复合污染土壤中土霉素的吸附行为及其对土壤重金属解吸影响的研究

SORPTION BEHAVIOR OF OXYTETRACYCLINE IN COMPLEX CONTAMINATED SOIL AND ITS EFFECTS ON DESORPTION OF HEAVY METALS IN THE SOIL

参考经济合作与发展组织（OECD）化学品试验导则No.106,采用批量平衡试验的方法,探讨了土霉素（Oxytetracycline,OTC）在3种土壤中的吸附解吸特性,并考察了土霉素外加量对土壤中4种代表性重金属元素（铜、锌、铅、镉）解吸量的影响。试验设置的土霉素初始浓度为0.01、0.1、1.0、5.0、10.0、25.0、50.0、100、200和400 mg L-1。结果表明：（1）存在一个土霉素特征浓度,高于或低于该浓度值时土霉素的吸附性质有所差异,且高低两个浓度范围内的数据均能用Freundlich模型与Langmuir模型较好地拟合;（2）当土霉素浓度在0~25 mg L-1之间时,能在土壤表面与重金属发生竞争吸附,且重金属解吸量随土霉素浓度的增加而增加;当土霉素浓度在25~100 mg L-1之间时,部分游离态重金属以与土霉素的络合物形式重新固定于土壤表面,土壤重金属的解吸量随土霉素浓度增加而减少;土霉素浓度高于100 mg L-1时,体系p H相对于对照有明显下降,土壤重金属的解吸量与土霉素浓度又呈正相关。

Tetracyclines （TCs） is one of the antibiotics most commonly used in animal husbandry nowadays, for it is, cheap and little in side-effect. It is often released into soils through application of animal manure and disposal of phar- maceutical waste and so on, thus not only affecting microbial activities and plant growth, but also interacting with other pollutants existing in the soils, which might eventually lead to eco-toxicity and changes in pollutant characteristics in agri- cultural soils. In order to explore sorption behavior of oxytetracycline （OTC） , a typical TCs, in complex contaminated soil and its effect on desorption of other existing pollutants （especially heavy metals （HMs） , such as cadmium, copper, lead and zinc） in three different types of complex contaminated soils, a batch equilibrium experiment was conducted, in line with Guideline No. 106 of the Organization for Economic Co-operation and Development （OECD）. Samples of three dif- ferent types of contaminated soils were collected from three sites different in soil type and were contaminated with HMs- Polycyclic aromatic hydrocarbons （PAHs） , HMs, and PAHs. The experiment was designed to have 10 treatments relative to OTC concentration, i.e. 0, 0.01, 0.1, 1.0, 5.0, 10.0, 25.0, 50.0, 100, 200 and 400 mg L-1. After the addition of OTC, concentrations of cadmium, copper, lead and zinc in the soils were determined. Results show： 1 ） a threshold value was found with OTC concentration. Around the point, below or above, OTC adsorption characteristics changed in opposite ways. However, all the data in the two ranges of concentration could be well fitted with the Freundlich model and Langmuir model; 2） OTC, varying in the range from 0 to 25 mg L-~ in concentration, competed for adsorption sites on the surface of the soils with heavy metals and as a result, HMs desorption rate increased with the rising OTC concentration; however, when OTC concentration varied between 25 and 100 mg L-1 , some free HMs ions formed complexes with OTC and got fixed again on the surface of the soils; and when OTC concentration exceeded 100 mg L-1 , HMs desorption rate rose slightly as the addition of a high rate of OTC declined pH of the system. The changes in HMs availability in contami- nated soils are mostly attributed to the competition for adsorption and complexation reaction of OTC with HMs, and the change in pH, which upsets the dynamic equilibrium, adsorption or desorption, of the pollutants in the soils. Since HMs desorption rate in solution could, to a certain extent be analogous to its toxicity, it is necessary to study in depth effect of the addition of oxytetracycline, relative to application rate, on desorption of HMs in complex contaminated soils, which is not only conducive to the research on mechanism and toxicity of the complex contamination of antibiotics and heavy metals, but also of a certain significance in guiding maintenance of food security and remediation of complex contaminated soils.