Modeling coupled sorption and transformation of 17β-estradiol–17-sulfate in soil–water systems

• This study modeled the fate and transport of 17β-estradiol–17-sulfate in soil–water systems.
• The model fit was satisfactory with reliable parameter estimates.
• Deconjugation of 17β-estradiol–17-sulfate was not the major pathway.
• Hydroxylation of 17β-estradiol–17-sulfate was the predominant pathway.

Animal manure is the primary source of exogenous free estrogens in the environment, which are known endocrine-disrupting chemicals to disorder the reproduction system of organisms. Conjugated estrogens can act as precursors to free estrogens, which may increase the total estrogenicity in the environment. In this study, a comprehensive model was used to simultaneously simulate the coupled sorption and transformation of a sulfate estrogen conjugate, 17β-estradiol–17-sulfate (E2–17S), in various soil–water systems (non-sterile/sterile; topsoil/subsoil). The simulated processes included multiple transformation pathways (i.e. hydroxylation, hydrolysis, and oxidation) and mass transfer between the aqueous, reversibly sorbed, and irreversibly sorbed phases of all soils for E2–17S and its metabolites. The conceptual model was conceived based on a series of linear sorption and first-order transformation expressions. The model was inversely solved using finite difference to estimate process parameters. A global optimization method was applied for the inverse analysis along with variable model restrictions to estimate 36 parameters. The model provided a satisfactory simultaneous fit (R2adj = 0.93 and d = 0.87) of all the experimental data and reliable parameter estimates. This modeling study improved the understanding on fate and transport of estrogen conjugates under various soil–water conditions.