EFECTS OF CLAYS AND ALKYL-AMMONIUM CLAYS ON THE BIOAVAILABILITY OF NAPHTHALENE

Authors: KEHRMEYER, STACI - UNIV OF TN-KNOXVILLE; TRAINA, SAMUEL - OHIO STATE UNIV; PETERS, N - UNIV OF TROMSO/NORWAY; SIMS, GERALD

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Microbial degradation of organic pollutants slows down when the compounds move into soil organic matter (sorption), and are not available to microbes until the compounds move back into the soil water phase (desorption). Desorption can be slower than microbial degradation, retarding bioremediation of contaminated soil. Researchers have examined bioavailability problems using microorganisms with and without soil as an adsorbent. The presence of soil, however, changes microbial activity in more ways than just limiting bioavailability of the pollutant. We conducted an experiment in which organisms were exposed to clays that were altered internally with surfactants (detergents) to produce different affinities for naphthalene. This experimental system separated bioavailability effects from other effects of clay on the microorganisms. From experiments including a treatment without clay, it was clear that the presence of clay slowed down degradation even in the absence of surfactant. The surfactant decreased bioavailability and slowed down the organisms' production of enzymes that degrade naphthalene. This study showed that simply varying the presence or absence of an adsorbent does not really test for bioavailability effects. The study also showed that bioavailability can slow down induction (production of degradative enzymes), a critical step in degradation. These data will guide scientists in enhancing bioavailability and designing models to predict the time required to clean up contaminated sites using bioremediation. Accurately predicting and reducing clean up time cuts costs to consumers by allowing increased adoption of bioremediation, a less expensive remediation technology.

Technical Abstract: Alkyl-ammonium surfactant-clay complexes of varying surfactant loading were used as model adsorbents to assess the bioavailability of sorbed naphthalene. Fluorescence spectrometry of cell/clay suspensions along with direct extraction and analysis by high-pressure liquid chromatography (HPLC) was used to monitor naphthalene degradation. Bioavailability of naphthalene to Pseudomonas putida AC10R was significantly decreased by sorption of the compound to tetramethylammonium (TMA) or hexadecyltrimethylammonium (HDTMA). Growth of P. putida on naphthalene was substantially reduced when substrate availability was limited by sorption. Presence of the adsorbent had no effect on growth of the organism on a non-sorbing substrate. Substrate sorption negatively affected degradation rates and the time required for complete naphthalene degradation. In some cases, the increased time appeared to result from a longer lag period in surfactant-clay treatments before rapid degradation began. Naphthalene degradation rates in clay-free systems were significantly greater than those in the presence of clay or surfactant-clay. These results validated the need to compare treatments of similar particle densities, but different sorptive capacities, rather than making comparisons between particle-free and slurry systems.