Introduction: Microcystin-leucine arginine (MC-LR) is a toxin with harmful effects on the liver, kidney, heart, and gastrointestinal tract. So, effective removal of MC-LR from water resources is of great importance. The aim of this study was to remove microcystin-LR (MC-LR) from aqueous solution by Titanium Dioxide (TiO₂).
Materials and Methods: In the present study, TiO₂, as a semiconductor, was used for photodegradation of MC-LR under ultraviolet light (UV). The Response Surface Methodology was applied to investigate the effects of operating variables such as pH (A), contact time (B), and catalyst dose (B) on the removal of MC-LR. The MC-LR concentration was measured by high-performance liquid chromatography (HPLC).
Results: The results showed that single variables such as A, B, and C had significant effects on MC-LR removal (p_value < 0.05). In other words, increase of the contact time and catalyst dose had a positive effect on enhancing the removal efficiency of MC-LR, but the effect of pH was negative. The analysis of variance showed that BC, A², and C² variables had a significant effect on the MC-LR removal (p_value < 0.05). Finally, the maximum removal efficiency of MC-LR was 95.1%, which occurred at pH = 5, contact time = 30 minutes, and catalyst dose = 1 g/l.
Conclusion: According to the findings, TiO₂, as a photocatalyst, had an appropriate effect on degradation of the MC-LR.

Introduction: Contamination of water sources with toxins is an environmental problem and a serious threat to the health of societies. This study aimed to ascertain the remaining levels of toxins in urban drinking water networks and compute the water quality index.
Materials and Methods: To examine the residual concentration of diazinon, chlorpyrifos, and dichlorvos in urban drinking water distribution networks, 35 underground and surface water sources were sampled in Tiran-o-Karvan in Isfahan province, Iran. GC-ECD device was used to analyze the samples.
Results: Diazinon was not observed in any of the sampling seasons. The maximum concentration of chlorpyrifos and dichlorvos was 61 and 100 ppb, respectively. Although chlorpyrifos was seen more in the hot season and dichlorvos in the cold season, the mean concentration of these toxins in different seasons was lower than the guidelines of Iran and the World Health Organization (WHO). The mean concentration of nitrate, and hardness, in wet and dry seasons was 46.23 and 46.42, and 343.7 and 338.8 mg/l, respectively.
Conclusion: The mean and standard deviation of quality index of Iran's water resources (IRWQI) in wet and dry seasons were 52.16 ± 45.3 and 50.69 ± 15.8, respectively. The residual concentration of toxins in some water sources of this city exceeded the guidelines of Iran and the WHO in summer and spring.