Abstract
This study tested two sediment amendments with active sorbents: injection of aluminum (Al) into sediments and thin-layer capping with Polonite (calcium–silicate), with and without the addition of activated carbon (AC), for their simultaneous sequestration of sediment phosphorus (P), hydrophobic organic contaminants (HOCs), and metals. Sediment cores were collected from a eutrophic and polluted brackish water bay in Sweden and incubated in the laboratory to measure sediment-to-water contaminant release and effects on biogeochemical processes. We used diffusive gradients in thin-film passive samplers for metals and semi-permeable membrane devices for the HOC polychlorinated biphenyls and polycyclic aromatic hydrocarbons. Al injection into anoxic sediments completely stopped the release of P and reduced the release of cadmium (Cd, −97%) and zinc (Zn, −95%) but increased the sediment fluxes of PAH (+49%), compared to the untreated sediment. Polonite mixed with AC reduced the release of P (−70%), Cd (−67%), and Zn (−89%) but increased methane (CH4) release. Adding AC to the Al or Polonite reduced the release of HOCs by 40% in both treatments. These results not only demonstrate the potential of innovative remediation techniques using composite sorbent amendments but also highlight the need to assess possible ecological side effects on, for example, sedimentary microbial processes.
Highlights
Emissions of anthropogenic pollutants to natural waters in Europe have generally decreased due to stricter environmental regulations
Ecotoxicological risks from hazardous substances such as hydrophobic organic contaminants (HOCs) and metals are high in the coastal areas of the Baltic Sea, and many such areas in Sweden will need remediation to achieve good status as demanded by the EU Water Framework Directive (WFD; 2000/60/EC).[3]
The aims of our study were to investigate (i) the capacity of Al injection and Polonite to reduce the release of P from a nutrient-rich sediment, (ii) their ability to reduce the mobility of metals of environmental concern in the sediment−water interface, (iii) their performance in composite treatments with activated carbon (AC), for both P, metal, and sorption of HOCs, and (iv) potential physico-chemical and ecological side effects of these treatments, that is, on pH, exchange of greenhouse gases, or effects on sediment microorganisms and the nutrient cycling processes they mediate
Summary
Emissions of anthropogenic pollutants to natural waters in Europe have generally decreased due to stricter environmental regulations. Among the most utilized and studied sorbents for in situ remediation are lanthanum-modified clay (Phoslock)[6] and various forms of aluminum (Al) addition[7,8] for P sequestration, and activated carbon (AC) for the immobilization of HOCs.[9] Many other sorbents have been evaluated in laboratory studies but are yet to be tested in large-scale field trials These include variants of zeolite for the sorption of nutrients and metals[10,11] and apatite and organoclays for metals and HOCs.[12,13] Current literature reports no sorbent amendment, or mixture of Received: April 9, 2021 Revised: August 15, 2021 Accepted: August 16, 2021 Published: August 26, 2021
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