Respirometric experiments were performed to evaluate the role of nitrogen in aerobic diesel biodegradation. Specific objectives included 1) evaluating the effects of water potential induced by various nitrogen amendments on diesel biodegradation rates in arid region soils, 2) comparing concurrent effects of C:N ratios and soil water potential on diesel degradation rates, and 3), measuring gross rates of nitrogen cycling processes in diesel-contaminated soil to determine duration of fertilizer bioavailability. In all studies, increasing nitrogen fertilization resulted in a decrease in total water potential and correlated with an increase in lag phase and overall reduction in microbial respiration. Highest respiration and estimated diesel degradation was observed in the 250 mg N/kg soil treatments regardless of diesel concentration, nitrogen source, or soil used, suggesting an inhibitory osmotic effect from higher rates of nitrogen application. The depression of water potential resulting in a 50% reduction in respiration was much greater than that observed in humid region soil, suggesting higher salt tolerance by microbial populations of arid region soils. Due to the dependence on contaminant concentrations, use of C:N ratios was problematic in optimizing nitrogen augmentation, leading to over-fertilization in highly contaminated soils. Optimal C:N levels among those tested were 17:1, 34:1, and 68:1 for 5,000, 10,000 and 20,000 mg/kg diesel treatments respectively. Determining nitrogen augmentation on the basis of soil pore water nitrogen (mg N/kg soil H₂0) is independent of hydrocarbon concentration but takes into account soil moisture content. In the soil studied, optimal nitrogen fertilization was observed at an average soil pore water nitrogen level of 1950 mg N/kg H₂0 at all levels of diesel contamination. Based on the nitrogen transformation rates estimated, the duration of fertilizer contribution to the inorganic nitrogen pool at 5,000 mg/kg diesel was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg/kg nitrogen treatments respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and nitrification were assumed as losses of fertilizer with only gross mineralization of native organic nitrogen contributing to the most active portion of the nitrogen pool.

M. Tech. Chemistry. / The aim of this study was to develop and evaluate an analytical method for the determination of Cr(VI) in ferrochrome dusts and to apply the method in the analysis of environmental samples (grass, soil and tree bark) for Cr(VI) content (that might be caused by dust emissions originating from the smelter). Both the public and Xstrata Wonderkop ferrochrome plant will benefit from data of Cr(VI) determination generated from the study. The information can potentially be incorporated into health risk assessments of the affected geographical areas. The results of the investigation showed that ferrochrome smelter dust emissions were the source of contamination of the environment with Cr(VI). With time, Cr(VI) could accumulate in soil to unacceptable levels, thereby endangering both plants and animals.

No description available.

No description available.

No description available.

The use of agricultural chemicals often results in water pollution. This research, comprising three parts, was designed to investigate the role of soil and grass strips and water table management in reducing pesticide and nitrate residues in drainage waters. / The first part of the research was made on lysimeters to investigate the effects of soil and grass cover under two water table management regimes. Four treatments were involved: subsurface drainage, controlled drainage, grass cover, and bare soil. Each treatment consisted of three replicates. Contaminated water containing atrazine, metolachlor, and metribuzin residues was applied to the lysimeters and samples of drain effluent were collected. Significant reductions in pesticide concentrations were found in all treatments. / In the first year (1993), herbicide levels were reduced significantly, from an average of 250 mug/L to less than 10 mug/L. In the second year (1995), water polluted at a concentration of 50 mug/L, was applied to the lysimeters, and herbicide residues were reduced significantly to less than 1 mug/L. Subsurface drainage and grass cover lysimeters (SDG treatment) reduced herbicide concentration levels to a greater extent than the other treatments and the controlled drainage lysimeters reduced nitrate concentration levels to a greater extent than the free drainage lysimeters. / The second part of the research was a field study that reports the development and testing of an on-farm pollution control system using soil as a biological filter for trapping herbicide residues. A field site with four shallow surface ditches, underlain with four perforated drain pipes, was used to carry-out field measurements. Polluted water with concentration levels of 30 mg/L of nitrate and 100 mug/L of three commonly-used herbicides was applied to the ditches for 10 days continuously; and no water was applied for the following ten days. This cycle was repeated three times. Water samples were collected both before application and after the water came out of the drains. Herbicide levels were reduced significantly in drainage waters. The average concentration level of nitrate in drainage water was found to be 17 mg/L in comparison to 30 mg/L in applied water. Also, the bio-degradation of herbicide residues in the soil was found to occur between water applications. Thus, it appears that the system would be self-sustainable in the long term. / The third part of the research utilizes a water table model, DRAINMOD, for simulating drainage waters from agricultural land and a solute transport model, PRZM2, for simulating pesticide concentrations in the drain effluent coming out of the grass filter area. DRAINMOD was used to estimate the daily drain outflows that would occur in a 100 ha subsurface drained field in the for a 1-in-20 year annual rainfall period. It was found that 6% of the farm area could be used to bring down the concentrations in drainage water from 50 mug/L to less than 1 mug/L for the three herbicides. (Abstract shortened by UMI.)

A standard methodology was developed for performing avoidance-preference tests, using Rainbow Trout (Salmo gairdneri) as the test organism. Experiments were conducted in a hydraulic channel, 9.15 m long by 0.30 m wide, partly divided along its length, and at a flow depth of 0.30 m. The design combined steep and shallow gradient characteristics. The toxicants investigated included Cu(II), Cr(III) and Cr(VI). The lowest avoidance threshold values were established at 2.1 $ mu$g/l for Cu(II) and 0.0026 mg/l and 0.026 mg/l for Cr(III) and Cr(VI) respectively while avoidance reactions increased with levels of toxicant in the channel. Similar experiments were performed with rainbow trout which were pre-exposed at sublethal levels to the toxicant, in order to assess the influence of toxic pre-exposure to the subsequent fish avoidance response. The length of pre-exposure varied between 7-20 weeks. Avoidance threshold values were correlated with safe levels of toxicant exposure. / Pre-exposed fish exhibited decreasing avoidance reactions compared to non-exposed populations. Increased tolerance to the toxicant, was suggested by the increase in avoidance threshold values with pre-exposure levels. Fish exposed to test concentrations matching their pre-exposure levels, clearly preferred this same concentration over the adjacent lower or higher test concentration. / A two mechanism avoidance model was proposed independent of toxicant used or level of pre-exposure. The toxicant concentration where the second mechanism begins to dominate was referred to as avoidance breakpoint, and was correlated to a MATC level for the toxicant in question. Olfactory responses were proposed to be associated with fish avoidance responses below the avoidance breakpoint, while hypoxic stress along with osmo- and iono regulatory stress appeared to be responsible for driving fish avoidance reactions beyond the avoidance breakpoint. / A clearance period of 7 days was sufficient to allow fish to recover normal avoidance behaviour following pre-exposure to Cr(VI) below the avoidance breakpoint.

No description available.

No description available.

Organochlorine (OC) compounds that include several pesticides as well as an array of industrial chemicals were very efficacious for their intended use but were also characterized by deleterious environmental impacts when released either intentionally or inadvertently. Their lipophilic nature, long persistence in the environment and threat to human health caused all the developed countries to ban the production of these chemicals as well as restricted the use of formulations containing these material for food production. / A number of scientists have become involved in the development of intentional degradation methods/techniques for these compounds using zero-valent metals or bimetallic mixtures. To date, there is no single, simple and continuous procedure available to completely dechlorinate lindane or pentachlorophenol (PCP). This work describes the complete dechlorination of lindane and pentachlorophenol by zero-valent Zn, Fe and Fe/Ag bimetallic mixture as well as a supercritical fluid extraction technique for a more efficient mass transfer of the substrates to the surfaces of the metal catalyst. The dechlorination reaction occurs on the surface of metal particles with the removal of all the chlorine atoms from lindane and PCP in a matter of minute, and yields completely dechlorinated hydrocarbon molecules and chloride as products. (Abstract shortened by UMI.)