Abstract:

Estrone (E1) and its sulphate conjugate estrone-3-sulfate (E1-3S) are chemicals that interfere with endocrine in animals. This disruptions can cause developmental disorders, birth defects, and cancerous tumors. Both chemicals are released to the environment in animal waste in significant amounts, and direct exposure occurs in grazed pasture systems. Both compounds have been shown to potentially contribute to endocrine disruption in wildlife, and knowledge about the sorption behavior of these compounds is necessary for a sound riskassessment. For labile compounds such as E1 and E1-3S, however, the standard protocols might overestimate sorption by not considering metabolite formation or allowing for equilibration that exceeds the commonly reported half-lives of these compounds. Modified batch sorption experiments with mediator solution of 555 mg/L calcium chloride (CaCl₂) and artificial urine solution were therefore conducted to determine the influence of these mediator solutions on the sorption of E1 and E1-3S in three agricultural soils from Nasarawa state of Nigeria. Sorption isotherms of both compounds were nonlinear, and the Freundlich equation was found adequate to describe the isotherms. The sorption potential of E1-3S (2.4-6.4 L/kg) was about one order of magnitude lower than for the free counterpart (34.2-46.8 L/kg), and the Kf values significantly changed between the two mediator solutions. Different organic carbon content (Lafia: 8.2%；Doma: 4%；Azara: 5%), clay mineralogy and pH value were the main causes of various adsorption ability. Effective distribution coefficients of estrone in Azara soil with CaCl₂ and artificial urine solution were 71.7 L/kg, 39.8 L/kg respectively. The calculation of concentration-dependent effective distribution coefficients (K_d) revealed that for a range of realistic exposure concentrations in a grazed farming system, the common approach of using CaCl₂ would deliver incorrect inferences for a sound risk assessment.

Key words: estrone, estrone-3-sulfate, sorption, mediator solutions, effective distribution coefficient