Assessment of hydrophobic organic contaminant availability in sediments after sorbent amendment and its complete removal

Sorbents amended to sediments in situ for sequestration of hydrophobic organic contaminants (HOCs) may be swept away from the treated sites due to hydrodynamic forces applied to the sediment surface. The purpose of this study is to examine the possibility of recovery of HOC availability in sorbent-amended sediment after complete removal of the sorbent. Sediment contact with an easily separable model sorbent Tenax beads for 28 days in a slurry phase resulted in 74–98% reduction in polycyclic aromatic hydrocarbon and polychlorinated biphenyl availability compared to the untreated controls. HOC availability in the sorbent-treated sediment slightly increased by sorbent removal and after one month of mixing in a slurry phase because the slowly-desorbing HOC fraction was released and repartitioned back to the sediment, partially replenishing the rapidly-desorbing HOC fraction. However, HOC availability did not further increase during an extended mixing period of 12 months suggesting that the repartitioning process was not an infinite source. HOC availability after the 12-month post-treatment mixing for the sorbent-treated sediment was 53–97% lower than that of the untreated sediment because of the combined effect of HOC mass removal from sediment (with the sorbent) and incomplete recovery of available HOC fraction in the sorbent-treated sediment. [Display omitted] •Sorbent-sediment contact substantially reduces HOC availability in sediment.•HOC mass transfer to sorbent ranges 14–90% by 1-month slurry-phase contact.•Sorbent winnowing causes slight rebound of HOC availability in sediment.•HOC availability of treated sediment does not reach close to the initial value by sorbent winnowing. HOC availability in sorbent-amended sediment is slightly increased but not fully recovered by removal of the sorbent and subsequent agitation of the remaining sediment.