Decontamination of dense nonaqueous-phase liquids in groundwater using pump-and-treat and in situ chemical oxidation processes: a field test.

Groundwater remediation is difficult because of the complexity of the treatment area and the presence of various pollutants, and it is difficult to achieve using a single process. A combined pump-and-treat (P&T) and in situ chemical oxidation (ISCO) system was used to remove dense nonaqueous-phase liquids (DNAPLs) from groundwater at the field scale in this study. The underground water pH, electrical conductivity, dissolved oxygen concentration, and SO4 2- concentration were used as indirect evidence of in situ chemical reactions. Groundwater remediation using the P&T-ISCO process using 1.5% sodium persulfate and 0.03% sodium hydroxide had a remarkable effect on DNAPLs, and the DNAPL diffusion distance was much higher under pumping conditions than under natural conditions. During groundwater remediation, the pollutant concentration positively correlated with the pH, electrical conductivity, and dissolved oxygen concentration and negatively correlated with the SO4 2- concentration. In summary, P&T-ISCO can effectively accelerate DNAPL degradation to give efficient groundwater remediation.

[Molluscicidal effect comparison between TDS and MNSC in field].

OBJECTIVE: To compare the molluscicidal effects between "Luo-wei" (TDS), a plant molluscicide in 4 percent, and metaldehyde and niclosamide (MNSC) in the field. METHODS: A natural ecological environment with Oncomelania hupensis was selected as the test area, the test concentrations of TDS and MNSC were 2.5 g/m3 and 2 ml/m3 respectively by the immersion method; the test doses of TDS and MNSC were 3 g/m2 and 2 ml/m2 respectively by the spray method; the doses of WPN in a control group were 2 g/m3 and 2 g/m2 respectively by the two methods above-mentioned. The molluscicidal effects between TDS and MNSC were compared by using the synchronous design method and parallel comparative method. RESULTS: In the TDS group, the death rate of snails was 90.70% by immersion for 24 hours, reached to 81.40% after spraying for 7 days, and there were no significant differences among the observation time points in molluscicidal effects (P > 0.05). One day after the spraying, the death rate of snails was less in the TDS group compared with that in the MSCN group (P < 0.01), but the death rates of snails were similar in both groups 3 days after the spraying (P > 0.05). In the MSCN group, the death rate of snails was 99.17% by immersion for 24 hours, reached to 66.07% by spraying for 1 day. In the WPS group, the death rate of snails was 97.15% by immersion for 24 hours, reached to 71.43% after spraying for 1 day, and there were no significant differences (both P > 0.05). CONCLUSION: TDS has a good molluscicidal activity and stable efficacy, and the molluscicidal effect of TDS is similar to that of MSCN in the filed, but the molluscicidal sensitivity of TDS is lower than that of MSCN.

[Comparative evaluation of models for infectious source control of schistosomiasis in lake and marshland regions].

OBJECTIVE: To compare the effect of different models for the control of infectious source of schistosomiasis, so as to explore the control models suitable for lake and marshland regions. METHODS: The models of "replacement of cattle with machine" and "grazing prohibition and establishing fixed pasture" were implemented in 2 towns of Gong'an and Jianli counties, Hubei Province, respectively, and the data of infection situation of human and livestock, Oncomelania hupensis snail situation and the contamination status of wild faeces were collected and analyzed from 2008 to 2010. RESULTS: In 2010, for the model of "replacement of cattle with machine", the infection rate of residents in the observation group decreased by 56.82% comparing to that in 2008, the difference had a statistical significance (chi2 = 78.197, P < 0.01), and the decrease extent in the observation group was larger than that in the control group; the infection rates of cattle and snails, and the density of infected snails of the former were all decreased to 0. No wild faeces were discovered in the observation group, while 58 pieces of wild faeces were discovered but no schistosome eggs were found in these faeces in the control group. In 2010, for the model of "grazing prohibition and establishing fixed pasture", the infection rate of residents in the observation group decreased by 39.00% without a statistic significance (chi2 = 1.594, P > 0.05), and the infection rate of cattle decreased by 43.98% without a statistically significant difference (chi2 = 0.751, P > 0.05) comparing to those in 2008. The density of living snails decreased by 89.83% in the observation group, while that in the control group increased by 6.80%. A total of 11 pieces of wild faeces were collected in the observation group, with a positive rate of 18.18%, and 7 pieces were collected in the control group, all of which were negative. During the 2 years, no acute and advanced schistosomiasis patients were newly discovered. CONCLUSIONS: "Replacement of cattle with machine" and "grazing prohibition and establishing fixed pasture" are the main measures for schistosomiasis control in lake and marshland regions, the former is suitable for inner embankment regions, while the latter is suitable for the outer-embankment areas.

[Survey of causes of infected Oncomelania snails and infectious sources of schistosomiasis in marshland and lake region of Jingzhou City].

OBJECTIVE: To explore the causes of infected Oncomelania snails and the sources of infection of schistosomiasis in marshland and lake regions of Jingzhou City, so as to provide the evidence for the establishment of control strategy. METHODS: The snail environments in villages with or without cattle in Gong'an and Jianli counties, Hubei Province were selected, the snail status, infection status of people and livestock and wildlife reservoir host (mice), as well as the contamination status of wild faeces were surveyed, and the infectivity of water in investigated villages without cattle were detected by sentinel mice. The correlation between the densities of infected snails and positive faeces were tested by the rank correlation method. RESULTS: In villages without cattle, there were no positive faeces and infected sentinel mice discovered, while in the villages with cattle, 374 pieces of wild faeces were collected, the densities of wild faeces were 0.02 - 0.29 pieces/100 m2, and those of the positive ones were 0 - 0.01 pieces/100 m2, and the densities of infected snails were 0.001 - 0.040 snails /0.1 m2. The distribution of infected snails was consistent with that of the positive faeces, but the correlation coefficient between their densities had no statistical significance (r(s) = 0.123 5, P > 0.05). The average infection rates of human in villages with cattle inside embankment of Gong'an and Jianli counties were 2.87% and 1.37%, respectively, while that of the villages outside embankment of Gong'an County was 1.23%, and all the infection rates of cattle were 0. No infected wild mice were discovered. CONCLUSIONS: Human and cattle are the main sources of schistosome infection in the local areas, the possibility of wild mice as source of infection is low, and cattle is an important cause of infected snails in marshland and lake regions in Jingzhou City.