제주도 토양 중 중금속의 농도 및 화학적 형태

Abstract

For 63 soil series distributed in Jeju Island, uncultivated soils which are considered to be natural pedo-geochemical ones in each soil series, were collected. From the soils, 19 heavy metals including 8 heavy metals which are regulated by Korean Law of Soil Environmental Protection, were analyzed after they were pretreated with microwave assisted acid (HF/HNO3) digestion (US EPA 3052 method). The pH(H2O), pH(NaF) and organic matter content in soils which are major parameters of their physico- -chemical properties, were analyzed. From the results analyzed, the concentrations of heavy metals distributed in soils of Jeju Island, were examined and compared with those in foreigb countries. In addition, the correlation between heavy metal

concentrations and the parameters of physico-chemical properties in soils and among the heavy metals in soils of Jeju Island as analyzed. The concentrations of heavy metals extracted with microwave assisted acid digestion used in this study were compared with those extracted with 0.1 N HCl and with those digested with an aqua regia proposed as the pretreatment methods by Korean Law of Soil Environmental Protection, in order to evaluate the extent of those extraction in soils. Moreover, the five-step chemical extraction procedure was carried out to fractionate heavy metal chemical forms in order to examine their retention in soils or their mobility in water. The results obtained in this study were summarized as follows:

1. The studied soils were acidic, with 89% of the total soils having a pH(H2O) of less than 6.0. The soil pH(NaF), which can be indicative of amorphous material (volcanic ash soil) (>9.4), were in the range of 7.5-11.7. and by classification of volcanic ash soils with the value, the soils of Jeju Island compriesd of 42 volcanic ash soils and 21 non-volcanic ash soils. The organic matter content was in the range of 1.6-17.6% (mean 8.1%) in total soils, 2.3-17.6% (mean 10.4%) in volcanic ash soils and 1.6-5.8% (mean 3.6%) in non-volcanic ash soils. By the Munsell Color Chart, the soils of Jeju Island compriesd of 29 black soils, 13 very dark grey soils, 11 dark brown soils, 3 very dark grayish brown soils, 2 brown soils, 1 very dark brown soil, 1 dark reddish brown soil, reddish black soil, etc.

2. In total natural soils used in this study, the heavy metals which were distributed in the highest concentrations and the lowest concentrations were Mn and Ba, Hg and Tl, respectively. The concentrations (mg/kg) of heavy metals decreased in the following sequences with arithmetric mean value: Mn(730)>

Ba(493)> V(87)> Cr(73), Zn(71)> Ni (52)> Co(36)> Cu(20)> Pb(14)> Sb(9)> As(6.14)> Sn(1.15), Ag(1.12)> Mo(0.527), Se(0.529)> Be(0.345)> Cd(0.238)> Hg(0.146)> Tl(0.096). Comparing them between volcanic and non-volcanic ash soils with arithmetric mean value, the concentrations of Ba, Cr, Zn, Ni, Cu, As, Ag, Se and Hg, were higher in the former with 1.6 times, 1.2 times, 1.2 times, 1.2 times, 1.3 times 1.4 times, 1.6 times, 2.4 times, respectively, those of Mn and Tl were higher in the latter with 1.2 times, 1.7 times, respectively, and those of V, Co, Pb, Sb, Sn, Mo, Be and Cd were similar in both soils. 3. The coefficients of variation(CV), indicating the higher the values are, the greater difference of their concentrations in spatial distribution is, were in the range of 0.299∼0.940 in total soils, 0.234∼0.974 in volcanic ash soils, 0.319∼1.018 non-volcanic ash soils. The values among the heavy metals decreased in the order of As> Tl> Sn> Mo, Ag> Se> Be, Ba> Cu, Ni> Hg> Cr, Co, Mn> Zn> Cd> Sb> V> Pb in total soils, Sn> Tl> Ag> As, Mo> Be> Ni> Cu, Ba> Se> Cr> Mn> Co, Hg> Zn> Cd, Sb> V> Pb in volcanic ash soils, and Mo> As> Ag> Tl> Sn> Ba, Cu> Ni> Be> Co> Hg> Cd, Pb> Mn> Zn, Sb> V> Cr in non-volcanic ash soils.

4. When the concentrations of heavy metals in volcanic ash soils and non-volcanic ash soils were compared with those in foreign countries, they were highly different with soil properties, which is considered to be due to the difference in parent rock, weathering process, and the time of volcanic activity, etc.

5. The concentrations extracted with US EPA3052 method used in this study were higher with tens to thousands times and 1.2-2.2 times than those extracted with 0.1 N HCl and with aqua regia,

respectively.

6. It could be found that the correlations of pH(H2O) and heavy metals (Hg, Ni, Co, Se), pH(NaF) and heavy metals (Hg, Ba, Se, Tl), and organic matter content and heavy metals (Hg, Tl) were significant at the 0.05 level, and those of pH(H2O) and Mn, organic matter content and Se were significant at the 0.05 level. It could be found that from the correlation analysis among the heavy metal, there were 22 where there were significant at the 0.01 level and they showed positive correlation. The corelation coeficients were the highest in Sb-V(0.878), decreased in the orer of Mo-Sn(r=0.867)> Co-V(r=0.654)> Co-Sb(r=0.648)> Be-Sn(r=0.546)> Sn-Tl(r=0.528). The other values were below 0.5. There were 11 where there were significant at the 0.05 level, the corelations of As-Ni(-0.264), Ni-Be(-0.283), Be-Mn(-0.286) were negative, and those of the others were positive.

7. With the results of five-step chemical extraction, the heavy metals (Mn, Zn, Ni, Co) were present in oxidizable, reducible and residual forms (>90%) in most cases in soils and so they were not easily extracted in natural system. Although the heavy metals (Cr, Cu, Pb) wee present in reducible and residual forms with the values of above 80%, they were present in carbonate form with the values of 10%, indicating that they have the possibility to be extracted to natural system. Most of V was present in carbonate and residual forms, indicating that this metal was extracted to natural system easily and influxed into the vegetables and groundwater.