Low impact leaching agents as remediation media for organotin and metal contaminated sediments

Anna Norén,Karin Karlfeldt Fedje,Ann-Margret Strömvall,Sebastien Rauch,Yvonne Andersson-Sköld

doi:10.1016/j.jenvman.2020.111906

Abstract

All over the world, elevated levels of metals and the toxic compound tributyltin (TBT) and its degradation products are found in sediments, especially close to areas associated with shipping and anthropogenic activities. Ports require regular removal of sediments. As a result, large volumes of often contaminated sediments must be managed.The aim of this study was to investigate enhanced leaching as a treatment method for organotin (TBT) and metal (Cu and Zn) contaminated marine sediments. Thus, enabling the possibility to reuse these cleaner masses e.g. in construction. In addition to using acid and alkaline leaching agents that extract the OTs and metals but reduce the management options post treatment, innovative alternatives such as EDDS, hydroxypropyl cellulose, humic acid, iron colloids, ultra-pure Milli-Q water, saponified tall oil (“soap”), and NaCl were tested. Organotin removal ranged from 36 to 75%, where the most efficient leaching agent was Milli-Q water, which was also the leaching agent achieving the highest removal rate for TBT (46%), followed by soap (34%). The TBT reduction accomplished by Milli-Q water and soap leaching enabled a change in Swedish sediment classification from the highest class to the second highest class. The highest reduction of Zn was in HPC leached samples (39% removal) and Cu in EDDS leached samples (33% removal). Although high metal and OT leaching were achieved, none of the investigated leaching agents are sufficiently effective for the removal of both metals and OTs. The results of this study indicate that leaching with ultra-clean water, such as Milli-Q water, may be sufficient to treat TBT contaminated sediments and potentially allow mass reuse.

Highlights

Sediment dredging must be carried out regularly to maintain or in crease water depth in important maritime areas, such as ports
Physical characterization Ocular inspection (ISO 22412:2017) characterized Bjorlanda Kile (BK) and CV sediments as silty clay/clayey silt containing pieces of shells, which confirmed an earlier study about the area (Johannesson et al, 2000)
The sediments studied here con sisted of fine particles and the performed Environ mental scanning electron microscopy (ESEM)/energy dispersive X-ray spectrometer (EDS)-analyses indicated that the elements were fairly evenly distributed between particles and that marginally more metals are seen in CV (Supplementary material Figures S2–S3)

Summary

Introduction

Sediment dredging must be carried out regularly to maintain or in crease water depth in important maritime areas, such as ports. World wide, elevated levels of organotin compounds (OTs) and metals are found in the sediment, especially close to areas with high levels of anthropogenic activities, such as cities, industries, and marine struc tures, including ports and marinas. Organotins, which include tribu tyltin (TBT) and its derivatives dibutyltin (DBT) and monobutyltin (MBT), have a negative effect on biota through hormone disruption (OSPAR Commission, 2011). Negative effects have been found at con centrations as low as 1 ng/L TBT in water (European Commision, 2005). Tributyltin is a stable compound with hydrophobic properties (Euro pean Commision, 2005) and sorbs fairly to the A.

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Conclusion