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Platinum and Rhodium in Potato Samples by Using Voltammetric Techniques.

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Overview

This Italian study used differential pulse voltammetry and adsorptive stripping voltammetry to quantify platinum and rhodium in 38 peeled potato samples from Italy, France, Belgium, and Australia. It is the first reported application of voltammetric techniques to measure platinum group elements in a vegetable food matrix. Platinum concentrations ranged from 0.007 to 109 micrograms per kilogram dry weight, with the highest values found in Sicilian samples near industrial and refinery areas. Rhodium was much lower throughout (0.0008 to 0.030 micrograms per kilogram dry weight). All platinum concentrations fell below the European Medicines Agency Permitted Daily Exposure for platinum of 100 micrograms per day when assessed at a 100 g per day potato consumption rate.

Key numbers

Platinum concentrations in potato (micrograms per kilogram dry weight):

  • Range: 0.007 to 109 micrograms per kilogram dw
  • Approximate mean across all 38 samples: 12 micrograms per kilogram dw
  • LOQ (voltammetric): 0.007 micrograms per kilogram dw (13 ng/L in solution)
  • Highest individual samples: Sample 6 (Sicily) 109; Sample 8 (Veneto) 69; Sample 5 (Sicily) 65; Sample 3 (Sicily) 56 micrograms per kilogram dw

Rhodium concentrations (micrograms per kilogram dry weight):

  • Range: 0.0008 to 0.030 micrograms per kilogram dw
  • LOQ: 0.0008 micrograms per kilogram dw (1.6 ng/L)
  • Highest sample: Sample 23 (Emilia Romagna) 0.030

Platinum-to-rhodium ratio:

  • Mean ratio in potatoes: approximately 14,500
  • Earth’s crust ratio: approximately 100
  • Dramatic enrichment of platinum relative to rhodium in potatoes relative to crustal background

Geoaccumulation index (Igeo) for platinum:

  • Range: -11.2 to +2.9; mean -0.27
  • Approximately 80% of samples practically uncontaminated
  • 5 samples moderately contaminated; 3 moderately-to-heavily contaminated (Samples 3, 5, 6, 8 near industrial and refinery areas)

Enrichment factor (EF) for platinum:

  • Range: 6.5 x 10^-6 to 0.11; all below 1
  • Indicates natural-origin platinum in most samples; EF below 1 rules out anthropogenic dominance

Dietary intake estimates at 100 g dry potato per day:

  • Platinum: 0.0007 to 11 micrograms per person per day
  • Rhodium: 0.00008 to 0.003 micrograms per person per day
  • Reference adult Australian dietary platinum: 1.44 micrograms per day (Vaughan & Florence 1992)

Regulatory benchmarks:

  • EMA Permitted Daily Exposure: platinum 100 micrograms per day; rhodium 100 micrograms per day
  • FNB tolerable higher intake: 0.3 micrograms per day per kilogram body weight (approximately 15 micrograms per day for a 50 kg adult)

Food comparison data cited in paper (Vaughan & Florence 1992, Australian market basket; dry weight basis):

  • Liver: 8.1; eggs and offal: 5.8; grain: 3.2; fish: 1.8; fruit and vegetables: 0.82; milk products: 0.27; full-cream milk: 0.13 micrograms per kilogram

Methods

  • Sample preparation: potatoes peeled, dried 24 hours at 105 degrees C, ashed at 600 degrees C for 5 hours, digested in 5 mL concentrated HCl
  • Platinum: Differential Pulse Voltammetry/adsorption (DPV/a); supporting electrolyte H2SO4 1 M + hydrazine sulfate 1.2 mM + formaldehyde 0.6 mM; potential scan -0.3 to -1.0 V; catalytic hydrogen formation peak at -0.85 V vs Ag/AgCl; Amel Model 433-A polarograph, HMDE
  • Rhodium: Adsorptive Stripping Voltammetry; HCl 0.42 M + HCHO 0.02 M; deposition -0.7 V; peak at -1.1 V
  • Calibration R-squared: Pt 0.9957; Rh 0.9987
  • Precision (RSD): Pt 0.5-25%; Rh 0.9-24%

Relevance to this wiki

This paper provides the only food-matrix measured platinum concentration data in the current platinum deposit. It demonstrates that potatoes from areas proximate to industrial and refinery emissions can carry platinum concentrations orders of magnitude above background, while most agricultural potatoes remain near or below the detection limit. The geoaccumulation and enrichment factor analysis supports a natural-origin interpretation for most samples, with anthropogenic influence only in industrially proximate samples. The dietary intake calculations suggest potato-sourced platinum remains well below the EMA PDE threshold under typical consumption assumptions.

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