ENVIRONMENTAL CHEMISTRY A Global Concern Chem-440 1/19/2016Dr Seemal Jelani1.

ENVIRONMENTAL CHEMISTRY A Global Concern

Chem-440

05/03/23 Dr Seemal Jelani 1

CHAPTER 4

ENVIRONMENTAL HEALTH AND TOXICOLOGY


Health Hazards

• Infectious Diseases• Respiratory diseases

– pneumonia– tuberculosis– influenza– whooping cough


•Malaria•Parasitic Nematodes•Schistosomiasis•Onchocerciasis (river blindness)•Trachoma•STD’s


Toxic Chemicals• Irritants• Respiratory fibrotic agents• Asphyxiants• Allergens• Neurotoxins• Mutagens• Teratogens• Carcinogens05/03/23 Dr Seemal Jelani 5

• Natural and Synthetic Toxin• Physical Agents

– radiation• Trauma

– stress• Diet


Toxic Chemicals• Hazardous chemicals – dangerous (eg, flammables,

explosives, irritants, acids, etc)• Toxins – poisonous, kills cells• Allergens – activate the immune system• Mutagens – chemicals or radiation that

damage/alter genetic material (DNA)• Teratogens - chemicals or other factors that cause

abnormalities during embryonic growth & development

• Carcinogens – substances that cause cancer (out of control cell growth)


Chemical Hazards and Toxicology

• Dose and response– LD5O factor

• Acute effect• Chronic effect• Types

– toxic substances– hazardous– carcinogens– mutagens– teratogens05/03/23 Dr Seemal Jelani 8

What is a LD50

• LD stands for "Lethal Dose". • LD50 is the amount of a material, given all

at once, which causes the death of 50% (one half) of a group of test animals.

• The LD50 is one way to measure the short-term poisoning potential (acute toxicity) of a material.


• Toxicologists can use many kinds of animals but most often testing is done with rats and mice.

• It is usually expressed as the amount of chemical administered (e.g., milligrams) per 100 grams (for smaller animals) or per kilogram (for bigger test subjects) of the body weight of the test animal.


• The LD50 can be found for any route of entry or administration but dermal (applied to the skin) and oral (given by mouth) administration methods are the most common.


Why study LD50's?

• Chemicals can have a wide range of effects on our health.

• Since different chemicals cause different toxic effects, comparing the toxicity of one with another is hard.

• We could measure the amount of a chemical that causes kidney damage, for example, but not all chemicals will damage the kidney


• . We could say that nerve damage is observed when 10 grams of chemical A is administered, and kidney damage is observed when 10 grams of chemical B is administered.

• However, this information does not tell us if A or B is more toxic because we do not know which damage is more critical or harmful.


• Therefore, to compare the toxic potency or intensity of different chemicals, researchers must measure the same effect.

• One way is to carry out lethality testing (the LD50 tests) by measuring how much of a chemical is required to cause death.

• This type of test is also referred to as a "quantal" test because it is measures an effect that "occurs" or "does not occur".

•


What are some other toxicity dose terms in common usage?

• LD01 Lethal dose for 1% of the animal test population

• LD100 Lethal dose for 100% of the animal test population

• LDLO The lowest dose causing lethality• TDLO The lowest dose causing a toxic effect•


Acute and Chronic

• The difference between acute and chronic when used for diseases is that acute means extremely severe pain, brief and dangerous disease whereas chronic refers to a medical condition that lasts over a long period


What is Environmental toxicology ?

‘Ecotoxicology’‘Study of impacts of pollutants on the structure and function of ecosystems’ Manmade poisonous chemicals and their effect on the environment


Environmental toxicology is highly interdisciplinary field


• Xenobiotic

– A chemical that is foreign to the biosphere i.e. is not produced by a natural biological or abiotic source

– Also called anthropogenic, man-made, synthetic, pollutant, contaminant, recalcitrant, persistent, and toxicant


Movement, Distribution and Fate of Toxins

• Solubility• Bioaccumulation• Biomagnification• Persistence• Chemical Interactions


One of most important characteristics in determining the movement of a toxin.•Chemicals are divided into two major groups:

• Those that dissolve more readily in water.• Those that dissolve more readily in oil.

– Water soluble compounds move rapidly through the environment, and have ready access to most human cells.

Solubility –



Exposure and Susceptibility

• Airborne toxins generally cause more ill health than any other exposure.– Lining of lungs easily absorbs toxins.

• Largest toxin exposure reported in industrial settings.

• Condition of organism and timing of exposure also have strong influences on toxicity.


Exposure Routes


Bioaccumulation and Biomagnification

• Cells have special mechanisms for Bioaccumulation - Selective absorption and storage.– Dilute toxins in the environment can build to

dangerous levels inside cells and tissues.• Biomagnification - Toxic burden of a large

number of organisms at a lower trophic level is accumulated and concentrated by a predator at a higher trophic level.


Bioaccumulation and Biomagnification

• Cells have special mechanisms for Bioaccumulation - Selective absorption and storage.– Dilute toxins in the environment can build to

dangerous levels inside cells and tissues.• Biomagnification - Toxic burden of a large

number of organisms at a lower trophic level is accumulated and concentrated by a predator at a higher trophic level.


Persistence

• Some chemical compounds are very unstable and degrade rapidly under most conditions, thus their concentrations decline quickly after release.

• Others are more persistent. – Stability can cause problems as toxic effects may be

stored for long period of time and spread to unintended victims.

• (DDT)


Persistence

• Persistent Organic Pollutants (POP’s)– Polybrominated diphenyl ethers (PDBE)– Perfluorooctane sulfonate (PFOS) and

Perfluorooctanic acid (PFOA).– Phthalates– Bisphenol A (BPA) – Atrazine


Chemical Interactions

• Antagonistic Reaction - One material interferes with the effects, or stimulates the breakdown, of other chemicals.

• Additive Reaction - Effects of each chemical are added to one another.

• Synergistic Reaction - One substance exacerbates the effect of the other.


• Environmental toxicology depends on

– Lab work• Effects of toxicants on biochemistry and

physiology

– Field work• Field observations of reproduction and survival in

polluted vs. non-polluted sites


Minimizing Toxic Effects

• Metabolic Degradation• Excretion• Repair Mechanisms


Mechanisms for minimizing toxic effects

• Every material can be poisonous under certain conditions.– Most chemicals have a safe threshold under

which their effects are insignificant.• Metabolic Degradation

– In mammals, the liver is the primary site of detoxification of both natural and introduced poisons.


Excretion and Repair

• Effects of waste products and environmental toxins reduced by eliminating via excretion.– Breathing– Kidneys

• Urine

• Tissues and organs often have mechanisms for damage repair.– Any irritating agent can be potentially carcinogenic.


Measuring Toxicity

• Animal Testing• Toxicity Ratings• Acute vs. Chronic Doses and Effects• Detection Limits


Measuring toxicity

• Animal Testing– Most commonly used and widely accepted toxicity

test is to expose a population of laboratory animals to measured doses of specific toxins.• Sensitivity differences stance a problem.

– Dose Response Curves– LD50 - Dose at which 50% of the test

population is sensitive.


Toxicity Ratings

• Moderate toxin takes about (1) g/kg of body weight to produce a lethal dose.– Very toxic materials require about 10% of that

amount.• Extremely toxic materials require 1%

of that amount.– Supertoxic chemicals can be lethal in a

dose of a few micrograms.


Toxicity Ratings

• Many carcinogens, mutagens, and teratogens are dangerous at levels far below their direct toxic effect because abnormal cell growth exerts a form of biological magnification.


References

• users.ipfw.edu/.../cha...• Indiana University – Purdue University Fort

Wayne


ENVIRONMENTAL CHEMISTRY A Global Concern Chem-440 1/19/2016Dr Seemal Jelani1.

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