Toxicological studies on organic manures derived from municipal solid waste in Makindye, Rubaga and Kawempe divisions of Kampala, Uganda

Abstract

The study was carried out to estimate the levels of contamination and marketability of organic compost manures, derived from Kampala municipal solid wastes (MSW), sold along roads in the various suburbs of Kampala. The organic composts were sampled from five locations: Kawempe (KWP); Bwaise (BWS); Kitebi (KTB); Wankulukuku (WKK) and Ggaba-Kansanga (GGK~. The overall quality of the compost manures was determined by investigating selected physicochemical, trace metals and fertilizing properties, via standard methods. The pH of the manure was found to be within the range of 5.27-8.30. The electrical conductivity (EC) of manure samples ranged from 3.07 to 7.13 ~is/c1m A strong negative correlation was found between pH and both EC and trace metals in such manures. The study was found out that, apart from Cu and Zn which were within the permissible limits, the concentration of Pb, Cd, and Cr in all five areas were higher than the permissible limits set by UNBS, 2017. The results of ANOVA (F: 5, 0.05) showed that the there was significant difference in the manure samples collected from the various locations (p < 0.05). The study results indicated that majority of these manures had medium fertilizing potential but did not meet certain control guidelines set by standard agencies and may pose specific risks to the environment. Composts of KTB, BWS, KWP, GKK and were of medium quality (Class D) and had medium fertilizing potential. They could be conveniently applied in small scale farms and gardens. However, WKK, which did not comply for heavy metals should not be allowed into the market. It may only be used for developing lawns/gardens (with single application) or for the rehabilitation of degraded land. Post-treatment of these compost manures was recommended to improve their quality before being utilized for agricultural purposes.