살균제 Chlorothalonil의 기능성 신소재에 의한 분해 특성과 안전성 평가
Risk reassessment Chlorothalonil and its degradation by novel functional materials
해충 질병억제 살균제;
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Fungicide, chlorothalonil(2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile) was registered in early 1970s in Korea and has been widely used to control crop diseases in vegetables and fruit trees. Meanwhile, the fungicide has been criticized due to its crop residues and carcinogenicity as well as environmental toxicology from time to time. Thus, this study was aimed at reviewing recent informations related to risk assessment to develop more reasonable and reliable management measures to the fungicide. General properties such as residue and toxicity, results from integrated risk assessment, rating system introduced for the first time, and use pattern of the fungicide in registered crops were also reviewed. Risk assessment to soil earthworm was done, too. Dietary intake assessment of the fungicide on the basis of monitored data in/on apple and other agricultural commodities and reassessment to the MRLs established for apples and green fruits such as chilly pepper, cucumber, mini tomatoes, and watermelon were also undertaken in order to provide more reliable maximum residue limits and pre-harvest intervals in relevant crops. Assessed results obtained from the studies are as follows; In Korea eight formulations including chlorothalonil WP(75%) were registered for 16 crops including apple, pepper, and cucumber. Annual average consumption of factory gate of this fungicide on the basis of active ingredient for recent five years was below 400MT. Also, maximum residue limits(MRLs) for 41 agricultural commodities were established at the range of 0.1∼5.0 ㎎/㎏ as of 2003. Chlorothalonil and its hazardous impurity of hexachlorobenzene(HCB) are classified as a B_(2) carcinogen by US/EPA and ADI of 0.03 ㎎/㎏ bw/day was established by JMPR in 1992, based on the NOAEL of 3 ㎎/㎏ bw/day derived from a 2-year feeding study in dogs. Cancer risk from foods was estimated to be 1.2×10^(-6) by US/EPA and this figure is at a level which the Agency considers negligible for excess lifetime cancer risk estimates. In order to evaluate safety for hazardous pesticides comprehensively, rating system was introduced for the first time in Korea. This system was developed to determine safety evaluation priority for the target pesticides, and this system was composed of basic and final estimate, where basic estimate was consisted of human health, ecotoxicity, persistence, ADI, and antidotes, and in final estimate total score of basic estimates, special toxicity such as carcinogen, consumed amount, contents of regulatory actions and registration status in developed countries were considered as important factors. To develop the technique for remediation of soil and water contaminated with pollutants, degradation of the chlorothalonil by using novel functional materials was carried out. The photocatalytic degradation of chlorothalonil by mesoporous titanium oxo-phosphate (Ti-MCM) was investigated in aqueous suspension for comparison with TiO_(2) using as an effective photocatalyst of organic pollutants. Its adsorption isotherm for chlorothalonil reached at reaction equilibrium within 60 min under dark condition with 28% degradation efficiency. The degradation ratio of chlorothalonil after 9 hours under the UV radiation condition (254 nm) exhibited 100% by Ti-MCM and 88% by TiO_(2). However, these degradation kinetics in static state showed a slow tendency compared to that of stirred state because of a low contact between titanium matrices and chlorothalonil. Also, degradation efficiency of chlorothalonil was increased with decreasing initial concentration and with increasing pH of solution. As results of this study, it was clear that mesoporous titanium oxo-phosphate with high surface area and crystallinity could be used to photocatalytic degradation of various organic pollutants. ^(+)KClO_(3)-occluded zeolites have a high potential for effective removal of various organic pollutants as an environment-friendly oxidant. The removal isotherm of chlorothalonil by zeolite and KClO_(3) reached at reaction equilibrium within 6 hours by 18% and 47%, respectively. However, the chlorothalonil removal by the zeolite-KClO_(3) complex was slowly and steadily increased in reaction time up to 96 hours till 92%. Therefore, it is clear from this finding that zeolite-KClO_(3) complex could be applied for effective removal of organic contaminants in the soil and aqueous environment. Chlorothalonil was included in the first group of pesticides for the integrated risk assessment due to the carcinogen and other potential risk. Risk assessment was undertaken with the results of residue monitoring surveys carried out for 4 years (1992, 1994, 1995 and 1997). No sample was exceeded MRLs and total dietary daily intakes were below 0.3% of ADI. Dietary cancer risk estimates of the chemical were also below 1×10^(-6) which is negligible risk standard. Results of monitoring survey of chlorothalonil for apples in the NAQS(National Agricultural Products Quality Management Service) from 2001 to 2003 were reviewed. Detection rates were very high 93∼98% and average residue levels were also fairly high 0.15∼0.23 ㎎/㎏. However, dietary daily intake amounts from apples were very low, which ranged between 0.39∼0.61% of ADI and dietary cancer risk from apples was estimated to be 0.9∼1.4×10^(-6) and this figure was at a level which US/EPA considers negligible for excess lifetime cancer risk estimates. In order to improve the safe use guidelines of chlorothalonil WP and SC established for the fruit vegetables, crop residue data were reviewed. Safe use guideline for chlorothalonil WP in case of cucumber should be changed, that is application frequency has to be lessened from 5 to 3 or 4 times and pre-harvest interval from 3 to 2 days, based on the additional crop residue data from the supervised trials carried out under the good agricultural practice(GAP). Unless the MRL of 0.1 ㎎/㎏ established in watermelon should be remarkably increased to 5.0 ㎎/㎏, farmers are unable to follow the present safe use guideline established for chlorothalonil 53 SC, which are the 4 times of application and 7 days of pre-harvest interval. The same MRL established in tomatoes and pepper for chlorothalonil should be also remarkably increased from 1 to 5 ㎎/㎏, thereby, pre-harvest interval of safe use guideline established in both crops for chlorothalonil 75 WP could be lessened from 7 to 3 days. Generally, it is recognized that crops to be harvested sequentially during the growing season should be safe in the risk assessment of the residues in fruits 1∼3 days after application of pesticide. To assess the acute toxicity of the fungicide on earthworm, technical grade and formulation (75% WP) were investigated and their toxicity/ exposure ratios were also calculated. LC50 for the technical grade and formulation to earthworm was above 1,000 ㎎/㎏ soil and it was estimated that their acute toxicities were very low. Since the toxicity/exposure ratios of technical grade of chlorothalonil and formulation were more than 167, therefore, their risks to earthworm were rated negligible risk level. In conclusions, chlorothalonil is widely used to control crop diseases for horticulture in Korea. Total dietary intakes were below 1% of ADI and dietary cancer risk estimates were also below 1×10^(-6) which is considered as to be negligible risk standard. This fungicide was also estimated to be a valuable pesticide which had much benefits such as the reduction of disease control cost, substitution to local product of technical grade, and no resistance problems on the target pathogens. Accordingly, this fungicide is estimated to be a safe pesticide considering that it has been widely used for horticulture without any special regulatory actions in developed countries such as USA, Japan, United Kingdom and also it is not registered or included in UN consolidated list, PIC procedure, POPs, EDs chemical by WWF, and dirty dozen pesticides by PAN. Therefore, it is considered that the development of additional regulatory actions was not necessary at present, especially. However, it is estimated that the MRLs and safe use guidelines established for the crops which are harvested sequentially during the growing season should be changed.