Carbonaceous materials are often proposed for use in
restoring
soils or sediments contaminated with hydrophobic organic contaminants
(HOCs). However, the contamination of most sites is a result of historical
events, where HOCs have resided in the solid compartment for many
years or decades. The prolonged contact time, or aging, leads to reduced
contaminant availability and likely diminished effectiveness of using
sorbents. In this study, three different carbonaceous sorbents, i.e.,
biochars, powdered activated carbon, and granular activated carbon,
were amended to a Superfund site marine sediment contaminated with
DDT residues from decades ago. The amended sediments were incubated
in seawater for up to 1 year, and the freely dissolved concentration
(Cfree) and the biota-sediment accumulation
factors (BSAFs) for a native polychaete (Neanthes arenaceodentata) were measured. Even though the bulk sediment concentrations were
very high (6.4–154.9 μg/g OC), bothCfreeand BSAFs were very small, ranging from nd to 1.34
ng/L and from nd to 0.024, respectively. The addition of carbonaceous
sorbents, even at 2% (w/w), did not consistently lead to reduced DDT
bioaccumulation. The limited effectiveness of carbonaceous sorbents
was attributed to the low DDT availability due to prolonged aging,
highlighting the need for considering contaminant aging when using
sorbents for remediation.