Environ. Sci. Technol. 2000, 34, 2237-2242
Role of Natural Organic Matter in Accelerating Bacterial Biodegradation of Sodium Dodecyl Sulfate in Rivers S A M A N T H A J . M A R S H A L L , * ,† WILLIAM A. HOUSE,‡ AND GRAHAM F. WHITE† Cardiff School of Biosciences, Cardiff University, Biomedical Building, Museum Avenue, P.O. Box 911, Cardiff, CF1 3US, United Kingdom, and Institute of Freshwater Ecology, River Laboratory, East Stoke, Wareham, Dorset, BH20 6BB, United Kingdom
The influence of natural organic matter (NOM) on the adsorption of sodium dodecyl sulfate (SDS) and bacteria to riverine sediment surfaces and the effects of these interactions on the rates of SDS biodegradation in river environments were investigated. SDS was adsorbed substantially to native sediment (containing 16% w/w NOM) but not to organic-free sediment or organic-free sediment coated with either a commercial (Aldrich) or natural humic acid. The presence of NOM on the sediment surface did not influence the overall distribution of the SDSdegrading bacteria, Pseudomonas C12B, between sedimentattached and free-living states. However, the attachment of bacteria to native sediment was stimulated by the addition of SDS, and attachment was maximal within the period of SDS degradation. The rate of SDS biodegradation in the presence of native sediment was faster than that observed in the absence of sediment, and this increase in rate could not be solely attributed to the presence of indigenous bacteria in the sediment. In contrast, the rates of biodegradation in the presence of organic-free and humiccoated sediments were found to be comparable to that observed in the absence of sediment. The results indicated that NOM on sediment surfaces substantially influences SDS biodegradation by localizing both the surfactant and thus, in turn, bacteria at the sediment surface, thereby increasing the likelihood of catalysis.
Introduction The fate of organic pollutants arriving in river environments is dependent on inter alia their potential for biodegradation by microorganisms and on the way in which they adsorb to particle surfaces. This adsorption process is affected by the nature of the compound itself, the type of sediment surface present, and the surrounding water chemistry. In particular, the adsorption of hydrophobic pollutants to sediments can be substantially enhanced by the presence of natural organic matter (NOM) on the sediment surface (1-7). Adsorption to solid-liquid interfaces can influence the availability of * Corresponding author phone: +44 (0)29 20876877; fax: +44 (0)29 20874116; e-mail:
[email protected]. † Cardiff University. ‡ Institute of Freshwater Ecology. 10.1021/es990828p CCC: $19.00 Published on Web 04/29/2000
2000 American Chemical Society
pollutant molecules to biodegrading microorganisms (8). It is well established that in river environments most of the microbial activity, and therefore biodegradation potential, resides in attached bacterial populations on the surface of sediment particles and not in the water column itself (9). The surface properties of both the bacteria and the solidliquid interface can be altered substantially by the adsorption of compounds such as naturally occurring and synthetic surfactants (10). Such alterations in surface properties can greatly influence the type and magnitude of the interactions that occur between bacteria and solid surfaces and therefore also the attachment of bacteria to surfaces (11). Both Marchesi et al. (12) and Owen et al. (13) have shown that the addition of a biodegradable surfactant, such as sodium dodecyl sulfate (SDS), to river sediment resulted in an almost immediate increase in the number of bacteria attached to sediment particles and a corresponding decrease in free-living bacterial numbers. On biodegradation of the surfactant, the bacterial populations returned to their preaddition values. The aims of the work presented were to investigate the influence of NOM on the adsorption of SDS and bacteria to riverine sediment surfaces and to determine how these interactions may influence rates of SDS biodegradation.
Experimental Section Preparation of Pond Sediment. Surface sediment, henceforth termed native sediment, was collected at a depth of
