09:30 〜 09:45
[MZZ51-03] 大規模自然災害が引き起こす河川の汚染による生態への毒性影響の評価
キーワード：化学物質、地震、移流拡散モデル、水生生物、Natech、河川
In recent years, natural disasters called Natural hazard triggered technological accidents (Natech) has become a big issue around the world. For example, there was an outflow of sodium cyanide from the chemical plant due to the impact of the typhoon in 2019. Such an accident causes risks related to serious environmental contamination and has damage to ecosystem. However, research cases that consistently simulate from the occurrence of an accident to the effects after the accident are inadequate, including the types of chemical substances. In this research, we aimed to clarify the chemical accident impact to organism including aquatic organism, which could be released into the river due to the large-scale natural disaster, such as major earthquake.
As the target area, Yodo River in Osaka was selected, which is an essential water source that supports the infrastructure of Kansai area. This area has growing concerns for the risks caused by seismic motion and liquefaction and there are many chemical factories along the Yodo River.
As for chemical screening procedure, we selected chemicals that in Pollutant Release and Transfer Register (PRTR) which make it possible to grasp more actual discharge status. Among PRTR, these 38 substances have especially high toxicity for human (LD50 ≦300 mg/kg) (UN, 2015), and have difficulty to remove even in the water treatment process because of its high solubility in water (≧10,000 mg/L) and hydrophilic properties (octanol/water partition coefficients (Log Kow)≦ 1.5) (Ito et al., 2014). The prediction occurrence of chemical release accident caused by the earthquake was calculated as the expected value (Y) based on the statistical data in the world (Santella et al., 2011). Probability (Pn) of occurrence of the accident in Yodo basin area caused by Hanaore fault was calculated by the Poisson distribution. Subsequently, the maximum expected concentration of chemicals in the river was calculated in several points such as at the water-intake points using the advection-diffusion model based on hydrology-exposure analysis model (AIST-SHANEL ver. 3)(AIST, 2015). The accident date on the model is set for winter season since the streamflow is relatively low throughout the year from a factory which has the largest storage of chemicals. As judgement criteria for suspension of water supply, we evaluate subacute or acute toxicity as a criterion.
As a result of the model calculation, the concentration of methyl acrylate was 569 μg/l at the water-intake point which is the nearest to the damaged chemical factory. The duration time for the high-concentration water mass to pass through each intake point was 5 to 8 hours. In case company does not take any measures and all the stored chemicals are release, the five chemicals such as acrylic acid, aniline, xylene, methyl acrylate, and ethylene oxide exceed the aquatic acute toxicity standards by 2 to 6 times. Crustaceans were the most vulnerable to these accidents. It was also found that the chemical concentration in the river water will not decrease below the acute toxicity standard for aquatic organisms for about 21 hours without any counter-measure options. Since it is difficult to introduce post-measures in raw water, it is necessary to introduce proactive measures especially for methyl acrylate, which could exceed the standard value.
As the target area, Yodo River in Osaka was selected, which is an essential water source that supports the infrastructure of Kansai area. This area has growing concerns for the risks caused by seismic motion and liquefaction and there are many chemical factories along the Yodo River.
As for chemical screening procedure, we selected chemicals that in Pollutant Release and Transfer Register (PRTR) which make it possible to grasp more actual discharge status. Among PRTR, these 38 substances have especially high toxicity for human (LD50 ≦300 mg/kg) (UN, 2015), and have difficulty to remove even in the water treatment process because of its high solubility in water (≧10,000 mg/L) and hydrophilic properties (octanol/water partition coefficients (Log Kow)≦ 1.5) (Ito et al., 2014). The prediction occurrence of chemical release accident caused by the earthquake was calculated as the expected value (Y) based on the statistical data in the world (Santella et al., 2011). Probability (Pn) of occurrence of the accident in Yodo basin area caused by Hanaore fault was calculated by the Poisson distribution. Subsequently, the maximum expected concentration of chemicals in the river was calculated in several points such as at the water-intake points using the advection-diffusion model based on hydrology-exposure analysis model (AIST-SHANEL ver. 3)(AIST, 2015). The accident date on the model is set for winter season since the streamflow is relatively low throughout the year from a factory which has the largest storage of chemicals. As judgement criteria for suspension of water supply, we evaluate subacute or acute toxicity as a criterion.
As a result of the model calculation, the concentration of methyl acrylate was 569 μg/l at the water-intake point which is the nearest to the damaged chemical factory. The duration time for the high-concentration water mass to pass through each intake point was 5 to 8 hours. In case company does not take any measures and all the stored chemicals are release, the five chemicals such as acrylic acid, aniline, xylene, methyl acrylate, and ethylene oxide exceed the aquatic acute toxicity standards by 2 to 6 times. Crustaceans were the most vulnerable to these accidents. It was also found that the chemical concentration in the river water will not decrease below the acute toxicity standard for aquatic organisms for about 21 hours without any counter-measure options. Since it is difficult to introduce post-measures in raw water, it is necessary to introduce proactive measures especially for methyl acrylate, which could exceed the standard value.