| Atrazine and acetochlor are two conventional herbicides and they play an important role in the process of corn production. The use of them has long been practiced, and is wide in region and large in amount. Owing to the adverse effects on the environment, they have been successively forbidden by many countries in recent years. However, atrazine and acetochlor are extensively used in Jilin province, which is the largest maize producing province in China.. To the best of our knowledge, there has been no study on the residues and distribution of atrazine and acetochlor in farmland soil around the province.In this study, the soil samples were obtained from 145 sampling pots in 28 areas including Changchun, Baicheng, Songyuan, Siping, Jilin, Liaoyuan, etc. They were collected in fixed points from different layers of soil(0~10cm, 10~20cm and 20~30cm). The residual atrazine and acetochlor in different types of soil, different areas and seasons(April, July and October) was determined respectively. Arc GIS system and data analysis were used to study their space-time distribution characteristics, clarify the pollution situation, and evaluate the agro-ecological risks. The study will provide theoretical basis for agricultural production guidance and government decision-making. Moreover, it can provide many cases for the similar studies. The results are as follows:1. In the pretreatment of soil samples, a kind of MIPs was prepared as column extractor stuffing, and the samples were separated and purified by solid phase extraction. A retention analytical method for simultaneous detection of atrazine and acetochlor in soil samples was developed. Compared with other methods reported in literatures, the method was more accurate, sensitive, and required less solvent. Moreover, it was more suitable for analysis and detection of bulk soil samples. The gas chromatography for detecting atrazine and acetochlor simultaneously was established, which has further been partially adopted by Jilin provincial standard(Standard DB22 T 1753-2012).2. The atrazine was detected in all maize producing areas of Jilin province, at different times and in different soil layers. In the same layer of soil, the amount of atrazine displayed an order of July>October>April. The distribution proportion of atrazine in three layers of topsoil also varied from time to time. The average residues in every layer was 0.018~0.116 mg·kg-1 and the range of MRL was from 0.169 to 0.295 mg·kg-1. The overall distribution of a year was 0 ~ 10 cm > 10 ~ 20 cm > 20 ~ 30 cm. The residue levels of different districts were significantly affected by spring spraying. The differences decreased with the increase of time. The characteristic of the total distribution was that the amount of residues in the East was higher than that in the West.3. The acetochlor was detected in maize producing areas of Jilin province at different time and in different layers of topsoil. Although the residue amount in three layers of soil was affected by spring application and varied with time, its distribution relationship in the three layers was hardly affected. The amount of atrazine displayed an order of July>October>April. The average residues in every layer was 0.010~0.235 mg·kg-1 and the range of MRL was from 0.097 to 0.911 mg·kg-1. The overall distribution of a year was 0~10cm>10~20cm>20~30cm. The differences of acetochlor residue levels in different layers of soil and at different time were significant; the differences of residue amount in different districts decreased with the increase of soil depth. The distribution intensity showed that the residue levels in the middle and eastern areas such as Changchun and Jilin were higher than those of the western areas such as Songyuan and Baicheng.4. The differences between atrazine and acetochlor distribution were studied. Compared with acetochlor, the migration ability of atrazine in soil was greater, thus it had more residues in deep soil. The residual acetochlor, however, was almost in top soil. The differences between atrazine and acetochlor residue levels in different areas were also as above. The residue levels of atrazine and acetochlor in the three layers of soil in Changchun and Jilin districts displayed identical rules, resulting from the similar application method and similar soil and climatic conditions.5. The agro-ecological risk was evaluated. At present the residual amount of atrazine in maize producing area of Jilin province was lower than the intervention values in Netherlands and Hungarian, the maximum allowable limit in Vietnam, or the safety critical concentration of most crops, posing a low risk to the agro-ecological environment. The residual amount of acetochlor was lower than the safety concentration of common environmental impact objects, also posing a low risk to the agro-ecological environment. The maximum and average residual amount of acetochlor in Changchun and Jilin was significantly higher than that in other districts, indicating that residue monitoring in farmland soil of these districts should be strengthened. In the background of a large amount of application, the cumulative effects of atrazine and acetochlor on topsoil year by year were not obvious. Atrazine and acetochlor which had not been degraded were more likely to move to surface water and groundwater, therefore the residues of atrazine in water should arouse more concern. |
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