Use of polyacrylamide superabsorbent polymers and plantain peel biochar to reduce heavy metal mobility and uptake by wastewater-irrigated potato plants

Agriculture is the largest consumer of freshwater; therefore, use of alternate sources for irrigation, such as wastewater, could alleviate increasing stress on freshwater resources. However, wastewater may contain contaminants such as heavy metals (Cd, Cr, Cu, Fe, Pb, and Zn), which could be taken up by food crops and/or contaminate groundwater. To reduce the mobility of heavy metals in soil and deter their uptake by potatoes (Solanum tuberosum L.) irrigated with synthetic wastewater, polyacrylamide superabsorbent polymer (SAP) and a mixture of SAP and plantain peel biochar (SAP+BC) were tested as soil amendments. The experiment was performed in field lysimeters packed with sandy soil. SAP was incorporated into the soil layer from 0.15 to 0.25 m below the surface and BC was mixed into the top 0.10 m of soil, both at an application rate of 1% (w/w). Leachate and composite soil samples from different depths, collected after each irrigation event, were analyzed for heavy metals. Upon harvest, different plant parts were subjected to heavy metal analysis. Compared to the untreated control, the SAP+BC treatment led to significantly greater (p < 0.05) retention of Cd and Zn in the topsoil while significantly reducing (p < 0.05) Cd, Cu, and Zn uptake into potato tuber flesh tissue and Cd uptake into tuber peels. The SAP treatment also significantly reduced (p < 0.05) Cd uptake in the tuber as compared to the control. Acrylamide monomers were not detected in tuber flesh and peel samples for all treatments, indicating possible safe use of SAP and BC in soils to reduce heavy metal leaching and uptake by plants.