Assessment of pawpaw, tomato and cocoyam grown in dump sites in Ogbomoso metropolis, Nigeria for heavy metals.

Abstract

Urban backyard crop production is confronted with heavy metal soil pollution, the soil being mostly abandoned refuse dumpsites. This research is designed to investigate the impact of heavy metal soil pollution on pawpaw, tomato and cocoyam grown in dump sites in Ogbomoso metropolitan. Three heavy metal dump sites and one non-dump site were selected as sampling locations. Leaves, stems, roots, and fruits of the test crops were collected randomly from all the sites. The samples were enveloped, labelled and taken to the laboratory for analysis.  Soil samples were also taken at  the three locations per site with core sampler at 15cm depth and were put in labelled polythene bags and taken to the laboratory for analysis. Wet digestion was used and the concentration of heavy metals [Pb, Cd, Mn, Cu, and Cr] were determined usingn atomic absorption spectrrophotometric analysis. Soil pH, and organic matterr percentages werre also determined. The results showed that all the crops were accumulate heavy metals to appreciable propotion in their organs. The transfer ratio recorded for pawpaw, tomato and cocoyam leaves were respectively pb[0.76]>Cd [0.7]>Mn [0.65]> cu[0.41]>Cr [0.10]; Mn[1.19]>pb[0.51]>Cd[0.48]>cu[0.44]>cr[0.05], and Mn [2.99]>pb [0.85]>cd[0.80]>u [0.13]> Cr [0.10]. the extracted heavy metals got from the stem of the test crop were in the order of transferr ratio; Mn [2.49]>pb [0.73]>cd[0.70]>Cr[0.11]>Cu[0.08];Mn[1.24]>pb[0.5]> Cd [049]>Cu [0.06]>Cr[0.05] and Mn [2.91]>pb [0.98]>Cd[0.88]>Cu [0.14]>Cr [0.11] for pawpaw, tomato and cocoyam rrespectively.the roots of the respective crrops also contained the heavy metals despite the quality transfere to the other organs. The trend observed were Mn [2.46]>pb [0.69]> Cd [0.66]> Cr [0.12]> Cu [0.10]; Mn [1.29]>pb [0.48]> Cd [0.46]> Cu [0.05]> Cu [0.01] and Mn [3.0]> pb [1.05]>Cd[0.93]>Cr [0.15]> Cu[0.13] for the test crop respectively. The directly consumed parts of the crops were able to retain these heavy metals in their tissues. The following respective trends were observed for pawpaw, tomato fruits and cocoyam corn; Mn [1.60]>pb [0.67]>Cd [0.67]>cd [0.69]>cu [0.11]= Mn [1.23]> pb[0.54]>Cd [0.49]>cr [0.16]>cu[0.05] and Mn [3.10] pb [1.05]> Cd [0.93]>Cr [0.17]> Cu [0.14]. all these metal concentrations were high compared with international standards, and it was found out that they were on the high side