环境化学英文课件18

Atrazine
Malathion Aspirin
1,870
1,200 1,000
Nicotine
Dioxin (TCDD) Botulin toxin
1
0.001 0.00001
Almost every chemical is toxic at some level, and the difference between toxic and nontoxic chemicals is a matter of degree.
92
62-100 260-480 63 70 51-85 139
UK
US Hong Kong
70
18-192 105
Source: An Assessment of Dioxin Emissions in Hong Kong, HKEPD, 2000.
Average content of 2378-TCDD in various foodstuff (U.S)
How much dioxin do we congest?
Country
Estimated Dietary Intakes of PCDD/Fs per day
Dietary Intake (pg I-TEQ/day)
Canada
Germany Italy Japan Netherlands Norway Russia
– – – – – Birth defects Cancer Skin disorders Liver damage Suppression of the immune systems
• Variation in toxicity among species is large.
– Male guinea pig, oral, LD50 is 0.6 mg/kg. – Hamster, intraperitoneum, LD50 is 3000 mg/kg.
Dioxins
(二噁英):
General structures
• The term dioxins denotes a family of chemical compounds, known asBiblioteka Baidupolycholorinated dibenzopara-dioxins (PCDDs) and polycholrinated dibenzofurans (PCDFs)
Dioxin toxicity varies among the congeners
International Toxicity Equivalency Factors (TEF) for PCDDs and PCDFs
Congener
2378
PCDD series PCDF series
1 (defined) 0.1
Food Ocean fish Meat TCDD (pg/g) 500 35
Cheese
Sour cream Cream Ice cream Cottage cheese Milk Coffee
16
10 7.2 5.5 2.1 1.8 0.1
Orange juice
0.2
Formation of dioxins
• Paper pulp bleaching with chlorine
– Chlorine is used to bleach paper pulp. – PCDDs are formed probably through chlorination of the phenolic groups in lignin.
The TEFs allow the conversion of various congener concentrations into a single toxicity equivalent quantity (TEQ)
Dioxin toxicity: general rules
• TCDD is the most toxic of the dioxins • Toxicity decreases when Cl atoms are removed from 2,3,7,8 positions or added to the remaining positions on the rings. • There are similar toxicity pattern for PCDD and PCDF series.
• Combustion
– In any situation where Cl, C, H, and O come into contact with heat, PCDD/Fs could be formed as trace by-products. – Dioxin emission correlates with the Cl content of the combustion feed.
• Incomplete combustion of organic wastes in the combustion chamber leads to the formation of organic fragments which serve as organic precursors to the PCDD/F molecule. • The waste provides a source of chlorine, and of metals. The latter are incorporated into fly ash, which carries over to the cooler (250-400oC) post-combustion zone of the incineration system. • The organic precursors adsorb onto the surface of the fly ash in the post-combustion zone, and following a complex sequence of reactions which are catalyzed by metals (primarily copper) in the fly ash, lead to the formation of PCDD/Fs along with other chlorinated trace organics.
Multiple exposure pathways
Biochemistry of dioxin toxicity
• PCDD/Fs are planar aromatic molecules. • The planar structure allows them to bind to Ah (Aryl hydrocarbon) receptor protein that is present in all animal species. • The Ah receptor interacts with the cell’s DNA. • Dioxin toxicity is roughly proportional to the strength of binding to the Ah receptor. • This explains that 2378-TCDD is the most toxic one.
• Risk to humans is less clear
Human risk of dioxin exposure
• USEPA concludes that dioxins likely increase cancer incidence. • WHO classifies 2378-TCDD as a probable human carcinogen. • At high levels, PCDDs cause chloracne (氯痤倉), a painful skin inflammation. • Risk from breathing dioxin-laden air is minimal. • The main exposure route for human is dietary (meat, dairy products, and fish). (Due to bioaccumulation of dioxins) • Absorption of dioxins by infant through mothers’ milk is efficient.
9 8 1 9 2 8 1 2
O
7 6
O
4
3
7 6
O
4
3
Dibenzodioxin PCDD
Dibenzofuran PCDF
Cl
O
Cl
Cl
Cl
Cl
O
2378-TCDD
Cl
Cl
O
2378-TCDF
Cl
Toxicity of Dioxins
• Extraordinary toxic to lab animals (LD50 in male guinea pigs is only 0.6 mg/kg)
12378
23478 123478, 123678, 123789 1234678 octachloro
0.5
0.1
0.05
0.5 0.1
(also include 234678 congener)
0.01 0.001
0.01 (also include 1234789 congener) 0.001
• Manufacture of certain chlorophenol chemicals
– Dioxin was produced as a contaminant of the herbicide 2,4,5-T, a component of Agent Orange
Formation of dioxins in combustion processes
Index of acute toxicity:LD50
LD50 is the lethal dose for 50% of a population.
Dose is expressed as the weight of a chemical consumed by an experimental animal per kg of body weight of the animal.
Dioxins and PCBs
Acute (急性) and chronic (慢性) toxicity
• Acute toxicity refers to a rapid and serious response to a high but short-lived dose.
– Acute poisons interfere with essential physiological processes, leading to a variety symptoms of distress, even death.
• Chronic toxicity refers to a time-lagged response to a relatively low but prolonged exposure.
– Effects are more subtle. – Set in motion a chain of biochemical events that lead to disease states, including cancer.
General structure
O
Clx
O
Clx Cly Cly
O
Dibenzodioxin PCDD
Dibenzofuran PCDF
Dioxins: Congeners
Congener: a member of the same class, or group. Each individual PCDD or PCDF is termed a congener. There are 75 PCDD congeners and 135 PCDF congeners.
LD50 of selected chemicals for rats or mice
Chemical Sugar ethanol Vinegar Table salt LD50 (mg/kg) Chemical 29,700 14,000 3,310 3,000 Caffeine DDT Arsenic Parathion LD50 (mg/kg) 130 100 48 3.6