The control of ticks on cattle has long been a matter of prime importance to stock owners over most of the intensive natural grazing areas in the Southern Hemisphere. The only practical method of dealing with the cattle tick problem in the short term is by treating the infected bovine host with ixodicides i. e. by chemical control. This can be achieved by either plunging the cattle into a dip tank containing aqueous suspensions or emulsions of the ixodicide or by spraying them with dip suspensions in a spray race.

Microbial populations from subsurface soil collected from a hydrocarbon contaminated site and a pristine site with no history of contamination had the ability to degrade pentachlorophenol (PCP) in anaerobic enrichment cultures. Increasing concentrations of PCP in nitrate, sulfate and yeast extract-mineral salts media were used to acclimate the cultures. Nitrate enrichments, previously incubated in an anaerobic phenol-mineral salts medium, showed 23% degradation in medium containing 40 μg ml⁻¹ PCP during a 32 d incubation period. Cultures not adapted to phenol degradation did not degrade PCP at concentrations over 20 μg ml⁻¹. Enrichment cultures grown in the anaerobic yeast extract-mineral salts medium did not degrade PCP at concentrations over 20 μg ml⁻¹ and phenol adaptation did not enhance PCP degradation. The sulfate reducing enrichment containing 1 μg ml⁻¹ PCP showed 71.3% degradation after 32 d incubation. No degradation occurred at or above 5 μg ml⁻¹ PCP. PCP intermediates, 2,4,6-trichlorophenol (TCP) and 3,4,5 TCP were found in the spent culture of the nitrate reducing enrichment. In the spent culture of the sulfate reducing enrichment, 3,4,5 TCP and 2,3,4,5-tetrachlorophenol were found. Attempts to obtain a pure culture of an anaerobic PCP degrading bacterium were unsuccessful. / Master of Science

This study was conducted to isolate and characterize bacteria that have the capacity to degrade both carbofuran and dicamba. The pathways of degradation for both pesticides were elucidated. An aerobic, carbofuran-degrading bacterium was isolated from a high concentration carbofuran bioreactor. The isolate degrades carbofuran at the upper limit of carbofuran solubility (approximately 700 mg L⁻¹), to carbofuran phenol. In aqueous mineral salts medium with carbofuran as Furadan 4F (6 g L⁻¹ a.i.), degradation of carbofuran to undetectable levels required approximately 100 days. Although carbofuran phenol was not completely degraded, the cells remained viable in the presence of unusually high concentrations of both surfactant and carbofuran phenol. Additional nutrient sources had little effect upon the rate of degradation of carbofuran in pure culture. A dicamba-degrading consortium enriched from wetland soil, using the batch culture method, was used to elucidate the pathway of dicamba degradation under anaerobic conditions. The consortium consisted of one sulfate reducing bacterium, one fermenter, and three methanogens. The sulfate reducing bacterium was isolated from the consortium using sulfate as a terminal electron acceptor and 2-bromoethanesulfonic acid was added to inhibit the growth of the methanogens. Since the fermenter is dependent upon the methanogens, elimination of these organisms caused the elimination of the fermenter. Three methanogens (Methanothrix, Methanosarcina and Methanospirillum sp) were isolated with acetate and headspace gas consisting of H₂-CO₂. Degradation of dicamba proceded through an initial demethylation reaction yielding 3,6-dichlorosalicylic acid, as determined by high performance liquid chromatography (HPLC) analysis of aqueous medium. This was followed by a reductive dehalogenation reaction at the meta position of 3,6-dichlorosalicylic acid forming 6-chlorosalicylic acid. The metabolites were isolated using thin layer chromatography. Confirmation of metabolite identity was achieved using HPLC, and mass spectrometry. It appears that the fermenter was responsible for mediating the demethylation reaction. The consortium was unable to mineralize the aromatic ring. The substrate specificity of the dicamba-degrading consortium was investigated. The consortium was found to have the capacity to mediate the reductive dehalogenation of both 3-chlorosalicylic acid and 2,5-dichlorobenzoic acid at the meta position. The consortium was unable to dehalogenate either 3-chlorobenzoic acid, 4-chlorosalicylic acid, 5-chlorosalicylic acid, or 2,5-dichlorophenol. Addition of the reducing agent cysteine (0.025% and 0.050%) to a yeast extract amended (0.04%) mineral salts medium containing 3-chlorosalicylic acid reduced the rate of dehalogenation compared to medium containing sodium sulfide as the reducing agent. Only limited dehalogenation of 3- chlorosalicylic acid and 2,5-dichlorobenzoic acid was observed when the sulfate reducing bacterium was cultured alone in a yeast extract amended medium, suggesting that the mutualistic efforts of a mixed population of anaerobes were necessary to efficiently mediate reductive dehalogenation. / Ph. D.

Amitraz is a formamide acaricide used predominantly in the control of ectoparasites in livestock and honeybees. Amitraz hydrolysis is rapid and occurs under acidic conditions, exposure to sunlight and biodegradation by microorganisms. The main hydrolysis product of amitraz, 2,4-dimethylaniline, is recalcitrant in the environment and toxic to humans. An electrochemical method for the determination of total amitraz residues and its final breakdown product, 2,4-dimethylaniline, in spent cattle dip, is presented. Cyclic voltammetry at a glassy carbon electrode showed the irreversible oxidation of amitraz and 2,4-dimethylaniline. A limit of detection in the range of 8.5 x 10⁻⁸ M for amitraz and 2 x 10⁻⁸ M for 2,4-dimethylaniline was determined using differential pulse voltammetry. Feasibility studies in which the effect of supporting electrolyte type and pH had on electroanalysis of amitraz and its degradants, showed that pH affects current response as well as the potential at which amitraz and its degradants are oxidised. Britton-Robinson buffer was found to be the most suitable supporting electrolyte for detection of amitraz and its degradants in terms of sensitivity and reproducibility. Studies performed using environmental samples showed that the sensitivity and reproducibility of amitraz and 2,4-dimethylaniline analyses in spent cattle dip were comparable to analyses of amitraz and 2,4-dimethylaniline performed in Britton-Robinson buffer. In addition, the feasibility qf measuring amitraz and 2,4-dimethylaniline in environmental samples was assessed and compared to amitraz and 2,4-dimethylaniline analyses in Britton-Robinson buffer. Amitraz and 2,4-dimethylaniline were readily detectable in milk and honey. Furthermore, it was elucidated that 2,4-dimethylaniline can be metabolised to 3-methylcatechol by Pseudomonas species and the proposed breakdown pathway is presented. The biological degradation of amitraz and subsequent formation of 2,4-dimethylaniline was readily monitored in spent cattle dip. The breakdown of amitraz to 2,4-dimethylaniline and then to 3-MC was monitored using cyclic voltammetry.