Knox, A.S. and M.H. Paller. | Science of The Total Environment 713:136537(2020)

Sediments contaminated with As, Cd, Cu, Ni, Pb, and Zn were deposited over clean sediment capped with apatite, a sequestering agent, and clean uncapped sediment to simulate the recontamination of remediated sediment by influxes of particle-bound contaminants from unknown sources. The experiment aimed to determine whether apatite could sequester contaminants present in the deposited sediment, reducing their impact. Cap effectiveness was assessed in the presence and absence of Corbicula fluminea. Effectiveness was based on metal fluxes to sediment pore water and surface water, the distribution of mobile contaminants in sediment and surface water measured by the diffusive gradients in thin films technique, and contaminant bioaccumulation by Lumbriculus variegatus. The metal sequestration capacity of apatite caps was unaffected or improved by bioturbation for all elements except As. Effects with uncapped sediment were metal-specific, including reductions in the bioavailable pool for Ni, Cd, and to a lesser extent, Pb, increases in the bioavailable pool for As and Cu, and little effect for Zn. The reductions observed for some metals in uncapped, clean sediment were likely the result of burial and dilution of contaminated sediment combined with chemical processes such as sequestration by minerals and other compounds. Results indicate that apatite caps can control recontamination by metals regardless of bioturbation but point to the complexity of sediment recontamination and the need for further study of this problem.