Effects of physical treatments and moisture content on chitosan-based hydrogels designed to adsorb ethinylestradiol at low concentrations

Anthropogenic impacts on the environment have increased research regarding environmental pollution and water quality. Studies reporting emerging contaminants have raised concerns as their effects on health and ecosystems are unknown. Hormonally active agents are a prominent subcategories of emerging contaminant pollution consisting of natural and synthetic compounds. Ethinylestradiol is a synthetic pharmaceutical steroid hormone of interest because of its mechanisms of entering the environment and its metabolic resistance. Adsorption technologies are favourable methods of pollutant removal due to their relative ease of implementation, cost-effectiveness, and potential for environmental friendliness. Hydrogels are three-dimensional hydrophilic networks of chain polymers that are well documented for their adsorption capabilities. Chitosan hydrogels were used to adsorb ethinylestradiol, and crosslinking was performed with glutaraldehyde to increase the hydrophobicity of the matrix. Historically, materials designed to adsorb ethinylestradiol have been tested at high concentrations which are unrealistic of what is measured in the environment, thus low concentrations of ethinylestradiol were used in adsorption testing. Physical treatment methods including microwave treatment, liquid nitrogen submersion, and overnight freezing were explored to increase the pore size and exposed surface area of the hydrogels. Treatments performed after synthesis increased the adsorption capacity of the hydrogels, particularly when the moisture content was high. Microwave-treated hydrogels adsorbed the most ethinylestradiol with an adsorption efficiency of 62 % when tested at a low ethinylestradiol concentration (400 ng/mL). High moisture content liquid nitrogen-treated hydrogels and microwave treated hydrogels adsorbed the most ethinylestradiol when tested at higher concentrations (5000 ng/mL), resulting in a removal efficiency of 61 %. • Chitosan hydrogels were synthesized to adsorb ethinylestradiol (400 ng/mL) • Post-synthesis treatment methods were explored to increase adsorption capacity • A maximum adsorption capacity of 247 ng/mg was achieved • Efficiency was maintained at higher ethinylestradiol concentrations of 5000 ng/mL • Adsorption occurs largely within 15 mins of contact with ethinylestradiol