Effect of solid surface composition on the migration of tributyltin in groundwater

Tributyltin (TBT) is the most important organotin compound that has been in troduced into aquatic ecosystems. A better understanding of its interaction s with solid surfaces is essential to estimate the possibilities of TBT mig ration through subsurface environments. For this purpose, TBT sorption onto a porous matrix of natural origin, a quartz sand as an aquifer material, w as studied at low concentration levels with a monodirectional model of colu mn type allowing sequential investigation of sorption and desorption proces ses. Different treatments of the solid phase were performed by injecting al kaline solutions, NaOH at pH 10.8 or NaClO-NaCl at pH 11.5, by decreasing t he ionic strength or by adding kaolinite to change the surface composition and properties. The removal of iron and aluminum (hydr)oxides from the sand surface did not affect so much the sorption (decrease in 14% as compared t o sorption on the raw sand). The original use of X-ray photoelectron spectr oscopy to control treatment efficiency and to characterize sand surface mod ifications permitted to relate TBT sorption onto the aquifer material to qu artz, the main component of the sand, and clay minerals (mainly kaolinite) present at trace levels at the sand surface. A first attempt of transport m odeling with these two surface sites showed the consistency of our assumpti on. Moreover, estimation of Langmuir-type constants showed that TBT sorptio n affinity for the quartz surface (K-L = 26.7 L mu mol(-1)) was much greate r than for kaolinite (K-L = 6.3 L mu mol(-1)).