Vol. 7, Issue 8, Part J (2025)

Background and Aim: Bauxite mining alters the physicochemical properties of the soil and has increased the levels of some heavy metals in the soil. The study quantifies Al, Cd, Cr, Cu, Mn, Pb and Zn in soils and six food crops collected from three post-mined and one unmined district in two physiographic regions of Guyana.
Methods: Sampling were conducted in agreement with the reiteration student’s t-test that was performed to determine appropriate sample size whose margin of error was 10.4% calculated on encountering Pb in soil samples. Twenty-seven soil samples and twenty-four food plant samples (including Brassica rapa cv. chinensis; Spinacia oleracea; Cocos nucifera L, Manihot esculenta, Apium graveolens and Lycopersicon esculentum) were collected from four (three mined-out and one unmined) districts. Using ICP-OES/ICP-MS data, the author calculates geo-accumulation, and bioaccumulation factors and compares results with FAO/WHO Codex standards. In addition, chemical parameters like soil pH and organic matter contents were determined by Activation Laboratory Inc., an ISO 9001:2015: IEC/17025-accredited facility. With the data obtained the geo-chemical index and bioaccumulation factor were calculated and compared with the FAO/WHO Codex Standards using one-way ANOVA and Pearson correlation using version 20 of the Statistical Package for the Social Sciences. QA/QC were performed in accordance with the standard laboratory procedure of Act Lab Inc.
Results: In descending order, the mean heavy metals concentration (mg kg^-1) in the soils were: Al > Mn > Zn > Cr > Pb > Cu > Cd. The heavy metal concentration in all soil samples did not exceed the permissible limits set by the FAO/WHO. Bauxite-mined soils did not affect soil pH or organic matter content but had significantly higher levels of lead and zinc (p<0.05). Higher levels were observed in unmined areas compared to post-mined areas. The Pearson correlation showed a significant negative correlation between soil pH, organic matter and heavy metals in bauxite soil in unmined Hubu and post-mined Coomacka districts. However, in post-mined district Three Friends soil pH and organic matter showed a positive significant correlation (r=0.885*) suggesting a link with time. The quantitative geo-accumulation index results indicated pollution indices for various heavy metals, including Zn (0.8-1.2); Cu (0.8-4.0), Cu (0.7-2.3); Mn (0.7-2.3) and Pb (0.3-1.7).
Conclusion: A pH value of 6.4 and OM of 11.05% is desirable for the cultivation of food crops on the bauxite soil. It shows that leafy vegetables, tomato and cassava often exceed Joint FAO/WHO Codex permissible heavy metal limits, whereas coconut water remains below thresholds. The study indicates that some food crops grown in Guyana’s bauxite soils may have higher than normal permissible levels of heavy metals.