Microplastics and Toxic Metals Build Up in Edible Fish From an Indian Urban Lake, Study Finds

In the sprawling city of Thiruvananthapuram in the southern Indian state of Kerala, the Veli-Akkulam lake has long absorbed the runoff of urban life, from household wastewater to storm-borne debris. A new study published in the journal Environmental Monitoring and Assessment now offers the most detailed picture yet of what that contamination means for the fish that live there and the people who eat them. Researchers led by Adithya S. Suresh of the University of Kerala examined the edible muscle tissue of Nile tilapia, Oreochromis niloticus, one of the most widely farmed and consumed freshwater fish in the region, and found both microplastics and a suite of trace metals lodged in the flesh that ends up on local plates.

The investigation is described by its authors as the first of its kind for this urban coastal lake, a waterbody that has undergone intense urbanization along its banks. Fish are widely used as bio-indicators of environmental health because they accumulate contaminants in their tissues over time, providing an integrated record of pollution that water sampling alone cannot capture. By focusing on muscle tissue, the specific portion consumed by humans, the team aimed to connect environmental degradation directly to food safety, rather than treating the two as separate concerns.

The sampling design was deliberately rigorous. Fish were collected from five stations across the lake during three distinct seasons, allowing the researchers to track how contamination shifts both in space and through the year. Forty-five individual fish provided baseline measurements of malondialdehyde, a chemical marker of oxidative stress, while a coupled subset of thirty fish was analyzed in parallel for both trace metals and microplastics. Individual measurements were then aggregated into fifteen independent spatio-temporal groups for statistical analysis using Pearson correlation and multiple linear regression, a modeling approach that allowed the team to test which class of contaminant best explained the biochemical damage observed in the fish.

The microplastic findings were striking in their ubiquity. Every indication from the macro-level modeling pointed to widespread accumulation of plastic particles in the edible tissue, with blue fibers dominating the assemblage. Fibers of this kind typically originate from synthetic textiles, fishing lines, and laundry wastewater, and their prevalence in an urban lake is consistent with patterns reported in freshwater systems worldwide. When the researchers characterized the polymer types, they identified polycarbonate, a hard plastic used in electronics, eyewear lenses, and construction materials, and classified it under a Category IV hazard ranking, a scheme that grades polymers by the toxicity of their chemical composition.

Trace metal analysis told an equally concerning story. Of the ten metals measured, including mercury, iron, zinc, lead, chromium, copper, manganese, cobalt, nickel, and cadmium, two stood out for repeatedly breaching international safety thresholds. Concentrations of manganese and chromium in the edible tissue consistently exceeded the limits set by the Food and Agriculture Organization and the World Health Organization, which cap manganese at 1 milligram per kilogram and chromium at 0.05 milligrams per kilogram. Chromium, in particular, is a metal of concern because certain oxidation states are recognized carcinogens, and its persistent presence above guideline values in a food fish raises questions about long-term dietary exposure for communities that rely on the lake.

Perhaps the most scientifically consequential result came from the regression modeling, which pitted the two contaminant classes against each other as predictors of cellular damage. The team measured malondialdehyde, the end product of lipid peroxidation, as a proxy for oxidative stress, the imbalance that arises when reactive molecules overwhelm a cell’s antioxidant defenses. Levels of the marker reached 0.54 plus or minus 0.041 micromoles per milligram of tissue. The multiple linear regression revealed that trace metal accumulation, rather than the mere presence of microplastics, showed the stronger statistical coupling with elevated malondialdehyde. In other words, while the plastics were everywhere, it was the metals that tracked most closely with the biochemical signature of stress in the fish muscle.

This finding does not exonerate microplastics, and the researchers are careful not to frame it that way. Laboratory studies have repeatedly shown that plastic particles can induce inflammation, alter antioxidant enzyme activity, and damage tissue in Nile tilapia and related species. Moreover, microplastics are known to interact with trace metals in aquatic environments, sometimes acting as carriers that concentrate metals on their surfaces and transport them into organisms. But the present results suggest that, in this particular lake, the direct chemical burden of metals is the dominant driver of oxidative damage in the tissue that humans consume, a nuance with real implications for how monitoring programs prioritize their targets.

To translate the fish tissue data into human health terms, the team applied standard exposure models that estimate daily intake and compare it against toxicological reference values. The resulting Hazard Index, which sums the risks posed by multiple contaminants, remained safely below the threshold value of 1, indicating that, on average, consuming the fish does not currently pose an unacceptable non-cancer health risk. However, the analysis also revealed pronounced seasonal variation in the dietary risk parameters, meaning that the same meal carries different levels of exposure depending on the time of year it is caught.

The seasonal pattern took on sharper significance when the researchers calculated target cancer risk for chromium and nickel, two metals with established carcinogenic potential. Both pointed to elevated risks during the monsoon season, when heavy rains scour urban surfaces and flush accumulated pollutants into the lake, likely raising the contaminant loads available to fish. This monsoon-driven spike underscores a central message of the study: pollution risk in urban tropical waterbodies is not static, and monitoring regimes that sample only once a year may miss the periods when exposure to consumers is at its worst. The authors argue that localized, seasonally informed pollution monitoring is essential for protecting public health around such lakes.

The broader context makes the findings resonate well beyond a single Kerala waterbody. Urban lakes across South Asia and in rapidly growing cities worldwide face similar pressures, combining untreated wastewater, plastic debris, and industrial or vehicular metal inputs. Tilapia, being hardy and tolerant of degraded water, often thrives in exactly these environments, creating a direct pathway from pollution to the dinner table. The Veli-Akkulam study demonstrates a workable template for assessing that pathway, coupling contaminant chemistry with a biomarker of biological harm and formal risk modeling. It also delivers a sobering takeaway for consumers and regulators alike: the visible plastic problem in urban waters may be only part of the story, and the invisible metal burden flowing through the food web deserves equal, if not greater, attention.

Subject of Research: Bioaccumulation of microplastics and trace metals in Nile tilapia and associated human health risks in an urban Indian coastal lake

Article Title: Bioaccumulation trends of microplastics and trace metals in Oreochromis niloticus: A health risk assessment in an urban coastal lake, India

Article References: Suresh, A. S., S., J. D., E., S. W., Prasad, V., S., A. P., & Krishnan, A. (2026). Bioaccumulation trends of microplastics and trace metals in Oreochromis niloticus: A health risk assessment in an urban coastal lake, India. Environmental Monitoring and Assessment, 198(10), Article 1124. https://doi.org/10.1007/s10661-026-15930-w

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15930-w

Keywords: microplastics, trace metals, Oreochromis niloticus, Nile tilapia, bioaccumulation, oxidative stress, malondialdehyde, Veli-Akkulam lake, food safety, health risk assessment, urban pollution, Kerala