Transfer of metals from soil to Cucumis sativus fruit and possible health risk assessment under actual field condition

Abstract

Toxic metals levels in Cucumis sativus (cucumber) plant and soil in an area of the oil producing Niger Delta of Nigeria were investigated. The study was carried out in a small scale Cucumis sativus farm located in Idim Afia village in Eket Local Government area of Akwa Ibom State, Nigeria. Toxic metals levels in soil were lower than the background levels except cadmium. Bioconcentration factor revealed that both toxic and major metals concentrated more in the root except for lead and cadmium which concentrated more in the shoot. Though the fruit is a good source of potassium (bioconcentration factor=14.90), it also hyper-accumulates nickel (bioconcentration factor=84.00), qualifying it as an indicator of nickel pollution. Effective transfer (Transfer Factor>1) of metals were observed for lead and cadmium from root to shoot; zinc, nickel, chromium and cadmium from shoot to leaf; and nickel and chromium from shoot to fruit. Generally, transfer factor within the organs was less than one. Indices of soil pollution indicated low to moderate pollution of farm soil and, also anthropogenic origin for cadmium and chromium (concentration factor>1). Principal component analysis extracted three major components accounting for 94.351% of total variance, and characterised by strong associations with exhaust emissions, leaching of industrial and domestic waste and agricultural activities. The main human exposure route of all toxic metals in Eket was through ingestion of fruit. Non-carcinogenic chronic daily intake and non-carcinogenic hazard quotient were higher in farm and purchased fruit than in the farm soil. Non-carcinogenic hazard quotients of individual exposure pathways and the total non-carcinogenic hazard quotient was <1, indicating no potential health concern for zinc, nickel, lead, cadmium, and chromium pollution in Eket at the time of study. It was observed that chromium posed least risk to the local population, with hazard quotient ranging from 0.000 in soil to 0.0006 in farm fruit. However, cadmium in farm soil, and nickel and lead in the fruit, presented higher values for non-carcinogenic risk in the study area, hence more attention should be paid to cadmium, nickel and lead pollution in future studies. The results of this study may inform policy on the prevention of food contamination by toxic metals.

Key words: Health risk, Metals, Soil, Cucumber