Observations of limited secondary effects to benthic invertebrates and macrophytes with activated carbon amendment in river sediments

Abstract

Amendment of activated carbon to sediments has been shown to effectively reduce the bioavailability of hydrophobic organic contaminants, but concerns have been raised about the potential toxicological impacts of administering a strong sorbent into sediments. The present study provides a summary of several investigations carried out as part of a pilot-scale study in a river to understand the secondary effects of activated carbon added to reduce the bioavailability of sediment-associated polychlorinated biphenyls. While some previous laboratory amendment studies have found reduced lipid content in freshwater worms exposed to activated carbon-treated sediments, the authors did not observe an impact with fine-granular activated carbon-amended sediments aged in the field. Benthic community studies did not find differences between control and activated carbon-treated field sites over 3 yr of postapplication monitoring. Laboratory studies with submerged aquatic plants indicated reduced growth in sediments amended with ≥5% activated carbon, which was attributed to volume dilution of nutritional sediment or bulk density changes and was also observed when the sediment was amended with biochar and inert perlite. Since in situ sorbent amendment is likely to be implemented in depositional sediment environments, potential negative impacts will likely be short-term if the treated site is slowly covered with new sediment over time. Overall suitability of activated carbon amendment for a site will depend on balancing ecosystem and human health benefits from contaminant bioavailability reduction with any potential negative impacts expected under field conditions.

Response of marine benthic fauna to thin-layer capping with activated carbon in a large-scale field experiment in the Grenland fjords, Norway

“…Other studies on community responses to AC have often showed less negative effects, where causes for less susceptibility may be attributed to factors keeping up the resilience in these systems. For example, the larger AC particles (100–200 μm) and relative organic carbon-rich river sediment (TOC 4–6%) may explain the limited negative effects to a fresh water community in Grasse River (Beckingham et al 2013). Moreover, the mild initial effects and full recovery of the benthic community 1 year after exposure to powdered AC in an un-contaminated fresh water experimental ditch may also be attributed to less stress due to organic carbon rich (TOC 8%) sediment (Kupryianchyk et al 2012).…”

“…Further, a few studies on benthic community level exposed to AC also show contradictory results. No negative effects were shown with granular AC in a fresh water benthic community in Grasse River, USA (Beckingham et al 2013). A benthic community in a fresh water ditch (Veenkampen, The Netherlands) showed an initial perturbation followed by recolonization and recovery 1 year after exposure of fine particle AC (Kupryianchyk et al 2012).…”

In situ sediment treatment using activated carbon: A demonstrated sediment cleanup technology

“…Greater than 99% reductions in PCB aqueous equilibrium concentrations were observed during the third year of postplacement monitoring in plots where the AC dose in the 0‐ to 15‐cm layer was 4% or greater (Figure ), effectively demonstrating that PCB flux from sediments to surface water was almost completely contained. AC addition decreased PCB bioavailability as measured by in situ and ex situ bioaccumulation testing (using Lumbriculus variegatus ). The overall decrease improved during the 3‐year, post‐placement monitoring period, with greater than 90% reductions observed during the third year of post‐placement monitoring in plots where the AC dose in the 0‐ to 15‐cm layer was greater than 4% (Figure ). Benthic recolonization occurred rapidly after application and no changes to the benthic community structure or number of individuals were observed in AC amendment plots relative to background (Beckingham et al ). In laboratory studies using site sediment, aquatic plants grew at a moderately reduced rate (approximately 25% less than controls) in sediment amended with a dose of greater than 5% AC. The reduced growth rate was likely attributable to nutrient dilution of the sediment (Beckingham et al ). Although other project data (not shown) indicated the AC amendment slightly increased the erosion potential of sediments (although within the range of historical data for native sediments), all of the delivered AC remained in the sediments throughout the 3‐year, post‐placement monitoring period. Up to several centimeters of relatively clean, newly deposited sediment accumulated on the sediment surface in the pilot area over the 3‐year, postplacement monitoring period.…”

“…Benthic recolonization occurred rapidly after application and no changes to the benthic community structure or number of individuals were observed in AC amendment plots relative to background (Beckingham et al ).…”

“…In laboratory studies using site sediment, aquatic plants grew at a moderately reduced rate (approximately 25% less than controls) in sediment amended with a dose of greater than 5% AC. The reduced growth rate was likely attributable to nutrient dilution of the sediment (Beckingham et al ).…”