Melatonin as an omnipresent molecule is secreted by the pineal gland. It is a strong free radical scavenger, which reduces nitric oxide (NO) generation within mitochondria. Exercise has great impacts on many body's homeostatic systems. Most human's organisms display rhythms and have 24 hours environmental cycles, which are called circadian rhythm. Melatonin is one of the circadian rhythm generator in various physiological variables. Exercises could regulate plasma melatonin levels. Melatonin scavenges reactive oxygen spices (ROS) and reactive nitrogen spices (RNS) and acts as the antioxidant cascade. It not only decreases the exercise induced-oxidative stress in the muscles but also enhances muscle antioxidant enzymes, such as superoxide dismutase. Body lipids and unsaturated fatty acids are prone to oxidation, while the free radicals penetrate into bilayer membrane structure lipid peroxidation is going to happen. Malondialdehyde (MDA) is created by free radicals, and it is one of the most frequent marker of lipid peroxidation. Exercise, its duration, and time of the day have immediate and or delayed effects on melatonin secretion. The combination of aerobic exercise and melatonin reduces the exercise induced-free radicals agents. Melatonin supplementation, especially while it combined with aerobic training, could decrease the lipid peroxidation and malondialdehyde. Melatonin could impede exercise-induced ROS, increase body health, and exercise-related adaptation.

Arsenic is a toxic element, which is found naturally in water sources. Due to its high toxicity it has become a serious problem in drinking water sources and also affects the health of communities. Therefore, in the present study, risk estimation and the probability of adverse health effects of exposure to arsenic from drinking water was evaluated in the rural areas of Qom province. Water samples were taken from 44 rural areas with regard to the number of rural areas and also the type of water distribution systems. The intensity, duration and frequency of exposure to arsenic in drinking water were determined. Then the hazard quotient and cancer risks ware calculated. Results showed that more than 16% of the rural population was exposed to arsenic with level above 10 µg/L in the rural regions of Kahak County (10 ± 6.29 µg/L). Results of risk assessment showed that hazard quotient (HQ) were 1.7 and 2, while the cancer risk (CR) were 76 × 10 -5 and 42 × 10 -4 for 2 groups of age 1 and 2, respectively. The results indicated that the hazard quotient is higher than 1 (HQ > 1) for group 1 and group 2. For carcinogenic effects, the study indicated that the population in the Kahak region are exposed to arsenic in drinking water with the concentration of > 10 µg/L and they are at a very high risk for cancer, due to the fact that the cancer risk for the 2 groups are more than 7.6 and 42 times the environmental protection agency (EPA) criteria, respectively. Therefore it is recommended that at first, the source and water supply system in Kahak region is to be substituted with safe drinking water and to provide health facilities and screening tests for exposed populations.