Overview
Field/farm sampling along a distance gradient from gold mines (paired surface soil and cassava tissues) of Cassava tubers uprooted from farms; washed, rinsed with distilled water and peeled; flesh (core), Peel-A (periderm/outer skin) and Peel-B (cortex) analysed separately. Leaves analysed but out of scope (see notes).. Growing area or market: Grown on farms in the vicinity of Bogoso and Prestea gold mines (Western Region, Ghana), sampled directly from the plants; not purchased.. Collection period: not reported. Method: Tissues dried at 35 °C to constant weight, ground, sieved (120 µm); 1 g digested with conc. H2SO4 + HNO3 at 80 °C, KMnO4 and K2S2O8 oxidation at 90 °C, hydroxylamine hydrochloride; total mercury (Hg) by cold-vapour AAS (Shimadzu 6400AA, SnCl2 reduction, 253.7 nm).. Basis: Not labelled in Table 2 (µg/kg). Samples were oven-dried at 35 °C to constant weight and analysed as dried powder, so values are most plausibly dry weight; recorded as ‘unstated’ because the paper does not say so..
Key numbers
cassava root flesh (peeled): total mercury mean 127.45 32.12 (Entrance of Bogoso Gold Ltd. (1.5 km from mine); tissue Flesh; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Entrance of Bogoso Gold Ltd. / Flesh; p. 1108); total mercury mean 167.67 12.54 (Dumasi Site A (5.5 km from mine); tissue Flesh; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Dumasi Site A / Flesh; p. 1108); total mercury mean 122.08 35.51 (River Bogo River Bank (8.4 km from mine); tissue Flesh; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row River Bogo River Bank / Flesh; p. 1108); total mercury mean 152.11 24..08 (Prestea Ankobra Before Bridge (14.0 km from mine); tissue Flesh; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Prestea Ankobra Before Bridge / Flesh; p. 1108).
cassava root peel: total mercury mean 66.60 16.13 (Entrance of Bogoso Gold Ltd. (1.5 km from mine); tissue Peel-A; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Entrance of Bogoso Gold Ltd. / Peel-A; p. 1108); total mercury mean 75.62 12.28 (Entrance of Bogoso Gold Ltd. (1.5 km from mine); tissue Peel-B; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Entrance of Bogoso Gold Ltd. / Peel-B; p. 1108); total mercury mean 89.29 12.07 (Dumasi Site A (5.5 km from mine); tissue Peel-A; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Dumasi Site A / Peel-A; p. 1108); total mercury mean 98.25 5.35 (Dumasi Site A (5.5 km from mine); tissue Peel-B; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Dumasi Site A / Peel-B; p. 1108); total mercury mean 105.46 15.66 (River Bogo River Bank (8.4 km from mine); tissue Peel-A; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row River Bogo River Bank / Peel-A; p. 1108); total mercury mean 78.75 22.28 (River Bogo River Bank (8.4 km from mine); tissue Peel-B; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row River Bogo River Bank / Peel-B; p. 1108); total mercury mean 121.58 41.75 (Prestea Ankobra Before Bridge (14.0 km from mine); tissue Peel-A; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Prestea Ankobra Before Bridge / Peel-A; p. 1108); total mercury mean 195.47 51.32 (Prestea Ankobra Before Bridge (14.0 km from mine); tissue Peel-B; Table 2 ‘Mercury levels in cassava tissues near Bogoso/Prestea gold mine’, row Prestea Ankobra Before Bridge / Peel-B; p. 1108).
Limitations
Table 2 prints four values (columns 1-4) per site and tissue, but the methods describe tubers from three plants per site and three sub-sites per site; what the four columns represent (plants, sub-sites or replicate digests) and therefore the number of independent samples cannot be determined. Result basis (dry vs fresh weight) is not labelled; analysis on 35 °C-dried tissue suggests dry weight but this is not stated. Collection date/period not reported. Only four of the six soil sites (Dumasi Site B and Prestea Old Mine are absent) have cassava data; the reason is not given. The abstract says a speciation exercise showed mercury bound to hydroxides and organic complexes, but no speciation data or method are reported in the paper. Prestea Ankobra flesh SD printed ‘24..08’ (typographic); recomputed 24.08 used. No LOD/LOQ reported.