Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

Department of Chemistry

CHEM1020 General Chemistry***********************************************

Instructor: Dr. Hong ZhangFoster Hall, Room 221

Tel: 931-6325

Email: [email protected]

CHEM1020/General Chemistry_________________________________________

Chapter 20. (L31)-Chemical Toxicology

• Today’s Outline

…Chemical carcinogens

carcinogens and cancers

what causes cancershow cancers developchemical carcinogensanticarcinogens

…Testing for carcinogens

the Ames test: bacteria screening

animal testingepidemiological studies


• Carcinogen…Carcinogen: something that causes the growth of tumors.…A tumor is an abnormal growth of new tissue and can be either benign or malignant.

Benign tumors grow slowly, often regress at the same time, do not invade neighboring tissues.

Malignant tumors, cancers, can grow slowly or rapidly, but their growth is generally irreversible, which invades and destroy neighboring tissues.

Cancer is a complicated disease.


• What causes cancer…Major causes

genetic

environmental

natural carcinogens

anthropogenic (pollution, such as chemical carcinogens)

life-style or behavior

see Fig. 20.7 (pp.657)


• How cancers develop…Development mechanisms

modifying DNA

gene activation (oncogenes)

other mechanisms under investigation


• Chemical carcinogens…A variety of chemicals are carcinogenic

Examples:Polycyclic aromatic hydrocarbon (PAHs)

3,4,-benzpyrene, notorious onePAHs come from incomplete burning

of organic compounds e.g., charcoal-grilled meats, cigarette

smoke, automobile exhaust, coffee, brunt sugar, etc.



Examples:

Aromatic amines

β-naphthylamine

benzidine

in dye industries



Examples:

Non-aromatic amines

dimethylnitrosamine

vinyl chloride

Heterocyclic rings containing N and O


• Anticarcinogens…Yin and Yang

anticarcinogens:

antioxidant vitamins

butylated hydroxytoluene (BHT), a food addictive

there are more we just don’t know yet


• Tests for carcinogens…Question: how do we know if something is carcinogenic?

We get to know or guess by running some tests (not on human subjects)

Thus, we have to know something about possible carcinogens by these tests conducted not directly on human subjects


• Tests for carcinogens…The Ames test: bacterial screening

A simple lab procedure done in a petri dish. The test is based on the assumption that

most carcinogens are also mutagens. The Ames test was developed by Bruce N.

Ames of UC Berkeley A special strain of bacteria called

Salmonella that have been modified so that they require histidine as an essential amino acid.


• Tests for carcinogens…The Ames test: bacterial screening

The modified bacteria is put in a petri dish with all nutrients needed except for histidine, plus a potential carcinogen to be tested.

The bacteria can only grow if they can mutate to another type that does not require histidine as the essential amino acid.

If the growth of the bacteria is observed, then this suggests that the substance tested could potentially be a carcinogen.


• Tests for carcinogens…Animal testing

The suspected chemicals can be tested on animals. Approaches:

low doses with many animal subjectshigh doses with less animal subjectscontrols

If more occurrences of cancers are observed on the animals treated with the chemical than on the controls, then the chemical is potentially carcinogenic. …Shortcomings of animal tests


• Tests for carcinogens…Epidemiological studies

The best evidence that a substance may cause cancer in human beings comes from epidemiological studies.

Using biostatistical tools to analyze epidemiological data and identify the possible correlation between certain cancer and a suspected carcinogen.

Not necessarily cause-effect relationship, but the correlation is still useful and can server as a guideline.


• Hazardous wastes…Classification of hazardous wastes

Four types:

reactive

flammable

toxic

corrosive



Four types:

A reactive waste tends to react spontaneously or vigorously with air or water.

2Na(s) + 2H2O(l) = 2NaOH(aq) + H2(g)



Four types:

A flammable waste burns readily on ignition, presenting a fire hazard

Example: Hexane, a hydrocarbon solvent

2C6H14(l) + O2(g) = 12CO2(g) + 14H2O(g)

Accident: Louisville, KTOther examples: gasoline, fuels



Four types:A toxic waste contains or releases toxic

substances in quantities sufficient to pose a hazard to human health or to the environment.

PCB, Hg, heavy metals, and on and on.



Four types:A corrosive waste is one that requires special

containers because it corrodes conventional container material.

Acid cannot be stored in steel drums

Fe(s) + 2H+(aq) Fe2+ + H2(g)Strong base solution cannot be stored in glass

containers. Reactions between the substance of concern and

the container material.


• Green chemistry…Production of chemicals that are not or less toxic or hazardous or can naturally disappear to non-hazardous substances in the environment.

A very active field.


• Waste treatment…Incineration

A technology to treat organic wastes at 1260 ºC (Fig. 20.10, pp.664)

Bioremediation

Plants: phytoremediation

Microbes: microbial remediation

Genetic engineering and remediation


Quiz TimeTBA

Documents

Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel: