Thesis (Ph. D.)(Microbiology)--University of Pretoria, 2007. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds that are composed by at least two aromatic rings. PAHs can be found in coal and petroleum, but can also be formed from incomplete combustion of for example fossil fuels, tobacco, wood and when smoking food. PAHs has been shown to cause several health risks such as carcinogenic effects, which led to that the U.S Environmental Protection Agency (U.S. EPA) selected 16 PAHs as priority pollutants. Those 16 PAHs is usually analysed when investigating PAH exposure. To analyze dermal exposure of PAHs a tape-stripping technique can be used. The tape-stripping method involves that a tape piece is placed on the skin to absorb the present PAHs and then the tape is removed and the PAHs can be extracted and cleaned-up from the tape. The aim of this study is to optimize a recently elaborated clean-up method for PAHs sampled by the tape-stripping technique. Also, to apply the method and measure the dermal exposure of 16 PAHs among soil remediation workers. Two clean-up methods were evaluated, Florisil SPE columns and deactivated silica (10%). Clean-up using Florisil columns were evaluated using 10 and 12 ml of n-hexane. For elution, poor recoveries were achieved for both elution volumes tested. On the other hand, tests using deactivated silica generated good recoveries for both elution solvents tested (i.e. 4 ml n-hexane:dichloromethane + 4 ml dichloromethane and 8 ml n-hexane). As for the elution solvents, no significant difference could be seen in the recoveries and the mixture of n-hexane and dichloromethane was used for the real samples. The dermal exposure of PAHs for the soil remediation workers were investigated using dermal tapes from the palm and neck of 18 soil remediation workers. Samples from the palm were sampled before and after a working day and there was a small difference between the total PAH concentration before and after a work-shift. For all categories of workers (office staff, machine operators and persons performing sampling) an increase in dermal concentration of PAHs could be observed for ten of the workers, but this increase were highest among the workers active in taking samples at the contaminated site. However, an increase in PAH exposure was not observed for all study participants and possible this is due to hand-washing after toilet visits. Overall, the concentrations of PAHs on the dermal samples from soil remediation workers were low, especially in comparison to other occupations such as chimney sweeps and pavers where PAH exposure is known to exist. The detected PAHs on the dermal tapes corresponded to PAH profiles in soil samples from the site.

Contaminated soils are a large issue worldwide and much effort has been made to find efficient remediation methods. At many contaminated sites, mixtures of dif­ferent contaminants with different properties are present, which may lead to addi­tional problems, and thus additional costs, during the remediation process. This thesis presents the results from soil remedia­tion of two mixed contaminated soils, containing explosives and heavy metals and polycyclic aromatic hydrocarbons (PAH) and arsenic, respectively. The re­sults demonstrate that bioremediation may be an efficient method for moderate explosives concentration, but that too high contaminant concentrations may prevent the biodegradation, measured by both chemical and ecotoxicological analyses. If the contaminant concentration is very high, soil washing with alkaline pH (~12, NaOH) may be a good alterna­tive, which was observed to remove both explosives and heavy metals. For a PAH and arsenic contaminated soil, little degradation of organics was ob­served during the bioremediation. However, the arsenic present was re-distributed in the soil, which could poten­tially lead to increased availability and thus in­creased risk for contaminant spreading. Soil washing at alkaline pH (~12-13; Ca(OH)2) with a combination of a biodegradable non-ionic sur­factant and a biodegradable chelating agent, executed at high temperature (50°C), reached treatment goals for both arsenic and PAH after 10 min treatment. Measurement of ecotoxicity using Microtox® demonstrated that remaining surfactant in the soil may lead to increased toxicity despite lower con­taminant concentrations. Soil is a basically non-renewable resource and thus re-cycling of remediated soil ought to be commonly occurring. Yet, the re-cycling of remediated masses has so far been limited in Sweden, mainly because of the risk of spreading of pollu­tant remains. However, a recent proposition from the Swedish EPA opens for re-cycl­ing, even though the thresholds are very con­servative. Risk assessment of the re­mediated soil includes the utilization of leach­ing tests to estimate the risk of spreading of remaining pollutants. A comparison of the leaching from four reme­diated soils using three different leaching solutions reveals that leaching of both heavy metals and PAH occurs. In addition, differ­ences between different legisla­tions were observed, which could imply that the same soil could be re-cycled in one country (the Netherlands) but not another (Sweden).

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The study of acid rock and mine (ARD and AMD) environments mainly focused on the mineralogical and microbiological conditions and responses of such systems. Most of the research that involved some organic viewpoint was related to the amelioration of the environmental conditions, sometimes with contradictory results. How organic matter (OM) participates and which organic fractions are involved in ARD and AMD processes remain unclear. In this work we have applied organic geochemistry tools combined with mineralogical ad molecular microbiology techniques to study of ARD and AMD environments. The main objectives were to identify and characterise the natural sources of OM occurring both at ARD and AMD sites, and to determine whether the OM sources identified are involved in the generation or amelioration of AMD/ARD. This study shows that multiple OM sources occur naturally in acid drainage environments, included plant derived material and mature, petroleum-derived hydrocarbons, originating from the source rocks, apparently have not directly influence on the processes. This suggests that the generation of ARD and AMD is a completely chemoautotrophic process. Particle size of the iron phases present at ARD sites seems to be involved in the iron bioavailability. The presence of goethite in ARD/AMD systems may have a relationship with the presence of OM. Stimulation of ARD sediments using plant derived OM, abundantly present in and around ARD and AMD ponds systems does not result in the neutralisation of ARD or AMD. This suggests that plant material is not used by Fe(III)-reducing bacteria. However, it fuels fermentation processes and it is likely that fermentation products such as acetate, detected in microcosms and in situ, could limit Fe(III)-reduction. In contrast, the stimulation of ARD sediments using manure (particularly sheep manure) raises the pH up to near neutral conditions. Although it remains unclear which OM fraction from the manure is actively involved in the neutralisation of ARD; these results suggest that manure may make an interesting and non-expensive electron donor in AMD/ARD treatments.

In Boden, northern part of Sweden, there is a site called Solgårdarna which has been used for wood impregnation. The activities on the site have led to soil contamination with chrome (Cr), copper (Cu) and arsenic (As), where the arsenic contamination is the most problematic. This master’s thesis has studied the possibility to stabilise As in-situ with iron (Fe). The aim of the thesis was to investigate how well the distribution of Fe in the soil with the help of electrokinetics occurs. The work was divided into 3 parts, where part 1 and part 2 were performed in the laboratory and part 3 was performed in field. Part 1 investigated how Fe can distribute depending on how the electrodes were connected. This was done using quartz sand so visual assessment of the distribution could be done. Part 2 used the results from part 1 for a similar experiment performed on soil from Solgårdarna to see how stabilisation of As in the soil will work. Part 3 was a field test at Solgårdarna where it was tested on a pilot scale. Part 1 of was performed in two sets, 7 days each. It showed that it is possible to spread iron in the sand with the help of this method. The sand experiments achieved a covering area of 27 % respectively 28 % of rust over the entire profile during one week. Measurement with the XRF showed that where the electrode had been located the concentration of Fe increased up to 0.21-0.29 % and the concentration of Fe between the electrodes were 0.04-0.06 %. Part 2 of the experiment was performed in one setup over a 51-day period, after day 35 the experimental setup was changed due to highly fluctuating pH. The results from the experiment with soil showed that the pH is highly affected by how long the electrodes close to the sampling points were anodes or cathodes. During the experiment, a general trend for increasing As concentration in the different locations in the cell were seen. After the experiment the leachable amounts of As decreased down to 0.8-1.7 mg/kg TS compared to the untreated soil, 2.9 mg/kg TS. Part 3 of the experiment represent a 2-month field pilot test period during the autumn. Towards the end of the sampling period there was a general decrease in dissolved As and Fe in the groundwater, during the same time the groundwater level decreased, the redox potential increased and the electrical conductivity decreased. The laboratory experiments with the sand showed a removal rate around 90 % or higher, which is a good result. Those experiments were however performed using a clean inert material which is not comparable with real conditions. The field experiment was done over a short period of time due to time limitations of this thesis, while follow up of the pilot test was done within the scope of a continued research project at LTU. The given results showed a decrease in dissolved arsenic in groundwater which is a positive result. To determine whether the decrease is due to the natural adsorption of As to soil or due to the impact of provided Fe oxides requires longer monitoring of the experiment.

Thermal desorption (TD), a remediation method used to remove hydrocarbons from contaminated soils, may cause changes in soil properties that threaten soil function and plant productivity. The goal of this research is to better understand the effect that TD treatment has on soils intended for agricultural use. A series of soil phosphorus (P) sorption and desorption experiments were conducted on soils before and after TD treatment to determine P availability for plant uptake and risk for run-off. TD-treated soils retained more P, likely due to mineral transformations of Fe- and Al-oxides. In addition, a three-year field study using mixtures of topsoil (A), crude-contaminated soil (SP), and TD-treated soils (TDU) was conducted. Yields were significantly greater in plots that included A in the mixture compared to SP and TDU soils alone. TD-treated soils can be a replacement for topsoil, but the addition of topsoil will reduce the time to successful reclamation.

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