TP036 (MAC-1117-829575) Stochastic probability modeling to predict the environmental stability of nanoparticles in aqueous suspension.
Start time: 8:00 AM
Mackay, C¹, Johns, M¹, Salatas, J¹, Bessinger, B², ¹ Exponent, Bellevue, WA, USA² Exponent, Lake Oswego, OR, USA
Nanomaterials are preparations where the paricle size is on the order of 10 to 100 nm in diameter. These particles are able to form suspensions in fluid media such as air and water that can dramatically increase the environmental transport potential in comparision to like materials of larger particle sizes. Quantifying such transport requires an ability to predict the stability of such suspensions as to their tendancy to aggregate or interact with other environmental constituents. In this presentation, we introduce a method for predicting the magnitude and uncertainty associated with nanoparticle suspension stability. The critical buoyancy properties are predicted using the Boltzmann equation. The rates of aggregation are then predicted on the basis of molecular collision and adhesion coefficients. The progress of particle growth is simulated across all potential pathways probabalistically using the Gillespie model to characterize the uncertainty.

TP037 (KWO-1117-817950) Adsorption of five selective serotonin reuptake inhibitors to sediments and soils.
Start time: 8:00 AM
Kwon, Jeong-Wook¹, Armbrust, Kevin¹, ¹ Mississippi State Chemical Laboratory, Mississippi State University, Mississippi State, MS, USA
Selective serotonin reuptake inhibitors (SSRIs) are widely used for the treatment of clinical depression in humans. Recent reports on the detection of SSRIs in surface water and sediments have heightened concerns about the presence of these emerging contaminants. Adsorption processes are particularly important because they influence the mobility and transports of chemicals in surface and sub-surface environments. The adsorption of five SSRIs (citalopram, fluoxetine, fluvoxamine, paroxetine, sertraline) to two sediments and three soils were investigated using a batch equilibrium methods similar to those employed in pesticide registration studies. Adsorption isotherms followed the Freundlich equation. Greater than 91% of the applied mass of each SSRI sorbed to soil or sediment, except fluvoxamine at 73%, over a range of concentrations of 0.5-10 mg/L, indicating that all SSRIs should strongly sorb to sediments and soils. The isotherm shapes were classified as L-type for most SSRIs. In general pH was the main factor influencing the adsorption of SSRIs to sediments and soils. No correlation between adsorption characteristics and organic matter, CEC or clay content was found. Values of K_f, K_d, and log K_oc ranged from 39 to 18342, from 60 to 42579, and 3.35 to 6.02, showing a very wide range of values depending upon kinds of drug and soil. In conclusion, SSRIs were found to be quickly and highly adsorbed to sediments and soils in the environments and will quickly dissipate from water phase due to adsorption.