同位素示踪研究气态甲基汞对水稻甲基汞富集的影响
文献类型：学位论文
| 作者 | 孙婷 |
| 学位类别 | 硕士 |
| 答辩日期 | 2016-04 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 王章玮 |
| 关键词 | a stable isotope addition technique 同位素示踪 open top chambers experiment 开顶气室熏蒸实验 atmospheric methylmercury 气态甲基汞 rice 水稻 methylmercury accumulation 甲基汞富集 |
| 其他题名 | Investigating the influence of Gaseous Methylmercury on accumulation of Methylmercury in Rice(Oryza sativa L.) Using a Stable Isotope Tracer Technique |
| 学位专业 | 环境科学 |
| 中文摘要 | 甲基汞（MeHg）具有很强的神经毒性，因而被人们广泛关注。在汞污染地区，水稻中 MeHg的含量已经受到影响，因此，认清水稻中 MeHg的来源与富集特征对人体健康和生态系统的风险评估具有重要意义。目前，尚未有水稻MeHg直接大气来源的研究报道。本文采用同位素示踪技术，并结合开顶气室熏蒸 (open top chambers,OTCs)实验和土壤加汞培育实验(soil Hg enriched experiment)，研究水稻各部位对气态甲基汞浓度的响应关系，进而探讨气态甲基汞是否是水稻 MeHg的一个大气来源。此外，本文还研究了气态单质汞（GEM)对水稻 MeHg富集的影响。结果如下： 建立了可连续产生浓度低、发生效率高的气态二甲基汞（DMeHg）发生系统。即在甲基钴胺素（MeCo）:标准汞溶液（Hg2+）的质量浓度比为 10:1，盐度（0-0.01 mol•L-1），pH=4及载气流速为 20 mL•min-1的条件下，通过改变标准汞溶液的浓度及反应温度来获得浓度低且相对稳定的气态 DMeHg。结果为：9℃条件下，0.025 mg•L-1、0.015 mg•L-1 的汞标准溶液与 MeCo 反应得到的气态DMeHg的产生速率在 0-40 h内缓慢上升，在40-140 h期间基本趋于稳定，产生速率分别维持在 300 pg•min-1和150 pg•min-1；在 18℃条件下，0.025 mg•L-1、0.015 mg•L-1的Hg2+溶液产生 DMeHg的速率在 0-50 h内缓慢上升，在50-130 h期间基本趋于稳定，产生速率分别维持在 500 pg•min-1和 300pg•min-1。气态DMeHg的发生系统为系统研究气态甲基汞对水稻各部位 MeHg富集的影响，提供了可靠的技术支撑。 发现了气态甲基汞是水稻各部位中 MeHg的大气来源。本部分利用稳定同位素（199Hg2+）示踪技术，并结合开顶气室熏蒸实验和土壤加汞培育实验，研究气态甲基汞对水稻 MeHg富集的影响及 MeHg在水稻各部位中的迁移。结果表明水稻各部位中同位素标记的 Me199Hg 的含量与气态甲基汞（199Hg2+标记）的浓度显著正相关（R=0.8993~1, p<0.05），表明气态甲基汞是水稻各部位 MeHg的重要来源；此外，水稻各部位中同位素标记的 Me199Hg浓度占总 Me199Hg（包括来自环境中的 Me199Hg 和同位素标记的 Me199Hg）浓度的比例随气态甲基汞浓度的增加和生长期的延长不断增加，且在 3200pg•m-3的气态甲基汞浓度熏蒸条件下成熟期的水稻，比例接近 100%，表明气态甲基汞对水稻各部位中MeHg富集的贡献随气态甲基汞浓度的增加和生长期的延长不断增加，且在3200pg•m-3 的气态甲基汞浓度熏蒸条件下的成熟期的水稻，水稻各部位中的MeHg主要来自大气。值得关注的是，在OTCs实验中，水稻精米和糙米中MeHg的含量及气态甲基汞对水稻精米和糙米 MeHg富集的贡献值基本一致，表明精米具有很强的 MeHg富集能力，籽粒中的 MeHg主要富集在精米中。水稻对空气中 MeHg 的富集是一个“吸收-转移-累积”的动态过程。对不同气态甲基汞浓度熏蒸下的水稻不同生长阶段各部位 MeHg含量的分析发现：水稻成熟前，茎叶从空气中吸收气态甲基汞；在成熟期间，茎和叶中的 MeHg则被转移、富集至精米中。 发现了GEM 对水稻各部位中 MeHg 的富集没有显著的影响。水稻根中MeHg的含量与与GEM 含量无线性关系（p>0.05），与土壤中 MeHg的含量明显正相关（R=0.9462-0.9870, p<0.05），表明在 GEM熏蒸实验中，GEM对水稻根中 MeHg 的富集影响不明显，水稻根中的 MeHg 主要来自土壤。水稻茎中MeHg的含量随土壤 MeHg含量的增加而线性增加（上部茎：R=0.8560,p>0.05;下部茎：R=0.9178-0.9484,p<0.05），与GEM 含量没有明显的相关性(p>0.05)，但在气室熏蒸实验中上部茎中 MeHg的含量高于下部茎；而在土壤加汞培育实验中下部茎 MeHg 的含量高于上部茎，表明在 GEM 熏蒸实验中，GEM可能对水稻上部茎 MeHg的富集有一定的影响，但水稻茎主要受土壤汞的影响。水稻叶中 MeHg含量与土壤 MeHg含量显著相关（R=0.9708, p<0.01），与 GEM含量无线性关系，但在气室熏蒸实验中实验组叶中 MeHg的含量高于对照组，表明水稻叶中的 MeHg 可能受 GEM 的影响。水稻籽粒中 MeHg 的含量与土壤MeHg呈显著正相关（R=0.9046-0.9865,p<0.05），与 GEM含量无明显的线性关系(p>0.05)，表明在 GEM 熏蒸实验中，GEM 对水稻籽粒中 MeHg 的富集影响不明显，水稻籽粒中的 MeHg主要来自土壤，但在水稻上部茎和叶中MeHg的含量受一定程度大气汞含量影响的情况下势必会对水稻籽粒甲基汞的富集产生影响，究竟多大程度或量化其贡献还需进一步实验研究。 |
| 英文摘要 | Methylmercury (MeHg) is known as its highly hypertoxicity. In areas polluted by mercury, the MeHg concentration in rice has be influenced, therefore, it is very significant to figure out the sources and accumulation of MeHg in rice for risk assessment of human health and ecosystem. There is no report about the direct atmospheric source of MeHg in rice at present. In this study, a stable isotope(199Hg2+)addition technique was used, combined with field open top chambers(OTCs) and soil mercury enriched experiments to study the response of MeHg accumulation in each rice part to the gaseous MeHg concentration, and then to figure out if the gaseous MeHg is an atmospheric source of rice MeHg. Results showed that: We established a system which can continuously produce low concentration and high efficiency of gaseous DMeHg. In this study, when the mass concentration ratio of methylcobalamin(MeCo) and standard mercury solution(Hg2+)=10:1, salinity (0-0.01 mol•L-1), pH=4.0 and carrier gas flow rate at 20 mL•min-1, DMeHg generation rates of 0.025 mg•L-1 and 0.015 mg•L-1 mercury concentrations were increasing slowly during 0-40 h and stable during 40-140 h, and maintaining about 300 pg•min-1 and150 pg•min-1 at the temperature of 9℃,and the rates of 0.025 mg•L-1 and 0.015 mg•L-1 mercury concentrations were increasing slowly during 0-50 h and stable during 50-130 h, and maintaining about 500 pg•min-1 and300 pg•min-1 at the temperature of 18℃.Therefore this system can continuously produce low concentration and high efficiency of gaseous DMeHg, and is safe and reliable.This DMeHg generation system is benefit to further research the effect of gaseous MeHg on rice MeHg accumulation. We discovered that gaseous MeHg is an atmospheric source of MeHg in eath rice part. A stable isotope (199Hg2+) addition technique, combined with OTCs and soil Hg enriched experiments were used to study the influence of gaseous MeHg on rice MeHg accumulation, and MeHg translation in eath rice part. The results showed that MeHg concentrations spiked by 199Hg2+ in eath rice parts were significantly correlated with gaseous MeHg concentrations (R=0.8993~1,p<0.05), suggesting that gaseous MeHg was important atmospheric source of MeHg in eath rice parts; In addition, the ratio of MeHg concentration spiked by 199Hg2+ and total Me199Hg in eath rice part(include Me199Hg which came from surrounding and Me199Hg spiked by 199Hg2+) was increasing with the gaseous MeHg concentration and extension of growth period, in addition, when the gaseous MeHg concentration was 3200pg/m3 and the growth period was ripening stage, the ratio was gradually closed to 100%,indicating that with the gaseous MeHg level increasement and the extension of growth period, the contribution of gaseous MeHg to MeHg accumulation in eath rice parts was increased, and when the gaseous MeHg concentration was 3200pg/m3 and the growth period was ripening stage, MeHg in eath rice parts were mainly came from armosphere; To be noticed, in OTCs experiment, MeHg concentrations in polished and unpolished rice grain and the ratio of MeHg concentration spiked by 199Hg2+ and total Me199Hg in eath rice parts was almost consistent, indicating that polished rice grain has strong ability of MeHg accumulation, and grain MeHg was mainly accumulated in polished grain. MeHg accumulation in rice is a dynamic process, which include absorption,transfer and accumulation. The analyzation to MeHg concentrations in eath rice parts of different growing seasons and in different gaseous MeHg concentrations fumigation showed that, leaf and stem could absorb gaseous MeHg before ripening stage, and most of MeHg in leaf, stem was translated to rice grain during the ripening stage. We discovered that there were no obvious influences of GEM on rice MeHg accumulation. MeHg levels in root were significantly correlated with soil MeHg concentrations (R=0.9462-0.9870, p<0.05) but insignificantly correlated with air Hg concentrations (p>0.05), indicating that MeHg in rice root was mainly from soil. The MeHg concentrations in stem increased linearly with soil MeHg concentrations (upper stem：R=0.8560,p>0.05;bottom stem：R=0.9178-0.9484,p<0.05), and no obvious linear correlation with the GEM. However, MeHg concentrations in upper stem were generally higher than those in bottom stem in OTCs experiment, and MeHg levels in bottom stem were usually higher than that in upper stem, suggesting that MeHg in stem was mainly from soil, and the upper stem might be affected by the GEM. MeHg concentrations in leaf were significantly correlated with soil MeHg (R=0.9708, p<0.01), and did not linearly correlate with air Hg (p>0.05). However,the MeHg concentrations in these experimental groups were higher than those in control group in OTCs experiment, indicating that MeHg in leaf might be influenced by both soil MeHg and air Hg. MeHg concentrations in grain were linearly correlated with soil MeHg concentrations (R=0.9046-0.9865, p<0.05), and were not linearly correlated with air Hg(p>0.05). Moreover, view of the effects of GEM accumulation in upper stem and leaf, it certainly will impact on the MeHg accumulation in rice grain. However, the quantification of the effect need more research work. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/36957]  |
| 专题 | 生态环境研究中心_大气环境科学实验室 |
| 推荐引用方式 GB/T 7714 | 孙婷. 同位素示踪研究气态甲基汞对水稻甲基汞富集的影响[D]. 北京. 中国科学院研究生院. 2016. |
入库方式： OAI收割
来源：生态环境研究中心
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