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A photolytic cell system suitable for the treatment of wastewater streams containing three pesticides, i) acephate, ii) glyphosate and iii) malathion is reported. The system is capable of destroying these three organic compounds, commonly present in wastewater streams originating from agrochemical industries in Malaysia, and can lead to complete mineralisation under the optimum conditions. The system is based on an advanced oxidation process and involves the production of hydroxyl free radicals in the presence of a UV source. The performance of the system, for the three pesticides, was optimised by investigating the effects of i) UV source, ii) pH of the solution, iii) initial concentration of the substrate, iv) addition of oxidants, v) hydrogen peroxide (H2O2) in the presence and absence of single and mixed metal ions. To monitor the degradation efficiency of the system, the residual concentrations of these organic compounds and metal ions were analysed using five analytical techniques i) total organic carbon (TOC), ii) high performance liquid chromatography (HPLC), iii) ion chromatography (IC), iv) UV/Visible spectroscopy (UV/Vis), and v) atomic absorption spectroscopy (AAS). The data show that the developed photolytic cell system is capable of achieving complete mineralisation of the three pesticides with the use of both 400 W and 600 W UV lamps. However, the 400W UV lamp was used, for economic reasons, to optimise the system for the remaining factors. Changes in the pH of aqueous solutions influenced the degradation efficiency and a complete degradation of the three pesticides was achieved at their self-pH values ranging from 5.0-5.5. The degradation of acephate increased and malathion decreased at their higher initial concentrations whereas no significant effect related to concentration was observed for glyphosate. Results show that the degradation followed a first order kinetics and the degradation rates were: malathion > acephate > glyphosate. The addition of 30 mg/L of H2O2 enhanced the degradation of the pesticides and after 5 hours irradiation these were 95.7%, 91.5% and 81.3% for malathion, acephate and glyphosate respectively. The presence of metal ions was observed to affect degradation (Table 1). With 5.0 mg/L of Fe(II) the degradation of all three pesticides increased, and in all cases acephate removal was improved. Removal of both malathion and glyphosate was negatively affected by copper, an effect that work with mixtures indicated was stronger than the positive effect of iron. The addition of H2O2, in the presence of single metal ions, increases the degradation. However, the addition of H2O2, in the presence of mixed metal ions, has no significant effect on the degradation of glyphosate and malathion. The effect of mixed metal ions on the three pesticides and the effect of Zn(II) ions on acephate and malathion are reported for the first time in this thesis. The developed photolytic cell system can be used for the treatment of wastewater streams originating from point sources, for example, agrochemical industries, under the optimum conditions. The synergistic combination of the developed system with the existing standard technologies is also proposed for the treatment of surface water at water treatment facilities in Malaysia. The application of the developed system can also be extended, with minimum modifications, for the treatment of wastewater streams originating from different manufacturing industries in Malaysia, for example, textile, paper/pulp, printing, coke, petroleum, paint, solvent, pharmaceuticals and wood-preserving chemicals. All these industries produce wastewater streams containing low concentrations of organic pollutants and heavy metal ions.

Global climate change promotes warming temperatures and altered salinities that pose threats to aquatic ecosystems and species, such as Hyalella azteca. Moreover, these threats to aquatic ecosystems are exacerbated by agricultural, urban, and industrial pesticide runoff. In the state of California in 2012, pyrethroid insecticides were the seventh most applied group by licensed professional applicators for pest control and landscape maintenance. Some species, specifically H. azteca have developed non-target resistance to pyrethroids in California. It is imperative to understand whether the bioenergetic cost of resistance makes H. azteca more susceptible to warming and salinity effects in the presence of contaminants. This research presents an assessment on how multiple stressors can affect the toxicity of permethrin (pyrethroid insecticide) on one Wild-type and two pyrethroid- resistant species of H. azteca, belonging to different clades. A series of 96-h acute toxicity tests exposing animals to a concentration range of permethrin were performed with compounding stress from temperatures (18, 23 and 28 °C) and salinities (0.2, 1.0, and 6.0 practical salinity units [PSU]). Findings indicate resistant H. azteca cultured in pyrethroid-free settings have maintained resistance to permethrin over time, whereas the wild-type population did not develop any resistance over the course of experimentation. For resistant H. azteca, changes in salinity and temperature both increased and decreased survival of H. azteca exposed to permethrin. Between the two resistant clades, not only was survival affected, but the average slope of the dose-response curve was significantly different (p < 0.05); clade D was more susceptible to pyrethroids when coping with warming and higher salinity than clade C., Differential susceptibility potentially indicates that distinct resistance mutations confer a difference in the potency and mode of toxic action. The results provide insight to how changes posed by climate change, coupled with pyrethroid pesticides could be detrimental to this species, and conversely, how in some scenarios, changes to temperature and salinity might actually benefit the survival of H. azteca. These findings further indicate the importance of considering global climate change effects into risk assessments of emerging and legacy use contaminants.

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