Gupta and Arunachalam 2024 — Heavy metals in Tilapia from the Cauvery River, Tamil Nadu, India
This study measured eight heavy metals (Cr, Cd, Fe, Ni, Zn, Co, Pb, Cu) in muscle, liver, and gills of 16 Tilapia fish (Oreochromis mossambicus) from four sites along the Cauvery River near Erode, Tamil Nadu, India, using Atomic Absorption Spectroscopy (AAS), and assessed human health risks via pollution indices (PI), estimated daily intake (EDI), and target hazard quotient (THQ). Cadmium, chromium, and lead in liver and gills greatly exceeded permissible limits, with Cd and Cr cancer risks above the USEPA 10⁻⁵ acceptable threshold, and THQ values above 1 for Cd, Co, Pb, and Cr in liver and for Co and Cr in gills. Muscle tissue showed more modest contamination; the main public health concern is consumption of whole fish including offal from heavily industrially impacted river sections.
Key numbers
Pollution Index (PI) — muscle (4 sites R1–R4):
- Cd PI: 8.22–12.42 (8–12x permissible limit)
- Pb PI: 5.19–7.05
- Cr PI: 21.01–24.44
- Ni PI: 50.64–62.74
- Fe PI: 225.93–261.51 (extremely high, likely industrial discharge)
- Co PI: 65.82–85.77
Pollution Index (PI) — liver:
- Cd PI: 34.35–62.05
- Pb PI: 25.82–38.64
- Cr PI: 69.79–162.69
- Ni PI: 192.62–334.25
Pollution Index (PI) — gills:
- Cd PI: 12.00–22.05
- Pb PI: 7.44–12.69
- Cr PI: 20.27–72.00
Estimated Daily Intake (EDI) — muscle (mg/kg bw/day, adults, 25.2 g fish/day):
- Cd: 0.0006–0.0009 (reference RfD 0.001 mg/kg bw/day; near threshold)
- Pb: 0.0008–0.0011 (reference RfD 0.004 mg/kg bw/day; below threshold)
- Cr: 0.0016–0.0018 (reference RfD 0.003 mg/kg bw/day; above threshold)
THQ >1 findings (adult, muscle consumption):
- Co: THQ >1 in muscle — non-negligible non-carcinogenic risk
- Cd, Co, Pb, Cr: all THQ >1 in liver
- Co, Cr: THQ >1 in gills
Cancer risk (Cr and Cd, all organs):
- Both Cd and Cr cancer risks exceed USEPA acceptable limit of 10⁻⁵ in muscle, liver, and gills
- Pb cancer risk within tolerable level
Concentrations (raw, mg/kg dry weight): The paper reports PI ratios against permissible limits rather than presenting absolute concentration tables as the primary reporting format; EDI values at n=16, four sites combined, dry weight basis.
Methods (brief)
AAS (Varian AA240) measuring Cr, Cd, Fe, Ni, Zn, Co, Pb, Cu in dry-weight homogenates of muscle, liver, and gills after acid digestion with HNO3/H2SO4 followed by H2O2 clarification. No arsenic or mercury measured. Conversion factor of 0.208 dry-to-wet weight applied for EDI. Pre-monsoon sampling only; n=16 fish total from 4 sites. Limitations: small sample size; single season; Cr measured as total Cr (not speciated for Cr-VI, despite Cr cancer risk being based on Cr-VI carcinogenicity). Cancer risk calculation for Cr and Pb used USEPA CSF values; applying hexavalent Cr’s CSF to total Cr concentrations likely overstates risk.
Implications
Certification: Freshwater fish from industrially impacted Indian rivers show systematic multi-metal contamination at levels well above food safety thresholds; Cd and Cr in liver exceed EU limits by 34–162x (PI). Muscle concentrations are lower but still above several permissible limits. This is relevant to supply-chain geography flags for freshwater fish-derived ingredients (e.g., tilapia protein) sourced from India.
Courses: The liver/muscle contrast illustrates the tissue-accumulation pattern: offal (liver) concentrates heavy metals 3–10x higher than muscle — directly relevant to discussions of whole-food vs. muscle-protein risk. The Cr cancer risk calculation caveat (total Cr vs. Cr-VI) is a methodological teaching point: total Cr measurements cannot be used directly with Cr-VI cancer slope factors.
App: Freshwater fish matrix from industrial-river catchments in India flags as high-risk for Cd, Cr, Ni, and Pb. The paper does not report arsenic or mercury; those remain data gaps for this specific matrix and source geography.