Abstract
Endocrine disrupting chemicals (EDCs) are exogenous substances or mixtures that alter the functions of the endocrine system and consequently cause adverse health effects in an intact organism, or its progeny, or (sub) populations. During the past decades, EDCs have received significant scientific and public attention, because of their widespread occurrence in the environment and harmful influence, particularly, on aquatic organisms. Many studies have shown that EDCs are able to mimic natural hormones or interfere with the action of endogenous hormones, and thus cause various ecological and health problems, such as abnormalities in male reproductive systems and development in fish and other wildlife species. Photodegradation orphotolysis of organic pollutants in water is an efficient way to eliminate pollutants from the environment. The photochemical behavior of the synthetic estrogen EE2 was investigated in this study. The effects of substrate concentration, pH, and in the presence or absence of methanol, humic acid, nitrate and nitrite on the photodegradation of EE2 were studied. Photolysis experiments were conducted at different pH in the range from pH 4.00 to 10.00. The direct photodegradation of EE2 increased with increasing pH in the basic pH range from 7.00 to 10.00along with the deprotonation of EE2. The degradation of EE2 decreased as the pH decreased from 6.00 to 4.00. The photodegradation rate constant decreased with increasing concentrations of EE2 under simulated sunlight. Methanol suppressed the photodegradation of EE2, while humic acid, nitrate and nitrite greatly accelerated the degradation of EE2. The pH of the solution and the concentrations of these ions and catalysts in the solution strongly affected the degradation rate of EE2. The degradation of EE2 was enhanced markedly in the presence of humic acid (AH) under simulated sunlight at all pH values studied. HA could effectively induceEE2 photodegradation in aqueous solutions. In addition, experiments for the photodegradation of EE2 were conducted at different pH in the range from 4.00 to 10.00 in the presence of nitrate and nitrite at different concentrations. The photodegradation of EE2 in the presence of NO2- was much faster than that in the presence of NO3- at the same concentration. Finally, carbonate/bicarbonates are two of the most common inorganic salts present in natural surface water and may affect aquatic photochemical processes. The scavenging of the hydroxyl radicals by water matrix components, such as carbonate and bicarbonates, can significantly decrease their ability to induce targeted pollutant degradation. Carbonate ions did not significantly affect the photodegradation of EE2 at low concentration but increasing the concentration of carbonate/bicarbonate showed a significant influence on the photodegradation of EE2. The effects of carbonate/bicarbonate in the presence of HA, NO₂⁻ and NO₃⁻ was also studied to see if they can influance the photodegradation of EE2. In the presence of HA, carbonate had no significant effect on photodegradation of EE2 at low concentration. However, carbonate shows a huge effect on the photodegradation of EE2 in the presence of NO₂⁻and NO₃⁻.