Photodegradation of pyrene on soil surfaces under UV light irradiation.

The rates of photodegradation of pyrene (Pyr) on soil surfaces under UV light have been studied. Different parameters such as temperature, soil particle sizes, soil depth, and humic acid (HA) concentration responsible for photodegradation have been monitored. The results obtained indicated that Pyr photodegradation follows pseudo-first-order kinetics. Pyr degradation was fastest at 30 degrees C, while the photodegradation rate was increased with the temperature from 20 to 30 degrees C. The degradation loss was about 35% at 30 degrees C, 30% at 25 degrees C and 25% at 20 degrees C, respectively. The rates of Pyr photodegradation at different soil particle sizes followed the order: less than 1mm>less than 0.45 mm>less than 0.25 mm. The results showed that the relationship of Pyr half-life with soil depth was linear (significant correlation, p<0.01). When the soil depth increased from 1 to 4mm, the half-life increased from 19.80 to 37.46 d. HA treatments significantly increased the photodegradation of Pyr on soil surfaces under UV light. However the concentration of HA increased from 5 to 40 mg kg(-1), the pseudo-first-order rates of Pyr decreased due to the shielding effect of HA.