Retention of estrogenic steroid hormones by selected New Zealand soils.

We performed batch sorption experiments for 17beta-estradiol (E2) and 17alpha-ethynylestradiol (EE2) on selected soils collected from dairy farming regions of New Zealand. Isotherms were constructed by measuring the liquid phase concentration and extracting the solid phase with dichloromethane, followed by an exchange step, and analysis by HPLC and UV detection. The corresponding metabolite estrone, (E1) formed during equilibration of E2 with soil was taken into account to estimate the total percentage recoveries for the compounds, which ranged from 47-105% (E2 and E1) and 83-102% (EE2). Measured isotherms were linear, although some deviation from linearity was observed in a few soils, which was attributed to the finer textured particles and/or the allophanic nature of the soils having high surface area. There was a marked difference in K(d)(eff) (effective distribution coefficient) values for E2 and EE2 among the soils, consistent with the soils organic carbon content and ranged from 14-170 L kg(-1) (E2), and 12-40 L kg(-1) (EE2) in the soils common for both compounds. The sorption affinity of hormones in the soils followed an order: EE2<E1<E2 in Manawatu and Horotiu soils, and, E1<EE2<E2 in Pukekohe soil with average log K(oc) of about 3 (+/-0.1-0.2 log units) which was consistent with earlier published values. Formation of the transformation product E1 appears to be concomitant with E2 sorption in all but one soil. Given that quite a large amount of E1 was generated during 72 h of contact time, and given E1 sorbed to solid phases greater than the liquid phase, dissolved organic carbon facilitated transport of these hormones needs to be considered when assessing the leaching risk for these compounds in the environment.