Item talk:Q143670

Temperature-dependent sorption of naphthalene, phenanthrene, and pyrene to low organic carbon aquifer sediments

Sorption experiments were conducted with naphthalene, phenanthrene, and pyrene on low organic carbon sediments at 4 and 26 °C using batch and column techniques. Experimental controls ensured the absence of biologic and photolytic activity and colloid-free solution supernatants. Equilibrium distribution coefficients (K_d) increased 1.1−1.6 times with a decrease in temperature of 22 °C. Fraction instantaneous sorption (F) values did not change significantly with a decrease in temperature of 22 °C. Desorption rate constants (k₂) decreased 1.2−2.6 times with a decrease in temperature of 22 °C. Times to equilibrium were at least 40 h. The magnitude of observed K_d and k₂ values and the effect of temperature on K_d (e.g., low enthalpy of sorption) are consistent with sorbate partitioning between the aqueous phase and small amounts of organic matter (f_oc = 0.02%) on the sediments. The temperature dependence of K_d and k₂ may be small as compared to the effects of heterogeneities in field-scale aquifer systems. Thus, thermal gradients may not be of major importance in most saturated subsurface regimes when predicting solute transport. However, aquifer remediation pump-and-treat times could be decreased because increased temperature decreases both retardation and tailing.