Kyung-Hee Shin

Toxic effect of biosurfactant addition on the biodegradation of phenanthrene

The effect of the biosurfactant rhamnolipid on phenanthrene biodegradation and cell growth of phenanthrene degraders was investigated. To compare the effect of rhamnolipid addition, two bacterial strains, 3Y and 4-3, which were isolated from a diesel-contaminated site in Korea, were selected. Without the biosurfactant, large amounts of phenanthrene were degraded with both strains at neutral pH, with higher rates of phenanthrene degradation when the cell growth was higher. Upon the addition of 240 mg/L rhamnolipid, the phenanthrene degradation and optical density were reduced, with this inhibitory effect similar for both 3Y and 4-3. To explain this inhibition, the cell growths of both strains were monitored with various concentrations of rhamnolipid, which showed significant toxic effects toward strain 3Y, but was nontoxic toward 4-3. Combining the inhibitory and toxicity results with regard to the biodegradation, different mechanisms can be suggested for each strain. In the biodegradation experiments, the toxicity of rhamnolipid itself mainly was responsible for the inhibitory effect in the case of 3Y, whereas the toxicity of solubilized phenanthrene or the increased toxicity of rhamnolipid in the presence of solubilized phenanthrene could have resulted in the inhibitory effect in the case of 4-3. This study demonstrated that the effectiveness of biosurfactant-enhanced biodegradation can be significantly different depending on the strain, and the toxicity of the biosurfactant should be considered as an important factor.

Earthworm toxicity during chemical oxidation of diesel‐contaminated sand

An ecotoxicity test with Eisenia fetida was performed to monitor the removal of diesel and toxicity variation during the ozonation process. The three-dimensional (3-D) cell test was introduced for the monitoring of the ozonation process, and the removal rate based on total petroleum hydrocarbons (TPHs) mass was about 95% near the ozone inlet ports. This high removal rate might be caused by the low soil organic matter (SOM) content and low water content of sand. The use of a fiber-optic transflection dip probe (FOTDP) demonstrated that more than half of the injected ozone was consumed by reactions with diesel or natural ozone-consuming materials. The earthworm toxicity test using Eisenia fetida demonstrated that diesel concentrations in soil exceeding 10,000 mg/kg caused a dose-dependent weight loss in earthworms and increased mortality. Toxic effects were reduced greatly or eliminated after ozonation, and the degradation products of the ozonation were not toxic to the earthworms at the concentrations tested. One specific result was that the sublethal test on the earthworm might be more sensitive for the evaluation of the quality of contaminated soil, for some samples, which did not result in mortality and produced an adverse effect on weight.

Progress in Earthworm Ecotoxicology

Earthworms are regarded as one of the most suitable animals for testing the toxicity of chemicals in soils and have been adopted as standard organisms for ecotoxicological testing. In several guidelines concerning earthworm toxicity tests, Eisenia fetida/andrei (E. fetida/andrei) was chosen because it can be easily cultured in the laboratory and an extensive database on the effects of all classes of chemicals exists for this species. Acute and chronic toxicity tests have been used traditionally to assess the toxicity of contaminants, with mortality and changes in biomass, reproduction rates and behavioral responses representing endpoints. Moreover, the avoidance behavior test (AVT) using earthworm is under development and standardization, which records the ability of earthworms to choose or avoid a certain soil. Recent studies have shown that neutral red retention time (NRRT) has the potential for a rapid assessment of the toxic effects for earthworms of soils contaminated with heavy metals and metalloids. Toxicity is the apparent expression of the metal accumulation in earthworm body. The uptake, accumulation and elimination properties of metals by earthworm are the major part of toxicology, which is called toxicokinetics. Geochemical factors may have signifi cant effects on metal transport or bioavailability. Prediction models for metal accumulation and toxicity in soils are being developed based on metal bioavailability. In this study, methodologies and research trends in earthworm toxicity are reviewed for understanding metal bioavailability. Toxicity prediction models are introduced for terrestrial environment and several studies are referred to understand the role of geochemistry in toxicology.

A biosurfactant-enhanced soil flushing for the removal of phenanthrene and diesel in sand.

In order to examine the potential of biosurfactants in soil remediation, and to investigate the effects of several operating conditions, such as flow rate, biosurfactant concentration and surfactant type, biosurfactant-enhanced soil flushing was conducted. In the biosurfactant-enhanced soil flushing process, the removal efficiency increased as the flow rate decreased. Rhamnolipid showed no effect on the removal efficiency of phenanthrene and diesel from sand in the concentration range 0.3–0.5%. However, rhamnolipid showed higher efficiencies for the removal of phenanthrene and diesel from sand than Tween 80. Based on total recovery, following an equivalent pore volume flush, it was more difficult to remove diesel than phenanthrene. In order to obtain the specific removal efficiency, more pore volumes of surfactant solution may be required in field applications. Under optimum conditions, the biosurfactant removed as much as 70% of the phenanthrene and 60% of the diesel in the sand. These results indicate that the use of biosurfactants in the flushing process is favorable, not only with respect to the environment, but also on removal efficiencies.

Ecotoxicity monitoring of hydrocarbon-contaminated soil using earthworm (Eisenia foetida).

In order to assess the applicability of an earthworm bioassayas a technique for monitoring the soil flushing process, short-term and long-term toxicity tests were conducted on remediatedsoil using various pore volumes of surfactant solution. Resultsobtained on short-term toxicity testing indicated that biomassincreased as the soil flushing proceeded, and on diesel-contaminated soils this testing showed that the effect of dieselis lethal and that 25 pore volumes of soil surfactant were notsufficient to abrogate the toxic effect of diesel. These short-term tests also showed strong sublethal relationships between the development of biomass, and the concentrations of toxic chemicals in the soil. Although relationships between contaminants and the various bioassay parameters examined werenot significant in long-term testing, an increase in the numberof juveniles was observed over time, which may have been a consequence of a reduction in toxicity associated with the flushing process.

Chemical and ecotoxicity assessment of PAH-contaminated soils remediated by enhanced soil flushing

Development of remediative techniques for PAH-contaminated soils and evaluation of residual toxicity after remediation are important issues in the assessment of soil quality. To investigate the efficiency of soil remediation technology using biomonitoring assay, soil flushing experiments with surfactant and ecotoxicity tests with Eisenia fetida were carried out for artificially phenanthrene-contaminated soils. Mortality and growth of the earthworms were significantly influenced by phenanthrene concentration and exposure time to the contaminant. Sublethal toxicity effects such as weight variation of the organisms appeared to be more reliable factors than acute effects (e.g., mortality) to represent soil toxicity when compared with chemical determination of remaining phenanthrene. The contaminated soils remediated with more than 15 pore volumes of the surfactant were not significantly toxic to the earthworms with respect to average weight development, which was clearly confirmed by the results of chemical a...