Assessment of Biomass, Proximate Composition and Heavy Metal Accumulation in Tropical Vegetable (Amaranthus hybridus) Irrigated with Fresh Untreated Abattoir Effluent in Akure, Ondo State, Nigeria

Abstract

Abattoir waste constitutes a significant environmental concern in Nigeria's peri-urban and urban areas as they often end up in rivers, groundwater and canals, contaminating the environment and increasing human health risks. Therefore, the objective of this paper was to assess the dry biomass, proximate composition and heavy metal accumulation in the Tropical vegetable, Amaranthus hybridus, irrigated with fresh untreated abattoir effluent in Akure, Ondo State, Nigeria using standard methods. The results showed that the abattoir effluent increased the vegetable’s dry biomass from 7.79 to 23.66 g. Similarly, there was a general increase in the carbohydrate, fibre and moisture contents of the vegetable with increasing concentration of the abattoir effluent, reaching up to 20.42%, 30.42% and 16.41% respectively. However, the protein, fat and ash contents generally decreased in the abattoir effluent irrigated treatments, from 25.38% to 18.23%, 11.38% to 6.70% and 9.63% to 7.34% respectively. This is probably due to the plant variety or metabolic activities of pathogens carried over from the effluent. The four heavy metals analysed (Cadmium, Cd; Lead, Pb; Zinc, Zn; Iron, Fe) were all accumulated in the tissues of the vegetable in amounts well-above the WHO limits, with Fe showing the highest bioaccumulation from 0.22 to 17.20 mg/L. In conclusion, although fresh untreated abattoir effluent can serve as organic fertilizer, it poses huge human health risks due to heavy metal bioaccumulation. Therefore, pre-treating before use to eliminate heavy metals and pathogens is highly recommended, as it would be a relatively cheaper means of growing Tropical vegetables.