| 英文摘要 |
This project belongs to the second year work of Dacheng environmental heavy metal investigation which is a two-year project. The investigation methods were established in the first year. The environmental investigation was also conducted with the local residents’ assistance. Since the chemical analysis results of indoor dust and drinking water showed no abnormality in the first year, this part of examination were no longer included in this year. This project focused on the ambient air monitoring and investigation of the environmental media that raised public concern including aqueous environment, agricultural goods. In addition, hexavalent chromium ambient air monitoring, submarine sediment and fish and shellfish arsenic investigation were added in this project.
For the ambient air and air pollution investigation, monitoring on heavy metals and hexavalent chromium were conducted twice in August 2019 by using portable PM₁₀ monitoring devices. The concentrations of arsenic, nickel, cadmium, beryllium, lead, classified as group A to B2 by Integrated Risk Information System (IRIS), corresponded to the monitoring results at the general monitoring station in other domestic regions conducted by Taiwan Environmental Protection Administration (EPA). The concentration of hexavalent chromium, classified as group A by IRIS, showed similar results with the monitoring results at general monitoring stations and nearby industrial site monitoring stations. Continuous monitoring results on heavy metals in ambient air at the Xiahai bang levee (located in Dacheng Township, Changhua County) showed that the concentration of cadmium, iron, potassium, manganese, strontium, titanium and other heavy meatal substances rose when the south and southwest wind speed was higher the 4 m/s. The higher concentration may due to the dust from the nearby bare ground and Zhuoshui River. Both zinc and nickel had higher concentrations when there was north wind or low wind speed. 25 possible emission sources were selected in this project. We promised the local residents that heavy metal stack tests of all the suspected sources will be conducted. Since some of the stack tests were already completed by Yulin Environmental protection Bureau, part of the investigation would not be included in this project. In the past two years, 16 possible emission sources in No. 6 Naphtha Cracking Complex and 4 in Changhua County were investigated. The sources included coal-fired boilers, oil-fired boilers, incinerators and catalytic heaters. The heavy metal stack test results all show full compliance with the emission standards. Heavy metal analysis on motor gasoline, fuel oil for boilers and marine diesel showed that the concentration of nickel and zinc in fuel oil for boilers were significantly higher than others. The statistic corresponds to the studies using nickel and zinc as indicators for fuel oil burning.
For the aqueous environment investigation, manganese and iron concentrations in part of the underground water samples exceeded the regulation limits (iron: 1.5mg/L, manganese: 0.25mg/L). The monitoring results conducted by EPA showed that the examined area in this project had the highest frequency of exceeding the underground regulation limits in Taiwan. The relatively high concentration in this region is a long term condition. Part of the irrigation water from the underground had higher iron, manganese and arsenic concentrations. Arsenic pollution issues in Taiwan are mainly located in Chianan Plain, Pingtun Plain and Choushui River Alluvial Fan which is the investigated area in this project. The main arsenic source is the inorganic arsenic adsorbed on the magnesium hydroxide and oxide. Arsenic concentration in groundwater rises when the adsorbate is released. The heavy metal concentration in irrigation water was found exceeding the standard in both this project and 2018 investigation. The ocean samples from the coastal area had a higher manganese concentration than the Marine Environment Classification and Marine Environmental Quality Standards (0.05mg/L). This trend correspond to the EPA investigation results in the western coastal area. The shellfish and rice samples from the locations having higher heavy metal concentration showed no abnormality.
According to the heavy metal investigations results of soil, each element demonstrated lower concentration than Soil Pollution and Agricultural Farmland Monitoring Standards. The chromium concentration in topsoil was higher than that in subsoil according to the investigation result in 2017. However in this project the difference was insignificant. The investigation targeting on sediments in marine area showed that the concentrations were similar to the nearby area.
The heavy metal concentrations in 13 edible rice and 7 crop samples were fully compliant with the Sanitation Standard for Contaminants and Toxins in Food (SSCTF). Edible rice samples’ heavy metals concentration corresponded to other domestic research. Among 18 shellfish and 11 fish samples, only two of them had a higher lead concentration and higher inorganic arsenic concentration than SSCTF respectively. Methylmercury concentration in fish and shellfish were in compliance with SSCTF.
Most of the heavy metal concentrations in the investigated environmental media were compliant with the corresponding regulations. The results were similar to that in other areas. As for the samples that had a higher concentration than the standards, EPA has informed the department concerned to achieve environment protection and secure local residents’ health.
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