department of chemistry chem1020 general chemistry ***********************************************

Department of Chemistry

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

Instructor: Dr. Hong ZhangFoster Hall, Room 221

Tel: 931-6325

Email: [email protected]

CHEM1020/General Chemistry_________________________________________

Chapter 20. (L29)-Chemical Toxicology

• Today’s Outline

…Oxidizing agents

…Poisons affecting oxygen transport and oxidative processes…Heavy metal poisons

HgPbCdCr


• Oxidizing agents…Poisonous oxidizing agents in the air

Air pollutants can damage living cells

The poisonous agents include pollutants such as:

ozone

peroxyacetyl nitrate (PAN)

other oxidizing components of photochemical smog


• Oxidizing agents…Effects of poisonous oxidizing agents in the air

The damage by the poisonous air pollutants:deactivation of enzymesthe active sites of enzymes often involves

the sulfur-containing amino acidcysteine and methionine

HS-CH2-CHNH2-COOH + O3

HO-SO2-CH2-CHNH2-COOH



The damage by the poisonous air pollutants:

deactivation of enzymes

the active sites of enzymes often involves

the sulfur-containing amino acid cysteine:

HS-CH2-CHNH2-COOH (cysteine) + O3

HO-SO2-CH2-CHNH2-COOH






the sulfur-containing amino acid methionine:

CH3-S-CH2CH2CHNH2-COOH (methionine) + O3

CH3-SO-CH2CH2CHNH2-COOH






the amino acid tryptophan:

tryptophan + O3 oxidation product

ring-opening oxidation at the double-bond



Oxidizing agents can break chemical bonds in many other chemical substances in a cell.

Powerful oxidizing agents, such as ozone, are more likely to attack the living cells indiscrimately than just to cause targeted specific reactions.


• Poisons affecting oxygen transport and oxidizing processes…Review of respiration (biological oxidation)…Toxicological effects of certain poisonous chemicals:

They can prevent cellular oxidation of metabolites by blocking the transport of oxygen in the bloodstream or by interfering with oxidative processes in the cells.

These poisonous chemicals act on the iron atoms in the complex protein molecules.


• Poisons affecting oxygen transport and oxidizing processes

…Blood agents

A typical example: CO

CO can binds firmly to the iron atom in hemoglobin in the blood, thus blocking the transport of oxygen molecules (hemoglobin is supposed to bind to oxygen)


• Poisons affecting oxygen transport and oxidizing processes

…Blood agents, another example: nitrates (NO3-):

microorganisms in the digestive tract can reduce nitrates to nitrites (NO2

-):

NO3- + 2H+(aq) + 2e- NO2

- + H2O

NO2- + Fe(II) Fe(III) + product

The oxidation of Fe(II) to Fe(III) by nitrites leads to conversion of hemoglobin to methemoglobin, which is incapable of carrying oxygen

The consequent disease of oxygen deficiency is called methemoglobinemia; for infants, it is known as blue-baby syndrome.


• Heavy metal poisons

…Metals with densities at least five times that of water are called heavy metals (also, > 3 g/cm3)

Many heavy metals are transition metals

Examples of toxic heavy metals:

Hg, Pb, Cd, Cr

Some heavy metals are toxic because they can inactivating enzymes

C&EN’s “Mercurial” IssueC&EN just celebrated its 80’s anniversary with a special issue

devoted to the Periodic Table of Elements

C&EN, September 8, 2003

The God Mercury

C&EN / Sept 8, 03

Hg is named after Mercurius, the speedy messenger of the other Roman Gods.

MERCURY AT A GLANCE

Name: Named after the planet Mercury, which was named for the Roman god of eloquence, skills, and commerce. The symbol comes from the Latin for liquid silver, hydrargyrum.

Atomic mass: 200.59.

History: Known since ancient times.

Occurrence: Rare in Earth's crust. It is primarily found in cinnabar ore.

Appearance: Silvery white, liquid metal.

Behavior: The only metal that is liquid at room temperature. It alloys easily with most metals and is very volatile. The element vapors are toxic, as are all mercury compounds. It is a cumulative poison that affects the central nervous system and the mouth, gums, and teeth. Uses: Used in thermometers, barometers, diffusion pumps, and other instruments. It is also used for making batteries, switches and other electrical apparatus, some pesticides, and antifouling paint. Mercury is the basis of dental amalgams and preparations. Gaseous mercury is used in mercury-vapor lamps and advertising signs.

C&EN / Sept 8, 03

Chemical Profile of Elemental HgName: Hydrargyrum (Hg),

Mercury, Quecksilber, Mercure, PTYTb, Mercurio, Ground-state configuration: [Xe]4f145d106s2 Atomic Radius: 1.503 ÅDensity: 13.534 g cm-1 (25 ºC)m.p.: -38.87 ºCb.p.: 356.58 ºC

Reduction Potential (Hg2+ + 2e = Hg0): 0.851 V Vapor Concentration (20 ºC): 13.176 mg m-3 Solubility: 64 µg L-1 (25 ºC)

Droplets of mercury on a green surface. The surface tension of mercury is so high that the smaller droplets

from almost perfect spheres.

C&EN / Sept 8, 03

Toxicological Profile of Hg…Hg Toxicology-Non-carcinogenic, non-mutagenic

-Prenatal effect (the unborn)

Hg(0)vapor .toxic to central nervous system

.increased excitability (mad hatter disease)

Hg(II) .abdominal cramping

.ulceration

.renal toxicity

.enzyme malfunction or damage (S-affinity)

Toxicological Profile of Hg…Hg Toxicology (continued)

Methyl-Hg .most toxic (can be lethal)

.highly lipophilic (lipid soluble)

.strong neuro-toxin (central nervous system and brain damage)

-Exposed by eating fish bioaccumulated with methyl-Hg through food web (accumulation factor of ~105)

-Fish consumption advisories, ~33 states in USA

Hg Poisoning and HistoryWell-known examples of Hg poisoning connected to methyl

Hg:

1. In 1950’s, Minamata disease, Minamata Bay, Japan, fishermen and their families (also seabirds, household cats) ate the fish in the bay, weakness, vision & balance loss, coma.

2. In the middle 1960’s, grain seeds treated with Hg-containing preservative (fungicides); starving people eating the seeds were poisoned, e.g., in Iraq.

3. In 1997, chemistry Prof. Karen Wetterhahn of Dartmouth College tragically died as a result of 1 drop of (CH3)2-Hg during research on Hg.

Chemistry: A Humanistic Approach by L.M. Vallarino & J.V. Quagliano, 1975, McGraw-Hill

Methylation and Evolution

Hg methylation, a consequence of microbial evolution (dimethyl-Hg volatile, detoxification)

Microbial methylation converts toxic metals (e.g., Pb, Sn, Ge, Sb, As, Se), to volatile species by attaching the metals with methyl groups and thus degassing of the volatile methylated metals is a natural cleansing and decontamination for microbes.

Me2Hg

MeHg+

FoodChain

Environmental Hg Research-The Clean Air Act Amendments of 1990, Hg was in the list of the

persistent, bioaccumulative hazardous pollutants and Hg research has been hot ever since

-Mercury Study Report to Congress (EPA, Dec, 1997)-Mercury Research Strategy (EPA, Sept, 2000) -6th International Conference on Hg As A Global Pollutant (Minamata,

Japan, Oct, 2001)-7th International Conference on Hg As A Global Pollutant will be held in

Slovenia in 2004

-Recently, a new air pollution control requirement released by EPA, requiring 9 remaining US Hg-cell chlor-alkali plants to have better house-keeping, monitoring, record keeping, reporting, and installation of new C absorption equipment to capture Hg before its release into the environment.


• Heavy metal poisons: Lead (Pb)…Lead uses: housepaints, tetraethyllead in gasolines, lead-sealed pipes…Toxicology of Pb as Pb2+: It can damage brain, liver, kidneys, and the situation can be fatal.…Pb poisoning is especially harmful to children.

large amounts of Pb2+ in a child’s blood can cause mental retardation, behavior problems, anemia, hearing loss, development delays, and other physical and mental problems. …The story of Un-leaded gas


• Heavy metal poisons: Cadmium (Cd)

…Cd uses: alloys, electronic industries, Ni-Cd rechargeable batteries

…Toxicology of Cd as Cd2+: Loss of Ca2+ from bones, severe abdominal pain, vomiting, diarrhea, choking sensation

…The story of “itai-itai” disease (Japan) or “ouch-ouch” disease


• Heavy metal poisons: Chromium (Cr)…Cr uses: metal plating, stainless steal, wear-resistant cutting-tool alloys, anticorrosive addictive to cooling water, pigments, primer paints, fungicides, wood preservatives, leather-tanning…Major pollution sources: industrial and waste treatment discharges…Species in the environment: Cr(III), Cr(VI) …Toxicology of Cr as Cr(VI) chromate or dichromate: human carcinogen …The story of Erin Brockovich


Quiz TimeHomework, To be assigned

department of chemistry chem1020 general chemistry ***********************************************

Documents

l29chemical toxicologypoisons

poisonous air pollutants

powerful oxidizing agents

chemical substances

chemical bonds

oxygen transport

airoxidizing agents

airthe damage