Study On Distribution Behavior Characteristic Of PAHs In The Forest Soil And Plant Leaves

Persistent organic pollutants (POPs) are one kind of chemicals, which harm to the environment ecosystem and human health. POPs can reach forest ecosystem through the long-range atmospheric transport, and into the forest terrestrial ecosystems with dry/wet deposition. POPs distributed in the forest soil and plant leaves not only depend on their physical and chemical properties (molecular weight, lipophilic, hydrophobic) but also affected by environmental factors (temperature, movement of air masses, dry/wet deposition). Environmental factors change (such as temperature changes), can affect POPs environmental behavior, and further, affect the distribution of POPs in different environmental media. Dry/wet deposition is the main way of POPs into the forest soils? and also the main way to clear POPs from the forest atmosphere. However, change of POPs in the forest atmosphere directly affected the distribution of POPs in plant leaves. Soil and plant leaves, itself characteristics also affect POPs adsorption and enrichment process.At present, many research are committed to uncover distribution process of POPs in forest. But the forest ecosystem environmental factors are complexity, so there is no clearly POPs distribution pattern in forest and the influencing factors. In this paper, PAHs as a target compound, study of PAHs distribution characteristics in different forest soil and plant leaves. Further research geographical environmental conditions and the characteristics of soil and plant leaf how to effect the distribution behavior of PAHs in the forest.To achieve the purpose, we have conducted sampling in the Changbai Mountain area. Changbai Mountain has a complete forest ecosystem, and have abundant of plant resources. Changbai Mountain is configured southwest to northeast, the southern and western side located in windward, northern side located in leeward. Thus, in different side have different geographical environmental factors. And as the altitude increases, the temperature, precipitation and other climate conditions changed significantly. In order to study the distribution behavior characteristics of PAHs in Changbai Mountain soil and plant leaves, at different side (northern side, western side and the southern side), along with the altitude collected a total of 32 surface forest soil samples. To analyze the affected Changbai Mountain local source, collected a total of 28 ginseng cultivation soil samples surrounding in Changbai Mountain. Plant leaves sampling were performed twice, the first time sampling is carried out on the same latitude of different side in Changbai Mountain,15 families including 33 species of 41 plant leaves were collected. The second sampling is carried out in the different altitudes of northern and western side in Changbai Mountain,13 families including 24 species of 56 plant leaves were collected. In order to study plant leaves seasonal distribution characteristics of PAHs, willow leaves as the study of species, from budding to defoliation, with the time change collected the plant leaves. A total of 29 plant leaves samples were collected, in the same time, collected 29 gas samples and 29 particle samples.After analyzing the PAHs in collected soil and plant leaves samples, the following results were obtained:1. PAHs concentration in different geographic and environmental conditions plant leaves and soil as follows:1.1 Range of PAHs concentration in northern side soil is 38.5-212.2 ng g-1 (average: 110.4 ng g-1),range of PAHs concentration in western side soil is 83.9-313.9 ng g-1 (average:170.7 ng g-1), range of PAHs concentration in southern side soil is 52.6-238.6 ng g-1 (average:141.8 ng g-1).1.2 Range of PAHs concentration in northern side plant leaves at first time sampling is 119.0-271.2 ng g-1(average:195.2 ng g-1), Range of PAHs concentration in western side plant leaves at first time sampling is 99.2-280.5 ng g-1 (average:160.6 ng g-1). Ranges of PAHs concentration in northern side plant leaves at second time sampling are N1 (altitude:796 m):113.0-381.8ng g-1 (average:204.9 ng g-1), N2 (altitude:1800 m): 92.9-202.4 ng g-1 (average:165.2 ng g-1), N3 (altitude:2000 m):125.3-220.7 ng g-1 (average:190.4 ng g-1). Ranges of PAHs concentration in western side plant leaves at second time sampling are W1 (altitude:1800 m):49.6-137.8 ng g-1 (average:107.0 ng g-1), W2 (altitude:2000 m):65.4-132.9 ng g-1 (average:110.1 ng g-1).2. The concentration level of PAHs in soil located on the northern side (leeward) is below than the concentration level of PAHs in the western and southern side (windward). However, distribution of PAHs concentration in the plant leaves is on the contrary from the soil. Because wet deposition in the windward is significantly greater than the leeward, while wet deposition is the main way letting PAHs from the atmosphere into the forest soils, so the windward PAHs concentration level in soil is higher than the leeward. But the wet deposition is also the main way to remove PAHs from the atmosphere, yet the concentration of PAHs in the atmosphere is an important factor influence the PAHs in plant leaves. Therefore with the wet deposition increasing in the windward, PAHs in the atmosphere is removed and then leading the PAHs concentration level in plant leaves decreasing in the windward.3. Through the analysis of air mass trajectory in Changbai mountain found all sides of the Changbai Mountain are influenced by a similar mixture of PAHs source. But different PAHs composition distribution found in soil and plant leaves between the windward (western and southern side) and the leeward (Northern side). Because, high molecular weight PAHs have high KPA value, so tend presented in the particle phase of air. And Changbai Mountain is a natural barrier can block off the moist air in the windward, make the high molecular weight PAHs, which bounded in particle phase more efficiently through by dry/wet deposition into the soil. And not cleared dry/wet deposition low molecular weight PAHs can move to the leeward with the air mass movement. This makes the windward and leeward side have different PAHs composition in the air, further lead to the PAHs composition distribution in soil and plant leaves are different between windward and leeward.4. In the windward (western and southern side) soil, PAHs appeared the cold trapping phenomenon, but it does not appeared on the leeward (northern side). Because the windward side soil trapped most of high molecular weight PAHs, however, the high molecular weight PAHs have relatively high octanol-air partition coefficient (KOA), octanol-water partition coefficient (KOW), soil organic carbon adsorption coefficient (KOC).Therefore, with time went by, it is mbre conducive to the enrichment in the soil. And with the altitude increasing, the precipitation is increasing, making the high molecular weight PAHs easier to concentrate in the high altitude of the forest soil with the precipitation. However, there isn’t occurring any cold trapping phenomenon in plant leaves at any side of Changbai mountain. Because, the cold trapping phenomenon is caused by PAHs long time enrichment process; however, PAHs in plant leavesis the short time enrichment process.5. All plant leaf samples can detect PAHs, and PAHs concentration were different in different types plant leaves in the same sampling site. Because the leaves parameters between different types of plant leaves are different. When have similar specific leaf area,PAHs concentration increased with lipid content increase, and when have similar lipid content, PAHs concentration increased with specific leaf area increase, when the leaf parameters have similar, similar concentration distribution of PAHs in plant leaves. PAHs composition distribution is similar in the same sampling site plant leaves, that means plant leaves can reflection of the local PAHs composition distribution.6. The concentration distribution of PAHs in plant leaves is obviously change with the seasons change. In the spring, the concentration of PAHs compered increasing trend with the plant leaves growth, but appeared decreasing trend in summer. And in autumn, start of the heating, the concentration of PAHs in plant leaves begin to increase. In addition, between PAHs concentration in air and plant leaves in the spring season, there have no obviously correlation. Because of in spring, concentration of PAHs in plant leaves are obviously affected by the plant leaf parameters. Distribution of PAHs in plant leaves can also response to the climate change, such as rainfall and air mass movement.These results illustrate that; wet deposition is the most important environmental factor affected the distribution of PAHs in the forest, it can remove the PAHs from the atmosphere and enrichment to the soil, but not conducive to the enrichment of PAHs in plant leaves. Physical and chemical properties of PAHs can effect the different molecular weight PAHs response to the climate change, this makes PAHs distribution in soil and plant leaves in different geographic and environmental conditions have changed. The plant leaf parameters can affect the concentration distribution of PAHs. However, leaf parameter does not affect the composition distribution of PAHs in plant leaves. It is worth noting that the plant leaves can response to the concentration distribution of PAHs in atmosphere well, and plant leaves can also respond to the climate change in a short time. In forest ecosystems, PAHs distribution behavior in soil is the result after long process enrichment. On the contrary, PAHs distribution behavior in plant leaves is the result by short reaction result of atmospheric PAHs.