Pentachlorophenol (PCP) vertical transportation in soil column during its phototransformation on the soil surface was investigated using a new designed photoreactor. Three kinds of soils were used to study the effect of soil water and soil properties. In air-dried sandy loam, no obvious PCP transportation occurred in the soil profile when PCP was phototransformed on the soil surface. And the average removal of PCP in the whole soil column was close to zero after 48 h irradiation. In the moist sandy loam, PCP in the deeper soil could transport to the soil surface with water evaporation and then be transformed during UV irradiation, thus the average PCP removal in the whole soil column was improved. When the initial water contents are 9.3 and 19.2%, the average PCP removal in the sandy loam after 48 h irradiation accounted to 20.9 and 39.9%, respectively. The improving of PCP removal induced by soil water was limited in the clay and silt soils where PCP transportation was impeded because of their higher adsorption capacity. In the silt soil where the initial water content was 19.7%, not only PCP transportation in the deeper soil but also PCP phototransformation on the surface was inhibited seriously because of the high organic matter content of 18%.

Numerous sites are contaminated with both heavy metals and polycyclic aromatic hydrocarbons (PAHs) and the technologies to treat such mixed contaminants are very limited. Electrokinetic remediation has the potential to remediate mixed contaminants in soils, including low permeability soils; however, the efficiency of this technology depends on the extracting solution employed. Previous studies on electrokinetic remediation have focused on the removal of heavy metals and organic compounds when they exist individually in clayey soils. In the present study, the feasibility of using cosolvents to enhance the electrokinetic removal of PAHs from clayey soils in the presence of heavy metals is investigated. A series of laboratory electrokinetic experiments was conducted using kaolin soil spiked with phenanthrene and nickel at concentrations of 500 mg/kg each to simulate typical field mixed contamination. Experiments were performed using n-butylamine (cosolvent) at concentrations of 10 and 20% and deionized water, each mixed with 0.01 M NaOH solution and circulated at the anode to maintain alkaline conditions. A periodic voltage gradient of 2 VDC/cm in cycles of 5 days on and 2 days off was applied in all the tests. During the initial stages when the soil pH was low, nickel existed as a cation and electromigrated towards the cathode. However, as the soil pH increased due to hydroxyl ions generated at the cathode and also flushing of high pH n-butylamine solution from the anode, nickel precipitated with no further migration. Phenanthrene was found migrating towards the cathode in proportion to the concentration of n-butylamine. The extent of phenanthrene removal was found to depend on both the electroosmotic flow and the concentration of n-butylamine, but the presence of nickel did not influence the transport and removal of phenanthrene.

In this paper, downward movement and availability of copper in soils irrigated with CuSO₄ algaecide treated water were examined using column leaching experiments. Two simulations considering 1 and 10 years irrigation period were conducted at copper application rate of about 18.7 kg CuSO₄/ha/year. Effluent copper concentrations and vertical distribution of acid and DTPA-extractable copper in the soil columns were determined. Nearly 99% of the applied copper was retained in the soil with a C e/C ₀ values on the order of 10⁻³. Retention profiles showed that copper was retained in the upper 2 to 3 cm of the soil. However, a significant fraction of the retained copper was detected in available form (DTPA-Cu) suggesting that plants toxicity could be a major limitation for the use of CuSO₄ treatment in irrigation water.