Environmental toxicology
Milena Černá
Institute of General Hygiene
Definition of toxicology
Toxicology is, scientific discipline focused chemical
and biological interactions of environmental
stressors with human being.
The history of toxicology is very long – the poisons
were studied and used in many ancient cultures.
Poisons were used in policy or as tools for solving
private problems.
Taxus (yew-tree) – toxon (bow) – toxicon (poison for
arrow)
History of toxicology
Ancient Egyptians – hydrogen cyanide from peach
stone
Sokrates – decoct from Conium maculatum (hemlock)
Nero – arsenic
Claudius and Aggripina – intoxication with mushrooms
Theophrastus Bombastus von Hohenheim (1493-1541)
known as Paracelsus
Dosis facit venenum (the doce alone makes a thing
poisonous)
Further development of toxicology
Scientific development in the frame of chemistry
and pharmacy
Occupational toxicology – carbon monooxide
poisoning in mines, in metal-processing industries
Italian physician Bernardo Ramazzini (1633-1714)
described the diseases of workers (1700) do
precisely that the text remained a textbook of
occupational hygiene for a century
Percival Pott (1714-1788) described soot as the
cause of skin cancer on the scrotum of London
chimney sweeps.
Diversification of toxikology
General t. – a study of common regularities, theories and
conseqiences: mechanisms of effects,
biotransformation, exposure, interactions of chemical
compounds, etc. Development of methods to study
toxici effects.
Special t. – description, study and evaluation of toxic
effects of particular chemicals and preparations.
Environmental t. – (entox) is a multidisciplinary field of
science concerned with the study of the harmful effects
of various chemical, biological and physical agents on
living organisms
Ecotoxicology – subdiscipline of environmental t.
investigating the effects of toxicants at the ecosystem
level
Analytical t. – detection of chemicals in the environmental
media and human body
Diversification of toxikology (cont.)
Experimental t. – study of effects of chemicals by
means of in vivo or in vitro experiments.
Clinical t. – study of effects of chemicals on human
being
Industrial t. – examines the toxic effects of raw
material, products, interproducts and waste in
industry. Importants for occupational medicine.
Forensic t. in forensic medicine
Military t. – chemical warfare agents and their
antidota
Predictive t. – an assessment of potential effects by
meant of alternative methods (quantitative structure
– activity relationship QSAR, in silico)
Pharmacological toxicology
Health effects of chemical compounds
Acute – subacute- chronic toxicity
Systemic toxicity (organ-specific)
Stochastic – nonstochastic (thresholds) effects
Delayed effects ) – mutagenic (genotoxic)
- carcinogenic
- allergenic
Environmental toxicology
Toxicological adverse effects of environmental
toxicants depend on the exposure
Exposure is defined as contact over time and space
between a person and an environmental toxicants
Dose is the amount of toxicant entering the human
body.
Exposure ways are:
• Inhalation
• Ingestion
• Transport through skin and mucosa
• transplacentally
Fate of chemical in human body
ADME
• Absorption
• Distribution
• Metabolism (biotransformation)
• Excretion
ADME
Absorption - Resorption
depends on the exposure way
on the bioavailability of compound
Bioavailability – the rate and extent to which a
substance becomes available to target organ/cell
on the distribution of compound in body
compartments
ADME
Toxicokinetics (pharmacokinetics)
– what the body does with the substance (absorption,
distribution, biotransformation, excretion)
Clearence – measure of the body´s ability to eliminate
a substance
Age- or gender- related dependency of kinetics
Effect of low doses in humans
Toxicology
Toxicodynamics (pharmacodynamics)
-what the substance does to the body (effects and
mechanisms of actions):
Stochastic or non-stochastic effect (threshold)
Organ-specific toxic effect
Age-related differences in kinetics (children, elderly)
Acute – subchronic – chronic effect
Delayed effect: mutagenic, carcinogenic, teratogenic,
allergenic
Xenobiotic metabolism
Biotransformation:
Phase I: oxidation, reduction, hydrolysis (more
water soluble interproducts)
Phase II: conjugation
Biotransformation via intestinal microflora:
reduction, deconjugation
Enzymes implicated in xenobiotic metabolism
Phase 1
P450-dependent monooxigenases (CYP)
Flavin containing monooxygenases (FMO)
Monoamine oxiases (MAO)
Cyclooxygenases (COX)
Phase II
Glutation-S-transferases (GST)
UDP-glucuronosyltransferases (UGT)
Sulfotransferases (SULT)
Acetyltransferases (AT)
Acyl-CoA aminoacid N-acyltransferases
methyltrasferases
Factors influencing xenobiotic metabolism:
Induction of expression of the enzyme protein
(upregulation)
Repression of the expression of the enzyme
protein (downregulation)
Direct activation of the enzymatic function
Direct inhibition of the enzymatic function
Genetic polymorphisms
Cytochromes P450
Interspecies differences
Ethnical differences
Gender-related differences
GST
Six families (GSTM, GSTT
N-acetyltransferases (NAT-1, NAT-2)
NAT-2 slow acetylator, rapid acetylator
Free radicals
Chemical entities with one or more unpaired electrons.
Biological efects: reaction with virtually all molecules
in living cells.
Cytotoxic and genotoxic effects
Damage of cellular membranes,
Interaction with proteins,
Interaction with lipids (lipid peroxidation)
The degree of damage will depend on the balance
between radical formation and radical inactivation
Genetic toxicology
Genotoxic carcinogens
DNA interactions
DNA adducts and mutations
DNA repair
Tumor iniciators – stochastic effect
Tumor promotors – threshold effect
Complete and incomplete carcinogens
Contribution of environmental factors to the etiology of cancer
(Doll and Peto, 1981)
Factor
Mean estimate %
Ranges
Smoking
30
25 - 40
Nutrition
35
10 - 70
Alcohol
3
2-4
Sexual behavior
7
1 - 13
Occupat. exp.
4
2-8
Food additives
1
-5 - 2
Environ. pollution
2
1-5
Industrial products
1
1-2
Medical drugs, therapy
1
0,5 - 3
10?
1-?
Geophys. factors
3
2-4
Unknown
3
?
Infection
Detection of carcinogenic characteristic of
the environmental factors
Epidemiological study
Testing on animals
In vitro tests
Classification of carcinogenicity
(IARC, US EPA)
Chemical carcinogens
Type
Example
Genotoxic: Direct
Indirect
Alkylating agents
PAHs, Aromatic amines,
nitroarenes, mycotoxins
Inorganic carcinogens
Ni, Cr, Cd, As
Epigenetic (nongenotoxic):
Cytotoxic
Mitogens, proliferating agens
Solid bodies, fibres
Asbestos
Tumor promotors
TCDD, DDT
Hormones
Estradiol, DES
Immunosuppressant
Azathioprine, cyclosporin A
Peroxisome proliferators
Phthalates, clofibrate
IARC Monographs, 2004
Group 1 – carcinogenic to humans
Elements and their compounds:
Arsenic, beryllium, Cadmium,
Chromium VI, Nickel.
Drugs (cytostatics):
azathioprine, chlornaphazine,
cyclosporin, cyclophosphamide,
methyl-CCNU, Melphalan,
Methoxypsoralen, Myleran,
MOPP.
Hormonals:
diethylstilbestrol, oestrogens,
oral contraceptives,
tamoxifen*.
Organics:
4-aminobiphenyl, benzene,
benzidine,
bischlormethylether,
ethylene oxide, mustard gas,
2-naphtylamine, 2,3,7,8-TCDD,
thiotepa, vinyl chloride,
formaldehyde
Miscelaneous:
aflatoxins, asbestos, radon,
silica (inhaled in the form of
quartz or cristobalite from
occ. sources), talc with
asbestiform fibres, solar
radiation
Group 1 – carcinogenic to humans continued
Biological factors:
Epstein-Barr virus,
Hepatitis B, C (chronic
inf.), HIV 1, Human
papilomavirus type 16,18,
Helicobacter pylori,
Opisthorchis viverrini,
Schistosoma
haematobium.
Mixtures:
Alcoholic beverages,
analgesic mixtures
with phenacetin, betel
quid with tobacco,
coal-tar pitches, coaltars, mineral oils,
salted fish (Chinese
style), soots, tobacco
products, tobacco
smoke, wood dust.
Group 1 – carcinogenic to humans –(cont.)
Exposure circumstances:
Aluminium production,
Auramine manufacturing,
Boot and shoe manufacture
and repair, Coal
gasification,
Coke production,
Furniture and cabinet
making,
Haematite mining (radon)
Iron and steel founding,
Isopropanol manufacturing,
Magenta, manufacture,
Painter (occup. exposure),
Rubber industry,
Occ. exp.to strong inorganic
acid mists containing
sulfuric acid
Workplace carcinogens
Agent
Aromatic amines
Arsenicals
Tumor location
Urinary bladder
Lung, skin
Asbestos
Benzene
Diesel exhaust
Nickel
Vinyl chloride
Hair dyes
Mineral oils
Lung, mesothelioma
Industry
Rubber
Glass, metals,
pesticides
Insulation
Leukemia
Solvent, gasoline
Lung
Engine operation
Lung
Metals
Liver (angiosarcoma) Plastics
Bladder
Hairdressers
skin
Metals
Monitoring of exposure to environmental
chemicals
Determination of environmental pollutants in
environmental media (air, water, food, soil)
Calculation of exposure based on the concentration of
chemical and amount of environmental media comming to
the body through 24 hours.
Human biomonitoring – biomonitoring of exposure
Measurement of chemical or its metabolites in human
body fluids
External exposure – internal dose – biol. target dose – biol.
Effect – impaired biol. function - clinical disease
Biomarkers of exposure
■ compound itself or its more polar metabolites
(example - Pb in blood)
■ volatile compounds in expired air
■ covalent adducts with macromolecules (DNA, proteins
– hemoglobin, albumin)
Biomarkers of early biochemical effect
Biomarkers of bioactive dose
■ delta-aminolevulic acid in urine: increase in Pb
exposure
■ acetylcholinesterase activity in erytrocytes:
decrease after the exposure to organophosphates
■ specific antibodies in plasma after the exposure to
alergens
Biomarkers of adverse effects:
■ liver enzymes in plasma: increase after the
exposure to hepatotoxic compounds
■ -microglobulin in urine: renal damage after the
exposure to Cd
Biomarkers of susceptibility
Biotransformation enzymes with polymorphisms:
■ acetyltransferases
■ P450
■ glutathiontransferases
■ epoxidhydrolases
Example.: Carcinogenic aromatic amines (benzidin etc.) are
metabolic activated by means of flavinmonooxygenases to
nitrosoarenes which then react with DNA. The detoxicated
metabolic pathway is acetylation by means of acetyltransferases.
Persons who are low acetylators are in the increased risk of
urinary bladder carcinoma.
Dose – response curves
Stochastic effect –without threshold.
Probability of adverse effect increases with the dose
since the beginning (mutagenicity, carcinogenicity)
Non-stochastic effect – with threshold.
Effect can be observed when the dose reaches
certain level.
Biological exposure tests in CR / Legislation
limit values BET in urine
Biological exposure tests in CR / Legislation
limit values of BET in urine (cont.)
Biological exposure tests in CR / Legislation
limit values in blood
Metals
Toxic metals:
Cadmium, Lead, Mercury, Arsenic
Essential metals:
Copper
Zinc
selenium
Mercury
Elemental mercury vapor.
Acute toxicity: inhalation - rare, pneumonia, emphysema, orally – GIT
problems
Chronic: akrodynia, nephrotic syndrome, gingivitis, tremor
mercurialis, erethism, polyneuropathy
Mercury salts:
Acute: Orally erosive effect, hemorrhagic vomiting, renal damage
Chronic (see vapor)
Methylmercury:
Acute: CNS effect; paresthesia, ataxia, loss of sensation, difficulties
with speaking and hearing.
Chronic: similar to acute
Teratogenic, mutagenic, carcinogenic effects
Lead
Occupational exposure: battery manufacturing, lead
smelters
Acute toxicity of inorganic lead:
Intestinal colics, nausea, constipation, diarrhea, abdominal pain,
capillary spasm, irritation, encephalopathy, ataxia
Chronic toxicity of inorganic lead:
Affect hematopoetic system (micro-or normocyte anemia based on
the interaction with hemoglobin synthesis in bone marrow).
GIT (abdominal pain, constipation, diarrhea),
Organic lead: Central and peripheral nervous system (loss of
concentration, impaired memory, pasing through placenta, behavioral
problem in infants)
Correlation between blood lead level
and effects
B-Pb mg/l
Effect
>150
Inhibition of -aminolevulinic acid
dehydratase
100-200
Impaired intellectual and cognitive
development of children
200-600
Increased erythrocyte protoporphyrin conc.
>400
Increased urinary coproporphyrin and -ALA
concentration
500-600
Chronic encephalopathy in children
>800
Chronic encephalopathy in adults
600-800
Peripheral neuropathy
700-1000
Impaired renal function
800-3000
Acute lead encephalopathy
Cadmium
Very long biological half-life (10 – 30 y)
Occupational exposure to Cd dust or aerosols
Inhalation exposure – 40 to 50 % of inhaled Cd is
absorbed. Cigarette smoke
Absorption from GIT is about 2 – 8 % (higher
resorption in women)
Albumin-bound Cd – liver - metalothionein
Cd does not cross substantially the placenta barrier
Renal cortex is the target organ
Cadmium – adverse health effects
Carcinogen for human (Class 1 according to IARC)
Kidney dysfunction (proteinuria, increased excretion
of albumins, globulins, 2-microglobulins
Osteoporosis, interference with calcium metabolism
Itai-Itai disease (osteomalacia)
Hypertension??
Aromatic hydrocarbons
Benzene, toluene, xylene
Benzene:
According to ILO convention in 1972, the use of
benzene is prohibited if suitable substitute products
are available
Inhalation is dominant route of human exposure
Occupational exposure: petrochemical industry, petrol
station
Environmental exposure: ambient air, indoor air,
smoking
Benzene – kinetics and health effects
Inhalation and dermal absorption,
Because of lipophilic character the highest level is in
organs with the high lipid amount.
Acute toxicity:
Mild form - dizziness, excitation, euphoria, headache,
nausea, vomiting
Severe form – visual disturbance, shallow and rapid
pulse, breathlessness, profound CNS depression, loss
of consciousness, collapse
Benzene – chronic and delayed effects
Hematopoetic disorders:
Erythropoetic system: aplastic anemia, erythroblastic myelosis,
acute erythremia
Leukopoetic system: leukopenia, leukemia, lymphocytosis
Thrombopoetic system: thrombocytopenia
Carcinogenicity (leukemia)
Immunotoxicity
Halogenated hydrocarbons
Use:
Lipophilic compounds, mostly used as solvents:
dichloromethane, trichloroethylene, trichloroethane
(chloroform), tetrachloroethylene (perchlorethylene).
Vinyl chloride = monomeric constituent for PVC (liver
angiosarcoma)
Kinetics: inhalation absorption, extensive
biotransformation
Halogenated hydrocarbons
Adverse health effects:
Irritation, anesthetic effect, depressive effects on
CNS
Damage to parenchymal organs (liver, kidney)
Mutagenicity, potential carcinogenicity
Reproductive and developmental toxicity
Organophosphate insecticides
Large and well-defined class of pesticides
The toxicity is the result of excessive stimulation
of cholinergic nerves based on the ability to inhibit
acetylcholinesterase.
Rapid hydrolysation of acetylcholin at the
postganglionic membrane of the synapse.
Organophosphates bind more tightly to the
enzymes active site that does acetylcholine.
Accumulation of acetylcholine at the receptor
Organophosphate insecticides
Symptoms of toxicity result from cholinesterase
inhibition:
Headache, giddiness, nervousness, blurred vision,
weakness, nausea, cramps, diarrhea.
Sweating, miosis, vomiting, cyanosis, convulsions, coma,
cardiac arrhythmia, respiratory failure.
Delayed neuropathy
Therapy: atropine
Carcinogens on workplace
Cytogenetic analysis:
1) Biomarker of exposure to genotoxic
carcinogens
2) Biomarker of early adverse effect
(reversible)
Chromosomal aberrations and cancer risk
Three epidemiologic studies:
Nordic countries – Italy – Czech Republic
found a significant association between the number
of chromosomal aberrations in population and the
risk of cancer
Elimination or reduction of occupational exposure is
therefore very important to prevent
occupationally-related neoplasms
Environmental toxicants - prevention
Identification and reduction of sources of
pollutants (industry, burning, traffic etc.)
Monitoring of environmental pollutants (long term
time trends, preventive measures according to
current situation)
Health Risk Assessment approach
Legislation
Education