percent organic matter and another with about 10 percent, to test whether organic carbon changes the story.

The team then read the animals’ biochemical diaries through a battery of biomarkers. In mussels, the neutral red retention time assay revealed that hemocyte lysosomes, the cellular recycling centers whose membrane stability is a frontline indicator of chemical stress, lost integrity at 10 and 100 micrograms per liter after 96 hours. Retention times fell from 97.5 minutes in the acetone control to 33 and 15 minutes respectively, a dose-dependent collapse of lysosomal stability. Notably, the authors point out that TBT produced cytotoxicity in the mussel Mytilus edulis at concentrations above 0.5 micrograms per liter, suggesting dichlofluanid is less acutely cytotoxic than its banned predecessor, though still far from benign.

The biochemical picture in mussels was one of a defense system working overtime. Glutathione S-transferase activity rose in the digestive glands at the highest concentrations, while gills responded with elevated glutathione levels and glutathione peroxidase activity. This makes mechanistic sense: dichlofluanid’s primary mode of action involves reactions with cellular thiols, and glutathione is precisely the sulfhydryl-containing molecule the compound attacks. The pro-oxidant properties of the biocide and its metabolite DMSA can imbalance the glutathione pool and generate reactive oxygen species, which enzymes like GPx then scramble to neutralize. Lipid peroxidation in digestive glands actually dropped below control levels, and no DNA damage or neurotoxicity appeared, suggesting the antioxidant machinery largely kept oxidative damage in check. Principal component analysis, which explained nearly 65 percent of the variance, cleanly separated animals exposed above 0.1 micrograms per liter from controls, indicating a metabolic shift beginning at concentrations well within the environmental range.

The clam results were more alarming, and they overturned the researchers’ initial hypothesis. The team had expected organic matter to bind dichlofluanid and reduce its bioavailability, softening the blow to burrowing bivalves. Instead, clams in the organically richer Ariri sediment fared distinctly worse. In their gills, high-organic sediment triggered increased GST and EROD activities at the top concentration, depleted GSH, and elevated GPx and acetylcholinesterase activities at 100, 1,000, and 10,000 nanograms per gram, alongside lipid peroxidation at concentrations as low as 1 and 10 nanograms per gram. Digestive glands showed enhanced GST at intermediate concentrations, increased EROD and lipid peroxidation at 10,000 nanograms per gram, and DNA damage at just 10 nanograms per gram. In low-organic sediment, most biomarkers barely moved. The pattern suggests that dichlofluanid adsorbed onto organic particles is effectively delivered to filter- and deposit-feeding clams through ingestion, turning the sediment itself into a contamination route.

The integrated biomarker sequence in clams tells a coherent toxicological story: phase I biotransformation via EROD, conjugation via GST, consumption of glutathione, and then, when the antioxidant system proves insufficient, lipid peroxidation and DNA damage. Signs of neurotoxicity also emerged, with altered acetylcholinesterase activity in both tissues, an enzyme whose induction has been linked to cellular apoptosis. These findings echo earlier work in rat hepatocytes, where dichlofluanid induced lipid peroxidation and cytotoxicity above 25 micromolar, and in ascidians, where hemocytes showed apoptosis, shrinkage, and reduced phagocytic activity at 3.33 to 33.3 micrograms per liter. The authors caution that dichlofluanid’s rapid degradation, quantified at 87 percent within six hours at the 1,000 nanograms per gram level, complicates dose-response interpretation, since animals may have experienced transient exposure to the parent compound alongside potentially toxic transformation products.

The bottom line is a regulatory headache. Effects in mussels appeared from 0.1 micrograms per liter in water, comfortably below the maximum measured environmental concentration of 3.37 micrograms per liter, while clam effects began at 1 nanogram per gram in sediment, near the reported environmental maximum of 0.8 micrograms per gram. In scenarios of localized contamination near ports, marinas, and shipyards, ecological risk appears likely, and the authors argue that regulatory action is needed. More broadly, the study demonstrates that the organic content of sediments, a factor often overlooked in toxicity assessments, can amplify exposure to hydrophobic antifouling biocides, just as it does for diuron and TBT. As the shipping industry continues to rely on booster biocides to keep hulls clean, this research delivers a clear early warning: the chemicals replacing TBT are not harmless, and the tropical benthic ecosystems they drift into are paying attention.

Subject of Research: Ecotoxicological effects of the antifouling biocide dichlofluanid on tropical marine bivalves

Article Title: Effects of dichlofluanid in tropical marine bivalves exposed to water and spiked sediments: an assessment of biomarker responses

Article References: Cruz, A. C. F., Gusso-Choueri, P. K., Pauly, G. D. F. E., de Campos, B. G., Perina, F. C., de Castro, Í. B., & de Souza Abessa, D. M. (2026). Effects of dichlofluanid in tropical marine bivalves exposed to water and spiked sediments: an assessment of biomarker responses. Ecotoxicology, 35(8), Article 180. https://doi.org/10.1007/s10646-026-03164-y

Image Credits: AI Generated

DOI: 10.1007/s10646-026-03164-y

Keywords: dichlofluanid, antifouling biocides, marine bivalves, biomarkers, ecotoxicology, Perna perna, Anomalocardia flexuosa, sediment contamination, organic matter, oxidative stress, tropical marine ecosystems, lysosomal stability