Effect of treated sewage sludge on the quality of okra fruit

Abstract

Sewage sludge (treated or untreated) if applied to the soil has been identified to increase heavy metals in the soil which are in turn transferred to plants. In view of this, the study aimed at assessing the effects of treated sewage sludge on the quality parameters of okra fruit. The randomized block design was employed in raising okra plants with three treatments (0 t ha-1, 10 t ha-1, and 20 t ha-1 sewage sludge amendments) over a land area of 56.3 m2. Soil analysis was used to determine the level of nitrogen, phosphorus, and potassium in the soil. After two months, the okra fruit was harvested by cutting the pods off, slicing, oven drying, milling prior to laboratory analysis. The heavy metal contents in the okra fruit were analysed using atomic absorption spectrometer. The parameters analyzed were Cd, Pb, Cu, Fe, and Zn. The concentration of the selected heavy metals was subjected to descriptive statistics and one-way analysis of variance (ANOVA). The transfer factor was also determined. Most soils in the okra field was sand. Study found out that the soil was deficient in phosphorus and potassium. Bioaccumulation of heavy metals were not found in the okra fruit since Cu, Zn and Fe have transfer factors of less than one. In addition, transfer factor order in okra fruit was Zn>Cu>Fe>Cd>Pb. The study revealed that the application of sewage sludge at 10 t ha-1 and 20 t ha-1 resulted in high uptake of Zinc (Zn) and Iron (Fe) whereas cadmium and lead were not detected. The study concluded that consumption of the okra fruit grown on 10 t ha-1 and 20 t ha-1 were very safe since Cu, Fe, and Zn in the okra fruit were less than desirable limit as recommended by FAO and WHO. There is need to determine hazard quotient, the health risk index, morbidity status the enrichment factor and degree of contamination in okra fruit. Effect of sewage sludge at different application rates between 25 t ha-1 and 60 t ha-1 should be seriously investigated so as to determine the optimal level of heavy metal in the okra fruit.