Multispecies Mesocosms Evaluating Ongoing PCB Recontamination of Novel In Situ Sediment Remedies

Novel thin-layer sand coverings for in situ sediment remediation may be vulnerable to recontamination, elevating bioavailable polychlorinated biphenyls (PCBs) within and just above the thin layer. A series of 3-month marine mesoscale experiments containing sheepshead minnows (Cyprinodon variegatus), hard clams (Mercenaria mercenaria), and sandworms (Alitta virens) were conducted to simulate full-system, in situ sediment remedies (i.e. 3 to 3.5-cm sand covering or low dose activated carbon amendment) followed by ongoing sediment deposition. Ongoing deposition was either clean or spiked with PCB congeners (PCB-13, −54, and −173). Input sourced PCB bioaccumulation was more than three times as high in clams (a 212% increase on a lipid-normalized basis, with moderate significance, p = 0.08) from the sand cover treatment for “fast” (log octanol-water partition coefficient <6) input congeners relative to the control (i.e. no sand cover). While clams filter feed near the sediment-water interface and are preferred for monitoring remedy effectiveness in mesocosms, similar trends were also observed in the other species. These results indicate that ongoing inputs, in the form of contaminated sediment deposits and associated dissolved contaminants, may prevent fish bioaccumulation-related risk reductions from being achieved at sites implementing widespread, low sorption-capacity, sand as a cover.