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Bioturbation Delays Attenuation of DDT by Clean Sediment Cap but Promotes Sequestration by Thin-Layered Activated Carbon
journal contribution
posted on 2014-01-21, 00:00 authored by Diana Lin, Yeo-Myoung Cho, David Werner, Richard G. LuthyThe effects of bioturbation on the
performance of attenuation by
sediment deposition and activated carbon to reduce risks from DDT-contaminated
sediment were assessed for DDT sediment-water flux, biouptake, and
passive sampler (PE) uptake in microcosm experiments with a freshwater
worm, Lumbriculus variegatus. A thin-layer of clean
sediment (0.5 cm) did not reduce the DDT flux when bioturbation was
present, while a thin (0.3 cm) AC cap was still capable of reducing
the DDT flux by 94%. Bioturbation promoted AC sequestration by reducing
the 28-day DDT biouptake (66%) and DDT uptake into PE (>99%) compared
to controls. Bioturbation further promoted AC-sediment contact by
mixing AC particles into underlying sediment layers, reducing PE uptake
(55%) in sediment compared to the AC cap without bioturbation. To
account for the observed effects from bioturbation, a mass transfer
model together with a biodynamic model were developed to simulate
DDT flux and biouptake, respectively, and models confirmed experimental
results. Both experimental measurements and modeling predictions imply
that thin-layer activated carbon placement on sediment is effective
in reducing the risks from contaminated sediments in the presence
of bioturbation, while natural attenuation process by clean sediment
deposition may be delayed by bioturbation.