The study on PCDD/Fs transportation and contribution from environmental media to forages

• Main Authors: Yi-tzu Chen, 陳義賜
• Other Authors: Ching-chang Lee
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/89733700213208323927

碩士 === 國立成功大學 === 環境醫學研究所 === 95 === The past investigations showed that the PCDD/F levels of beef, mutton and milk were related to PCDD/F levels of forages (grass and maize). If cattle or sheep were fed with forages contained high PCDD/Fs levels, the PCDD/F levels in the beef, mutton and milk would be increased. It revealed that if we would like to reduce PCDD/Fs levels in these products, we should identify the PCDD/Fs contamination sources of the forages and their contribution. In this study, maize and nilegrass were selected as study subjects, and congener patterns of PCDD/Fs in environmental media (ambient air, dust fall and soil) and forages (maize and nilegrass) were analyzed and assessed for identification of the transfer pathway and sources contribution from environmental media into forages. Methods of NIEA A809.10B and NIEA S102.61B were referred to implement air and soil sampling, and then the PCDD/F levels of samples were analyzed according to Methods of NIEA A810.11B, NIEA M801.11B and USEPA M1613B. Principal Component Analysis (PCA) and USEPA Multiple Medium Model were used to assess the association between PCDD/Fs congeners and levels of environmental media and forages and the contribution of environmental media to forages respectively. Two maize and two nilegrass production areas were selected as study areas, and the air, dust fall and soil samples were monthly sampled around the production areas during growing period of the forages. In this study, 12 airborne (gas and particle), 12 soil, 12 forages and 7 dust fall samples were collected and analyzed for 17 PCDD/Fs. The results showed average airborne PCDD/Fs levels was 0.097（0.032-0.284）pg I-TEQ/Nm3,and 1.17（0.495-2.36）pg I-TEQ/g d.w. in soil, 26.52（4.13-55.3）pg I-TEQ/g d.w. in dust fall, 0.762（0.183-1.50）WHO98-TEQDF/g (12% water) in maize and 0.667（0.138-1.50）WHO98-TEQDF/g (12% water) in nilegrass. Besides, the PCDD/Fs levels in forages decreased with plant growing, and all harvested plants were below the maximum limits of European Union (EU) for dioxin in feedingstuffs. After comparing PCDD/Fs congener patterns between environmental media and forages, the results showed that the PCDD/Fs congener profile of dust fall and forages were both dominated by highly chlorinated PCDD/Fs such as OCDD, OCDF, 1,2,3,4,6,7,8-HpCDF,and 1,2,3,4,6,7,8-HpCDD. Forages and soil were both dominated by OCDD、OCDF、1,2,3,4,6,7,8-HpCDF、1,2,3,4,6,7,8-HpCDD, these data showed that forages may be influenced by soil within these congeners. When comparing the PCDD/Fs congener patterns between forages and gas-particle phase of air, it showed the high chlorinated congener profile of forages was similar with particle phase, but the lower chlorinated congener profile of forages were similar with gas phase within PCDFs. All the data were further analyzed by PCA. At one site of maize production area, the results showed that the first and second principal components could account for a total of 70.7% of the variance, and maize was more related to gaseous phase PCDD/Fs and dust fall. At the other site of maize production area, the PCA results showed the first and second principal components could accounted for a total of 68.1% of the variance, and maize was related to dust fall and particle phase PCDD/Fs. Hence, maize was mainly influenced by airborne PCDD/Fs and dust fall because maize was high-stem crop. On nilegrass, the first and second principal components of nilegrass and environmental media could account for a total of 83.5% of the variance, and nilegrass was more related to soil and dust fall. When nilegrass grew up to 60 cm, it will bend and be closer to the ground, and therefore nilegrass will easily affected by dust fall and re-suspension of soil. Finally we used Multiple Medium Model to assess contribution of environmental media, and the result showed the PCDD/Fs contribution from dry and wet deposition was higher than gas phase PCDD/Fs sorption for both maize and nilegrass. The average contribution of gas phase PCDD/Fs to the forages was 17.9% and 82.1% from dry and wet deposition, indicating that the PCDD/Fs levels in forages mainly came from dry and wet deposition.