Alam et al. 2023 — Heavy metals in dairy cattle fodder from urbanised lake shores, Bengaluru
This study combined a structured interview survey of 151 dairy farmers in the Greater Bengaluru metropolitan area with chemical analysis of 92 lake-shore forage samples (alligator weed, Bermuda grass, para grass, water hyacinth, and mixed grasses) and 5 food-leftover samples fed to dairy cattle. The key finding is that 43% of the 97 analysed samples exceeded official threshold concentrations for at least one of four heavy metals (As, Cd, Cr, Pb), with Cr exceedance rates being particularly high: 92% of lake-fodder samples exceeded the WHO threshold of 1.30 mg/kg DM. The paper is primarily a veterinary and animal health study; direct relevance to the human food chain rests on the chain from contaminated fodder to cattle health to milk quality, which the authors explicitly identify as unknown and requiring follow-up. Evidence tier B is assigned because the journal is veterinary/animal science, not a food-safety analytical journal, and the human food-chain link is indirect and unquantified.
Key numbers
Heavy metal concentrations in lake fodder (n=92) and food leftovers (n=5), mg/kg DM:
| Metal | Detection rate (%) | % above EU/WHO threshold | Lake fodder mean ± SD | Lake fodder median | Food leftovers mean ± SD | EU/WHO threshold (mg/kg DM) |
|---|---|---|---|---|---|---|
| As | 55 | 43 | 2.54 ± 1.71 | 1.92 | ND | 2.00 |
| Cd | 97 | 14 | 0.72 ± 1.79 | 0.18 | 0.10 ± 0.02 | 1.00 |
| Cr | 96 | 92 | 11.02 ± 15.71 | 5.79 | 3.47 ± 1.48 | 1.30 (WHO) |
| Pb | 98 | 22 | 3.99 ± 5.47 | 1.82 | 1.35 ± 1.21 | 5.00 |
Ranges: As 0.58–8.69, Cd 0.02–6.25, Cr 0.62–48.47, Pb 0.48–29.99 mg/kg DM.
By lake, Bellandur had notably higher Cd (1.81 mg/kg DM) and Cr (16.32 mg/kg DM) than most other lakes. Narasappanahalli had the highest Pb (13.09 mg/kg DM). No significant differences in As between lakes. Para grass showed consistently higher means across all four metals than other fodder types, though differences were not statistically significant.
Note: concentrations are in mg/kg DM (ppm DM), which equals 1,000 ppb DM. All values are total metals (ICP-OES, not speciated). Cr values are total chromium; Cr-VI data are absent.
Logit model finding: use of lake fodder was the strongest significant negative predictor of perceived cattle health (AME = -0.29, p < 0.01), stronger than insufficient drinking water (AME = -0.18) or high shed temperature (AME = -0.13).
Methods (brief)
Forage samples collected May 2022, microwave-assisted HNO3/HCl digestion; measurement by ICP-OES (Spectrogreen, SPECTRO). LODs: As 0.006, Cd 0.0001, Cr 0.00075, Pb 0.003 mg/L. Three technical replicates. CRM validation: ERM-CD281 rye grass (Cd, Cr, Pb within certified range). Inter-laboratory comparison of 10% of samples with AGROLAB LUFA GmbH; differences insignificant (P < 0.05). Basis: dry matter throughout. Total metals only; no speciation of As or Cr.
Implications
Certification: Indirect relevance. This paper does not measure metals in milk or milk products; it measures contamination in the feed inputs to dairy cattle producing urban milk. If contaminated fodder leads to carry-over into milk, this would affect dairy ingredient risk profiles, but that carry-over is uncharacterised. Not a direct evidence source for milk or dairy product concentration profiles.
Courses: Useful case study for supply-chain contamination pathways: urbanisation creates pressure on animal producers to use contaminated environmental forage, which may enter the human food chain through dairy. Illustrates Cr, Pb, and As co-contamination in urban lake vegetation at concentrations well above animal feed thresholds.
App: Not usable as a food-occurrence data source; the endpoint is cattle feed, not human food matrices.
Microbiome: Not applicable.