Development of a sensitive and rapid method for the measurement of total microbial activity using fluorescein diacetate (FDA) in a range of soils. Soil Biology and Biochemistry,

The use of plant-based systems to remediate contaminated soils has become an area of intense scientific study in recent years and it is apparent that plants which grow well in contaminated soils need to be identified and screened for use in phytoremediation technologies. This study investigated the effect of diesel fuel on germination of selected plant species. Germination response varied greatly with plant species and was species specific, as members of the same plant family showed differential sensitivity to diesel fuel contamination. Differences were also seen within plant subspecies. At relatively low levels of diesel fuel contamination, delayed seed emergence and reduced percentage germination was observed for the majority of plant species investigated.Results suggest the volatile fraction of diesel fuel played an influential role in delaying seed emergence and reducing percentage germination. In addition, the remaining diesel fuel in the soil added to this inhibitory effect on germination by physically impeding water and oxygen transfer between the seed and the surrounding soil environment, thus hindering the germination response.

Groundwater contamination by fuel spills from aboveground and underground storage tanks has been of growing concern in recent years. This problem has been magnified by the addition of oxygenates, such as ethanol and methyl-tertiary-butyl ether (MTBE) to fuels to reduce vehicular emissions to the atmosphere. These additives, although beneficial in reducing atmospheric pollution, may, however, increase groundwater contamination due to the co-solvency of petroleum hydrocarbons and by the provision of a preferential substrate for microbial utilisation. With the introduction of ethanol to diesel fuel imminent and the move away from MTBE use in many states of the USA, the environmental implications associated with ethanol additive fuels must be thoroughly investigated. Diesel fuel movement was followed in a 1-m soil column and the effect of ethanol addition to diesel fuel on this movement determined. The addition of 5% ethanol to diesel fuel was found to enhance the downward migration of the diesel fuel components, thus increasing the risk of groundwater contamination. A novel method using soil packed HPLC columns allowed the influence of ethanol on individual aromatic hydrocarbon movement to be studied. The levels of ethanol addition investigated were at the current additive level (approx. 25%) for ethanol additive fuels in Brazil and values above (50%) and below (10%) this level. An aqueous ethanol concentration above 10% was required for any movement to occur. At 25% aqueous ethanol, the majority of hydrocarbons were mobilised and the retention behaviour of the soil column lessened. At 50% aqueous ethanol, all the hydrocarbons were found to move unimpeded through the columns. The retention behaviour of the soil was found to change significantly when both organic matter content and silt clay content was reduced. Unexpectedly, sandy soil with low organic matter and low silt clay was found to have a retentive behaviour similar to sandy subsoil with moderate silt clay, but little organic matter. It was concluded that sand grains might have a more important role in the adsorption of petroleum hydrocarbons than first realised. This method has shown that soil packed HPLC columns can be used to provide a quick estimate of petroleum hydrocarbon, and possibly other organic contaminant, movement in a variety of different soil types.

Diesel oil is a complex mixture of hydrocarbons with an average carbon number of C8-C26. The majority of components consist of alkanes, both straight chained and branched and aromatic compounds including mono-, di-and polyaromatic hydrocarbons. Regardless of this complexity, diesel oil can be readily degraded by a number of soil microorganisms making it a likely candidate for bioremediation.The concept of using plants to enhance bioremediation, termed phytoremediation, is a relatively new area of scientific interest. It is particularly applicable to diesel oil contamination as diesel oil generally contaminates the top few metres of soil (surface soil) and contamination is not uniform throughout the site. By encouraging plants to grown on diesel oil contaminated soil, conditions are improved for the microbial degradation of the contaminant.During this study, establishing plants on diesel oil contaminated soil proved difficult. Diesel oil is phytotoxic to plants at relatively low concentrations. At concentrations below this phytotoxic level, the development of plants grown in diesel oil contaminated soil differs greatly from plants grown in uncontaminated soil. Tolerance of plants to diesel oil and ability to germinate in diesel oil contaminated soil varied greatly between plant species as well as within plant species. The broadest differences in germination were seen within the grasses with certain species thriving in low levels of contamination (e.g. Creeping bent) while others were intolerant of diesel oil contamination (e.g.Rough meadow grass). The herbs, legumes and commercial crops screened appeared to be largely unaffected by low levels of diesel oil contamination (25g diesel kg -1 ). At the higher level of contamination (50g diesel kg -1 ), half of the twenty two plant species screened failed reach a germination rate equal to 50% of the control rate. Two species of grass failed to germinate at all at this contamination level. Plant species that successfully germinated and grew were studied further to determine the effect of diesel oil contamination on the later stages of plant development. This work investigates the effect of diesel oil on plant growth and development.

Abstract. When petroleum hydrocarbons contaminate soil, the carbon:nitrogen (C:N) ratio of the soil is altered. The added carbon stimulates microbial numbers but causes an imbalance in the C:N ratio which may result in immobilization of soil nitrogen by the microbial biomass, leaving none available for plant growth. As members of Leguminosae fix atmospheric nitrogen to produce their own nitrogen for growth, they may prove more successful at growing on petroleum hydrocarbon contaminated sites. During a wider study on phytoremediation of diesel fuel contaminated soil, particular attention was given to the performance of legumes versus other plant species. During harvesting of pot experiments containing leguminous plants, a recurring difference in the number and formation of root nodules present on control and contaminated Common vetch (Vicia sativa L.) plants was observed. The total number of nodules per plant was significantly reduced in contaminated plants compared to control plants but nodules on contaminated plants were more developed than corresponding nodules on control plants. Plant performance of Common vetch and Westerwold's ryegrass (Lolium multiflorum L.) was compared to illustrate any difference between the ability of legumes and grasses to grow on diesel fuel contaminated soil. Common vetch was less affected by diesel fuel and performed better in low levels of diesel fuel contaminated soil than Westerwold's ryegrass. The total amount of diesel fuel remaining after 4 months in Common vetch planted soil was slightly less than in Westerwold's ryegrass planted soil.

A method for the quantification of biofilm formation on hydrogel protective coatings for optical sensors and cameras has been developed using fluorescein diacetate (FDA) hydrolysis. In conjunction with these measurements the release of the fouling resistant cationic surfactants benzalkonium chloride, tallowbenzyldimethylammonium chloride and dicocodimethylammonium chloride was measured, using high performance liquid chromatography (HPLC), to enable correlation to be made between release and biofilm resistance and thus determine the active lifetime of such coatings. Results indicate that the twin-chained material, dicocodimethylammonium chloride, produced superior biofouling resistance as, at the 12 week time point, little fouling was detected on this coating. The hydrogel containing the long-chained tallowbenzyldimethylammonium chloride (mainly C16 and C18 chains) was the next best fouling resistant material, withstanding biofilm formation for 9 weeks. This correlates with the fact that each of these materials had an extremely slow to zero release rate, due to their irreversible binding to the hydrogel over the experimental timescale. Incomparison the shorter chained benzalkonium chloride (mainly C12 and C14), showed signs of biofilm formation at the 3 week time point.