Environmental Fate and Effects of Pesticides - American Chemical

Chapter 11

Evaluation and Effective Extraction Method of Paraquat Residue of Soil in Korea Kyu Seung Lee and Jin Wook 1

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Downloaded by CORNELL UNIV on July 17, 2012 | http://pubs.acs.org Publication Date: July 31, 2003 | doi: 10.1021/bk-2003-0853.ch011

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Department of Agricultural Chemistry, Chungnam National University, Yusong, Taejon, 305-764, Korea Toxicology Research Center, Korea Research Institute of Chemical Technology, Yusong, Taejon, 305-6000, Korea Current address: National Veterinary Research and Quarantine Service, 620-2 Amnam-dong, seo-gu, Busan 602-833, Korea

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Abstract Paraquat, a contact herbicide that has been widely used in Korea, was reviewed for its use pattern and social issues brought forward environmental and consumer groups. Orchard soils in Korea were monitored for two years, and paraquat was detected in more than 95% of the samples, and the average residue level was8.1mg/kg, in 1996 and 6.87 mg/kg in 1997, respectively. At the same time, SAC-WB, regarding as safety margin of paraquat adsorption in soil, were carried out wheat bioassay at the equilibrium concentration and was observed to the same soil sample. Average SAC-WB value were 223.40 mg/kg in 1996 and 296.12 mg/kg in 1997, respectively. An extraction method for paraquat residue in soil was looked over to improve reproducibility and efficiency of recovery. Pre-washing with concentratedHClfor 1hr.is suggested for that purpose. Finally, capillary zone electrophoresis was used for the detection of low amounts of paraquat residue as level of 10 ~10 g/l in paddy water. -13

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© 2003 American Chemical Society

In Environmental Fate and Effects of Pesticides; Coats, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

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Paraquat (l,l-dimethyl-4,4'-bipyridylium dichloride), a para-substituted quaternary bipyridyl cation, was introduced commercially in 1962 as a contact herbicide and has been used in Korea since 1970. It exists as very strong soluble chloride salts in dry conditions, and very stable bipyridyl cation in aqueous environments [1]. These characteristics allow for foliar application. Paraquat was strongly bound to soil clay minerals such as montmorillonite and other negatively charged soil components, including organic matter [2].

Paraquat is inactivated when adsorbed, therefore no translocation through the roots and no harmful effects to following crops were found after paraquat application to the soil. Because degradation by microorganisms and chemical processes were not especially effective [3, 4], we assume that the paraquat residues can continuously increase and accumulate in the soil [3]. Nevertheless, the residue levels of paraquat in soil after continuous use in the same soil were not much higher than expected [5,6], while paraquat residue levels decreased in soil after application stopped [7]. These results suggest degradation by microorganisms or other routes such as photo-decomposition. In fact, monopyridone, an oxidized metabolite of paraquat was found during degradation of plant residues [4] and was also identified in fungal-degradation studies[8]. The strong binding property of paraquat was mainly dependent on the kinds of clay mineral, clay content, and organic matter. Therefore, residual forms of paraquat where divided into two categories, loosely bound and tightly bound paraquat [9]. The former is desorbed by saturated ammonium chloride solution, and the latter by refluxing with cone. H2SO4. Tightly bound paraquat residues can not be extracted easilyfromsoil, and they did not translocate or diffuse into the environment. Plants can not take up these residues in soil, and soil microbes cannot be affected even in the kaolinite-dominated soils which favor strong cation adsorption, although kaolinite shows less cation adsorption than other clay minerals. Various methods to determine of paraquat residues have been introduced like spectrophotometry [10 - 1 5 ] , gas chromatography [16], H P L C [17, 18], ion-pair chromatography [19], enzyme-linked immunosorbent assay(ELISA) [20] and capillary electrophoresis [21-23]. Current extraction methods have low recovery, are time consuming, and give relatively high errors in reproducibility. Therefore, an effective extraction method of paraquat residue in soil needs to be developed for evaluation andriskassessment of paraquat- treated soil.


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Status of paraquat use in Korea Paraquat has been used for weed control in orchards and non-crop land since it was introduced in Korea in 1970. Since then, the consumption rate increased until 1995[24] (Figure 1). The ratio of paraquat amounts per the applicable area which include orchard and mulberry cultivation area were calculated. (Figure 2) Three applications of the recommended dose per applicable area per year is regarded as a normal spray pattern and a standard application amount. In Korea, 56% of the total paraquat use was for upland crops, 4% in direct rice, 6% in pre-planting rice and 5% in barely[25], and 44% for non-crop areas, including 28% in rice and upland bund, and 16% in other non-agricultural use. However, die total consumption amounts of paraquat were 3-4 times more than that of estimated from standard application to the applicable areas. Therefore, the environmental and consumer groups indicate that paraquat residues in the soil may be hazardous by steady accumulation and excess of die maximum holding capacity of soil in near future. Moreover, paraquat is notorious for being drunk in suicide attempts, leading consumer groups to insist on the banning of paraquat application because of toxicity to humans. A reportfromJune, 1992 to October, 1996 in Korea [26] found that the paraquat intoxication ratio was 36.4%, slightly higher than that of total organophosphorus insecticides, 35.6%. Hence, die National Regulatory Committee of pesticides decided to manage the special review for the environmental safety of paraquat during 1996 ~ 1997 including: 1) Current levels of paraquat residues in the orchard soil and products, and 2) biological effects of paraquat use on crops that follow.

Evaluation of paraquat residue in soil Sixty orchard soils were observed in 1996 and 1997, respectively. Twenty soils were from apple, 15 from pear, 12 from grape and 13 from peach orchards in 1996. Also, 15 soils from each orchard were sampled in 1997 (Table I). The loosely bound residues of paraquat in soil were also determined for all samples, and residue amounts were below detectable limit in all of tested soils.



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Environmental Fate and Effects of Pesticides - American Chemical

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