• Journal of Soil and Groundwater Environment
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• v.28 no.1
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• pp.1-14
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• 2023

In this study, column tests using relatively uniform Jumunjin sand media were conducted to evaluate the feasibility of calcium polysulfide (CaS_x, CPS) in removing high concentration of Zn²⁺ in groundwater. The injected CPS solution reacted rapidly with Zn²⁺ in artificial groundwater and effectively reduced Zn²⁺ by more than 99% through metal sulfide precipitation. Since the density (d = 1.27 g/cm³ ) of CPS solution was greater than that of water, CPS solution settled down rapidly while capturing Zn²⁺ and formed stable CPS layer similar to dense nonaqueous phase liquid. Mass balance analysis on Zn²⁺ in CPS solution suggested that CPS solution effectively reacted with Zn²⁺ to form metal sulfide precipitates except for high groundwater seepage velocity of 400 cm/d. With greater groundwater seepage velocity, injected CPS did not completely dissolve at the CPS-water interface, but a partially-misible CPS layer continuously moved and reacted with Zn²⁺+ in the direction of groundwater flow. Since hydraulic conductivity (K_h) decreased slightly due to the generated metal precipitates in the inter-pores of media, injection of CPS solution should be optimized to prevent clogging. As evidenced by both XRF and SEM/EDS results, ZnS precipitates were clearly observed through the reaction between the CPS solution and Zn²⁺. Further study is warranted to evaluate the feasibility of CPS to remove high-concentration heavy metalcontaminated groundwater in complex and heterogeneous media.

• The Korean Journal of Pesticide Science
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• v.7 no.4
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• pp.280-287
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• 2003

To assess the risk of pesticides on earthworm, the acute toxicities of 10 pesticides were investigated and their toxicity exposure ratios(TERs) were calculated. As the TERs of paraquat dichloride and pendimethalin were more than 100, their risks were rated negligible. Risk of benfuracarb, cadusafos, chlorpyrifos-methyl, endosulfan, isazofos and parathion which have TERs of $10\sim100$ were rated low. However, risk of imidacloprid and phorate which have TER of less than 10 were estimated highly to need a reproduction study. Earthworms were exposed to twenty two pesticides including dazomet 98% GR having PECs of more than $5mg{\cdot}kg^{-1}$ in artificial soil at standard and double dose for 14 days. All the earthworms exposed to dazomet 98% GR and metam-sodium 25% SL were died to show their high risk, while no serious adverse effects were observed in the soil treated with 15 pesticides, calcite 95% WP, calcium polysulfide 36% CF, chlorothalonil 75% WP, daminozide 85% WP, dichlonil 6.7% GR, etridiazole 25% EC, fosetyl-Al 80% WP, glyphosate 41 % SL, hymexazol 30% SL, iprodione 50% WP, machine oil 95% EC, mancozeb 75% WP, propineb 70% WP, terbuthylazine 80% WP and triazophos 40% EC. In case of thiophanate-methyl 70% WP, copper hydroxide 77% WP, dimethoate 46% EC, tolclofos-methyl 50% WP and propamocarb hydrochloride 67% SL, any effect did not show clearly, suggesting an additional subchronic toxicity study. The risk of thiophanate-methyl 70% WP to earthworm was estimated high, considering its subchronic effect, while effects of copper hydroxide 77% WP, dimethoate 46% EC, tolclofos-methyl 50% WP and propamocarb hydrochloride 67% SL to earthworms were negligible, considering no adverse effects in subchronic tests.