祸害无穷的多氯联苯 PCB
一、什么是PCB多氯联苯？

PCB多氯联苯是在1929年直至70年代末期北美商业上使用的一种人工合成的有机化合物，一直被广泛用于电气设备绝缘、热交换机、水利系统以及其它特殊应用中。虽然加拿大没有加工生产过这种化学物质，但也一直广泛使用。

经过几十年以后人们才认识到多氯联苯对全球性环境的污染，它是各种氯化联苯的混合物，对人体有极大的危害。加拿大政府曾经采取措施试图消除PCB，但是1977年在加拿大发生了非法进口、加工和销售PCB的现象，并在1985年将PCB非法释放到自然环境中，而加拿大的宪法允许PCB设备拥有者继续使用PCB直到设备的寿命期。1988年起加拿大各省政府才开始对PCB的储存、运输以及销毁进行了规定。

PCB在自然环境中不容易分解，而且传播的非常远，PCB在生产加工、使用、运输和废物处理过程中进入空气、土壤和河流以及海洋，小的海洋生物以及鱼类将PCB吸入体内，而它们又成为大的海洋生物的食物，这样一来，PCB就进入所有海洋生物的体内，包括哺乳类海洋生物。PCB在海洋生物体内的累积远远超出它在水中的含量，几乎是几千倍的数字。

二、PCB对人体健康有哪些危害？

1、PCB对皮肤和肝脏有很大危害并影响大脑发育
2、导致癌症，如肝癌和胆管癌等，PCB可致使免疫力低下
3、造成男性精子畸形，引起生育缺陷


三、PCB多氯联苯的一些特性

它几乎不会燃烧、不易被热分解、不易被氧化、不溶于水、不易导电，又抗强酸强碱，所以是一种相当稳定又好用的绝缘体。所以，早期的多氯联苯被用在电容器、变压器、可塑剂、润滑油、农药效力延长剂、木材防腐剂、油墨、防火材料等。由于PCB对人类健康的危害很大，所以加拿大法规禁用PCB。


四、PCB污染事件

1968年，日本米糠油事件
1979年，中国台湾油症事件
1986年，加拿大PCBs泄漏事件


1、1968年，日本米糠油事件

日本米糠油事件是世界有名的“八大公害事件”之一，1968年3月发生在日本北九州市、爱知县一带。

1968年3月，在日本的九州、中国、四国等地有几十万只鸡突然死亡（所以该污染事件也称作“火鸡事件”）主要症状是张嘴喘，头和腹部肿胀，而后死亡。经检验，发现鸡饲料中有毒，但没弄清楚毒的来源，也没有追究。

1968年6月至10月，日本福岛县先后有4家13人原因不明的皮肤病到九州大学附属医院求诊，患者表现为痤疮样皮疹伴有指甲发黑、皮肤色素沉着，眼结膜充血、眼脂过多等，疑是氯痤疮。由家庭多发性和食用油使用情况，怀疑与米糠油有关。

九州大学医学部、药学部和县卫生部组成研究组，有农学部、工学部、生产技术研究部及久留米大学公共卫生学专家参加，分为临床、流行病学和分析组开展调研。临床组在3个多月内确诊325名患者（112家），平均每户2.9个患者，证实本病有明显家庭集中性。以后全国各地逐年增多（以福岗、长崎两县最多）。到1978年12月，日本有28个县正式承认1,684名患者（包括东京都、京都郡和大阪府），到1977年已死亡30余人。

事件发生之后，日本卫生部门不得不成立专门部门——“特别研究班”。经解剖分析，在死者尸体五脏中和患者的皮下脂肪中都发现多氯联苯（PCBs）。流行病学组调查患者的发病时间、年龄、性别及地理分布特征，对患者共同食用的食油进行了追踪调查，发现所有患者使用的食用米糠油均系Kamei仓库公司制油部2月5日至6日出厂的产品，而在食用该产品的266人中有170人患病，于是分析组不到一个月就阐明了米糠油中的病因物质是PCBs。在患者的分泌物、指甲、毛发及皮下脂肪等样品中都发现PCBs，证实了PCBs来自用作热载体的KC-400。

经跟踪调查，发现九州大牟田市一家粮食加工公司食用油工厂，在生产米糠油时，为了降低成本追求利润，在脱臭过程中使用PCBs液体作导热油。因生产管理不善，使PCBs混进米糠油中。于是，随着这种有毒的米糠油销售各地，造成人的中毒生病或死亡。生产米糠油的副产品——黑油作家禽饲料售出，也使大量家禽死亡。

在米糠油事件调查中，采用了环境流行病学调查法中的病例对照调查法，即随机选出与米糠油事件受害者性别、年龄条件一致、住在同处的未患病者作为对照组，对患者组和对照组食用油脂的情况进行了调查，食用天然黄油、人造黄油、猪油的患病家庭和对照组家庭的百分比没有差别，食用菜籽油或其他食用油的对照组比患者组多，食用米糠油的患者组则比对照组多得多。通过环境流行病学的回顾性调查，终于查明在米糠油生产过程中的PCBs污染是米糠油事件发病的主因。

早在1966年，美国就受到PCBs的污染，在一些报刊上展开议论，并有人警告说，这种污染已扩及到人们吃用生活的各个方面，但没有引起日本当局和食品工业企业的重视，而且还认为PCBs对日本来说没有构成威胁。令人悲哀的是只经过两年，PCBs中毒就使日本遭遇到一场新的灾难，所以日本的米糠油事件又称“多氯联苯污染事件”。


2、1979年，中国台湾油症事件

这是世界上发生过的最大的一次多氯联苯（PCB）污染事件仍在困扰着当年的男性受害者，使他们生育男孩的能力下降。1979年，台湾Yu-Cheng 2000人食用了受到多氯联苯污染的油。“米糠油”中毒遗患三代人。据2002年7月13日出版的《柳叶刀》(Lancet)上刊登的一项由伦敦和台湾研究人员组成的研究小组共同完成的研究数据，受此次食用油污染暴露的青年男性生育的后代中，男孩只占46%（世界平均水平为51?2%）。此次事件中受到暴露的女性所生育后代的性别比例无异常。

多氯联苯是一种人工合成有机化合物，被广泛用于电气设备绝缘已有五十多年。在Yu-Cheng毒油事件中，多氯联苯在大米油加工过程中被用作传热介质。因管路意外泄露，多氯联苯进入食用油，并在加工过程及后来的烹饪过程中产生副产品聚氯二苯醚（PCDFs）。

中国台湾网2004年9月17日消息：因1979年台中部发生的多氯联苯（米糠油）事件而中毒的患者如今已分布到台岛屏东、花莲等许多县市，台卫生部门发现这些病患的第二代，甚至第三代也受到了不同程度的毒害。

据台媒报道，彰化县溪湖镇彰化油脂公司于二十五年前（1979年）生产食用米糠油时，冷凝器的多氯联苯液体外泄，污染了食油，造成误食者中毒。这种残毒非但不能完全代谢掉，还会遗传后代。当年深受其害的部分油症患者虽已亡故，但有关卫生单位已经陆续发现了第二、三代患者。

彰化县卫生局委托医院做血液筛检时，发现一名两岁幼儿血液里含有多氯联苯，浓度比母亲、外祖母低，显现在外观的症状也较轻微，应属遗传致病，是第三代油症患者。

苗栗县有五十五名油症患者，多住在南庄乡和苗栗市，其中四名患者仅二十多岁，卫生人员认为他们应是在母亲怀孕时被遗传了多氯联苯，也可能出生后喝母乳而引进残毒，变成皮肤略黑、发育迟缓的可乐儿。（当孕妇因多氯联苯中毒，使婴儿透过胎盘受到多氯联苯影响，以致胎儿出生时皮肤深棕色素沉着，全身黏膜黑色素沉着，发育较慢，很像一瓶可口可乐，故台湾称其为“可乐儿”。）

另外，油症患者最初分布台中县、彰化县、苗栗县、新竹县，后来因结婚或迁徙扩散到云嘉南、高屏、花莲等县市。这些病患不仅自己身心受创，并且绝大多数留下了后遗症。（潇凝）


3、1986年，加拿大PCBs泄漏事件

1986年4月13日，加拿大一辆卡车载着一台有高浓度多氯联苯液体的变压器去废物储存场，途中在经过安大略省北部的凯拉城附近时，有400 多升PCBs从变压器中泄漏，污染了100公里的高速公路和其它车辆。


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What are polychlorinated biphenyls (PCBs)?
Polychlorinated biphenyls, commonly known as chlorobiphenyls or PCBs, are industrials chemicals which were synthesized and commercialized in North America in 1929. They were used in the manufacturing of electrical equipment, heat exchangers, hydraulic systems, and several other specialized applications up to the late 1970s. They were never manufactured in Canada but were widely used in this country.

PCBs are very persistent both in the environment and in living tissue. The most obvious signs of environmental harm caused by PCBs are in aquatic ecosystems and in species that eat primarily aquatic organisms. Because of concern for the environmental and health effects of PCBs, the Canadian government took action to eliminate PCBs from Canada. The import, manufacture, and sale (for re-use) of PCBs were made illegal in Canada in 1977 and release to the environment of PCBs was made illegal in 1985. However, Canadian legislation has allowed owners of PCB equipment to continue using PCB equipment until the end of its service life. The storage of PCBs has been regulated since 1988. Handling, transport and destruction of PCBs are also regulated, mostly under provincial regulations.

Despite the large reductions in PCB inventories since the implementation of regulatory controls, releases of PCBs to the environment through spills and fires continue to occur. If action is not taken to "speed up" the pace of PCB phase-out, Environment Canada is concerned that the goal of elimination of PCBs from Canada may not be reached for another generation. In addition Canada is signatory to, or is negotiating to enact, several international agreements on the phase-out of a number of persistent toxic substances including PCBs. Environment Canada has therefore proposed revisions to the existing Chlorobiphenyl Regulations of the Canadian Environmental Protection Act (CEPA) that would set specific dates for the complete destruction of all PCBs in service and in storage.


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What happens to polychlorinated biphenyls (PCBs) when they enter the environment?
PCBs entered the air, water, and soil during their manufacture, use, and disposal; from accidental spills and leaks during their transport; and from leaks or fires in products containing PCBs.

PCBs can still be released to the environment from hazardous waste sites; illegal or improper disposal of industrial wastes and consumer products; leaks from old electrical transformers containing PCBs; and burning of some wastes in incinerators.

PCBs do not readily break down in the environment and thus may remain there for very long periods of time. PCBs can travel long distances in the air and be deposited in areas far away from where they were released. In water, a small amount of PCBs may remain dissolved, but most stick to organic particles and bottom sediments. PCBs also bind strongly to soil. PCBs are taken up by small organisms and fish in water. They are also taken up by other animals that eat these aquatic animals as food. PCBs accumulate in fish and marine mammals, reaching levels that may be many thousands of times higher than in water.


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How might I be exposed to polychlorinated biphenyls (PCBs)?
Using old fluorescent lighting fixtures and electrical devices and appliances, such as television sets and refrigerators, that were made 30 or more years ago. These items may leak small amounts of PCBs into the air when they get hot during operation, and could be a source of skin exposure.

Eating contaminated food. The main dietary sources of PCBs are fish (especially sportfish caught in contaminated lakes or rivers), meat, and dairy products. Breathing air near hazardous waste sites and drinking contaminated well water. In the workplace during repair and maintenance of PCB transformers; accidents, fires or spills involving transformers, fluorescent lights, and other old electrical devices; and disposal of PCB materials.


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How can polychlorinated biphenyls (PCBs) affect my health?
The most commonly observed health effects in people exposed to large amounts of PCBs are skin conditions such as acne and rashes. Studies in exposed workers have shown changes in blood and urine that may indicate liver damage. PCB exposures in the general population are not likely to result in skin and liver effects. Most of the studies of health effects of PCBs in the general population examined children of mothers who were exposed to PCBs.

Animals that ate food containing large amounts of PCBs for short periods of time had mild liver damage and some died. Animals that ate smaller amounts of PCBs in food over several weeks or months developed various kinds of health effects, including anemia; acne-like skin conditions; and liver, stomach, and thyroid gland injuries. Other effects of PCBs in animals include changes in the immune system, behavioral alterations, and impaired reproduction. PCBs are not known to cause birth defects.


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How likely are polychlorinated biphenyls (PCBs) to cause cancer?
Few studies of workers indicate that PCBs were associated with certain kinds of cancer in humans, such as cancer of the liver and biliary tract. Rats that ate food containing high levels of PCBs for two years developed liver cancer. The Department of Health and Human Services (DHHS) has concluded that PCBs may reasonably be anticipated to be carcinogens. The EPA and the International Agency for Research on Cancer (IARC) have determined that PCBs are probably carcinogenic to humans.


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