Microbiological, Physicochemical and Heavy Metals Assessments of Soils and Selected Vegetables Grown on Rumde-Doubeli Irrigated Farmland in Yola Nigeria

Abstract

Leaf parts of vegetable plants grown on irrigated farmlands and are easily accessed by contaminants; pose greater risks of being contaminated with heavy metals. Soil, irrigation water and edible vegetable plants were collected and evaluated for concentrations of heavy metals using Atomic Absorption Spectrophotometry (AAS) and standard laboratory methods. Physicochemical parameters of irrigation water, compared with WHO limits for chloride (326.14 + 7.03 mg/L, 250 mg/L), total hardness (196.0 + 8.72 mg/L, 150 mg/L), chemical oxygen demand (286.4 ±1.35 mg/L; 150 mg/L) and alkalinity (171.0 + 4.36 mg/L, 120 mg/L) were significantly (p ˂ 0.05) higher than the control sites and respective reference values. Zinc (0.92 + 0.06 mg/L, 2.00 mg/L) and biological oxygen demand (115.7 + 6.46 mg/L, 200 mg/L, except for site C, which had 211.5 + 1.11 mg/L, 200 mg/L) had lower values compare to the control sites and respective reference values. For the control site, the physicochemical parameters were within the permissible limits but with increase of trace metal contents in soil and consequently into the vegetables (p ˂ 0.05).  Microbiological analysis revealed a high count of faecal coliforms, above the WHO recommended limit. Three significant pathogens identified included Salmonella, Klebsiella, Pseudomonas, Staphylococcus, and Streptococcus species. Farmers should be enlightened on the need for hygienic water for irrigation, and proper disinfection of raw vegetables before its consideration for consumption.