| As an efficient organic solvent degreasing, CAHs were widely used in metal surface cleaning. However, due to the inappropriate use and unorganized emissions, CAHs lead to soil and groundwater pollution, especially in the shallow groundwater in Yangtze river delta region where manufacturing was developed. There were more likely to appear CAHs contaminated site, CAHs were highly toxicity and highly volatile, harmful to ecological environment and human health. Therefore, for the Yangtze river delta region, it’s necessary and important to carry out investigating and monitoring the typical CAHs polluted site, and study the risk of CAHs to the ecological environment and human health.In this study, we selected a typical CAHs of manufacturing contaminated site in Shanghai as an object, on the basis of analysis method for CAHs in soil and groundwater. First, investigated and analyzed the geological conditions and the hydrogeological conditions in the soil:Second, sampled and tested the concentration of CAHs in soil and groundwater, and made sure the horizontal and vertical distribution characteristics of CAHs in soil and groundwater. On this basis, established the human health risk model to evaluate the risk of CAHs in soil and groundwater to the health of human; Then, according to the monitoring of CAHs in groundwater, combined with the characteristics of the existence environmental factors in groundwater, elaborated the natural attenuation regularity of CAHs in groundwater, predicted CAHs migration transformation rule in the groundwater by using this model; Finally, discussed the environmental toxicology effect of CAHs in the groundwater by using ecotoxicology, combined with human health risk comprehensive to judge the CAHs pollution level of the site, provided detailed reliable basis for further repair work data. As follows were the main conclusions:（1） According to history contamination condition of 1,1,1-TCA in the site, divided the site into five suspected pollution areas （A1, A2. A3. A4, A5）, set up 56 soil sampling points and the corresponding groundwater monitoring well, investigated and analyzed the geology and hydrogeology conditions of the soil. The results showed that the stratigraphic structure of the site were backfill soil, silt clay/clayey silt, sandy silt muddy silt clay, silt, clay and silt clay and sandy silt. In the silt clay layer, the horizontal permeability coefficient was 1.7 to 4.5 times as that of vertical permeability coefficient （5 m below ground was sandy silt）. In the clay layer, horizontal permeability coefficient was close to vertical permeability coefficient. The permeability coefficient of the silt layer （glue powder soil or sandy silt） was one or two orders of magnitude to that of the underneath clay stratum （silt clay or clay）. On the whole, the shallow groundwater flew from southeast to northwest, the groundwater flow wasn’t obvious, the scale height of groundwater was between 2.70 m to 3.35 m. Confined aquifer distributed in the silt clay layer. The horizontal hydraulic gradient of the shallow groundwater was between 0.0010 to 0.0040 m/m. The vertical hydraulic gradient change was obvious, from one well to the neighbor, down from 0.3 m to 1.2 m vertical distance was 4.1 m to 7.6 m.（2） Detailed sampling in 56 points and tested the concentration of CAHs in soil and groundwater, the results showed that there had two-chlorinated aliphatic hydrocarbons and one-chlorinated aliphatic hydrocarbons in soil and groundwater. There were five kinds of CAHs which respectively were 1,1,1-TCA,1,1-DCA,1,1-DCE, CA and VC. Horizontally, the CAHs centrally distributed in the 1,1,1-TCA cleaning unit, the maximum concentration of CAHs was 2920312.00 μg·kg-1 in this area, the average range of CAHs concentration was 3618.30 μg·kg-1 -40007.50 μg·kg-1 in the rest regional; The horizontal distribution of CAHs in the groundwater was similar to that in the soil. Pollution was mainly concentrated in the old cleaning unit A2 and new cleaning unit A3. The maximum concentration of CAHs was 1701700.00 μg·L-1 in groundwater of this area, the average range of CAHs concentration was 2327.39 μg·L-1 81442.23.50 μg·L-1 in the rest regional. The main reason of the horizontal distribution characteristics of CAHs in the soil and groundwater might be that there had inappropriate operation in the cleaning unit with 1,1,1-TCA cleaning the metal surface, made large doses of 1,1,1-TCA leaked into the ground, by a long time of diffusion migration and accumulation, caused serious pollution in soil and groundwater. There wasn’t appear tank dumping accidents in the ground storage area of 1,1,1-TCA, the soil pollution in these areas was possibly caused by the groundwater flowing. Vertically, the CAHs concentration in shallow soil was far lower than in the deep soil （above silt clay）, CAHs had good migration ability in high permeability coefficient soil, this might be because of its higher density, good penetrability, strong fat-soluble physical and chemical properties; It’s found that DNAPL in groundwater, DNAPL were main focused at 6 m-8 m underground, where was sandy soil layer upper the silt layer. The pollution range of DNAPL was overall around 80 m east to west, north to south about 24 m, the area was about 1400 m2, and the CAHs pollution area of A2 was about 4500 m2. DNAPL should be the pollution sources of A2 area, it continually dissolved into the groundwater and caused the pollution of groundwater in the surrounding area. （3） On the basis of soil geological, hydrogeological conditions of the site and the CAHs concentration in soil and groundwater, established the human health risk model, to evaluate the human health risk of soil and groundwater. The results showed that the pollution sources in soil and groundwater were five kinds of CAHs,1,1-DCA and VC had the risk of cancer. The exposed ways of CAHs in soil were oral intake, respiratory inhalation and skin contact, the exposure way of CAHs was respiratory inhalation. The exposed receptor were factory worker. According to the risk assessment, there had 16 points where the cancer risk and non-cancer hazard of a total of CAHs in soil and groundwater were higher than acceptable levels （cancer risk:10-6, carcinogenic hazards:1）, calculated the risk control values of CAHs in soil and groundwater, respectively:in soil-VC 0.56mg·kg-1’, CA213 mg·kg-1,1,1-DCE 54mg·kg-1,1,1-DCA 5.8 mg·kg-1,1,1,1-TCA 1865 mg·kg-1; in groundwater-VC 0.79 mg·L-1, CA 3.26 mg·L-1, 1,1-DCE 2.27 mg·L-1,1,1-DCA 1.67 mg·L-1,1,1,1-TCA 2.88 mg·L（4） Combined with the characteristics of the existence groundwater environmental factors, analyzed the relationship between CAHs in groundwater and environmental factors using multiple factors, traced monitoring on the environmental factors and CAHs concentration in groundwater as well. The results showed that the accumulation of chlorine ions in groundwater meant the natural attenuation of CAHs in groundwater. The pollution sources and natural attenuation might be the two mainly factors that leaded to the distribution of CAHs in this site. Over time, the conductivity and the chloride ion concentration in groundwater increased. The relationship between chlorine and ion conductivity was good positive correlation, the concentration of chloride ions could be speculated by the conductivity of numerical through the linear relation, which provided the basis theoretical for monitoring of groundwater water quality. The main pollutants in the groundwater of this site were 1,1,1-TCA,1,1-DCA and CA, as time goes on, the concentration of 1,1,1-TCA and 1,1-DCA gradually decreased. When 1,1,1-TCA and 1,1-DCA existed in groundwater, the concentration of CA increased continuously. Once 1,1-TCA and 1,1-DCA in the groundwater were dechlorinated completely, CA would occur dechlorinating reaction, the concentration of CA would begin to reduce. It’s easy for CAHs to have level of dechlorinating reaction, but difficult to produce secondary dechlorinating reaction. Dechlorinating index showed that the concentration of CAHs was high in groundwater, the dechlorinating index was generally low, the possible reason was that high concentration of CAHs inhibited the main way of natural attenuation dechlorinating process of microorganisms, high concentrations of CAHs produced toxicology and effected on microorganism itself to low the activity of microorganisms. Using the Visual MODFLOW model simulated 1,1,1-TCA contamination spread to the west boundary in the 15 years or so. the highest concentrations decreased from about 9000000 μg·L-1 to about 1000000 μg·L-1; the highest concentration 1,1-DCA decreased from about 200000 μg·L-1 to about 80000 μg·L-1 after 20 years; the highest concentration of CA decreased from about 150000 μg·-1 to around 50000 μg·L-1 in 25 years later. （5） Using acute toxicity of luminescent bacteria and enzyme activity to discuss the environmental toxicology effect of CAHs in groundwater. The results indicated that the acute toxicity of luminescent bacteria increased as the increase of CAHs concentration. Preliminary analysis from toxicity of luminescent bacteria, when the CAHs concentration was less than 1000 μg·L-1 in groundwater, the ecological toxicology effect on groundwater was lower, the harm to ecosystem groundwater was less, the ecological toxicology of CAHs could be ignored; When the CAHs concentration was more than 1000 μg·L-1 in groundwater, It’s necessary to pay close attention to CAHs toxicology effect on groundwater ecosystem.Overall, the luminescent bacteria toxicity of CA was higher than that of 1,1,1-TCA and 1,1-DCA. It’s necessary to pay more attention to the risk of CA, when considering the ecological risk. The relationship of toxicity between 1,1,1-TCA and 1,1-DCA was not obvious, both of them should be paid attention at the same time. The activity of lactate dehydrogenase, alkaline phosphatase and protease increased with the reduce of total concentration of CAHs, when the total concentration of CAHs dropped to less than 200 μg·L-1 , the activity of this three enzymes increase highly, and then the enzyme activity increased slowly as the reducing of CAHs concentration. From the perspective of the activity of three kinds enzymes, when the CAHs concentration was less than 200 μg·L-1 in groundwater, the ecological toxicology effected to the groundwater was low, the ecological toxicology of CAHs could be ignore; when the CAHs concentration was more than 200 μg·L-1 in groundwater, the toxicology effects of CAHs on groundwater ecosystem should be pay close attention to. In order to combine with human health risk to judge the CAHs pollution level of the site comprehensively, providing detailed reliable basis data for further remediation work. |
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