Alteration and release of aliphatic compounds by the polychaete Nereis virens (Sars) experimentally fed with hydrocarbons

Abstract

In the laboratory, marine worms were fed with a mixture of algae and several aliphatic hydrocarbons for 15 days. After ingestion by the worms, 34.9% of hydrocarbons are found in the faeces and only 3.1% accumulated in the gut. The comparison between the initial mixture and the faeces shows that the worm’s digestive process lead to changes in the distribution of the n-alkane mixture. These changes are different from those only due to physical processes in the experimental conditions. In our experiment, no variation in the distribution of hydrocarbons in faeces with time and no microbial hydrocarbon biodegradation were evidenced. Our results suggest that marine worm feeding can substantially affect the fate of hydrocarbons in the sedimentary marine ecosystem by predominantly stimulating dissolution processes.

Introduction

The activity of benthic organisms modifies the physical and chemical nature of marine sediments (Aller, 1982). In the case of petroleum pollution, if the changes in the chemical environment can affect the sedimentary biota, all the biological processes included under the term ‘bioturbation’ play an important role with regard to the fate of hydrocarbon pollutants (Lee and Swartz, 1980).

Previous works dealing with the role of bioturbation in the fate of hydrocarbons have more particularly taken into account their overall weathering related to the biological distribution and transfers of pollutants adsorbed onto the sediment (Gardner et al., 1979, Karickhoff and Morris, 1985, Reynoldson, 1987, Gilbert et al., 1994, Gilbert et al., 1996, Kure and Forbes, 1997). During the mixing of sediments, bioturbating macrofauna stimulates hydrocarbon desorption for particles (Koerting-Walker and Buck, 1989), and then greatly favours their bioavailability (Mihelcic and Luthy, 1991, Madsen et al., 1997) and resulting bacterial biodegradation (Gordon et al., 1978, Bauer et al., 1988, McElroy et al., 1990). In areas of intensive reworking, where the benthic macrofauna ingests the surface sediment several times a year (Myers, 1977), the digestive activity of macro-organisms, and more especially worms, may represent a non-negligible part of the hydrocarbon handling thus exposed to microbiological transformations (Plante and Jumars, 1992) and to a chemical environment controlled by the digestive chemistry of the organism (Mayer et al., 1997, Gilbert et al., 1998). More especially, passage of hydrocarbons through the worm gut may also result in metabolisation and accumulation (Lee and Singer, 1980, McElroy and Sisson, 1989, Forbes et al., 1996, Fergusson and Chandler, 1998, Sheedy et al., 1998). Moreover, recent works have demonstrated the high hydrocarbon solubilising potential of extracted gut digestive fluids (Mayer et al., 1996, Weston and Mayer, 1998a, Weston and Mayer, 1998b).

The aim of our work was to provide more information on the direct role of macrofauna during its digestive activity with regard to the fate of hydrocarbons in marine sediments. To this end, a laboratory experiment has been carried out with the aim of monitoring the uptake, release and alteration of a mixture of aliphatic hydrocarbons ingested by the marine polychaete Nereis virens. The Nereidae, due to their wide distribution and easy laboratory maintenance and acclimation, are the most suitable genus to test the fate of persistent pollutants in marine animals (Goerke, 1984). In the Saint Lawrence estuary, N. virens is one of the most important mudflat species because of its high density (Desrosiers et al., 1994). This worm builds U-shaped burrows in the sediment layer with extension, for adults, up to 30–50 cm below the sediment surface (Goerke, 1976, Kristensen et al., 1985, Miron et al., 1991a). This species inhabits extensive soft substrates in littoral and sub-littoral zones on the coasts of NE North America and NW Europe. Due to urban and industrial activity, this type of environment is highly exposed to the impact of many types of pollutants, particularly hydrocarbons.