Effects of NPK fertilizers on trace metals loads in soil and vegetables, bioavailability in vegetables and the related health risk using simulation techniques

Abstract

The impact of inorganic fertilizers on the accumulation of trace metals in surface soil, Telfairia occidentalis, Talinum triangulare, Spinacia oleracea, and  Amaranthus viridis using Plot experiment was carried out in this study. Four experimental plots were prepared, the pre-fertilization soil samples were  collected before the cultivation of these vegetables. Twelve weeks after, the pre-fertilization vegetable samples were also obtained. NPK fertilizers were  applied to the different plots and six months after the post-fertilization soil and vegetable samples were obtained from each plot. The different plots were  irrigated during the pre and post-fertilization periods with distilled water using the sprinkling method. The different fertilizers used and the  samples obtained were treated using standard analytical techniques and analyzed for their Cd, Cu, Ni, Pb, Zn, and Cr content using Unicam 969  spectrophotometer. Results obtained showed the following mean concentrations (mgkg^-1 ) for Cd, Cu, Ni, Pb, Zn, and Cr in the fertilizers: 2.72±0.48,  6.56±0.61, 9.58±0.86, 7.88±0.55, 14.56±1.40, and 2.23±0.14, respectively. The results revealed relatively higher concentrations of these metals in the post- fertilization than in the pre-fertilization samples for both the soil and vegetables. The transfer factor of each of the trace metals was less than one. It was  also realized that, the plots were heavily contaminated with trace metals using different environmental pollution models. Telfairia occidentalis and Talinum  triangulare displayed very high potentials for absorbing these metals from the fertilizers-impacted soil. The principal component analysis  identified two and three major factors for the accumulation of metals in soil and vegetables, respectively. Results of health risk analysis indicated that, Cd,  Pb, and Ni levels in the vegetables were higher than their recommended oral reference limits. It was also observed that, the consumers of these vegetables may be affected by Cd and Pb toxicity and the children population was more vulnerable. Accordingly, the study has shown the effect of  inorganic fertilizers on the buildup of trace metals in soil and vegetables. The pollution status of the fertilizers-impacted soil and the health risk  associated with the exposure to the studied vegetables were also revealed.