The adsorption and leaching characteristics of five ionic pesticides including four acidic pesticides (2,4-D, dicamba, MCPA, and MCPP) and one amphoteric pesticide (imazaquin) in agricultural soils were investigated. Soils around spring waters that were heavily affected by pesticide run-off and soils around wells considering the regional characteristics in Jeju Island were collected at 24 stations. The Freundlich constant, KF value, which is a measure of the adsorption capacity, decreased in the order of 2,4-D > MCPA > MCPP > dicamba > imazaquin. The adsorption capacity of these ionic pesticides decreased with increasing pH owing to the effects of ionization of pesticides and different ionizable functional groups of soils. The leaching of ionic pesticides in the soil column showed a reverse relationship with their adsorption in soils, namely, the ionic pesticides were leached more quickly for the pesticides with lower adsorption capacity. The groundwater contamination potential of the ionic pesticides was evaluated in the order of imazaquin > MCPA > MCPP > dicamba > 2.4-D according to the groundwater ubiquity score based on soil Koc and the half-life of the pesticide.

Agricultural soils around springwaters heavily affected by pesticide run-off and around wells considering the regional characteristics were collected at 24 stations in Jeju Island, and the physicochemical properties and adsorption and leaching characteristics of four nonionic pesticides (diazinon, fenitrothion, alachlor, and metalaxyl) were investigated. The values of the major soil factors affecting the adsorption and leaching of pesticides, namely, soil pH(H2O), organic matter content, and cation exchange capacity (CEC), were in the range of 4.64 ∼ 8.30, 0.9 ∼ 13.1% and 12.7 ∼ 31.7 meq/100 g, respectively. The Freundlich constant, KF value, which gives a measure of the adsorption capacity, decreased in the order of fenitrothion > diazinon > alachlor > metalaxyl, which was identical to their lower water solubility. Among the collected soils, the KF value was very highly correlated with organic matter content (r2 = 0.800 ∼ 0.876) and CEC (r2 = 0.715 ∼ 0.825) and showed a high correlation with clay content (r2 = 0.473 ∼ 0.575) and soil pH(H2O) (r2 = 0.401 ∼ 0.452). The leaching of pesticides in the soil column showed a reverse relationhip with their adsorption in soils, i.e., the pesticides leached more quickly for the soils with lower values of organic matter content and CEC among the soils and for the pesticides with higher water solubility.

The aim of this study was to evaluate the occurrence of vanadium in Jeju Island groundwater, focusing on the spatio-temporal patterns and geochemical controlling factors of vanadium. For this, we collected two sets of groundwater data: 1) concentrations of major constituents of 2,595 groundwater samples between 2008 and 2014 and 2) 258 groundwater samples between December 2006 and June 2008. The concentrations of groundwater vanadium were in the range of 0.2 71.0 μg/L (average, 12.0 μg/L) and showed local enrichments without temporal/seasonal variation. This indicated that vanadium distribution was controlled by 1) the geochemical/mineralogical composition and dissolution processes of original materials (i.e., volcanic rock) and 2) the flow and chemical properties of groundwater. Vanadium concentration was significantly positively correlated with that of major ions (Cl-, Na+, and K+) and trace metals (As, Cr, and Al), and with pH, but was negatively correlated with NO3-N concentration. The high concentrations of vanadium (>15 μg/L) occurred in typically alkaline groundwater with high pH ( 8.0), indicating that a higher degree of water-rock interaction resulted in vanadium enrichment. Thus, higher concentrations of vanadium occurred in groundwater of Na-Ca-HCO3, Na-Mg-HCO3 and Na-HCO3 types and were remarkably lower in groundwater of Na-Ca-NO3(Cl) type that represented the influences from anthropogenic pollution.

To understand the characteristics of vanadium leaching from soils formed by the weathering of basalts, paleo soil at Gosan, Jeju Island, Korea, and several present-day soils from neighboring areas were collected. Leaching experiments were carried out by two approaches: 1) batch experiments under various geochemical conditions (redox potential (Eh) and pH) and 2) continuous leaching experiments under conditions similar to those of natural environments. From the batch experiments, leached vanadium concentrations were highest under alkaline (NaOH) conditions, with a maximum value of 2,870 μg/L, and were meaningful (maximum value, 114 μg/L) under oxidizing (H2O2) conditions, whereas concentrations under other conditions (acidic-HCl, neutral-NaHCO3, and reducing-Na2S2O3) were negligible. This indicated that the geochemical conditions, in which soil-water reactions occurred to form groundwater with high vanadium concentrations, were under alkaline-oxidizing conditions. From the continuous leaching experiments, the pH and leached vanadium concentrations of the solution were in the ranges of 5.45 5.58 and 6 9 μg/L, respectively, under CO2 supersaturation conditions for the first 15 days, whereas values under O2 aeration conditions after the next 15 days increased to 8.48 8.62 and 9.7 12.2 μg/L, respectively. Vanadium concentrations from the latter continuous leaching experiments were similar to the average concentration of groundwater in Jeju Island (11.2 μg/L). Furthermore leached vanadium concentrations in continuous leaching experiments were highly correlated with pH and Al, Cr, Fe, Mn and Zn concentrations. The results of this study showed that 1) alkaline-oxidizing conditions of water-rock (soil) interactions were essential to form vanadium-rich groundwater and 2) volcanic soils can be a potential source of vanadium in Jeju Island groundwater.