- 发帖可能变空内容，邪门暂不知所以然
- 『稷下学宫』新认证方式，24年网站打算和努力目标
主题：【求助】PX的毒性 -- 燕人
这个论坛上在讨论某地一家大型化工厂的环保隐患，其中一个关键问题是该厂化工产品的毒性问题。
该工厂的成品是PX.
据说该物质毒性其实并不大。与制鞋厂所产生的废气相当。
有专业人士请解惑。
http://www.fyan.org/forum/showthread.php?tid=1456
本帖一共被 1 帖 引用 (帖内工具实现)
Xylenes are not highly toxic as indicated by the high values of the LD50, which range from 200 to 4000 mg/kg for animals. The principal mechanism of detoxification is oxidation to methylbenzoic acid and hydroxylation to hydroxylene.
这个文章仔细讲了xylene的毒性：
http://onlinelibrary.wiley.com/doi/10.1002/14356007.a28_433/full
Environmental Aspects. In Germany xylenes are assigned to water hazard class 2 (WGK 2) [55]. The solubility of xylenes in water is low (ca. 0.14 g/L). Because of the comparatively low vapor pressure (7 – 8 mbar at 20 °C), the danger of vapor emissions in air is relatively low. However, xylenes can react with other air pollutants to give environmentally damaging products. This applies particularly to the UV-catalyzed photooxidation of xylenes by nitrogen oxides. However, compared with some other hydrocarbons, the reactivity of xylenes is comparatively low, with a reaction rate of ca. 2×10–9 min–1 [55]. For example, disubstituted internal olefins have a reaction rate of ca. 50×10–9 min–1.
Toxicology. Exposure to xylene is possible through inhalation of vapors and resorption through the skin. The MAK value is 100 ppm (ca. 440 mg/m3) for all three isomers [54].
General Activity. Xylene exhibits acute prenarcotic and narcotic activity. Chronic exposure to xylene leads to disturbance of the CNS (e.g., headaches, sleep disturbance) [56] and damage to the blood picture (dyspepsia). Provided that there is no long-term chronic overexposure, these effects are reversible. Besides developing a certain tolerance, frequent exposure to xylene can also lead to habituation or even addiction (solvent abuse).
Acute Toxicity. The LD50, LC50, and TCLo values for oral administration and inhalation vary widely, depending on the animal investigated and the isomer composition. The following values give an indication of the toxicity of xylene isomer mixtures [54], [57]: LD50 (rat, oral) 4300 mg/kg, LDL0 (rat, i.p.) 2000 mg/kg, TCLo (humans, inhalation) 200 ppm.
A very high exposure to xylene of ca. 10 000 ppm caused by an accident led to lung edema and subsequent death in one person [58]. In other cases severe damage to the CNS, kidneys, and liver were observed.
Irritant Effects. On repeated application xylenes can cause irritation of the respiratory passages and mucous membranes of the eye. Frequent skin contact can lead to blister formation and dermatitis [57], [59-62].
Subchronic and Chronic Toxicity. At a concentration range of 100 to over 1000 ppm xylene in inhaled air, damage to the CNS with disturbance of balance or slowing of reactions is observed. Inhalation of xylene vapors can also cause nausea and headaches [63-65].
A change in the blood picture is also frequently observed. In ca. 10 % of persons who had been exposed to xylene vapors in concentrations of up to ca. 100 ppm for ca. 5 years, a leucocyte level of < 4500 mm–3 was established [66]. A decrease in the immunobiological activity has occasionally been observed [58].
Carcinogenicity, Mutagenicity, and Embryotoxicity. The assessment of the carcinogenicity of xylenes is not consistent [67-69]. While in one study no indications of carcinogenicity or cocarcinogenicity were found, another investigation indicated that xylenes act as tumor promoters for skin tumors in rats.
None of the three xylene isomers showed mutagenicity in the Ames test [70]. However, slight mutagenicity was detected in a recessive lethal test on drosophila [71].
In animal experiments long-term exposure through inhalation of xylenes causes small changes to fetuses [72].
Pharmacokinetics and Metabolism. All three xylene isomers are resorbed in the same way. Various investigations have shown that ca. 60 – 70 % of the xylene reaching the organism via the lungs is retained [73-76]. This percentage remains approximately constant over the whole exposure period. The ratio of the concentration in the air in the alveoli (mg/m3) and in the blood (mg/kg) changes with the degree of bodily activity. When the body is at rest the ratio is ca. 15 : 1 and when moving ca. 30 – 40 : 1 [77]. Xylene can be resorbed at a rate of ca. 2.5 (0.7 – 4.3) mg/m3 per minute through intact skin [78].
Xylenes are deposited rapidly in body fat (up to ca. 5 %) and remain there for hours after exposure. The half-life in fat deposits is ca. 0.5 – 1.0 h [78]. The metabolism of the individual xylene isomers is identical. The main biotransformation pathway initially involves oxidation to methylbenzoic acid, which forms the corresponding methylhippuric acid by conjugation with glycine (A) [74], [79-81]. The methylhippuric acid can be excreted rapidly via the kidneys. Another, less favored biotransformation pathway involves the hydroxylation of the xylene on the aromatic ring, forming xylenols (B) [73].
一个化工工厂一毒性如何要从原料看到工艺看到产品看到排放。我不太清楚他们要采用的原料和工艺。如果这个生产过程中会产生剧毒物质如多环芳烃（PAH），那就毒大发了....
甲基苯类的毒性比苯低很多，因为苯环上的甲基在自然界和人体中很容易被氧化成羧基从而转化为对人体比较安全的苯甲酸类，在人体中可以和甘氨酸结合排出体外。所以甲苯，二甲苯之类的还是比较安全的。
至于PX的生产的话，工业上PX本身应该主要是靠甲苯歧化制备的，至于初始原料有可能直接是用石油化工产业获得的C7，C8，C9芳烃，或者从较长链的烷烃重整芳烃得到，这些都是连续过程，最终产物除了各种二甲苯之外主要的毒性较高的产物就是苯。
总得来说PX项目也就是一普通的化工项目而已，一般性的问题都有，易燃易爆有味道，但是也没什么特殊的问题，设计合理的大化工项目对环境的危害其实比有些坑爹的小工厂比如小电镀之类的都要小。
PX这种东西其实就是因为厦门PX项目被妖魔化了，厦门那个项目貌似确实因为规划问题离居民区比较近，要是发生泄漏或者火灾的话确实有风险，所以为了阻止这个项目自然需要编造点PX毒步天下之类的谣言煽动下民意给政府压力，归根结底还是在中国政府和民众的一种畸形的博弈。
何况还有一些人信奉：直接与己有关的事，再小也是大事；与己无直接关系的事，再大也是个P！
利益取向割裂，传统权威失范！
只要权利，不要责任！
大到核电站、化工厂，小至变压器、无线基站、公厕、垃圾站，都不能设在咱的周围，但俺还必须享受高品质的现代生活，贵了还不成。
歌中唱到：
这个时间问关于P*X的问题，我懂的。
毒性是一方面，还有个问题是：是否致癌？在环境中长期有微量的PX，致癌的可能性有多大，这个有相关的研究吗？这才是我们要考虑的。即使不发生险些被“梅花”冲垮那样的大灾难，常年累月的微量泄露，也够让人揪心的了。
兄弟我以前学高分子化学的时候，天天苯萃取，制备对二甲苯、间二甲苯、临二甲苯那简直是家常便饭。也没看什么特殊防护措施的，顶多就戴手套而已。
这些物质主要是可以自然或生物降解，或者自然氧化。比如硫化氢，突然大量溢出，浓度到了危险浓度，甚至几秒中就要人命。但是长期在安全浓度下接触问题也不大，因为硫化氢很容易被空气中的氧气缓慢氧化，不会像DDT那样在体内聚集。
这里只是普遍情况，不敢说大连PX的情况就一定是这样。
原始社会好，
原始社会好，
男男女女光着屁股跑，
男的追，
女的跑，
碰上老虎都吃掉。。。。。。
性不是极大）。但其毒害仍然是无法否认的：
Clear liquid澄清溶液
- FLAMMABLE LIQUID AND VAPOR易燃液体/蒸汽
- MAY CAUSE CNS DEPRESSION有可能抑制中枢神经系统
- HARMFUL OR FATAL IF SWALLOWED 吞咽可能致命
- CAN ENTER LUNGS AND CAUSE DAMAGE进入肺部，肺部损伤
- MAY CAUSE RESPIRATORY TRACT IRRITATION IF INHALED吸入呼吸道损伤
- VAPOR HARMFUL有害蒸汽
- CAUSES EYE IRRITATION眼部刺激
- MAY CAUSE AN ALLERGIC SKIN REACTION有可能皮肤过敏
- CAUSES SKIN IRRITATION皮肤刺激
- BIRTH DEFECT HAZARD - MAY CAUSE BIRTH DEFECTS 有可能造成出生缺陷- INHALATION MAY CAUSE NERVOUS SYSTEM EFFECTS 吸入可能找成中枢神经损伤
- CONTAINS MATERIAL THAT CAUSES CENTRAL NERVOUS SYSTEM EFFECTS
- MAY CAUSE DAMAGE TO:
- - - - - - AUDITORY SYSTEM
- HIGHLY TOXIC TO AQUATIC ORGANISMS对水生生物有高度毒性
另外，化工品的危险性不仅是毒害程度，还在于它是否易燃易爆品。他们是真的不懂呢，还是故意对PX本身是高危的易燃易爆品这个事实视而不见呢？
看看这个链接中引用的BP 自己出的产品说明书上是怎么说的吧：
http://bbs.taizhou.com/simple/index.php?t130198.html
FIRE CLASSIFICATION:
OSHA Classification (29 CFR 1910.1200): Flammable liquid.NFPA RATINGS: Health: 2 Flammability: 3 Reactivity: 0
FLAMMABLE PROPERTIES:
Autoignition: 466°C (870.8°F)
Flammability (Explosive) Limits (% by volume in air): Lower: 1.1 Upper: 7
注意黑体部分的意思是：
1.PX是3级可燃液体。
2.闪点为27°C. 就是说在达到相应浓度后，只要27°C就可以被点燃了。
3.爆炸极限为1.1-7%。液化石油气的爆炸极限是 1.5-9.5%。大家可以自行对比这个PX的危险程度。
______________________________________________________________________
Revision Number: 24
Revision Date: 06/26/2007
6 of 9 Paraxylene
MSDS : 700
The description shown may not apply to all shipping situations. Consult appropriate Dangerous Goods Regulations, for
additional description requirements (e.g., technical name) and mode-specific or quantity-specific shipping requirements.
Shipping Descriptions per regulatory authority.
US DOT
UN1307, XYLENE , 3, III , RQ
ICAO / IATA
XYLENE, 3, UN1307, III
IMO / IMDG
XYLENE, 3, UN1307, III, (27°C )
RID / ADR
UN1307, XYLENE, 3, III, ADR
国际海运业也规定该产品的运输必须按照3.3级危险品要求进行。
READ AND OBSERVE ALL PRECAUTIONS ON PRODUCT LABEL . REFER TO PRODUCT LABEL OR MANUFACTURERS
TECHNICAL BULLETINS FOR THE PROPER USE AND HANDLING OF THIS MATERIAL .
Precautionary Measures: This material presents a fire hazard. Liquid quickly evaporates and forms vapor (fumes) which
can catch fire and burn with explosive violence. Invisible vapor spreads easily and can be set on fire by many sources
such as pilot lights, welding equipment, and electrical motors and switches. Fire hazard is greater as liquid temperature
rises above 15°F. Do not breathe vapor or fumes.
实际上在温度高于华氏15度时，起火危险就在增加。
总体来说，如果是严格按照要求操作，再危险的化工品在平时对于操作人员和公众的危险性都会降低。但人们更关心的是出现意外、出现事故会有多大危害。
PX如果发生泄漏，不单是对人体和海域水产品的毒害问题，更可怕的是其相当低的闪点容易导致的大火或者爆炸。如果不幸被别的易燃易爆品发生事故时产生的大火或者爆炸波及，那PX可不会客气。特别是那么大的储罐，其威力会有多大，我现在量化不出来。
至于用于PX生产的原材料以及副产品之类，可以自己查他们的MSDS，进行类似分析。
本帖一共被 1 帖 引用 (帖内工具实现)
城市里的加油站，郊区的储油罐，还有几百万到上千万吨级的炼油厂，哪个不是比这个小小的几十万吨的PX项目厉害。
基本上来说，这些事件的客观因素是广大群众对政府的普遍不满，主观上有特定的一些组织利用这些事件演练如何搞群众运动。
毒性小，安全。 上面这些帖子里的数据都是针对这样的观点而言的。并没有否认有比PX更危险的项目存在。
加油站的级别和70万吨的PX项目，也不是一个数量级，没什么可类比性。
不能因为有比PX更危险的项目存在，就否认PX项目搬迁的合理性。
至于是否有人搞群众运动，那个不是我讨论的内容，因为我没看到确实的证据。如果有人只顾小团体利益，视百姓为空气，那被人家搞了群众运动也是咎由自取，没什么值得同情的。
换句话说，这个事情的讨论者分为两方面：一方面主要从技术上讨论是否应该搬迁，到底有多大危险；一方面的人主要从政治斗争上讨论。而有一种论调就是，从技术上论证PX安全性后，来佐证事件本身是被利用的。
我针对的就是以技术讨论来否定事件本身对于大连市民意义的这些人。至于讨论政治，没有内幕消息，也没有公开信息，本人不参与臆测。