Accumulation And Brief Exploration Of Risk Reduction Of Polycyclic Aromatic Hydrocarbons (PAHs) In Crop Grown Near An Petrochemical Area

The petrochemical production can contribute to economic growth and development, but they can also pollute the surrounding environment. The pollutants such as PAHs(Polycyclic Aromatic Hydrocarbons) exhausted by petrochemical production can remain in crop, which would cause some edible safety risk. At present, the degradation of PAHs in crop has become an important issue in the agricultural polluted land. In this study, based on the survey of PAHs pollution in the farmland near a petrochemical industry, the farmland which contained a higher concentration of PAHs would be selected as a test base. The distribution characters of PAHs in farmland and crop would be investigated to choose some vegetable which was sensitive to PAHs, then the test experiment was carried out to study the degradation efficiency of the PAHs in the test base using the high efficient PAHs degradation microorganism and insecticide (potassium hypermanganate). The results are as follows:1. To select a field for test, contents of PAHs in farmland and crop were analyzed around a petrochemical industry. The results showed that the total concentrations of PAHs in the soils ranged from 45.4～964.3μg/kg, some of these areas were overproof and most signified slight pollution. It was found that crop had a higher contents of PAHs, ranging from 220.6～1001.3μg/kg. The isomer ratios revealed that the PAHs in the soils originated mainly from oil or oil combustion.It was found that T village was maily contaminated by oil, so selecting this area as the test base in accordance with this reason.2. Field experiments were carried out to planting commonly grown crop locally, including 4 types of vegetable were celery, brassica rapa, Chinese anise and carrot,3 types of grain crop were corn, sorghum and soybeans. Contents of PAHs in the soils were analyzed and ecological risk was assessed. The concentrations and distribution characters of PAHs in crop were investigated. The toxic benzo[a]pyrene equivalents(TEQ) and a contaminated land exposure assessment model was employed to assess the exposure risk of crop. The results showed that each of the 16 PAHs can all be detected in the soil samples and low molecularweight PAHs were dominant. The total concentrations of PAHs in the soils ranged from 69.8 to 1340.9μg/kg. The edible part of foodstuff and vegetables had much high concentration of PAHs, which ranged from 580.0 to 1999.6μg/kg and 274.6 to 1565.8μg/kg, respectively. Brassica rapa had a higher accumulation of PAHs than other vegetables samples, and so did soybeans for foodstuff samples, but corn opposed. The ADE (Average Daily Exposure) of children and adults who uptaked the food from this experimental base to the 16 PAHs compounds exposure were 1.6μg-kg-d-1 and 1.8μg·kg·d-1, respectively. Absolute exposure were 24.7μg-d-1 and 100μg·d-1, which had an 1.1 and 4.6 higher than food absolute exposure to the Beijing population, so uptaking the native crop may have the health risk.3. A kind of vegetable (brassica rapa) was selected to taking as the receptor and planted in the polluted farmland which had a higher en-richment coefficient to PAHs under the earlier field conditions. Then the PAHs degradation microorganism was added to the soils, the leaves of brassica rapa was sprayed by different concentration of potassium permanganate solution during crop growth period, or relaying intercropping a restoration plant, in order to establishing the technology and methods to degrading the PAHs of crop. To investigate the effect of the PAHs degradation microorganism on degradation of PAHs in the agricultural polluted soils and the enhancement by the PAHs degradation microorganism on phytoaccumulation of PAHs, the PAHs degradation microorganism was only added to the soils or having planted with restoration plant. The results showed that in 60 days,8 different treatments including the content of potassium permanganate solution at 0.05%,0.1% and 0.2%, the content of the PAHs degradation microorganism at 4%o,4%o PAHs degradation microorganism combining with 0.1% potassium permanganate solution, mixed cropping ryegrass,4%o PAHs degradation microorganism combining with ryegrass,0.1% potassium permanganate solution combining with ryegrass. In varied treatments,4%o PAHs degradation microorganism could effectively promote degradation of the total PAHs, especially for low molecularweight PAHs and a little for high molecularweight PAHs. The contents of low molecularweight PAHs in brassica rapa decreased by 75.9% in mature stage compared with grown in 20 days, and decreasing up to 40% compared with control at the same time. It was found that spraying potassium permanganate solution could also effectively promote the decreasing of high molecularweight PAHs. In mature stage, there was no significant differences in the contents of high molecularweight PAHs in brassica rapa between spraying potassium permanganate solution and control, but increasing degradation of PAHs up to 60%. Both of they had not an adverse effect on growth of brassica rapa. The agricultural polluted soils restoration justified that degradability of PAHs was the highest with the treatment of ryegrass added PAHs degradation microorganism, comparing with the treatment of only adding PAHs degradation microorganism, increasing degradation of PAHs by 47.8%, and compared with the treatment of only planting ryegrass, increasing degradation of PAHs by 168.9%. The results revealed that PAHs degradation microorganism could effectively promote ryegrass to degrade the total PAHs in soils.