Overview
Field/farm sampling with a laboratory boiling experiment (raw vs boiled, paired by composite) of Cassava tubers from farms; 50 g cut into 2-cm pieces; raw (control, same preparation without cooking) vs boiled in deionised water 1:3 at 100 °C for 20 min. Peeling is not stated.. Growing area or market: Grown on cassava/cocoyam farms 2 km from a gold mining site in Kade, Kwaebibirem municipality, Eastern Region, Ghana; collected at six points (P1-P6) 50 m apart; not purchased.. Collection period: 27 May 2024 (single sampling date). Method: cadmium (Cd): 2.01 g desiccated sample, HNO3 reflux, cloud point extraction (detector not stated). arsenic (As): 1.121 g, HNO3 at 60 °C + HClO4, AAS (Buck VGP 210). mercury (Hg): 1.11 g, HCl at 45 °C for 2 h, dithizone complex, UV-Vis at 488 nm.. Basis: Raw cassava: ‘mg/kg dry weight’ (Table 4 title). Cooked cassava: not stated (Tables 5 and 6). Cd method uses ‘desiccated’ sample..
Key numbers
cassava root, raw: total mercury mean 0.301 ± 0.021 (Sampling point P1 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Mercury, column P1; p. 7; repeated in Table 6 (RCS P1), p. 8); total mercury mean 0.426 ± 0.022 (Sampling point P2 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Mercury, column P2; p. 7; repeated in Table 6 (RCS P2), p. 8); total mercury mean 0.367 ± 0.010 (Sampling point P3 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Mercury, column P3; p. 7; repeated in Table 6 (RCS P3), p. 8); total mercury mean 0.382 ± 0.006 (Sampling point P4 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Mercury, column P4; p. 7; repeated in Table 6 (RCS P4), p. 8); total mercury mean 0.411 ± 0.009 (Sampling point P5 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Mercury, column P5; p. 7; repeated in Table 6 (RCS P5), p. 8); total mercury mean 0.321 ± 0.031 (Sampling point P6 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Mercury, column P6; p. 7; repeated in Table 6 (RCS P6), p. 8); total arsenic mean 0.020 ± 0.001 (Sampling point P1 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Arsenic, column P1; p. 7; repeated in Table 6 (RCS P1), p. 8); total arsenic mean 0.010 ± 0.000 (Sampling point P2 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Arsenic, column P2; p. 7; repeated in Table 6 (RCS P2), p. 8); total arsenic mean 0.015 ± 0.000 (Sampling point P3 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Arsenic, column P3; p. 7; repeated in Table 6 (RCS P3), p. 8); total arsenic mean 0.018 ± 0.002 (Sampling point P4 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Arsenic, column P4; p. 7; repeated in Table 6 (RCS P4), p. 8); total arsenic mean 0.020 ± 0.001 (Sampling point P5 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Arsenic, column P5; p. 7; repeated in Table 6 (RCS P5), p. 8); total arsenic mean 0.018 ± 0.011 (Sampling point P6 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Arsenic, column P6; p. 7; repeated in Table 6 (RCS P6), p. 8); cadmium mean 0.028 ± 0.001 (Sampling point P1 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Cadmium, column P1; p. 7; repeated in Table 6 (RCS P1), p. 8); cadmium mean 0.026 ± 0.001 (Sampling point P2 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Cadmium, column P2; p. 7; repeated in Table 6 (RCS P2), p. 8); cadmium mean 0.027 ± 0.002 (Sampling point P3 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Cadmium, column P3; p. 7; repeated in Table 6 (RCS P3), p. 8); cadmium mean 0.030 ± 0.003 (Sampling point P4 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Cadmium, column P4; p. 7; repeated in Table 6 (RCS P4), p. 8); cadmium mean 0.024 ± 0.001 (Sampling point P5 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Cadmium, column P5; p. 7; repeated in Table 6 (RCS P5), p. 8); cadmium mean 0.028 ± 0.011 (Sampling point P6 (uncooked cassava); Table 4 ‘Distribution of heavy metals and cyanide concentration in uncooked cassava from Kade, Ghana (mg/kg dry weight)’, row Cadmium, column P6; p. 7; repeated in Table 6 (RCS P6), p. 8).
cassava root, boiled: total mercury mean 0.043 ± 0.002 (Sampling point P1 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Mercury, column P1; p. 7; Table 6 CCS P1, p. 8); total mercury mean 0.023 ± 0.011 (Sampling point P2 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Mercury, column P2; p. 7; Table 6 CCS P2, p. 8); total mercury mean 0.101 ± 0.001 (Sampling point P3 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Mercury, column P3; p. 7; Table 6 CCS P3, p. 8); total mercury mean 0.108 ± 0.000 (Sampling point P4 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Mercury, column P4; p. 7; Table 6 CCS P4, p. 8); total mercury mean 0.102 ± 0.001 (Sampling point P5 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Mercury, column P5; p. 7; Table 6 CCS P5, p. 8); total mercury mean 0.020 ± 0.002 (Sampling point P6 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Mercury, column P6; p. 7; Table 6 CCS P6, p. 8); total arsenic not detected 0.000 (Table 6: ‘0.000 ± 0.000’) (Sampling point P1 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Arsenic, column P1; p. 7; Table 6 CCS P1, p. 8); total arsenic mean 0.001 ± 0.000 (Sampling point P2 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Arsenic, column P2; p. 7; Table 6 CCS P2, p. 8); total arsenic not detected 0.000 (Table 6: ‘0.000 ± 0.000’) (Sampling point P3 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Arsenic, column P3; p. 7; Table 6 CCS P3, p. 8); total arsenic not detected 0.000 (Table 6: ‘0.000 ± 0.000’) (Sampling point P4 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Arsenic, column P4; p. 7; Table 6 CCS P4, p. 8); total arsenic mean 0.001 ± 0.000 (Sampling point P5 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Arsenic, column P5; p. 7; Table 6 CCS P5, p. 8); total arsenic not detected 0.000 (Table 6: ‘0.000 ± 0.000’) (Sampling point P6 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Arsenic, column P6; p. 7; Table 6 CCS P6, p. 8); cadmium mean 0.002 ± 0.001 (Sampling point P1 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Cadmium, column P1; p. 7; Table 6 CCS P1, p. 8); cadmium mean 0.010 ± 0.001 (Sampling point P2 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Cadmium, column P2; p. 7; Table 6 CCS P2, p. 8); cadmium mean 0.001 ± 0.00 (Sampling point P3 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Cadmium, column P3; p. 7; Table 6 CCS P3, p. 8); cadmium mean 0.003 ± 0.001 (Sampling point P4 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Cadmium, column P4; p. 7; Table 6 CCS P4, p. 8); cadmium not detected 0.000 (Table 6: ‘0.000 ± 0.000’) (Sampling point P5 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Cadmium, column P5; p. 7; Table 6 CCS P5, p. 8); cadmium not detected 0.000 (Table 6: ‘0.000 ± 0.000’) (Sampling point P6 (cooked cassava, boiled 20 min); Table 5 ‘Distribution of heavy metals and cyanide concentration in cooked cassava samples…’, row Cadmium, column P6; p. 7; Table 6 CCS P6, p. 8).
Limitations
Cooked cassava results have no stated basis while raw results are dry weight; the reported boiling reductions may be partly or wholly a moisture/basis artefact. Whether cooked pieces were dried before analysis is not stated. Reduction percentages are internally inconsistent: abstract and conclusion say boiling reduced Hg by 65-80 %, As by 85-95 % and Cd by 60-75 % in both crops, but cassava Table 4 vs Table 5 gives Hg 72-95 % (text: ~70-90 %) and Cd 62-96 % (two points non-detect). No LOD/LOQ for any analyte; cooked non-detects printed as 0.000 cannot be bounded. Arsenic at 10-20 µg/kg by AAS without stated hydride generation and Hg by dithizone UV-Vis spectrophotometry: method sensitivity for these levels is not demonstrated; no CRM or recovery. Exposure arithmetic does not reproduce from the tables: e.g. raw cassava As mean 0.0168 mg/kg x 0.527 kg/day / 60 kg = 0.148 µg/kg bw/day vs Table 7 RCS adult EDI 0.0539; raw Hg mean ~0.368 mg/kg gives ~3.2 µg/kg bw/day vs Table 7 1.1990. Not used for occurrence but HI conclusions are unverifiable. Peeling of cassava before analysis is not stated; material is ‘cassava tubers’ cut into pieces. The ± is not defined (replicates of a composite assumed); n per point = 1 composite.