Effect of surfactants on solubilization and degradation of phenanthrene under thermophilic conditions

The bioavailability and biodegradation of polycyclic aromatic hydrocarbons (PAHs) can be increased through the addition of surfactants. Previous studies of this nature have been conducted under mesophilic conditions. Hence, the aim of the present study was to investigate the effects of synthetic surfactants and biosurfactants on solubilization and degradation of phenanthrene (PHE) in a series of batch solution experiments under thermophilic conditions. Tween 80, Triton X-100, and biosurfactants produced from Pseudomonas aeruginosa strain P-CG3 (P-CG3) and Pseudomonas aeruginosa ATCC 9027 (P. 9027) were used in this study. Surfactants effectively enhanced the solubility of PHE at 50 degrees C and the biosurfactant from P-CG3 was most effective with a 28-fold increase in apparent solubility of PHE at a concentration of 10 x critical micelle concentration (CMC) compared with the controls. However, addition of synthetic surfactants or biosurfactants inhibited the biodegradation of PHE in mineral salts medium by an isolate Bacillus sp. B-UM. Degradation of PHE diminished with increasing surfactant concentrations, and PHE degradation was completely inhibited for all the surfactants tested when the concentrations were greater than their respective CMC. The growth test suggested that Tween 80 and biosurfactants were degradable, but preferential utilization of these surfactants as substrates was not the mechanism for explaining the inhibition of PHE biodegradation. Because of the hydrophobic property of B-UM, degradation inhibition of PHE by surfactants was probably due to the reduction of direct contact between bacterial cells and PHE.     

Current issues and uncertainties in the measurement and modelling of air-vegetation exchange and within-plant processing of POPs

Air-vegetation exchange of POPs is an important process controlling the entry of POPs into terrestrial food chains, and may also have a significant effect on the global movement of these compounds. Many factors affect the air-vegetation transfer including: the physicochemical properties of the compounds of interest; environmental factors such as temperature, wind speed, humidity and light conditions; and plant characteristics such as functional type, leaf surface area, cuticular structure, and leaf longevity. The purpose of this review is to quantify the effects these differences might have on air/plant exchange of POPs, and to point out the major gaps in the knowledge of this subject that require further research. Uptake mechanisms are complicated, with the role of each factor in controlling partitioning, fate and behaviour process still not fully understood. Consequently, current models of air-vegetation exchange do not incorporate variability in these factors, with the exception of temperature. These models instead rely on using average values for a number of environmental factors (e.g. plant lipid content, surface area), ignoring the large variations in these values. The available models suggest that boundary layer conductance is of key importance in the uptake of POPs, although large uncertainties in the cuticular pathway prevents confirmation of this with any degree of certainty, and experimental data seems to show plant-side resistance to be important. Models are usually based on the assumption that POP uptake occurs through the lipophilic cuticle which covers aerial surfaces of plants. However, some authors have recently attached greater importance to the stomatal route of entry into the leaf for gas phase compounds. There is a need for greater mechanistic understanding of air-plant exchange and the 'scaling' of factors affecting it. The review also suggests a number of key variables that researchers should measure in their experiments to allow comparisons to be made between studies in order to improve our understanding of what causes any differences in measured data between sites.     

Estimation of critical loads for radiocaesium in Fennoscandia and Northwest Russia

The application of the critical loads methodology for radioactive contamination of Arctic and sub-arctic ecosystems, where natural and semi-natural food products are important components of the diet of many people, is proposed and discussed. The critical load is herein defined as the amount of radionuclide deposition necessary to produce radionuclide activity concentrations in food products exceeding intervention limits. The high transfer of radiocaesium to reindeer meat gives this product the lowest critical load, even though the intervention limit is relatively high compared with other products. Ecological half-lives of radiocaesium in natural and semi-natural products are often very long, and it is therefore important to take account of contamination already present in the event of an accident affecting areas where such products are important. In particular, the long ecological half-life for radiocaesium in moose meat means that the critical load is highly sensitive to prior deposition. An example of the potential application of the method for emergency preparedness is given for the Chernobyl accident.     

Using fiber optics to detect moisture intrusion into a landfill cap consisting of a vegetative soil barrier

The intrusion of moisture into landfills can pose a health hazard because of the possibility that the moisture will carry harmful substances into the groundwater. Early detection of moisture anywhere within these landfills is essential if corrective action is to be taken well before an occurrence of this kind. This paper presents the results of a field-scale simulation test of the use of fiber optics to detect the presence of moisture within landfill covers, using a detection method based on the thermal response of soils as a function of their moisture content. By sending electrical current through an embedded stainless-steel tube, soils of varying moisture content were heated and time-dependent temperature measurements were obtained with a fiber-optic distributed temperature sensor system. The optical fiber itself lay within the tube, but its temperature was a function of how rapidly heat was conducted into the surrounding medium. The results of this experiment, which are in agreement with those obtained using more traditional "point" sampling and laboratory analysis, are presented along with the strengths and limitations of the thermal-response method of detecting moisture.     

Interspecific differences in fouling of two congeneric ascidians (Eudistoma olivaceum and E. capsulatum): is surface acidity an effective defense?

Ascidian specimens were collected from the Indian River Lagoon, Florida, USA, in November 1987. Eudistoma olivaceum (Van Name) was fouled by only two species of epifaunal invertebrates and the percent cover of epibionts was negligible. Colonies of E. capsulatum (Van Name) were fouled by up to 17 species of epifaunal invertebrates, epibionts covered an average of 12.5% of the surface area of these colonies. Extracts of E. olivaceum exhibited potent cytotoxic, antimicrobial and antiviral activity in laboratory bioassays, while the activity of extracts of E. capsulatum was insignificant. The toxicity of extracts of each ascidian was negatively related to the percent cover of fouling organisms. Surface acidity of each ascidian was positively related to the percent cover of epibionts: E. olivaceum was nearly neutral (pH=6), while E. capsulatum was highly acidic (pH=1 to 2). Larval settlement and growth of ancestrulae of the cheilostome bryozoan Bugula neritina (Linnaeus) were inhibited at very low concentrations of crude extract of E. olivaceum. Crude extracts of E. capsulatum inhibited settlement and growth of B. neritina only at concentrations of approximately an order of magnitude greater than those of E. olivaceum. Differences in the degree to which these congeneric ascidians are fouled is related to differences in the chemical defenses they possess. Acidity is not an effective inhibitor of settlement by epifaunal invertebrates.     

Behaviour that influences dispersal and connectivity in the small,young larvae of a reef fish

Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology. Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish, Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined. Critical speed was 27.5 ± 1.0 cm s⁻¹ (30.9 BL s⁻¹), and in situ speed was 13.6 ± 0.6 cm s⁻¹. Fastest individuals were 44.6 and 25.0 cm s⁻¹, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed. Unfed larvae swam 172 ± 29 h at 8–10 cm s⁻¹ (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was 2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left (more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction. Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours, and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to behaviour of other settlement-stage pomacentrid larvae that are older and larger.