D.Phil. / South Africa is the highest produce-producing and therefore the highest pesticide consumer on the African continent. Although greatly beneficial to the industry, indiscriminate and over usage of these agrochemicals pose a risk to the aquatic ecosystems through non-point source pollution. Data on these risks are limited in the developing countries such as Africa since limited environmental monitoring of pesticides is undertaken. This is due to technical, logistical and economical constraints in determining the links between exposure and effect on non-target organisms. Methods that are able to screen for and monitor pesticides that could pose a risk according to site-specific scenarios are therefore necessary. Economical and easy-to-use predictive models incorporated into Preliminary Risk Assessments (PRA’s) are useful in this regard and have been developed and applied globally to assist in estimating the probability of risks of pesticides associated with aquatic ecosystems. Currently no such risk assessment model is applied in South Africa for this purpose. The main aim of the present study was to present and assess the suitability of selected PRA models as preliminary screening tools for estimating potential pesticide exposure and associated effects within aquatic ecosystems. To achieve this, the primary objectives were to apply and validate these models for assessing predicted risks and to relate these to actual ecological hazards by monitoring the exposure and effects of selected pesticides that were identified as potentially posing a risk. It was hypothesised that the data determined by these models would elucidate the association between potential risks of pesticides and actual environmental impacts and could therefore be applied and validated for South African conditions. A framework was thus developed using multidisciplinary approaches to predict the risks of agricultural pesticides to non-target aquatic organisms and to validate these risks in an area known to have a high pesticide usage, namely the Crocodile (west) Marico catchment. This area is representative of a typical farming community in the subtropical central area of South Africa. It is a catchment area that exhibits high urban and agricultural usage, which has compromised the overall ecological integrity of the aquatic systems. The focus of the study was on the Crocodile (west) and Magalies Rivers and the associated irrigation canal network systems. The present study was based on integrating multidisciplinary techniques following the implementation of a tiered approach for assessing the ecological risks of selected pesticides known to be used within the Crocodile (west) Marico catchment. Tier 1 starts with the PRA SUMMARY xx assuming a relatively worst-case scenario by identifying pesticides most commonly used (through surveys) and estimating exposures posing a potential risk to the aquatic environment using the PRIMET (Pesticide Risks In the tropics to Man, Environment and Trade) model. The second tier can establish a more realistic characterisation of risk for the pesticide application scenarios of interest by using models such as PERPEST (Predicting the Ecological Risks of PESTicides), PEARL (Pesticide Emission Assessment of Regional and Local Scales), TOXSWA (TOXic substances in Surface Waters), or SSDs (Species Sensitivity Distributions). Higher tiers then include comparing the results from the PRA model predictions to the actual hazards of pesticides and can determine if these risk models are valid under South Africa conditions. This can be achieved using a combination of laboratory- and field-based monitoring assessments in the form of a triad approach (using chemical, toxicological and ecological assessments) to construct several lines-of-evidence (LoEs). The risk assessment process ends with a summary and integration of the data based on the multiple LoEs gathered during monitoring using a weight-of-evidence (WoE) approach.

Doctor Educationis / The use of pesticides poses a serious threat to the limited water resources of South Africa. The amounts which are not taken up by crop plants, are often washed away by runoff into surface waters, or leached through the soil, causing groundwater pollution. The problem of pesticide pollution is often intensified by inappropriate usage, disposal and monitoring in agriculture and predictive models have proven to be an effective tool for improving management practices. Research, however, has focused mainly on surface water contamination and groundwater impacts are largely unknown. Furthermore, pesticide registration in South Africa is largely determined by international standards and there is a need for impact assessments to be carried out under local conditions. The aims of this study included the determination of priority pesticides in South Africa based on usage and properties, the determination of pesticide sorption in two selected South African soils, and an assessment of pesticide fate by modelling. / South Africa

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.

This study employed geographic information systems (GIS) technology to evaluate the vulnerability of groundwater to pesticide pollution. The study area included three provinces (namely, Kanchana Buri, Ratcha Buri, and Suphan Buri) located in the western part of central Thailand. Factors used for this purpose were soil texture, percent slope, primary land use, well depth, and monthly variance of rainfall. These factors were reclassified to a common scale showing potential to cause groundwater contamination by pesticides. This scale ranged from 5 to 1 which means high to low pollution potential. Also, each factor was assigned a weight indicating its influence on the movement of pesticides to groundwater. Well depth, the most important factor in this study, had the highest weight of 0.60 while each of the remaining factors had an equal weight of 0.10. These factors were superimposed by a method called “arithmetic overlay” to yield a composite vulnerability map of the study area. Maps showing relative vulnerability of groundwater to contamination by pesticides were produced. Each of them represented the degree of susceptibility of groundwater to be polluted by the following pesticides: 2,4-D, atrazine, carbofuran, dicofol, endosulfan, dieldrin & aldrin, endrin, heptachlor & heptachlor epoxide, total BHC, and total DDT. These maps were compared to groundwater quality data derived from actual observations. However, only the vulnerability maps of atrazine, endosulfan, total BHC, and heptachlor & heptachlor epoxide showed the best approximation to actual data. It was found that about 7 to 8%, 83 to 88% and 4.9 to 8.7% of the study area were highly, moderately, and lowly susceptible to pesticide pollution in groundwater, respectively. In this study a vulnerability model was developed, which is expressed as follow: V = 0.60CW + 0.10CS + 0.10CR + 0.10CL + 0.10CSL. Its function is to calculate a vulnerability score for a certain area. The factor “V” in the model represents the vulnerability score of a certain area, whereas CW, CS, CR, CL, and CSL represent the values or classes assigned to well depth, soil texture, monthly variance of rainfall, primary land use, and percent slope in that area.

No description available.

No description available.

The sorption of unformulated (98% pure) and formulated (86% pure + adjuvants) metolachlor to peat, rubber, and steam-exploded wood was studied. The concentration of pesticide ranged from 50 mg/L to 400 mg/L. Equilibrium concentrations for the batch reactors were reached within 24 hr. The sorption data for both unformulated and formulated metolachlor were best described by the Freundlich isotherm model. Metolachlor was preferentially sorbed in the following order: rubber > peat > wood fibers, with removal efficiencies of 80-85%, 70-80% and 50-65%, respectively. Differences in slopes of the isotherm lines and K values were negligible for each sorbent-type tested for both unformulated and formulated metolachlor. These results suggest that the presence of surfactants did not affect the sorption capacity of the sorbents at the concentration levels tested. However, isotherm plots showed S-shaped curve behavior for all of the sorbents in the presence of unformulated metolachlor, while a C-shaped curve was seen when the sorbents were mixed with formulated metolachlor. This suggests that different bonding mechanisms may be involved for the sorption of unformulated and formulated metolachlor to the sorbents. Various procedures were studied to improve removal efficiencies of formulated metolachlor. Sorption of metolachlor to peat was enhanced by hydrating the peat and pre-treating the peat with HCI. Circulation of formulated metolachlor through a rubber-packed column showed the greatest removal, with only 6 mg/L of the initial 400 mg/L remaining in solution. Removal efficiencies of steamexploded wood fibers were not improved by any of the methods investigated. / Master of Science

Bentazon, (3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-l-2,2-dioxide) a new experimental herbicide, was studied under the effects of sterile and non-sterile conditions, 12 hours light: 12 hours dark and totally dark conditions, and agitated and non-agitated conditions in aquatic sediment. The effects of the different levels of BOD/COD values on the decomposition of Bentazon were studied. Photoperiod, sterility, and BOD/COD levels appeared to have no influence in the breakdown of Bentazon. Agitation-time interaction appeared to be the only factor that influenced the more rapid degradation of Bentazon. Bentazon was the major 14C-residue found in the water; it was followed by an unknown. The third major metabolite was 2-amino-N-isopropyl benzamide, followed by anthranilic acid and N-isopropylsulfamoyl anthranilic acid at minor amounts. Only Bentazon was found in the soil. The ratio of radioactivity in the soil vs. the water was 1:1 in the agitated tanks and 1:3 in the non-agitated tanks. After 128 days, the concentration of Bentazon in the water decreased to an average of 50% in the agitated tanks and an average of 80% in the non-agitated tanks.

The purpose of the research was to determine if pesticides were being transported from the place of application by the shallow groundwater and discharged into the Chesapeake Bay and Atlantic Ocean, and quantify the pesticides if they were transported. One reference (undeveloped) and four agricultural sites were tested over a 11 month period from April 1992 to February 1993. Over 500 groundwater samples were analyzed from both shallow wells and seepage meters placed in the Chesapeake Bay and Magothy Bay. The samples were analyzed in accordance to EPA Method 525.1 by solid phase extraction with octadecyl bonded disks followed by gas chromatography. The samples were examined for 5 of the most commonly used pesticides: atrazine, alachlor, carbofuran, cyanazine, and metolachlor. Pesticides were detected in only 16 samples. All the detections were at low concentrations, with only one being over 1 μg/L. The study concluded that if pesticides were being transported by the groundwater, they were below a μg/L (ppb). / Master of Science

Kepone®, the registered trade name for decachlorooctahydro-1,3, 4-metheno-2H-cyclobuta cd pentalen-2-one, inhibited growth and reduced rates of photosynthesis and respiration of Chlorella sorokiniana Shihira and Kraus and Chlorocbccum hypnosporum Starr. The insecticide reduced rates of respiration more than photosynthesis. Uptake of ¹⁴C-Kepone by the algae was proportional to cellular concentration. A net efflux of Kepone was exhibited by Chlorella cells after 30 minutes of incubation, whereas, equilibrium occurred within 15 minutes of incubation for Chlorococcum. Desorption of Kepone was evident when both algal species were removed from Kepone treated solutions and incubated in untreated nutrient solutions. / Master of Science