Synthetic Chemicals

Toxicology

The study of poisonous substances and their effects on humans and other organisms

Toxicologists assess and compare toxic agents, or toxicants, for their toxicity, the degree of harm a substance can

inflict.

Environmental toxicology focuses on effects of chemical poisons released into the environment.

Environmental Toxicology

Studies toxicants that come from or are discharged into the environment, and cause

Health effects on humans Effects on animals

Effects on ecosystems Animals are studied:

For their own welfare

To warn of possible effects on humans

Prevalence of toxic agents in the environment Persistent organic pollutants (POP’s)

Bioaccumulation Biomagnification Epidemiology,

Animal testing, and dose-response analysis Factors affecting toxicity

Synthetic chemicals are everywhere !

•Many thousands have been produced and released.

•Some persist for long time periods or travel great distances.

•Of the 100,000 synthetic chemicals on the market today, very few have been thoroughly tested for harmful effects.

Synthetic Chemicals

People are largely unaware of the health risks of

many toxicants.

Types of Toxicants

Carcinogens: cause cancer

Mutagens: cause mutations in DNA

Teratogens: cause developmental defects

Allergens: cause unnecessary immune response Neurotoxins: damage nervous system

Endocrine disruptors: interfere with hormones

Toxicants Concentrate in Water

Surface water and groundwater can accumulate toxicants.

Runoff from large areas of land drains into water bodies, becoming concentrated.

Toxicants in groundwater or surface water reservoirs used for drinking water pose potential risks to human health.

Airborne Toxicants

Volatile chemicals can travel long distances on atmospheric currents.

PCBs (polychlorinated biphenyls) are carried thousands of miles from developed nations of the temperate zone up to the Arctic, where they

are found in tissues of polar bears and seals.

Persistence

Some chemicals are more stable than others, persisting for longer in the environment.

DDT and PCBs are persistent.

Bt toxin in GM crops is not persistent.

Temperature, moisture, sun exposure, etc., affect rate of degradation.

Most toxicants degrade into simpler breakdown products.

Some of these are also toxic.

(DDT breaks down to DDE, also toxic.)

Poisons move up the food chain

At each trophic level, chemical concentration increases:

biomagnification.

DDT concentrations

increase from plankton to fish to fish-eating birds.

Poisons Accumulate in Tissues

The body may excrete, degrade, or store toxicants.

Fat-soluble ones are stored.

DDT is persistent and fat soluble,

… so builds up in tissues: bioaccumulation.

Bioaccumulated chemicals may be passed on to animals that eat the organism—up the food chain…

The United Nations: “Dirty Dozen”

Persistent Organic Pollutants (POPs)

Compound Year of

entry

Σ world production (tons)

Usage

Aldrin 1949 240,000 insecticide

Chlordane 1945 70,000 insecticide

DDT 1942 3 million insecticide

Dieldrin 1948 240,000 insecticide

Endrin 1951 4,000 rodenticide/insecticide

Heptachlor 1948 ~1,000 insecticide

Hexachlorobenzene 1945 1 to 2 million fungicide

Mirex 1959 No data insecticide

Toxaphene 1948 1.3 million insecticide

PCBs 1929 1 to 2 million industrial chemical

Chlorinated dioxins ? ? never produced purposely

Chlorinated furans ? ? never produced purposely

Toxicity assessment

ED

: Effective dose for 50% of subjects LD

: Lethal dose for 50% of subjects

The therapeutic index

TI = LD⁵⁰ / ED⁵⁰ No drug is 100% safe

LC50 Lethal conc.

Acute & Chronic exposure

Acute - Generally one-time, high level;

symptoms/results are usually (but not always) immediate

Chronic exposure - Usually low-level over period of time; symptoms/results may be delayed for years

Definition

Toxicity test can be divided into three parts:

acute toxicity testing, chronic toxicity testing, and special testing .

Acute toxicity testing: single dosage everyday, to observe its toxic reaction after 7 days and 14 days.

Acute toxicity test: that is lethal in approximately 50% of animals.

Chronic toxicity test: 1 to 2 years. Required when drug is intended to be used in humans for prolonged periods.

Goals of chronic tests are to show which organs are susceptible to drug toxicity.

Physiologic signs, histology, electron microscopy studies.

To identify target organ of toxicity.

Toxic Effects

Metabolic Degradation Excretion

Repair Mechanisms

Routes of Exposure

Inhalation respiratory tract

Absorption tissue or mucus membrane Ingestion direct rout for toxins to enter

Risk Assessment for CoSHH

Identify the hazardous substance(s) eg

◦ Chemicals

◦ Biological materials

◦ Mixtures

◦ Proprietary products

◦ Reaction products and intermediates

(Control of Substances Hazardous to Health Regulations, 2004)

Step 1 :

Risk Assessment

New International Hazard Symbols

Danger Flammable Oxidiser

Step 1 :

Risk Assessment

New International Hazard Symbols

Explosive Corrosive Compressed or

liquefied gas

Step 1 :

Risk Assessment for

New International Hazard Symbols

Aquatic Warning

Toxicity

FLAMMABLE EXPLOSIVE

HARMFUL TO THE ENVIRONMENT

IRRITANT / HARMFUL

TOXIC

HIGHLY FLAMMABLE

CORROSIVE

OXIDISING BIOLOGICAL AGENT

VERY TOXIC