Heavy metals concentrations and risk assessment of roselle and jute mallow cultivated with three compost types

Field experiments were conducted at the research field of the CSIR-SARI near Nyankpala in the Northern region of Ghana during the major growing seasons of 2014 and 2015. The objectives of the study were to determine the effect of three compost types i.e. Accra compost and recycling plant (ACARP) compost; decentralised compost (DeCo) and composted deep litter chicken manure (CDLCM) on heavy metals concentrations in roselle (Hibiscus sabdariffa L.) and jute mallow (Corchorus olitorius L.) and the health risk of these vegetables to adults and children. The composts were each applied at the rate of 10 t/ha in a randomized complete block design in four replications. The concentrations of Cd and Pb in the leaves of roselle were 0.8 mg/kg and 5.0 mg/kg whiles in jute mallow, they were 0.7 mg/kg and 6.0 mg/kg, respectively. These concentrations were above the Maximum residue levels (MRLs) of 0.2 mg/kg for Cd and 0.3 mg/kg for Pb in the standards of the European Commission and Codex Alimentarius Commission. The low soil pH might have facilitated the bioavailability of the heavy metals resulting in concentrations that could be harmful to consumers of these vegetables. There is, therefore, the need to amend the soil pH of the study area. An upward adjustment of the pH of the composts used can also help in reducing the bioavailability of heavy metals to roselle and jute mallow cultivated in soils with low pH.