同意接收纽约时报中文网的产品和服务推广邮件查看往期电邮隐私权声明周一，人们在白宫的“我们人民”(We the People)平台提交请愿，恳求美国政府干涉该案。截至周四，有超过14.2万人签名请愿，呼吁奥巴马政府将头号嫌疑人遣返回国，尽管没有证据表明她还居住在美国。“朱令案一直让人感到愤怒、失望，但现在这种情绪得以爆发，”约翰·奥尔迪斯(John Aldis)说。“中国新一代的年轻人认识到朱令受到了不公平对待，他们想让大家听到自己的声音。”20世纪90年代，奥尔迪斯在北京的美国大使馆担任医生，从那时起，他就一直关注朱令的命运。上个月上海发生的一起耸人听闻的谋杀案促使朱令案再次受到关注。知名学府复旦大学的一名医科学生被控向室友所喝的水中投放有毒化学品。警方称，这名被控故意杀人的学生因为“琐事”怀恨在心，进而投毒。网民们最初讨论中国残酷的教育体制带来的压力及心理健康服务的缺乏，后来转而讨论中国其他的投毒案件，其中很多案件都是学生出于嫉妒造成的。但讨论的重心在朱令的谋杀未遂案，以及作案者是凭借政治出身而安然无事这一想法。这些怀疑源于人们普遍的看法，即中国共产党高官及其亲属凌驾于法律之上。朱令的父亲吴承之在简短的电话采访中表示，“我们想要我们一直想要的东西——真相和公道。”虽然此案充满尚未解答的问题及未经证实的指责，但根据官方媒体的报道，朱令的家人及支持者已经接受这样一个已知的事实：朱令在清华大学的室友——孙维有获得铊的途径，她接受了警方的讯问，但很快就被释放。警方表示由于证据不足，他们无法进行拘捕。批评者在没有任何证据的情况下推测，孙维的爷爷——在共产党掌权后的数十年一直身居要职——及另一位曾经担任北京市副市长的亲属摆平了这个问题。朱令的朋友称，在警方开始调查前，朱令宿舍的关键证据不见了。据朱令的父亲吴承之说，警方已于1998年结案，但在将近十年的时间里却从未告知过他们家。“如果重新调查，也应该调查警方的渎职，以及是谁试图干涉最初的调查，”朱令家人的代理律师张捷说。尽管面临的压力越来越大，但当局对重新过问此事并不热衷。周三，北京市公安局罕见地公开回复了媒体的质询，为自己的调查工作进行了辩护，并表示时间的流逝和证据的缺乏使其无法重新调查该案。该声明也否认了调查受到了局外人的干扰的指责。“专案组始终坚持依法公正办案，未收到任何干扰，”声明说。但对朱令的支持者而言，一个鼓舞人心的迹象是，在中国最受欢迎的微博平台新浪微博上，这个话题已经被解禁了，这表明，高层官员已经认定，压制这一争议事件会适得其反。对中国新一届领导层来说，这个案件已经成为某种公众关系的挑战。在被任命为共产党总书记后的5个月里，习近平一直试图通过打击官员腐败和权力滥用来应对公众的普遍不满，不过迄今为止，他的大部分努力普遍被认为流于表面。由党报《人民日报》发行的双语小报《环球时报》极其笨拙地试图应对这起争议事件，称朱令案引发公众愤怒在很大程度上是因为官方沟通不好造成的。但这篇社论承认，真正有权势的人能影响刑事司法系统，因为它坚称孙维的家庭背景“算不上很显赫”，不足以做到这一点。2005年，在自己的名字开始广泛传开后，朱令案的被怀疑对象在网上发了一封简短的澄清声明，称自己是无辜的，而且自己实际上也是受害人，因为无端指责都指向了她。但在过去的20年里，她一直消失在公众视线之外。“在网络上虽然每个人只是一个虚拟的ID，仍然应该理智客观，为自己的言行负责，”她写道。这个案例极好地显示了互联网的力量。1995年年初，在朱令的病症难倒了北京一家顶尖医院的医生后，她的一个高中同学绝望地在当时中国少数几台联网的电脑上发出了呼救。在西方医学专家发来的数百封回复中，大部分都准确地判断出那是铊中毒的症状，并建议服用一种名为普鲁士蓝(Prussian Blue)的商业染料解毒。这些信息救了朱令的命，但她依然属于重度残疾，她年迈的父母不得不时刻照料她。近年来，他们得到了一个总部位于美国的非营利组织的帮助，该组织一直在筹集资金，提醒人们这宗罪案依然还没侦破。对朱令案的再次关注引发了大量捐款，最近捐款金额已经超过了52万美元（约合319万元人民币）。“帮助朱令基金会”的志愿者何青被公众的响应以及网上表达的失望感动了。
Mass Spectrometry Sheds New Light on Thallium Poisoning Cold Case
UMD geologist Richard Ash developed a mass spectrometry standardization method for generating a timeline of thallium poisoning by analyzing the victim’s hair
In 1994, Chinese university student Zhu Ling began experiencing stomach pain, hair loss and partial paralysis. By the time doctors diagnosed Ling with thallium poisoning about four months later, she was in a coma. Ling survived, but she suffered permanent neurological damage. A police investigation determined that Ling was intentionally poisoned, but the case remains unsolved.
In October 2018, Ash published the results in the journal Forensic Science International, revealing for the first time that the victim had been exposed to multiple doses of thallium over a long period of time.
“To my knowledge, this is the first use of mass spectrometry to reconstitute the timeline of a prolonged case of intentional heavy metal poisoning,” Ash said. “The analysis showed that the victim was poisoned in many doses that increased in frequency and concentration over time.”
Mass spectrometry makes finding even low concentrations of thallium in hair easy, but measuring the amount of thallium in a hair sample is challenging. Other laboratories turned away Min He, the Ling family associate and Ash’s co-author of the study, because there was no established method for this type of analysis.
“Mass spectrometry is not good at measuring concentrations,” Ash said. “To do that, you need an established standard reference material to compare your sample against. And there are no such standards suitable for measuring thallium concentrations directly from a strand of hair.”
Ash made his own standard using a standard reference material made out of orchard leaves, which was developed by the National Institute of Standards and Technology (NIST) to measure certain elements in biological samples. Ash added known quantities of thallium to the NIST material to create a new set of standards that allowed him to determine how much thallium was in the victim’s hair.
As an additional level of quality control, Ash tested his measurements derived from the NIST-based standard against a powdered hair standard from China and found that his measurement of elements in the victim’s hair samples closely matched those in the powdered hair standard.
“To be honest, I was surprised that the new standard worked so well,” Ash said. “Developing my own standard was a shot in the dark, but it paid off.”
Next, Ash took advantage of the fact that human hair grows—and incorporates chemicals from the body—at a constant rate. Because of this characteristic, measuring the distribution of certain metals along a hair’s length is an established method to determine the timing and dosage of a person’s exposure to the metal.
To measure thallium in the victim’s hair, Ash scanned the length of the hair with an ultraviolet laser. The laser’s energy converted the outermost layer of the hair into tiny particles. Ash then used a mass spectrometer to analyze the particles for thallium. Using the growth rate of hair and the scanning speed of the laser, Ash converted his measurements into a timeline of thallium ingestion.
Ash used this technique to analyze several of the victim’s hairs, which were collected at different times in 1994 and 1995. One hair that began growing when Ling was asymptomatic revealed about four months of sporadic exposure to thallium, with increasing dosage and frequency until the hair fell out around December 1994. A second hair, which fell out around March 1995, showed about two weeks of constant ingestion of large doses of thallium.
Ash also discovered a large spike in thallium concentration in the first hair that corresponded to a brief period when Ling experienced vision loss but no gastrointestinal symptoms. As the study noted, this finding suggests that the victim might have been poisoned via eye contact at first, but later on, she was poisoned via oral ingestion.
By publishing his method and findings, Ash hopes that his work can help with heavy metal poisoning investigations in the future—and maybe even the decades-old case that introduced him to this research area in the first place.
“I hope that the new information our work has provided may one day lead to the perpetrator being brought to justice and Zhu Ling’s family gaining some solace from seeing that,” Ash said.
Media Relations Contact: Irene Ying, 301-405-5204, zying@umd.edu
University of Maryland College of Computer, Mathematical, and Natural Sciences 2300 Symons Hall College Park, MD 20742 www.cmns.umd.edu @UMDscience
About the College of Computer, Mathematical, and Natural SciencesThe College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 9,000 future scientific leaders in its undergraduate and graduate programs each year. The college’s 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $175 million.Date: Thursday, December 13, 2018Richard Ashthalliummass spectrometryGeologyResearch News
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