The re-evaluation of pesticide use patterns is a high priority internationally. The process has led to a reduction in the numbers of pesticides allowed for use in many countries. This withdrawal of pesticides is aimed at consumer and environmental protection. Pesticide mobility and persistence is of major importance especially when considering the protection of water sources. In order to evaluate the suitability of a pesticide for use it is essential that its environmental behaviour is understood and predictable. In this thesis several case studies in which damage to crops may have been caused as a result of herbicides migration are described. Pesticide adsorption and persistence determinations showed that the adsorption coefficients do not differ from those published. Pesticide half lives are however likely to be prolonged in South African soils. Field migration studies show that pesticides are vertically and horizontally mobile in South African soils, seemingly independent of soil type. Both migration as well as upward movement was found, due to the mobility of the pesticides in the test soils. Mobility evaluation was identified as an aspect of importance for registration of pesticides under local conditions. To this end a system is proposed whereby migration can be incorporated into the existing pesticide evaluation framework. The system proposed used the migration model PESTAN as a predictive tool for pesticide migration in the evaluation process. The model is used for the evaluation of pesticides, according to Proposed Pesticide Migration Categories (PPLC). Migration evaluation should be conducted in conjunction with GPS systems to aid in determining potential risk areas where certain pesticide should not be used. / Thesis (Ph.D. (Zoology))--North-West University, Potchefstroom Campus, 2009.

Substances of natural and synthetic origin were studied using analytical, bioassay guided isolation, metabolomics and medicinal chemistry techniques. In a section focused on the plant family Marcgraviaceae, a validated method for the quantification of six pentacyclic triterpenes (α and β Amyrin lupeol, ursolic acid, betulin and betulinic acid) in the Souroubea spp was developed. Quantification of the triterpenes in the crude extracts was achieved using HPLC-APCI mass selective detection. The calibration curves for the five triterpenes evaluated were highly linear (r2 >0.993) and percentage recovery from spiked samples were greater than 94% for all compounds. The LOD for betulinic acid was 0.01 µg for betulinic acid on column and LOQ was 0.03 µg. The method was successfully applied to 41 crude extracts from leaf and stem of Souroubea spp, from two locations in Costa Rica. The method is suitable for quality control of raw materials used in the manufacture of natural health products. The use of modern metabolomic techniques, UHPLC-QTOF allowed the identification of five putative makers that can potentially be used in distinguishing between the two Souroubea species. The validated method was used in the quantification of the above triterpenes in a total of thirteen Marcgraviaceae species collected in Costa Rica. It was established that betulinic acid and β- Amyrin could be used as makers for this family of tropical vines. These same thirteen plants extracts were evaluated in antifungal and quorum sensing inhibition bioassays. Marcgravia nervosa was the only species that showed significant activity in both bioassays. Bioassay guided fractionation of the crude ethanolic extract of M. nervosa led to the identification of 2-methoxynaphthoquinone as the bioactive compound responsible for the bioactivity. The crude leaf ethanolic extract from M. nervosa showed a significant inhibition of QS comparable or somewhat better than D. pulchra extracts with the M. nervosa extract showing stronger inhibiting QS with a halo of 21.8mm, more than D. pulcra extracts which generated a halo of 15.9mm. The active quinone has a MIC of 85 µM against Saccharomyces cerevisiaBY4741 (haploid) and 100 µM against Saccharomyces cerevisiae BY4743 (diploid) compared to berberine (positive control) with a MIC 600 µM for both strains. This quinone is not present in any of the other twelve species of Marcgraviaceae available to us. In work focusing on organic synthesis, a total of 57 semi-synthetic derivatives of dillapiol, safrol and piperonal were prepared and evaluated for their inhibitory activity in a CYP 3A4 bioassay to assess their potential use as pesticide synergists. The synergistic activity of dillapiol has been improved 45 fold; analog 31 has an IC50 = 0.2 µM compared with dillapiol IC50= 9.18 µM. A number of other compounds structurally related to 31 showed similar levels of activity. A screening of a compound library identified the amino sulfoxide 3 as a potential lead for the design of a selective connexin blocker with potential application in the treatment of spinal cord injuries. The use of X-ray crystallography permitted the correction of the original structure assigned to 3. Once the structure was corrected a total of 6 analogs were prepared. Compound 3 has the highest inhibition of GJIC whereas compound 8 and compound 2, reduced anionic hemi-channel activity. Compound 2 also reduced the cationic activity of the hemi-channels.

The re-evaluation of pesticide use patterns is a high priority internationally. The process has led to a reduction in the numbers of pesticides allowed for use in many countries. This withdrawal of pesticides is aimed at consumer and environmental protection. Pesticide mobility and persistence is of major importance especially when considering the protection of water sources. In order to evaluate the suitability of a pesticide for use it is essential that its environmental behaviour is understood and predictable. In this thesis several case studies in which damage to crops may have been caused as a result of herbicides migration are described. Pesticide adsorption and persistence determinations showed that the adsorption coefficients do not differ from those published. Pesticide half lives are however likely to be prolonged in South African soils. Field migration studies show that pesticides are vertically and horizontally mobile in South African soils, seemingly independent of soil type. Both migration as well as upward movement was found, due to the mobility of the pesticides in the test soils. Mobility evaluation was identified as an aspect of importance for registration of pesticides under local conditions. To this end a system is proposed whereby migration can be incorporated into the existing pesticide evaluation framework. The system proposed used the migration model PESTAN as a predictive tool for pesticide migration in the evaluation process. The model is used for the evaluation of pesticides, according to Proposed Pesticide Migration Categories (PPLC). Migration evaluation should be conducted in conjunction with GPS systems to aid in determining potential risk areas where certain pesticide should not be used. / Thesis (Ph.D. (Zoology))--North-West University, Potchefstroom Campus, 2009.

Bibliography: leaves 165-188. / ix, 188 leaves, [2] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This research examines biological and behavioural interactions among the diamond-back moth, Plutella xylostella L. (Lepidoptera: Plutellidae), Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) and the microbial insecticide, Bacillus thuringiensis Berliner. A deterministic simulation model is developed describing the influence of C. plutellae on the evolution of resistance to Bt in a diamond-back moth poulation. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1998

Thesis (Ph. D.)--University of Adelaide, Dept. of Crop Protection, 1998. / Includes bibliographical references (leaves 165-188).

Thesis (M.S.)--University of Wisconsin--Madison, 1970. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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Pesticides have been recognized as one major agricultural non-point source (NPS) pollution to the environment and surface water in United States. Numerous mathematical models have been developed over the last decades to simulate the fate and transport of NPS at watershed scale. Geographic Information System (GIS) combined with models extends the spatial and temporal scopes of the research by integrating a variety of climates, soils, land covers, and management practices. The Annualized Agricultural Nonpoint Source model (AnnAGNPS) has received considerable attention in the United States for estimating runoff, sediment yield, pesticide and nutrients transport from ungauged agricultural watershed. However, few studies have been conducted on pesticide loading prediction in surface water using AnnAGNPS. In this study, the AnnAGNPS model was calibrated and validated for prediction of stream flow and chlorpyrifos loading for an agricultural dominated watershed of Orestimba Creek, in Central Valley, California. Large amounts of chlorpyrifos are applied to almonds, walnuts and other stone-fruit orchards in this area every year, which caused significant concern regarding their contamination to the San Joaquin River. Variety of data obtained from multiple sources were utilized as model input, including climate, land use, topology, soil, crop management and schedule, non-crop data, and pesticide. The model's performance was quantitatively analyzed using mean, standard deviation, coefficient of determination (r2), coefficient of efficiency (NSE), and root mean square error (RMSE). Model's prediction was considered to be unsatisfactory if NSE < 0.36, satisfactory if 0.36 < NSE < 0.75 and good if NSE > 0.75. Monthly stream flow discharge prediction was satisfactory and fit the observed data during model calibration mode. The prediction had major improvement in validation mode with modified curve number and rainfall interception values (r2 = 0.78 and NSE = 0.77). The AnnAGNPS predictions of chlorpyrifos concentrations in runoff water were unsatisfactory in both calibration and validation modes. Predicted chlorpyrifos concentrations at rainfall events were 1/1000 of observed data and it was impossible to improve the results through any type of calibration. The overall results suggested the model's poor performance was most likely a result of coarse sampling resolution of observed chlorpyrifos concentrations and lack of irrigation data.

Made available in DSpace on 2014-06-11T19:35:07Z (GMT). No. of bitstreams: 0 Previous issue date: 1999Bitstream added on 2014-06-13T19:05:18Z : No. of bitstreams: 1 santos_tcr_dr_araiq.pdf: 3624220 bytes, checksum: f06a06f02effa5bf8d56e04e45a3b1f8 (MD5) / A aplicação de um pesticida sobre culturas agrícolas implica em processos de transformação do composto e no consequente aparecimento de produtos de degradação resultantes desses processos. Em campos de arroz onde, em geral, o cultivo é feito em solos alagados, as condições peculiares levam a processos característicos, predominando mecanismos diferentes daqueles observados nas culturas feitas em solos secos. Embora o herbicida propanil seja extensivamente utilizado em cultivos de arroz, poucos estudos têm tratado da degradação nas condições comumente encontradas nos campos. Propanil e seu produto de degradação majoritário, 3,4-dicloroanilina (DCA), foram monitorados em águas e solo de campos de arroz do Delta do Ebro (Espanha). A determinação em amostras de água foi feita por análise on-line SPE/LC/DAD/APCI-MS, utilizando como adsorvente estireno-divinilbenzeno (PLRP-S). Para amostras de solo, a extração foi feita com metanol (em sistema Soxhlet) e clean-up com Florisil. A análise por cromatografia líquida permitiu detecção sensível e reprodutiva por conjunto de diodos, bem como a confirmação inequívoca dos compostos por espectrometria de massas. As concentrações do herbicida nas águas dos campos de arroz variaram entre 1,89-71,07 ng/mL, enquanto maiores concentrações foram determinadas para DCA (18,54-469,97 ng/mL). Os tempos de meia-vida calculados para o herbicida e seu principal produto de degradação foram de 1,24-3,83 e 1,58-1,63 dias, respectivamente. Em solo, a transformação do propanil também foi rápida, com persistência do DCA até um mês após a aplicação do herbicida (concentração de 119,7 ± 22,1 ng/g).O estudo de degradação do propanil nas condições controladas em laboratório evidenciou a influência da matéria orgânica no processo de transformação do herbicida. / The aplication of pesticide over cultivated areas implies changes to the compound, resulting in degradation products. In general, rice is cultivated in swampy areas; therefore, these peculiar conditions result in specific processes differing from those observed on dry soils. Although the extensive usage of propanil herbicide around the world, few studies concerning degradation on paddy field conditions have been carried out. Propanil and its major degradation product, 3,4-dichloroaniline (DCA), were monitored in surface water and soil samples from the rice fields of the Ebro Delta area (Spain). The determination in water samples was made by on-line SPE/LC/DAD/APCI-MS, using styrene-divinylbenzene copolymer (PLRP-S) as a sorbent material. In soil samples, the extraction was made with methanol (using Soxhlet system) and then clean-up with Florisil. The liquid chromatographic analysis allowed a sensitive and reproductive detection by diode array, and also an unequivocal confirmation by using a mass spectrometric detector. Propanil’s concentration in water samples of the rice fields varied from 1.89- 71.07 ng/mL, while higher concentrations of DCA were determined (18.54-469.97 ng/mL). The herbicide and its degradation product exhibited half-lives of 1.24-3.83 and 1.58-1.63 days, respectively. In the paddy soil, propanil also transformed very quickly to DCA, with the evidence of this compound being persistant up to one month after herbicidal application (concentration of 119.7 ± 22.1 ng/g). Under controled conditions the laboratory studies demonstrated the influence of organic matter over the herbicide transformation. A strong interaction with humic acids extracted from sediments pointed out that, besides the biological factors already stated in literature, other mechanisms also influence the propanil degradation.

Chlorotoluron photochemical degradation in homogeneous phase (aqueous solutions) was studied. Photolysis by UV radiation, influence of metal (ferric, ferrous) ions, pH, and solvent composition on the reaction rate was investigated. Photosensitizing effect of humic samples was tested. Kinetic characteristics (rate constants, overall quantum yield), products of reactions and extent of mineralization was evaluated.