Chapter 10: Health Hazards & Toxicology

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Health Hazards & Toxicology

Objectives: By the end of this section, participants will be able to assess health risks provided standard reference materials.

Why this section is important: One must be able to identify and comprehend the extensive health and safety information available for workers and employers.

General Terminology

Toxicology: The study of the nature and actions of poisons.

Toxicity: The extent to which a chemical will cause harmful effects.

LD₅₀: The dose (the amount per unit of body weight) of a chemical that is sufficient to kill ½ of the population within a specified period of time by ingestion

LC₅₀: The concentration of a toxin that is sufficient to kill ½ the population within a specified period of time by inhalation

Odor Threshold: The minimum concentration at which the odor quality (description of smell) of the compound can be described

Toxicological Effects

Additive Effects: Biological effect from two chemical individually and added together.

Synergistic Effects: The total biological effect is > the sum of the individual biological effects. Classically exemplified by cigarette smoking and asbestosis.

Exposure Types

Acute Exposure: high concentration for short duration with symptoms that are usually immediately apparent but can be delayed and may be permanent or reversible.

Chronic Exposure: low concentration exposure for long duration with symptoms that are usually latent for several years and may be reversible or permanent.

Modes of Action

Direct Effect: Toxin affects that part of the body that it contacts. Example: Acid burns the skin that it contacts.
Systemic Effects: Exposure effects observed at other points in the body not related to point of contact. Example: heavy metals have little effect on the mouth or alimentary canal, but is destructive to fatty tissue.

Routes of Entry

Inhalation: Through the respiratory system. (Preventable with respiratory protective equipment).

Skin Absorption: Through the skin. (Preventable with chemical protective equipment).

Ingestion: Through consumption of contaminated food. (Preventable with proper hygiene practices).

Injection: From a sharp. (Preventable with proper bloodborne pathogen work protocols).

Regulatory & Guidance Exposure Levels

Permissible Exposure Limit (PEL): OSHA’s maximum allowable breathing zone concentrations of chemicals to which a worker may be exposed.

Threshold Limit Value (TLV): The maximum concentrations recommended by the American Conference of Government Industrial Hygienists (ACGIH).

Recommended Exposure Limit (REL): The maximum concentrations recommended by the National Institute of Occupational Safety and Health.

Ceiling: The maximum value to which a worker may be exposed.

Short Term Exposure Limit (STEL): The highest concentration that a worker may be exposed to for up to 15 minutes.

The ACGIH recommends that worker exposure levels may exceed 3 times the TLV-TWA for no more than a total of 30 minutes during a workday, and under no circumstances should they exceed 5 times the TLV-TWA, provided that the TLV-TWA is not exceeded.

Skin: Indicates harmful effects through skin absorption and one should wear gloves or personal protective equipment.

IDLH: Immediately Dangerous to Life and Health. A situation that either poses an immediate or delayed threat to life, or would cause irreversible adverse health effects; or would interfere with an individual’s ability to escape unaided from a permit space.
In the absence of known IDLH values, any air hazard concentration that exceeds its TWA by 20X is to be considered an IDLH situation.
Time Weighted Average (TWA): The average exposure over an 8 hour work day.
Formula:

[(C₁ T₁) + (C₂ T₂) + (C₃ T₃)+...+(C_n T_n)] ÷ 480 min.

where C = concentration of sample in ppm or mg/m³ and T = duration in minutes.

Mixture TWA: The average exposure to a mixture.

Formula:

C₁/P₁ + C₂/P₂ + C₃/P₃ + ... + C_n/P_n

where C_n is the ambient concentration of a chemical and P_n is the TLV of that chemical.

The permissible exposure limit = 1. The mixture formula can only be used for similar, non-reactive chemicals.

Routes of Entry

Inhalation: Through the respiratory system. (Preventable with respiratory protective equipment).

Skin Absorption: Through the skin. (Preventable with chemical protective equipment).

Ingestion: Through consumption of contaminated food. (Preventable with proper hygiene practices).

Injection: From a sharp. (Preventable with proper bloodborne pathogen work protocols)

Classification of Toxic Chemicals

Irritants: Cause reversible inflammation of mucous membranes, e.g., Ammonia.

Sensitizers: Cause mild to severe allergic reaction and the formation of antibodies upon first exposure, causes severe allergic reactions or death upon second and subsequent exposures.

Asphyxiants: Deprive the tissue of oxygen. Simple asphyxiants displace oxygen (e.g., carbon dioxide). Chemical asphyxiants bind to hemoglobin and prevent oxygen uptake by hemoglobin (e.g., carbon monoxide and cyanide).

Anesthetics: Depress central nervous system, primarily the brain (e.g., alcohols, organics).

Corrosives: Chemicals that cause burns, irritation or destruction of living tissue (e.g., strong bases and strong acids)

Hepatotoxins: Chemicals which produce liver damage including jaundice and liver enlargement (e.g., carbon tetrachloride).

Nephrotoxins: Chemicals which produce kidney damage including edema and proteinuria. Examples: halogenated hydrocarbons and uranium.

Neurotoxins: Chemicals which produce their primary toxic effects on the nervous system (e.g., mercury, tetraethyl lead and organic phosphate insecticide).

Agents which damage the lung: Chemicals which irritate or damage the pulmonary tissue (e.g., silica, asbestos and hydrogen sulfide).

Teratogens: Substances that cause a change in form, generally a birth defect (e.g., Thalidomide).

Mutagens: Cause changes in DNA sequence (genes).

Carcinogens

Substances that cause tumors (uncontrolled cell division). Tumors may be malignant and metastasize to other organs or be benign and not metastasize.

A chemical is considered a carcinogen if:

It has been evaluated by the International Agency for Research on Cancer and found to be a carcinogen or potential carcinogen; or

It is listed as a carcinogen or potential carcinogen in the Annual Report on Carcinogens published by the National Toxicology Program (NTP) (latest edition); or,

It is regulated by OSHA as a carcinogen:

2- acetylaminofluorene, acrylonitrile, 4-aminodiphenyl, arsenic (inorganic), benzene, bis (chloromethyl) ether, coke-oven emissions, 1,2-dibromo-3-chloropropane, 3,3-dichlorbenxidine, 4-dimethylaminoazobenzene, ethylene oxide, ethyleneimine, formaldehyde, 4,4-methylene(bis)-2-chloroaniline, methyl chloromethyl ether, alpha-napthylamine, 4-nitrobiphenyl, N-nitrosodimethylamine, beta-propiolactone, vinyl chloride

It is recognized by the ACGIH as a carcinogen:

4-Aminobiphenyl, Asbestos (Amosite, Chrysotile, Crocidolite, & Other Forms),Benzidine,Bis (chloromethyl) ether,Chromate or processing (chromate),Chromium (VI), certain water soluble compounds,Coal tar pitch volatiles,Beta-Naphtylamine ,Nickel sulfide roasting, fume and dust,4-Nitrodiphenyl,Vinyl Chloride,Zinc Chromates

Common Industrial Toxicants
Substance or Group	Compound	Uses	Target Organs	Potential Health Effects
Aromatic Hydrocarbons	Benzene, Ethyl Benzene, Toluene, Xylene	Commercial solvents and intermediates for synthesis in the chemical and pharmaceutical industries.	Blood, bone marrow, CNS, eyes, respiratory system, skin, liver, kidney	All Cause CNS depression, defatting dermatitis. Benzene suppresses bone marrow function, causing blood changes and chronic exposure can cause leukemia.
Asbestos (or asbestiform particles)		A variety of industrial uses including building, construction, cement work, insulation, fireproofing, pipes and ducts.	Lungs, gastro-intestinal system	Chronic effects: lung cancer, mesothelioma, asbestosis, gastrointestinal malignancies. Cigarette smoking has been shown to be synergistic with asbestos.
Halogenated aliphatic hydrocarbons	Methyl chloride, chloroform, carbon tetrachloride, tetra- and tri-chloroethylenes, & vinyl chloride	Commercial solvents and intermediates in organic syntheses	CNS, kidney, liver, skin	All cause CNS depression, kidney change, anemia, and liver change. Vinyl chloride is a known carcinogen, several others in this group are potential carcinogens.
Heavy Metals	Arsenic, Mercury, Beryllium, Cadmium, Chromium, Lead	Wide variety of industrial and commercial uses.	Cardiopulmonary, gastroin-testinal, kidney, liver, blood, CNS, skin	Lead can cause permanent kidney and brain damage; cadmium can cause kidney or lung disease; the others are suspected carcinogens
Herbicides	(2,4-D), (2,4,5-T), dioxin	Vegetation control	Kidney, liver CNS, skin	Chloracne, weakness or numbness of the arms and legs, may result in long-term nerve damage and may aggravate pre-existing liver and kidney diseases.
Organochlorine Insecticides	DDT, Aldrin, Chlordane, Dieldrin, Endrin, Lindane	Pest control	Kidney, Liver CNS	Acute symptoms of apprehension, irritability, dizziness, disturbed equilibrium, tremor, and convulsions. May cause convulsions, anemia and kidney damage. All cause extensive CNS damage.
Organophosphate and Carbamate Insecticides	Parathion, Zectran, Diazinon, Malathion, Baygon, Aldicarb	Pest control	CNS, liver, kidney	All cause extensive CNS damage
Polychlorinated Biphenyls (PCBs)		Wide variety of industrial uses	Liver, CNS (speculative), respiratory system (speculative), skin	Various skin ailments, including chloracne, may cause liver toxicity, carcinogenic to animals.

Thought Questions (you do not need to respond):

The Mad Hatter (from Alice in Wonderland) was considered crazy because of his occupational exposure to what chemical?

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