Occurrence and cycle of dissolved iron mediated by humic acids resulting in continuous natural photodegradation of 17α-ethinylestradiol.

17α-ethinylestradiol (EE2), a synthetic endocrine-disrupting chemical, can degrade in natural waters where humic acids (HA) and dissolved iron (DFe) are present. The iron is mostly bound in Fe(III)-HA complexes, the formation process of Fe(III)-HA complexes and their effect on EE2 degradation were explored in laboratory experiments. The mechanism of ferrihydrite facilitated by HA was explored with results indicating that HA facilitated the dissolution of ferrihydrite and the generation of Fe(III)-HA complexes with the stable chemical bonds such as C-O, CO in neutral, alkaline media with a suitable Fe/C ratio. 1O2, •OH, and 3HA* were all found to be important in the photodegradation of EE2 mediated by Fe(III)-HA complexes. Fe(III)-HA complexes could produce Fe(II) and hydrogen peroxide (H2O2) to create conditions suitable for photo-Fenton reactions at neutral pH. HA helped to maintain higher dissolved iron concentrations and alter the Fe(III)/Fe(II) cycling. The natural EE2 photodegradation pathway elucidated here provides a theoretical foundation for investigating the natural transformation of other trace organic contaminants in aquatic environments.

The photodegradation of 17 alpha-ethinylestradiol in water containing iron and dissolved organic matter.

17 alpha-ethinylestradiol (EE2) in natural waters can seriously harm ecosystems and human health. Dissolved organic matter (DOM) and iron minerals are ubiquitous in natural waters, and they can shorten the half-life of EE2 in the natural environment. The interaction between dissolved organics and iron affects pollutants' transformation pathways. The mechanism of EE2's adsorption on hematite, magnetite and pyrite was studied. A photo-Fenton system was constructed in which humic acid (HA) and iron minerals degraded EE2 under simulated natural light conditions. Pyrite showed the best adsorption and degradation in acidic conditions (52%) for 5 h. Hydroxyl radical was found to be the main active substance in the photodegradation. The degradation products of EE2 were identified and possible degradation pathways were inferred. These results can contribute to the understanding of the transformation pathways of persistent organic pollutants in natural waters.

Adsorption and photochemical capacity on 17α-ethinylestradiol by char produced in the thermo treatment process of plastic waste.

Plastic is a major component of solid waste. It is often thermally treated, generating microplastics and plastic-char which end up as landfill. This study investigated the potential of plastic-char for treating persistent organic pollutants of aqueous media using 17α-ethinylestradiol (EE2) as a target contaminant. The adsorption and photodegradation capacity of plastic-char were investigated, and the adsorption isotherms revealed that EE2 adsorption on char is heterogeneous and multilayered. The presence of Fe was found to greatly enhance EE2 adsorption rate and capacity as well as photochemical degradation ability of plastic-char. Quenching experiments proved that electron transfer between triplet states of plastic-char and Fe(III) and the production of H2O2 were the rate-limited steps in the generation of reactive species. Hydroxyl radical and holes were found to be the predominant reactive species contributing to the EE2 photodegradation. This study not only elucidated the possible environmental behavior of plastic-char discharged as bottom ash in the natural transformation of persistent organic pollutants, but also suggested that water treatment may offer a use for some of the enormous volume of plastic waste now being generated worldwide.