Geochemical assessment, distribution, and dynamics of trace elements in urban agricultural soils under long-term wastewater irrigation in Kano, northern Nigeria

摘要

A study was conducted to evaluate the distribution and origin of trace elements (Ti, Fe, Nb, Pb, Rb, Sr, Y, and Zr) in five representative long-term wastewater-irrigated urban vegetable gardens of Kano, Nigeria. Surface-soil concentrations (0–15 cm) of Ti (4600–14 300 mg kg–1), Fe (4000–31 800 mg kg–1), Pb (96–355 mg kg–1), and Y (33–98 mg kg–1) were high compared to mean concentrations in comparable soils elsewhere. However, soil-pollution assessment yielded no evidence of anthropogenic input of the trace elements studied. Indices such as the enrichment factor, the contamination factor, and the geoaccumulation index (I_geo) revealed little to no contamination with trace elements. The I_geo calculated for these metals varied across locations between 0.00 and 0.12 with Nb having the highest I_geo value. Similarly, the contamination factor was low for all metals with the exception of Fe reaching a contamination factor of 4.2 at one location. Geochemical-balance evaluations showed depletion of all trace elements except for Fe which was 176% higher than in a natural uncultivated and unirrigated reference soil. Correlation and factor analyses showed that all determined trace elements likely originated from the same natural sources, which probably are the soil parent material and atmospheric depositions.