lecture 3: chemical toxicology - lunds universitet courses/riskkursen...lecture 3: chemical...
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Environmental issues and hazards in the chemical research laboratory
Richard Johnsson
Lecture 3: Chemical toxicology
Lecture 3 - outline1. Introduction2. Toxicological concepts3. Toxicity4. Acute toxicity5. Toxicological testing6. Uptake and distribution of chemicals7. Metabolism - Phase I8. Metabolism - Phase II9. Excretion10.Electrophiles11.Examples (reference only)
1. Introduction
• What is a poison? Alle Ding sind Gi!, und nichts ohn Gi!; allein die Dosis macht, da ein Ding kein Gi! ist.
! All things are poison and nothing is without poison, only the dose permits something not to be poisonous.
Paracelsus, 1538
1. Introduction
• What is a poison? Alle Ding sind Gi!, und nichts ohn Gi!; allein die Dosis macht, da ein Ding kein Gi! ist.
! All things are poison and nothing is without poison, only the dose permits something not to be poisonous.
Paracelsus, 1538
! ! more than 1 liter of water each hour gives serious problems....
1. IntroductionCompoun d Lethal dose
Ethanol 700 g
Salt 300 g
Acetyl salicylic acid 100 g
D D T 8 g
Strycnine 150 mg
Nicotine 100 mg
Arsenic (III) oxide 100 mg
Tetrodotox in 10 mg
Dimethyl mercury 0,1 mg
2,3,7,8-tetrachlorodibenzodioxin e 0,1 mg
Botulinum toxin 0,001 mg
OCOOH
O
N
N
CCl3
Cl Cl
NO
N
H
O
H
H
O
OCl
Cl
Cl
Cl
As2O3
NaCl
CH3-Hg-CH3
OH
etanol
2. Toxicological conceptsa) Acute or chronic effects
Acute effects are observed immediately or shortly after an exposure at one single occasion or multiple doses within 24 h.
Subacute effects means exposure during less than 1 month
Subchronic means exposure over 1-3 months
Chronic effects are the result of a continous exposure during at least 3 months
Time
2. Toxicological conceptsa) Acute or chronic effects
example:
acute effect: narcotic
chronic effect: leukemia
2. Toxicological conceptsb) Reversible or irreversible effects
Reversible effects disappear if the exposure stops
-example: narcotic effect of solvents
Irreversible effects never disappear
-example: damages to nerves, tumors
2. Toxicological conceptsc) Local or systemic effects
Local effects are observed on the part of the body that first came in contact with the chemical
example: acid burns
Systemic effects require tha the chemical is uptaken and distributed to the target organ
Target organs: central nervous systemcirculatory systemthe liverthe kidneysthe lungsthe skin
musclesbones
often
rarely
2. Toxicological conceptsd) Total effect
It is difficult to estimate the total effect of a mixture of chemicals!
2. Toxicological conceptsd) Total effectIndependent effect - two compounds are toxic independent of each other! ! ! ! 2 + 2 = 2Additive effect - the total effect is the sum of the the two independent effects example: toluene + xylene!! 2 + 2 = 4
Synergistic effect - the united effect is stronger than the additive effect example: ethanol + carbon tetrachloride 2 + 2 = 8
Potentiating effect - one of the compounds is not toxic in itself but enhance the effect of another compound ! ! 0 + 2 = 4example: 2-propanol + carbon tetrachloride
Antagonistic effect - one compound opposes the effect of another 2 + 2 = 1-functional: one raise blood pressure and one lowers it -chemical: two compounds neutralize each other -dispositional: one compound lowers the uptake of another -receptoric: the two compounds bind to the same receptor
It is difficult to estimate the total effect of a mixture of chemicals!
3. Toxicitya) Physical state
The purity of a compound is important to evaluate the toxicity (impurities can have very strong effects)
The physical state of a compound cam influence the toxicity: -vapor or aerosols are easily uptakne by the lungs -some solids are not easily dissolved and thus not toxic -finely ground arsenic oxide is much more toxic compared to granlulates -solution can be uptaken by the skin
example: mercury
3. Toxicityb) Exposure
The route of exposure is very important for the toxicity
intravenous (ivn) - injected in a vein
inhalated (ihl)
intraperitoneal (ipr) - injected in the peritoneal cavity subcutaneous (scu) - injected into the skin
oral (orl) - swallowed
dermal (d) - applied on the skin
3. Toxicityc) The victim
-Sex-related differences! there are usually differences between males! and females
-Age-related differences! in general, infants (undeveloped systems) and! old people (poor immune system) are more! sensitive to toxic chemicals
a) Dose-response relationships
4. Acute toxicity
Number of deaths (%)!
log Dose log Dose
Sum of deaths (%)
LD50
4. Acute toxicitya) Dose-response relationships
!LD50 -the dose that will kill 50% of the exposed individualsLD10 -the dose that will kill 10% of the exposed individualsLDlow -the lowest dose known to cause deathLC50 -the concentration (mg/m3) that will kill 50% of the exposed individualsTDx -the dose that will give a toxic effect in X% of the exposed individuals
ex. LD50 = 25 mg/kg (or, rat)
economical and ethical issues (more than 100 animals for a normal test)
4. Acute toxicityc) non-specific toxicity -the toxicity is dependent on the lipophilicity
!
logP
toxicity
4. Acute toxicityd) selective toxicity -the toxicity is selective to one species or one organ example: penicillin, DDT!
5. Toxicological testingRisk assesment! -Comparison of the effects on different organisms (animals, cells....)
and men
! -Dose-response relationships
! -Weighing the risks against use, pleasure etc
!
6. Uptake and distributionuptake
distribution
excretion
gastro-intestinal
tract
skin lungs intravenous other(mucous
membranes)
faeces urine exhaled air secretion
circulatory system
liver
gall
kidney lung
bladder
portal vein
glands interstitial liquid
fat bone other tissue
6.1 By the skin
epidermis
dermis
blood vessels
Uptake of chemicals by the skin depends on:-the general condition (brusies etc)-the thickness (arms thin, palms thick) -the water content of the epidermis (gloves)
Many compounds enter easily by the skin (dichloromethane, methanol)
DMSO increase the permeability for other compounds (used in veterinary medicine)
6. Uptake and distribution
6.2 By the gastro-intestinal tract
mechanical degradation
chemical degradation
pH = 2
enzymatic degradation bacterial
degradation
Total surface 300 m2 (a tennis court)
6. Uptake and distribution
6.2 By the gastro-intestinal tractThe absorption takes place in villi
Toxic compounds sometimes fit into transport systems
examples:
Some compounds pass through the system
example:
-thallium and cobalt fit into the iron transporter
-lead fit into the calcium transporter
-elemental mercury
6. Uptake and distribution
6.3 By the lungs-100 m2 (a badminton court)-the exchange takes place in the alveoli where the distance between the blood and the air is only 1 μm
6. Uptake and distribution
6.3 By the lungsAerosols are particles or droplets that are sufficientlysmall to hover in the air! Dust (solid particles)! Fume (particles formed by combustion)! Smoke (particles formed by combustion of! organic material)! Fog, mist (liquid droplets)! Smog (particles from car exhausts)
6. Uptake and distribution
6.3 By the lungs
The uptake is dependent on size-small particles (< 1 μm) goes down in the alveoli and cancause e.g. silicosis or asbestosis-bigger particles are stopped in the mucus membranesand transported by the mucociliary escalator:
6. Uptake and distribution
6.3 By the lungs
-Hydrophilic gases are usually absorbed by the mucusmembranes
-Very reactive gases (HCl, NH3, SO2) are irritating andblocks respiration and can therefore not be inhaled inlarger quantities
-Chemicals with intermediate reactivity and lipophilicity(phosgene, ozone, isocyanates) can be inhaled and giveinjuries at all levels in the lungsThey harm the epithelial cells (by lipid peroxidation) so thatthese are leaking fluid - pulmonary oedema (internaldrowning) which takes up to 48 h to develop
6. Uptake and distribution
6.4 Bioaccumulation
Chemicals that are relatively stable and not rapidly converted may be absorbed by another organism that feeds on the first. (biomagnification)
example: polyhalogenated aromatic hydrocarbons (PCB)
Chemicals can be concentrated in organisms (bioconcentration) for example in fat
6. Uptake and distribution
uptake
distribution
excretion
gastro-intestinal
tract
skin lungs intravenous other(mucous
membranes)
faeces urine exhaled air secretion
circulatory system
liver
gall
kidney lung
bladder
portal vein
glands interstitial liquid
fat bone other tissue
6. Uptake and distribution
6.5 AccumulationAbsorbed compounds are distributed by the blood but aresometimes accumulated in target organs.
Brain, nerves, fatty tissue: lipophilic compounds
Bones: inorganic lead, barium, strontium, fluorine, tin
Liver: mercury vapour, manganese, organic lead
Kidneys: cadmium, mercury
Thyroid gland: iodine
Hair: Arsenic
6. Uptake and distribution
6.6 Biological barriersThe endothelial cells of the blood capillaries in the brain are held together and are surrounded by glial cells. This makes the passage of compounds difficult and constitute the blood-brain barrier.
Problem: elemental mercury is lipophilic enough to pass the blood-brain barrier. If it is oxidized to Hg2+ it will not get out again...
The placenta regulates the flow of chemicals to the fetus
6. Uptake and distribution
7. Metabolism - Phase I
Properties suitable for excretion of toxic compounds:
Is the compound useful in the normal metabolism?
If not, it has to be excreted in order not to be accumulated.
Low molecular weight Exhaled fromthe lungs
metabolism break bonds or converts functional groups
Properties suitable for excretion of toxic compounds:
Is the compound useful in the normal metabolism?
If not, it has to be excreted in order not to be accumulated.
Molecular weight > 500 Excreted with the bile
the compound is conjugated with some endogenous compound
7. Metabolism - Phase I
Properties suitable for excretion of toxic compounds:
Is the compound useful in the normal metabolism?
If not, it has to be excreted in order not to be accumulated.
High water solubility Excreted with the urine
functional groups are converted or the compound is conjugated
with polar compounds
7. Metabolism - Phase I
Biotransformation is not equal to detoxification!
The metabolism will effect the biological activity of a compound
7. Metabolism - Phase I
9.1 By the lungs-volatile compounds are exhaled by the lungs
9.2 By the liver-The liver metabolize compoundsSome compounds (e.g. mercury) are however excretedby bile which contains amphiphathic compounds suchas cholesterol and bile salts-The liver is the normal excretion way for compoundswith a molecular mass of more than 500 g/mol inhumans (lower for rats)-Compounds excreted by the liver can be uptaken bythe gastro-intestinal tract....
9. Excretion of chemicals
The kidneys is the most important excretion way
Some animals concentrate the urine (e.g. rats)
9. Excretion of chemicals
Milk is the major excretion way for DDT in breast-feeding women!
Cl Cl
ClClCl
9. Excretion of chemicals
• Electrophiles are very reactive and can destroy DNA
10. Excretion of chemicals
OO
smallrings
carbonyl-groups
isothiocyanates
NC
S
• Electrophiles are very reactive and can destroy DNA
• We have a safety system
10. Excretion of chemicals
HO NH
HN
OHNH2
O O
O
OSH
glutation
• Electrophiles are very reactive and can destroy DNA
• We have a safety system• Glutation
10. Excretion of chemicals
HO NH
HN
OHNH2
O O
O
OSH
glutation
• Electrophiles are very reactive and can destroy DNA
• We have a safety system• Glutation
10. Excretion of chemicals
NC
S
S
6-metyltiohexyl-isotiocyanat
NC
S
allylisotiocyanat
• Isothiocyanates
10. Excretion of chemicals
• Carbonyl compounds• Teargas -developed to be irritating but rather safe
kloracetofenon, CN(0.3-1.5 mg/m3)
OCl
10. Excretion of chemicals
• Small rings• Mustard gas
very strong electrophile that affect the skin, eyesand the lungs
10. Excretion of chemicals
• Small rings• Mustard gas
very strong electrophile that affect the skin, eyesand the lungs
10. Excretion of chemicals
• Small rings• Mustard gas
very strong electrophile that affect the skin, eyesand the lungs
ClS
Clsenapsgas
10. Excretion of chemicals
• Small rings• Mustard gas
very strong electrophile that affect the skin, eyesand the lungs
ClS
Clsenapsgas
ClS
episulfoniumjon
10. Excretion of chemicals
• Small rings• Mustard gas
very strong electrophile that affect the skin, eyesand the lungs
10. Excretion of chemicals
• Mustard gas-0,02 mg can give blisters -severe damage on skin-humidity give worse effects-infections
10. Excretion of chemicals
... but there is hope!
ClN
Clkvävesenapsgas
Cl
O
OHOHHO
OH NCl
Galactose 6-Mustard (G-6-M)
Cl
10. Excretion of chemicals
11.7 PAH (polycyclic aromatic hydrocarbons)
not a good substrate for epoxide hydrolase
11. Specific examples
11.12 Paracetamol
- limited amount of PAPS available for conjugation -more than a few grams a of paracetamol each day can give liver damage
11. Specific examples
11.15 Acidosis pH of the blood must be regulated to 7.35-7.40pH <7 or >8 is lethalthe blood is buffered and we can excrete CO2 in the lungs and acids with the urine
11. Specific examples