Screening of Tomatoes and Onions for Trace Metals from Irrigated Farmlands on the Bank of River Challawa, Nigeria

Abstract

The objective of this research investigation was to determine the concentrations of trace metals (Cd, Cr and Pb) in tomatoes and onions irrigated with tannery polluted water of river Challawa, Northern Nigeria using atomic absorption spectrometry. 32 samples of tomatoes and 16 samples of onion bulbs each were taken for analysis. In the study area, metal concentrations in tomatoes were found to be in the range 0.58-1.00 for Cd; 10.83-14.20 for Cr, 9.75-15.67 for Pb mgkg^-1 dry weight. Similarly, the mean concentrations of the same trace metals were also found to range from 0.82-0.98 for Cd; 5.20-8.54 for Cr and 8.50-11.67 for Pb, mgkg^-1 dry weight, for exposed onion bulbs. Also 0.58 - 0.70mgkg^-1 Cd; 0.45-0.84mgkg^-1 Cr; and 3.83-7.33mgkg^-1 Pb in respect of onions samples control. The findings of the investigation indicate the relative abundance of the trace metals in both the tomatoes and onions samples (exposed and control) analysed followed the sequence Pb>Cr>Cd. The trace metals values in both the exposed and controlled samples are higher than the WHO/EU and FAO/WHO acceptable limits for trace metals in food crops. However, the values for Pb and Cd are below the ICRCL (1987) values of Pb (1-50mgkg^-1) and Cd (0-1 mgkg^-1). This could put consumers of tomatoes and onions from River Challawa irrigated farmlands at risk of ingestion of toxic metals at an unacceptable concentrations.