L. Mugivhisa and J. O. Olowoyo, “Accumulation pattern of trace metals in Spinacia oleracea harvested from soil treated with urine in comparison with other soil amendments in Pretoria, South Africa”, Int. J. Recycl. Org. Waste Agric., vol. 6, no. 2, Mar. 2017, doi: 10.1007/s40093-017-0161-y.