Quantification of toxic metals in cropland soil using X-ray fluorescence

Abstract

We aimed to assess toxic heavy metals in soil samples from cropland in Weenen (KwaZulu-Natal, South Africa) using X-ray fluorescence (XRF) spectroscopy. The metal contents in the soil samples were detected and quantified by wavelength dispersive XRF (WD-XRF) spectroscopy. On average, the values of all elements (mg/kg) were: Al (91.4 ± 6.9), Ba (0.488), Ca (16.8 ± 5), Fe (39.3 ± 0.8), K (15.7 ± 0.04), Mg (10.1 ± 0.3), Mn (0.6), Na (8.0 ± 1), P (1.3 ± 0.4), Si (458 ± 8) and Ti (5.6 ± 0.3). Toxic metals such as Hg, Cd, As, Pb, and Cr were not detected in the soil samples. The macronutrient P, which is capable of causing eutrophication in water bodies, was present at a low level in soil samples. The metal contents in both control and field samples were comparable, suggesting that the metals were mostly of lithogenic origin and not entirely influenced by anthropogenic activities. The metal levels we detected were within the limits reported to be safe by other studies.

Significance:

Although they are within the detection range, the toxic heavy metals mercury, cadmium, arsenic, lead and chromium, which enter the environment through the use of fertilisers on agricultural land, were not detected in this WDXRF spectrometry analysis. The remaining elements detected are lithogenic and non-anthropogenic, as the field and control samples had comparable concentrations. Nitrogen was not quantified, but phosphorus was present in a low concentration, so the field water run-off into the water bodies need not directly lead to water pollution in the area studied.