Health Effects of Hazardous Materials

Toxicology

• The study of poison & substances that cause harmful effects to living things

• Toxic effects can range from minor irritation to lethal effects

• Toxins are poisons produced by living organisms (naturally occurring)

• Toxicants are manufactured by humans

Toxicology

• Dose differentiates a poison and a remedy

• Harmful substances are tested on animals

• How a chemical affects genetic material is determined using microorganisms (i.e. bacteria)

Toxicity

• Relative ability of a substance to cause harmful effects to living things

• What quantity does it take to cause damage

• Determined by the chemical makeup, what elements it contains and how they are combined, how readily it is absorbed and how the body metabolizes it

Dose

• Actual amount of chemical that enters and reacts with body systems to cause harm, measured in mass per unit time (mg/kg/day) [milligram of substance per kilogram of tissue per time of exposure]

Exposure

• The amount of toxic chemical our body comes in contact with

• In the air we breathe, the food we eat and our skin is exposed to

• The higher the concentration of the exposure the larger the dose

• The longer the exposure the larger the dose• Protective clothing, equipment and containment

can break the exposure chain

Routes of Exposure

• Dermal absorption

• Oral (Ingestion)

• Inhalation

• Injection

• Inhalation and injection are the most rapid

Dermal

• May cause itching, redness, burns, and solvents may dissolve skin oils leaving skin more susceptible to the absorption of chemicals

• The eyes are especially susceptible to harm

Ingestion

• Not common in the workplace, but issues of facial cleanliness, and eating are concerns

• Is a serious problem at home with children i.e. lead paint chips

Injection

• Greatest risk in medical facilities, or from microbial exposure from nail puncture

• Biological sources of toxins as well; insects, scorpions, spiders and snakes!

We Will Come Back to Inhalation later

Acute toxicity

• Result of short term exposure

• Causes effects that are felt at the time of exposure or soon thereafter

• Most toxic effects don’t cause permanent, irreversible damage (acute & chronic)

Back to toxicity:

Chronic toxicity

• Due to long-term exposure

• Effects appear after months or years of exposure

• Cancer, emphysema, or nervous system damage caused by heavy metals, drugs and alcohol are examples of some chronic health effects

Relative toxicity

• As the dose of a toxic substance increases the harmful effects are generally expected to increase

• Dose-Response Relationship

• LOAEL: Lowest Observable Adverse Effect Level - or the lowest dose that causes a lethal effect

• NOAEL - No Observable Adverse Effect Level

Threshold level

• The lowest concentration that could produce a harmful effect (doesn’t necessarily mean lethal)

• Varies among people exposed depending upon their sensitivity

• A safety factor is used to reduce the allowable concentration to assure no ill effects

Lethal Dose 50 (LD50)

• Dose at which 50% of the test population dies

• Used with dermal and oral toxicity

• LC50 - Lethal Concentration used for toxicity from inhalation

Effects other than death!

• The dose or concentration to produce toxic effects in 50% of the population

• Toxic Dosage 50 - TD50

• Toxic Concentration - TC50

Toxic Effects

• Local Effects – damage caused at the site of first contact with toxicant (eyes, nose, throat, lungs, skin)

• Systemic Effects – Damage done by toxicants carried by the bloodstream to vital organs (liver, kidneys, heart, nervous and reproductive system

Additional factors associated w/ Toxic Effects

• Local effects provide warning that exposure has occurred

• Systemic effects may occur without being felt or sensed

Accumulation

• Chronic, or long term exposure is particularly dangerous because some chemicals build up in the body

• The body does not get a chance to repair itself

Latency Period

• The delay between the exposure and the resultant harmful effects

• Some effects take a long time to manifest themselves

• For some chemicals, effects may not appear for 30 or 40 years– Example is asbestos

Interaction

• Chemicals can combine with toxicants and alter their behavior

Reaction

• Chemicals can combine and form new harmful substances

• i.e. bleach plus drain cleaner = chlorine gas and hydrochloric acid

Additive Effect

• Most health and safety regulations assume that the effects of two chemicals together is equal to the sum of each alone

Antagonism

• A subtractive effect

• One substance reduces the effects of another

Synergism

• Two chemicals can interact within the body to produce an effect different from the effect of either chemical alone, and greater than their sum

• A pack of cigarettes a day or exposure to asbestos increases the chance of lung cancer by six times

• The two exposures together increases one’s risk by 90 times!

Sensitivity

• Individuals vary in how they react• Age, sex, inherited traits, diet, state of health, use

of medication, drugs, alcohol and pregnancy • Includes Allergies

– Some people are affected by a very low dose of a substance (i.e. bee stings)

– Substances that initiate allergic responses are called sensitizers

Respiratory System

• Exchange of gases, oxygen in, carbon dioxide out

• The air we breathe contains 78% nitrogen, 21% oxygen, and 1% trace gases

• Evaporation of liquids such as gasoline or formaldehyde allows them to enter the body

Inhalation (Back to Routes of Exposure)

• Most critical route of entry for most workers handling toxic chemicals

• Quick entry and absorption into the bloodstream

• Ability of some toxic agents to accumulate in the respiratory system itself

• The nose and mouth warm and humidify the air we breathe

• The bronchial tubes lead to alveoli, 300 million tiny air sacs where air is exchanged

• Oxygen is transferred to hemoglobin within the red blood cells of the bloodstream and carbon dioxide is released

Fibrosis

• Some particles cause a build up of fibrous connective tissue – Emphysema is an example of this type of effect

• Hampers the transfer of oxygen to the bloodstream

• Silica from mining, quarrying and pottery glazing, coal dust and asbestos

Inhaling dusts or mists

• Harmful particles may be deposited in the bronchi or the alveoli

• Larger particles may be coughed up but smaller ones remain to cause lung damage

• Particles less than 10 microns penetrate deeper into the lungs causing bronchitis

• Low level long term exposure to smoke, vehicle exhaust can trigger chronic bronchitis and emphysema

• Sulfur dioxide and nitrogen oxides combine with water vapor in the alveoli forming acids

• Ammonia and chlorine gas can dissolve in the mucus of the lungs creating caustic solutions

• Injured lung tissue allows liquids to move from the capillaries into the alveoli causing pulmonary edema

• A person can literally drown in their own fluids

Smell

• Our sense of smell does not always warn of exposure

• Carbon monoxide is odorless

• We can become desensitized to some smells after exposure “olfactory fatique”– Example is H2S (page 81)

Cardiovascular system

• The heart and blood vessels transport oxygen and nutrients to all parts of the body

• The heart and brain are especially sensitive to a lack of oxygen

• Waste products are picked up and carried to the lungs and kidneys

Hemoglobin

• An iron containing protein in red blood cells which carry oxygen to the rest of the body

• Some chemicals (i.e.CO) interfere with this process causing chemical asphyxiation

• Hemoglobin has a much greater affinity for CO than oxygen (300 times greater)

Digestive and Filtration Systems

• Food and water supply the body with materials for maintenance and repair and a source of energy

• The digestive system breaks down large molecules like proteins, complex carbohydrates and fats

Liver

• Processes chemicals found in the blood traveling from the intestine

• Converts foods into other chemicals, destroys toxins, manufactures protein and stores glucose

Liver Disease

• Severe liver disease prevents the organ from rendering toxic chemicals harmless, some which may be normal body chemicals

• When they reach the brain they may cause tremors, confusion or coma

• Some chemicals are stored in the liver

• The liver can destroy toxic substances like alcohol and nicotine

• If exposure is chronic and long term, cells may be damaged and replaced by fibrous tissue, a condition called cirrhosis

Bloodstream and Kidneys

• Our body fluids must maintain a balanced amount of potassium, sodium, chloride and calcium ions and blood acids

• The kidneys maintain this balance and filter out waste materials

• The body must remain hydrated for the kidneys to perform their function

• If the body loses more that 10% of it’s weight in water cells will no longer function and the result is coma & death

• Kidney malfunction causes toxic chemicals to build up in the bloodstream which can result in coma and death

• Kidney cancers are known to be associated with exposure to some industrial chemicals

• Mercury in waterways is converted to methyl mercury, which is ingested by fish

• If the fish are eaten the chemical inhibits the kidney’s ability to balance the body’s chemicals which blocks nerve transmissions, Minimata Disease

Nervous System and Sensory Organs

• Brain, spinal cord are considered the central nervous system and process signals from the peripheral nervous system

• The two types of nerves are motor and sensory

• The autonomic nervous system takes care of all the bodily functions which are in the background

• Pesticides and metals, such as lead and mercury, can interfere with the chemical transfer of information

• This may cause tremors, paralysis, loss of reflexes and/or feeling

• Mercury caused “Mad Hatter’s Disease”

Brain

• Must receive a continuous supply of oxygen

• See chart on page 86 for symptoms of oxygen deficiency

Eyes

• Inflammation and infection of the mucus-membrane lining of the eyelids and eyeballs can be caused by irritation from chemical pollutants

• Acids and bases are corrosive and can penetrate to the interior of the eye very quickly i.e. lime in wall plaster

• Methyl or wood alcohol can cause total blindness from damage to the optic nerve

Skin

• Made up of three layers, the epidermis, the dermis and subcutaneous tissue

• The dermis, or live skin, contains blood vessels, nerves, nerve receptors, hair follicles and sweat and oil glands

• The skin protects against the invasion of bacteria, the sun’s rays and the loss of moisture

• It senses pressure, pain and temperature and regulates the body’s temperature through blood flow and sweat glands

• Corrosive chemicals can dissolve naturally protective coatings and/or react with the skin

• Some chemicals, like solvents that` dissolve fats, are absorbed directly into the bloodstream

Carcinogenicity

• The tendency for cancer to occur

• Cancer is the uncontrolled growth and spread of abnormal cells

• It is first indicated by malignant tumors which tend to invade the surrounding tissue and then spread to distant sites within the body

• During the 1970’s the public became aware of the potential for chemicals to cause cancer

• Studies of chemicals indicate that only a small number in commercial use cause cancer

• One in three people will develop cancer during their lifetime

• Yet only 10 – 15% of these are from occupational exposure to chemicals

• There are 30 chemicals considered to be human carcinogens and 200 that are suspect based on animal studies

Mutagenicity

• The ability of a substance to cause damage to genetic material

• A substance that is a carciogen is usually a mutagen

• But not all mutagens cause cancer

Teratogenicity

• A substances tendency to interfere with the development of an unborn child

• A teratogen causes birth defects

Determining Carcinogenicity

• Epidemiological studies are retrospective and look at past exposures to a sample group and compare this with their health history

• Lifestyle risk contributors like smoking, alcohol consumption and obesity are considered

• A prospective study maintains environmental data as well as exposure and medical records on workers as they are exposed

• These studies are difficult in companies where there is a large turnover of employees because the latency period of many cancers is over 20 years

Animal testing

• Usually performed on rodents using procedures endorsed by regulatory agencies like the EPA

• Animals are given doses likely to yield maximum incidence of tumor formation then statistical analysis is used to estimate the cancer risk of low doses in humans

Risk Management

• Government policy is determined by the public’s opinion of acceptable risk and is based on political considerations– Definition of risk– What defines acceptable risk

• Risk assessment uses scientific methods to determine the actual level of risk

Risk/Benefit Analysis

• Used by regulatory agencies in the decision making process

• Subjective concerns such as politics, lifestyles, freedoms, economics and progress are considered

Perception of Risk

• We tend to perceive voluntary risks as less perilous than those we are forced to take i.e. smoking

Risk Assessment

• Evaluating the toxic properties of a substance and the conditions of human exposure to determine

• The likelihood that exposed humans will be adversely affected

• And describe the nature of the effects they may experience

National Research Council Guidelines 1983

• Hazard evaluation - determining the toxic properties of the substance

• Dose-response relationships - how much it takes to cause negative effects

• Exposure assessment - how much the public is exposed to and for how long

• Risk characterization – determining a numerical risk factor

Risk Assessment II

• Risk assessments are required by regulatory agencies when contaminants have been released into the environment

• Aids in determining acceptable cleanup levels