Accumulation of chlorothalonil successively applied to soil and its effect on microbial activity in soil.

The effect of successive chlorothalonil applications on the persistence of chlorothalonil, soil respiration activity, and dehydrogenase activity (DHA) in soil was investigated under laboratory conditions. The persistence of chlorothalonil in soil was prolonged significantly with the increase in the concentration applied. Repeated applications of chlorothalonil at 25 mg kg⁻¹ led to its accumulation in soil. The effect of repeated chlorothalonil applications on soil respiration and DHA was found to be a concentration-dependent process. Soil respiration was permanently inhibited by the successive introductions of chlorothalonil at 25 mg kg⁻¹. DHA was reduced significantly on day 15 after four successive treatments of 10 mg kg⁻¹ and 25 mg kg⁻¹ of chlorothalonil, although a recovery trend could be found after the third and fourth treatments. Repeated chlorothalonil applications might increase the persistence of chlorothalonil in soil and thus alter soil microbial activity.

Combined remediation of DDT congeners and cadmium in soil by Sphingobacterium sp. D-6 and Sedum alfredii Hance.

Combined pollution of 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane (DDT) and cadmium (Cd) in agricultural soils is of great concern because they present serious risk to food security and human health. In order to develop a cost-effective and safe method for the removal of DDTs and Cd in soil, combined remediation of DDTs and Cd in soil by Sphingobacterium sp. D-6 and the hyperaccumulator, Sedum alfredii Hance was investigated. After treatment for 210 days, the degradation half-lives of DDTs in soils treated by strain D-6 decreased by 8.1% to 68.0% compared with those in the controls. The inoculation of strain D-6 into soil decreased the uptake of DDTs by pak choi and S. alfredii. The shoots/roots ratios of S. alfredii for the Cd accumulation ranged from 12.32 to 21.75. The Cd concentration in soil decreased to 65.8%-71.8% for S. alfredii treatment and 14.1%-58.2% for S. alfredii and strain D-6 combined treatment, respectively, compared with that in the control. The population size of the DDTs-degrading strain, Simpson index (1/D) and soil respiratory rate decreased in the early stage of treatment and then gradually increased, ultimately recovering to or exceeding the initial level. The results indicated that synchronous incorporation of strain D-6 and S. alfredii into soil was found to significantly (p < or = 0.05) enhance the degradation of DDTs in soil and the hyperaccumulation of Cd in S. alfredii. It was concluded that strain D-6 and S. alfredii could be used successfully to control DDTs and Cd in contaminated soil.

Using in situ pore water concentrations to estimate the phytotoxicity of nicosulfuron in soils to corn (Zea mays L.).

The phytotoxicity of an herbicide in soil is typically dependent on the soil characteristics. To obtain a comparable value of the concentration that inhibits growth by 50% (IC50), 0.01 M CaCl(2) , excess pore water (EPW) and in situ pore water (IPW) were used to extract the bioavailable fraction of nicosulfuron from five different soils to estimate the nicosulfuron phytotoxicity to corn (Zea mays L.). The results indicated that the phytotoxicity of nicosulfuron in soils to corn depended on the soil type, and the IC50 values calculated based on the amended concentration of nicosulfuron ranged from 0.77 to 9.77 mg/kg among the five tested soils. The range of variation in IC50 values for nicosulfuron was smaller when the concentrations of nicosulfuron extracted with 0.01 M CaCl(2) and EPW were used instead of the amended concentration. No significant difference was observed among the IC50 values calculated from the IPW concentrations of nicosulfuron in the five tested soils, suggesting that the concentration of nicosulfuron in IPW could be used to estimate the phytotoxicity of residual nicosulfuron in soils.

Plasmid-mediated bioaugmentation for the degradation of chlorpyrifos in soil.

To overcome the poor survival and low activity of the bacteria used for bioremediation, a plasmid-mediated bioaugmentation method was investigated, which could result in a persistent capacity for the degradation of chlorpyrifos in soil. The results indicate that the pDOC plasmid could transfer into soil bacteria, including members of the Pseudomonas and Staphylococcus genera. The soil bacteria acquired the ability to degrade chlorpyrifos within 5 days of the transfer of pDOC. The efficiency of the pDOC transfer in the soil, as measured by the chlorpyrifos degradation efficiency and the most probable number (MPN) of chlorpyrifos degraders, was influenced by the soil temperature, moisture level and type. The best performance for the transfer of pDOC was observed under conditions of 30°C and 60% water-holding capacity (WHC). The results presented in this paper show that the transfer of pDOC can enhance the degradation of chlorpyrifos in various soils, although the degradation efficiency did vary with the soil type. It may be concluded that the introduction of plasmids encoding enzymes that can degrade xenobiotics or donor strains harboring these plasmids is an alternative approach in bioaugmentation.