MEPS 197:151-167 (2000)  -  doi:10.3354/meps197151

Influence of particle type and faunal activity on mixing of di(2-ethylhexyl)phthalate (DEHP) in natural sediments

Joanna Sandnes1, Thomas Forbes2, Rikke Hansen3, Bjørnar Sandnes4,*

1Norwegian Institute for Water Research (NIVA), PO Box 173 Kjelsås, 0411 Oslo, Norway
2Department of Marine Ecology, National Environmental Research Institute, PO Box 358, Frederiksborgvej 399, 4000 Roskilde, Denmark
3Darling Marine Center, University of Maine, Walpole, Maine 04573, USA
4Department of Physics, University of Oslo, PO Box 1048 Blindern, 0316 Oslo, Norway
*Corresponding author. E-mail:

ABSTRACT: The influence of faunal activity and particle type on sediment-mixing processes of the particle-bound, organic contaminant di(2-ethylhexyl) phthalate (DEHP) were examined over a 48 d experimental period with natural box-cosm sediments. A dual-labelling radiotracer technique using 14C-DEHP and 51Cr determined the fate and utilization of DEHP associated with either sediment or phytoplankton particles. Particle-mixing was estimated using a 1-dimensional transient-state biodiffusion model and expressed as Db coefficients. Sediment 51Cr depth profiles fitted this simple biodiffusion model well, indicating randomized, vertical particle mixing. Particle reworking rates were approximately 9-fold higher in faunated treatments compared to defaunated control sediments, thus quantifying the importance of benthic fauna as agents of physical transport. Biodiffusion rates in faunated box-cosms were significantly higher in phytoplankton compared to sediment 14C-DEHP particle treatments (p < 0.05). This was attributed to an experimental urchin effect resulting from natural variations in the density of the large macrofaunal urchin Echinocardium cordatum between particle treatments. Sediment-mixing rates were independent of particle type when this urchin effect was removed. Examination of 14C and 51Cr relative depth profiles showed the 2 tracers to be coupled in defaunated sediments and decoupled with animals present. This effect was also independent of particle-type, indicating no selective transport associated with the particle-type treatments. The decoupling of tracers in faunated treatments, with 14C-DEHP having consistently higher depth-weighted mean values than the 51Cr tracer, suggested a decrease in surface 14C-DEHP concentrations through degradation processes at the sediment-water interface. Sediment-mixing rates increased significantly with increasing total community biomass, indicating that size (biomass) may be the single most important community parameter determining sediment-mixing intensity. Downward particle transport was strongly correlated with E. cordatum abundance (p < 0.01), the dominant species in the benthic community in terms of size. E. cordatum densities also correlated strongly with the number of benthic infaunal species present in the box-cosms, with maximum infaunal species numbers occurring at intermediate E. cordata densities. This is in accordance with theories on intermediate disturbance. The 2 14C-DEHP particle-type treatments had no significant effect on E. cordata body sizes or DEHP body burden. The large urchin E. cordatum clearly dominated sediment-mixing, and did so in a Œnon-selective¹ manner.

KEY WORDS: Bioturbation · Organic contaminants · Phthalate · Sediment · Tracers · Particle quality · Selective transport · Echinocardium cordatum · Disturbance

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