Bioaccumulation of chemical elements in vegetables as influenced by application frequency of municipal solid waste compost

Abstract

Municipal solid waste (MSW) compost is used to enrich soils by virtue of its bio-physicochemical properties. However, undesirable accumulation of chemical elements can reduce soil quality and cause food safety issues. A 5-yr field study was carried out to investigate the impact of Compost Quality Alliance (CQA)-tested MSW compost application frequency (annual, biennial and no-compost) on soil quality and chemical element accumulation in edible portions of lettuce (Lactuca sativa cv. Grand Rapids), beet (Beta vulgaris cv. Detroit Supreme), carrot (Daucus carota cv. Nantes), and green bean (Phaseolus vulgaris cv. Golden Wax). Analysis of soil showed that chemical elements were highest in annual application followed by biennial, but less in control (no-compost) and fallow soils. Soil background levels of chemical elements influenced the concentrations of iron (Fe) and manganese (Mn) in green bean, aluminum (Al) in green bean and beet, and barium (Ba) in carrot, beet, and lettuce. Cadmium (Cd) concentration in beet, lettuce, and green bean grown in the annual plot was increased by 48%, 52% and 62%, respectively while carrot recorded a 56% increase in the biennial plot compared with no-compost. Bioaccumulation factors were < 1 for all of the essential and non-essential trace elements in all of the plant species, except boron (B) and molybdenum (Mo). However, lettuce showed a higher tendency to accumulate Cd, rubidium (Rb), and strontium (Sr). Overall, the health risk for human consumption is low. Although long-term annual application of compost to vegetables seemed safe for human consumption, it is necessary to continuously monitor potential chemical element accumulation, particularly non-essential trace elements in soils and plants.