| Endosulfan was a widely used pesticide and mainly used in killing pests in cotton, tea bushes, tobacco and fruit trees, and also was a persistent organic pollutants which has joined the list in April2011. Currently, domestic and international researchers have predominantly focused on the quantitative detection, toxic effect and environmental distribution. Unfortunately, there have been few investigations of leaching characteristics of endosulfan although leaching process is the main route into environment for some toxic substances. Hence, it is essential to further understand the leaching characteristics of endosulfan. In this study, endosulfan from waste (waste residue and sludge) were used to carry out the experiments. Trough simulating typical storage scenario, the effects of various conditions including initial pH of leaching agent, particle size, liquid-solid ratio, leaching method and leaching time on leaching characteristics of endosulfan were investigated. This paper finally analyzed the leaching mechanisms of endosulfan and calculate the risk limits through models, which can provide a preliminary theory basis for environmental risk assessment and improve the Identification Standards for hazardous wastes. The main results are listed as follows:(1) Endosulfan from samples and leaching solution were extracted by ultrasonic extraction and liquid-liquid extraction methods and then determined qualitatively and quantitatively by gas chromatography. The results showed that a-endosulfan,(3-endosulfan and endosulfan-ether were all detected in waste. Waste residue and sludge were both a-endosulfan based, and specifically, a-endosulfan accounts for80percent of the total endosulfan, endosulfan-ether contributed less than1%. Leaching rate of endosulfan were10-4～10-3through detecting the leaching solution under different conditions (initial pH of leaching agent, particle size, liquid-solid ratio, leaching method and leaching time).(2) According to different conditions (initial pH of leaching agent, particle size, liquid-solid ratio, leaching method and leaching time), single factor test and orthogonal test were carried out to explore the leaching characteristics of endosulfan. Results showed from single factor tests that the amount of leaching a-endosulfan, β-endosulfan and endosulfan-ether in waste residue and sludge all increased with the initial pH of leaching agent. When the initial pH is5, the total leaching amount of endosulfan in waste residue and sludge reached those maximums of60.65ug/g and33.72ug/g separately. As the liquid-solid ratio increased, the leaching amount increased, but the leaching concentration decreased. Specifically, the leaching amount of a-endosulfan, P-endosulfan and endosulfan-ether in sludge increased linearly, but those in waste residue increased slowly. When the liquid-solid ratio was over20, leaching concentration of a-endosulfan, P-endosulfan and endosulfan-ether began to stabilize. The leaching amount of endosulfan increased but slowly with the particle size decreasing. The leaching method highly influenced the leaching amount of endosulfan: the leching method was in the order: flip oscillation> horizontal oscillation> standing oscillation. While under the same conditions, the leaching amount of three kinds of endosulfan was different, and leaching amount from the waste residuewas was in the order: a-endosulfan> β-endosulfan> endosulfan-ether, and from the sludge was endosulfan-ether>a-endosulfan> β-endosulfan. The leaching process could be divided into two parts over time: quick-release stage(0-48h)and slow-release stage(48-480h). There were differences between the leaching amount of three kinds of endosulfan in any time, and leaching amount from the waste residue was in the order: a-endosulfan> β-endosulfan> endosulfan-ether, and from the sludge was endosulfan-ether> a-endosulfan> β-endosulfan, which was due to the difference in composition and physicochemical property of waste residue and sludge. Orthogonal test showed that influencing on the leaching concentration of endosulfan was in the order: liquid-solid ratio> leaching method> leaching time> initial pH of leaching agent. Considering the real scenarios and the environmental risks control, the leaching experiments in the laboratory were under the following conditions: initial pH of leaching agent was5, the leaching time was2d, and the liquid-solid ratio was20:1, besides, the leaching method was flip oscillation.(3) Results showed a-endosulfan, p-endosulfan and endosulfan-ether of waste residue and sludge could be described properly by Elovich equation, and the correlation coefficient (R2) was0.915～0.974. The modeling results indicated that the leaching process of endosulfan was heterogeneous diffusion process. The relation between leaching rate and leaching time was inversely.(4) Basing on the field investigation, monitoring data of waste characteristic and statistical analyses, EPA suggested that the acceptable value at non-cancer risk is1. According to this, the acceptable limit value at risk of endosulfan from waste storage scenario through EPACMTP models was calculated as0.1mg/L. |
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