Biogeochemical Cycling of Domoic acid in Natural Waters: The Influence of Bioactive Trace Metal Complexation and Photochemistry

软骨藻酸（domoic acid）是一种由伪耐氏菌（pseudonitzschia）产生的强大海洋毒素，在北美沿海水域普遍存在。这种毒素对公众健康和一些海洋生物构成威胁，并给贝类和甲壳类捕捞业造成了严重的经济损失。软骨藻酸最初是在1987年加拿大东部一起人类致命中毒事件中被发现的病原体，后来又与其他动物流行病联系起来，特别是在北美西海岸，软骨藻酸已导致海鸟和哺乳动物死亡。尽管软骨藻酸对海洋系统的生物地球化学意义重大，但人们对没有通过食物链转移的那部分毒素的命运几乎一无所知——可以说，有害藻华产生的绝大多数有毒物质都是软骨藻酸。在这个项目中，北卡罗来纳大学威尔明顿分校的研究人员将确定软骨藻酸一旦释放到水柱中，控制其生物地球化学循环的过程。这一点很重要，因为初步证据表明，藻华期间软骨藻酸的水柱浓度可高达100纳米。研究小组将解决光（光化学介导）和暗（微生物和/或化学降解）过程和微量金属络合在自然水体中这种强大毒素的生物地球化学循环和命运中的作用。他们假设光化学反应特别重要，因为初步数据表明，软骨藻酸在暴露于模拟阳光的短期照射下会迅速转化为一系列几何异构体和脱羧衍生物。软骨藻酸的光化学降解是非常重要的，因为它减少了这种强大毒素在产生它的表层海水中的寿命，但同时也可能产生更有毒的光产生副产物。第二种假设是，根据最近的证据，软骨藻酸与铁（III）和铜（II）形成了强络合物，微量金属在毒素释放到自然水域后的命运中起着重要作用。这些具有氧化还原活性的微量金属与软骨藻酸的络合是重要的，因为这些络合物与未络合的软骨藻酸（或其光异构体）具有不同的光化学反应活性，因此可能在环境中具有非常不同的停留时间和命运。实验方法将是在各种条件下将海水中的软骨藻酸照射到其三种几何异构体和脱羧衍生物上，以量化光化学降解率并确定产生的副产物。使用暗控制的类似实验将提供有关沿海水域微生物和化学降解动力学的信息。一系列与同一组化合物的金属结合研究将决定金属络合的程度和形成的配合物的强度。该研究有望为研究影响软骨藻酸及其副产物在天然水体中停留时间和归宿的化学和物理因素提供重要的新信息。该提案直接解决了与软骨藻酸有关的基本生态和海洋学问题，软骨藻酸是一种强大而普遍的毒素，存在于北美沿海水域频繁的伪尼齐亚藻华中。申请资金的主要部分将用于每年资助一名博士后研究员、一名硕士研究生和四名本科生。本科生的参与将是研究者研究计划的一个组成部分。年轻学生被这种类型的研究所吸引，因为他们从事的是具有国际意义的环境研究。拟议中的研究将继续这种模式，允许沿海大学的本科生参与一个与有毒藻华有关的备受瞩目的研究问题。

ABSTRACTOCE-0326685Domoic acid, a powerful marine toxin produced by Pseudo-nitzschia species, is remarkably pervasive in North American coastal waters. This toxin is a threat to public health and some marine life, and has resulted in severe economic losses in the shellfish and crustacean harvesting industry. Originally discovered as the causative agent in an episode of fatal human poisoning in eastern Canada in 1987, domoic acid has subsequently been linked to other epizootics, particularly on the western coast of North America where it has resulted in the death of seabirds and mammals. Despite the significance of domoic acid to the biogeochemistry of marine systems, virtually nothing is known about the fate of that fraction of the toxin not transferred through the food chain - arguably the vast majority of toxic material produced during harmful algal blooms.In this project, researchers at the University of North Carolina at Wilmington will determine the processes that control the biogeochemical cycling of domoic acid once it is released into the water column. This is significant because preliminary evidence indicates water column concentrations of domoic acid can reach as high as 100 nM during a bloom event. The research team will address the role of light (photochemically-mediated) and dark (microbial and/or chemical degradation) processes and trace metal complexation on the biogeochemical cycling and fate of this powerful toxin in natural waters. They hypothesize that photochemical reactions are particularly important because preliminary data indicates domoic acid is rapidly converted to a series of geometric isomers and decarboxylated derivatives when exposed to short-term irradiations using simulated sunlight. Photochemical degradation of domoic acid is extremely significant because it reduces the lifetime of this powerful toxin in surface seawater where it is produced, but at the same time may also produce more toxic photo-produced byproducts. A second hypothesis, based on recent evidence showing strong complexes are formed by domoic acid with Fe(III) and Cu(II), is that trace metals play an important role in the fate of the toxin once it is released into natural waters. Complexation of domoic acid by these redox-active trace metals is important because the complexes will have different photochemical reactivities than uncomplexed domoic acid (or its photo-isomers) and may therefore have very different residence times and fates in the environment. The experimental approach will be to irradiate domoic acid in seawater to its three geometric isomers and decarboxylated derivatives under a variety of conditions to quantify rates of photochemical degradation and identify the byproducts produced. Similar experiments using dark controls will provide information on kinetics of microbial and chemical degradation in coastal waters. A series of metal- binding studies with the same suite of compounds will determine the degree of metal complexation and the strength of the complexes formed.The proposed research is expected to provide significant new information regarding the chemical and physical factors influencing the residence time and fate of domoic acid and its byproducts in natural waters. This proposal directly addresses fundamental ecological and oceanographic questions related to domoic acid, a powerful and pervasive toxin present in frequent Pseudo-nitzschia blooms in North American coastal waters. A major part of the requested funding will be used to support a post-doctoral researcher, a masters-level graduate student, and four undergraduate students per year. The involvement of undergraduates will be an integral part of the investigators research program. Young students are attracted to this type of study because they perform environmental research of international interest. The proposed research will continue this pattern by allowing undergraduates at a coastal university to become involved in a high profile research question associated with toxic algal blooms.