PU530 Environmental Health Unit 2 Environmental Hazards - Sources and Routes of Exposure

Question 1

What do we call the agents that pollute the environment?

Answer 1

Pollutants

Carbon dioxide is not normally considered a pollutant, but in its increased concentration has been responsible for global warming.

Question 2

What are the two types of pollutants?

Answer 2

Non-degradable and biodegradable pollutants

Examples of non-degradable pollutants include pesticides, heavy metals, rubber, plastic, nuclear waste.

Biodegradable pollutants such as paper, domestic sewage, garden waste, and fertilizers are broken down into simple components by bacterial composition.

Question 3

What are the natural and man-made sources of air pollution?

Answer 3

Natural sources - include volcanic eruptions [releasing
poisonous gases such as sulphur dioxide (SO2), hydrogen sulphide
(H2S), and carbon monoxide (CO)], forest fires, decay of organic
matter, marsh gases, pollen grains, fine sand particles, and fungal
spores.

Man-made sources - include increase in population,
deforestation, burning of fossil fuels, vehicular emissions, rapid
industrialization, and agricultural activities (use of agrochemicals
such as fertilizers, pesticides, insecticides, and herbicides). Some
other sources include wastes from nuclear reactors.

Question 4

What are the 8 significant sources of water pollution?

Answer 4

Sewage and domestic wastes - 75% of water pollution

Industrial effluents - toxic materials discharged from industries which contain chemicals and harmful compounds.

Agricultural discharges - mostly agrochemicals such as fertilizers, pesticides, insecticides, etc. discharged into water bodies as agricultural run-offs.

Detergents - Household detergents contain a number of pollutants that severely affect water bodies such as sodium and sodium silicate.

Toxic metals - industrial processes responsible for releasing toxic materials like mercury, cadmium, lead, etc.

Siltation - silt entering bodies of water brought down by rains and flash floods. The soil particles in the silt make the water turbid, thus hindering the free movement of aquatic organisms.

Thermal pollutants - unutilized heat from thermal power plants is released into water bodies, which adversely affect the aquatic environment.

Radioactive materials - Radioactive wastes enter water bodies
from sources such as nuclear power plants, nuclear tests, and
fission reactions. Extremely toxic radioactive elements such as
plutonium, uranium, thorium, and radium are produced from
neutron bombardment of atomic fuel. Once they enter the water
bodies, they disrupt the ecosystem and find way into the food
chain.

Question 5

What are the 5 significant sources of soil pollution?

Answer 5

Question 6

What are the six types of pollution?

Three main categories of pollution?

Answer 6

Air, water, soil/land, noise, pollution by radioactive substances, and thermal pollution.

These all fall under three main categories of biological, chemical, and physical.

Question 7

Where did the modern chemical manufacturing industry originate?

Answer 7

In Europe during the Industrial Revolution in the late 1700s and early 1800s (Sulfuric acid was the first)

Question 8

What is currently the most important chemical feedstock?

Answer 8

Petroleum

Question 9

Why are chemical workers at high risk of disease?

What are the three chemicals that pioneered the thought that chemicals cause cancer?

Answer 9

Chemically induced disease because they are often exposed to new chemicals, and their exposures are often quite high.

Aniline-based dyes, benzene, and asbestos.

Question 10

Where has chemical produced increasingly moved to?

Answer 10

LMICs

See attached for examples.

Question 11

What is a key risk factor when it comes to vulnerability to toxic chemical exposures?

Answer 11

Age

Question 12

What are the four differences between children and adults that contribute to children’s heightened susceptibility to toxic chemicals reported by the National Academy of Sciences?

Answer 12

• Children have proportionately greater exposures to toxic chemicals than adults.
• Children’s metabolic pathways are immature, and a child’s ability to metabolize toxic
  chemicals is different from an adult’s.
• Children’s exquisitely delicate early developmental processes are easily disrupted.
  Windows of vulnerability occur during critical periods in early development when
  exposures to even minute doses of toxic chemicals—levels that would have no adverse
  effect on an adult—can disrupt organ formation, increase lifelong risk of noncommunicable disease, and cause lifelong functional impairments.
• Children have more future years than adults to develop diseases of long latency that
  may be triggered by harmful exposures in early life.

Question 13

What is a critically important mechanism of chemical toxicity that has been extensively studied in recent years?

What does it disrupt?

What are the key principles of this mechanism?

Answer 13

Endocrine (hormonal) disruption.

Hormonal signaling which alters development, reduces cognitive function and intelligence, and impair reproductive capacity.

Large biological effects can occur at very low doses.

Toxic effects occur across multiple species, ranging from minnows to humans—illustrating that common biological pathways are shared with species across the biological
world.

The timing of exposures is important. Windows of unique vulnerability in early life,
determined by developmental pathways and stages, are associated with the most severe
and lasting effects. Effects sustained during those periods are not limited to childhood.

Effects can occur across the lifespan. One worrisome trend, for example, is that human
sperm counts in Western countries have declined significantly since the 1970s,44 falling by 50%–60% with no indication that the decline is slowing. Studies in China
show similar results, with declines in sperm counts of as much as 40% over recent
decades.45,46 Such trends are manifesting as reduced fertility sufficient to affect population growth rates. In a recent Danish study approximately 25% had sperm count
sufficiently reduced to increase time to pregnancy and 15% were so severely impaired
that it is unlikely they would be able to reproduce without fertility treatment.

Endocrine disruption is emblematic of the far-reaching human impacts of chemical
pollutants.

Question 14

What are the two sequences of events that have marked many historical missteps with chemicals?

Answer 14

• the enthusiastic introduction and wide dissemination of many thousands of chemicals
  and new products
• followed by the belated discovery that some of these
  apparently beneficial chemicals pose unanticipated threats to human health and the
  environment

Examples of this include addition of lead to paint and gasoline, use of asbestos for insulation and fireproofing products, the use of DDT as a pesticide, introduction of thalidomide to control nausea in pregnancy, widespread use of PCBs in electrical transformers, use of the synthetic hormone diethylstilbestrol (DES) to prevent miscarriage in pregnancy, the use of ozone-destroying chlorofluorocarbons (CFCs) in refrigeration units.

Question 15

What are the two core themes of the field of planetary health in respect to the corporate model?

Answer 15

• Those who benefit from environmental degradation and those who pay the costs are
  often very different populations, and
• Quantifying the human health costs of environmental degradation is an important
  step in moving these costs out of the realm of vague externalities and into the realm
  of cost–benefit analysis and policymaking.

Question 16

What % of chemicals used today have been screened for their potential to disrupt early human development or to cause disease in infants and children?

Answer 16

20%

An egregious policy gap is that fewer than half of the high-production volume chemicals currently on world markets have undergone any testing for safety or toxicity.

Question 17

What is at the root cause of the global problem of chemical pollution and toxicity?

Answer 17

The absence in most countries of a coherent chemical protection policy.

The results of this poor stewardship and lack of due diligence are as follows:

• Chemicals and pesticides whose potential to harm human health and the environment were never examined have repeatedly been responsible for the episodes of disease, death, and environmental degradation described in the preceding section of this
  chapter; and
• Little is known about the possible dangers to human health and the environment
  of most of the synthetic chemicals in the world today. Even less is known about the
  potential health effects of simultaneous exposure to multiple chemicals or about how
  chemicals may interact with one another in the human body, possibly causing synergistic adverse effects on health.

Question 18

Food for Thought

The extent of knowledge of neurotoxic chemicals.

Question 19

What term relates to poisonous or deadly effects on the body by inhalation (breathing), ingestion (eating), or absorption, or by direct contact with a chemical?

Answer 19

Toxic

Question 20

What is a chemical that can injure or kill humans, animals, or plants; a poison?

Answer 20

Toxicant

The term “toxicant” is used when talking
about toxic substances that are produced by or are a by-product of human activities.

Toxins are typically used to describe natural toxicants.

Question 21

What is a toxin?

Answer 21

The term is usually used when talking about toxic substances produced naturally.

A toxin is any poisonous substance of microbial (bacteria or other tiny plants or animals), vegetable, or synthetic chemical
origin that reacts with specific cellular components to kill cells, alter growth
or development, or kill the organisms.

Question 22

What is a term that describes any feeling or sign indicating the presence of a poison in the system?

Answer 22

Toxic symptom

Question 23

What is the term that refers to the health effects that occur
due to exposure to a toxic substance; also known as a poisonous effect on the
body?

Answer 23

Toxic effects

Question 24

What is toxicity?

Answer 24

This can be defined as the degree to which a chemical
inherently causes adverse effects. The concept of toxicity is not clear-cut. Cyanide, for example, is more toxic than table salt because toxic effects can result
from much lower amounts of cyanide.

However, as Stelljes (2000) points out,
we are not usually exposed to cyanide, but we are exposed to table salt daily.
Which chemical is more dangerous to us?

Question 25

What term means that a chemical will produce injury to one kind of living matter without harming another form of life, even though the two may exist together?

Answer 25

Selective toxicity

Question 26

How does toxicity develop?

Answer 26

The substance must come into contact with a body surface.

The dose of the chemical, or the amount one comes into contact with, is important when discussing how “toxic” a substance can be.

Question 27

What are two ways the dose of a toxin or toxicant is received (temporally)?

Answer 27

The dose received may be due to either acute (short-term) or chronic (long-term) exposure.

The amount of exposure and type of toxin will determine the toxic effect.

Question 28

What is a relationship between exposure and health-effect that can be established by measuring the response relative to an increasing dose?

Answer 28

Dose-response

This relationship is important in determining the toxicity of a particular substance.

It relies on the concept that a dose, or a time of exposure (to chemical, drug, or toxic substance), will cause an effect (response) on the exposed organism. Usually, the larger or more intense the dose, the greater the response, or the effect. This is the meaning behind the statement
“the dose makes the poison.”

It is important to point out that the dose-response relationship, which,
again, defines the potency of a toxin, is typically the primary thrust of basic
toxicology training. This is the case because the dose-response relationship
is the most fundamental and pervasive concept in toxicology. To understand
the potential hazard of a specific toxin (chemical), toxicologists must know
both the type of effect it produces and the amount, or dose, required to produce that effect.

Question 29

What do you call the graph that illustrates the relationship of dose to response?

Answer 29

Dose-response curve.

Question 30

What are the two types of dose-response curves?

Answer 30

• One that describes the graded responses of an individual to varying doses of the chemical
• One that describes the distribution of response to different doses in a population of individuals.

(The dose is the x-axis and the response is represented by the y-axis)

An important aspect of dose-response relationships is the concept of
threshold (Attached photo). For most types of toxic responses, there is a dose, called
a threshold, below which there are no adverse effects from exposure to the
chemical. This is important because it identifies the level of exposure to a
toxin at which there is no effect.

Threshold and non-threshold types of basic dose-response relations are illustrated in the attached figure. As shown in the figure, any dose can cause an effect in
a non-threshold relationship (Chemical B). As the dose increases, the relative
effect will also increase. For a threshold relationship, which is the more common of the two across all chemicals, effects only occur above a certain dose
(Chemical A).

Above the threshold level, there is little difference between the two relationships. At high doses, the lines are essentially parallel, indicating
that the response changes at the same rate for both chemicals. The rate at
which effects increase with the dose defines the potency of a chemical. This
is the slope of the line in Figure 3.1. We can use this principle to compare
the potencies of different chemical by comparing their slopes (Stelljes, 2000).

Question 31

How is potency defined?

How does it differ from toxicity?

Answer 31

Potency is the rate at which effects increase with the dose.

Toxicity is when the exposure causes adverse effects

A more potent chemical is more toxic meaning a smaller exposure will show toxicity effects.

Question 32

What describes the dose or exposure level below which the harmful or adverse effects of the substance are not seen in the population?

Answer 32

Threshold. That dose is referred to as the “threshold dose.”

This dose is also referred to as the no observed adverse effect level (NOAEL) or the no effect level (NEL). These terms are often used by toxicologists when discussing the relationship between exposure and dose. However, for substances causing cancer (carcinogens), no
safe level of exposure exists, since any exposure could result in cancer.

Question 33

What is individual susceptibility?

Answer 33

The term describes the differences in types of responses to hazardous substances, between people.

Each person is unique, and because of that, there may be great differences in the response to exposure. Exposure in one person may have no effect, while a second person may become seriously ill, and a third may develop cancer.

Question 34

What describes those persons who are more at risk from illness due to exposure to hazardous substances than the average, healthy person?

Answer 34

Sensitive sub-population

These persons usually include the very young, the chronically ill, and the very old. It may also
include pregnant women and women of childbearing age. Depending on the
type of contaminant, other factors (e.g., age, weight, lifestyle, gender) could
be used to describe the population.

Question 35

What is LD50/LC50?

Answer 35

A common measure of the acute toxicity is the lethal dose (LD50) or lethal concentration (LC50) that causes death (resulting from a single or limited exposure) in 50 percent of the treated animals, known as the population.

LD50 is generally expressed as the dose, milligrams (mg) of
chemical per kilogram (kg) of body weight. LC50 is often expressed as mg of
chemical per volume (with results expressed in terms of an air concentration,
e.g., ppm) the organism is exposed to. Chemicals are considered highly toxic
when the LD50/LC50 is small and practically non-toxic when the figure is
large.

Question 36

What are the three routes of entry for exposure in living things?

Answer 36

Inhalation, dermal contact, ingestion.

Exposures to toxic chemicals can be in the form of liquids, gases, mists,
fumes, dusts, and vapors. Generally, toxic agents are classified in terms of
their target organs, use, source, and effects.

Question 37

What toxicological term describes the passage of a chemical across a membrane and into the body?

What toxicological term describes the risk that is so low that no significant potential for toxicity exists, or a risk society considers is outweighed by benefits?

What toxicological term describes a single or short-term exposure period?

What toxicological term describes the adverse group of structurally related chemicals naturally produced by plants; many of these chemicals have high toxicity?

What toxicological term describes a popular laboratory in vitro test for mutagenicity using bacteria?

What toxicological term describes a toxic depressant effect on the central nervous system?

What toxicological term describes a toxicity study in which specific toxic effects from chemical exposure are measured in the laboratory using living organisms?

Answer 37

Absorption

Acceptable risk

Acute

Alkaloid

Ames Assay

Anesthetic

Bioassay

Question 38

What toxicological term describes a cancer-causing substance?

What toxicological term describes an exposure period encompassing the majority of the lifespan for a laboratory animal species, or covering a least 10 percent of a human’s lifespan?

What toxicological term describes the exposure to a chemical through the skin?

What toxicological term describes the contact with a chemical by a living organism?

What toxicological term describes the degree of likelihood of non-cancer adverse effects occurring from chemical exposure?

What toxicological term describes a pesticide that targets insects?

What toxicological term describes a change in normal DNA sequence?

Answer 38

Carcinogen

Chronic

Dermal contact

Exposure

Hazard

Insecticide

Mutagen

Question 39

What toxicological term describes a chemical used to control pests?

What toxicological term describes the relative degree of toxic effects caused by a chemical at a specific dose?

What toxicological term describes the probability of an adverse effect resulting from an activity or from chemical exposure under specific conditions?

What toxicological term describes the intrinsic degree of an individual’s susceptibility to a specific toxic effect?

What toxicological term describes the primary organ where a chemical causes non-cancer toxic effects?

What toxicological term describes a chemical causing a mutation in the DNA of a developing offspring?

What toxicological term describes a dose below which no adverse effects will occur?

What toxicological term describes a chemical foreign to a living organism?

Answer 39

Pesticide

Potency

Risk

Sensitivity

Target organ

Teratogen

Threshold dose

Xenobiotic

Question 40

Food for Thought - Relative Toxicity

Question 41

What are the seven classifications of toxic substances?

Answer 41

See attached

Question 42

What are some sub classifications of toxic substances?

Answer 42

See attached

Question 43

What four factors determines the amount of a toxin that reaches the target tissue?

These four factors govern the degree of toxicity, if any, from chemical exposure.

Answer 43

Absorption

Distribution

Metabolism

Excretion

Question 44

When we talk about absorption, which is defined as the passage of a chemical across a membrane of the body, there are four major factors that affect absorption and subsequent distribution, metabolism, and excretion. What are they?

Answer 44

1. Size of the molecule
2. Lipid solubility
3. Electrical charge
4. Cell membrane carrier molecules

Until a chemical is absorbed, toxic effects are only rarely observed and then only at points of contact (e.g., acid burns on the skin)

Question 45

After a chemical is absorbed by the body, what happens next?

Answer 45

It is distributed to certain organs via the circulatory system or blood stream.

Question 46

What affects the rate of distribution of a chemical after it has been absorbed? (3)

Answer 46

1. Blood flow through the target organs
2. Ease with which the chemical crosses the local capillary wall and cell membrane
3. Affinity of components of the organ for the toxin

Question 47

After absorption and distribution of a chemical, what is the sum of all physical and chemical changes that take place in an organism; it includes the breakdown of substances, the formation of
new substances, and changes in the energy content of cells?

Answer 47

Metabolism.

Metabolism can either increase or decrease the toxicity, but it typically increases the water
solubility of a chemical, which leads to increased excretion (Stelljes, 2000).

Question 48

After absorption, distribution and metabolism of a chemical, what happens to it next in the body?

Also, what are some other factors that affect toxicity?

Answer 48

Excretion

Excretion is defined as elimination from the body, either as urine, feces,
or through sweat or tears. The rate at which excretion of toxic substances
occurs is important in determining the toxicity of a substance. The faster a
substance is eliminated from the body, the more unlikely a biological effect
will be (Kent, 1998). Other factors affecting toxicity include:

• Rate of entry and route of exposure; that is, how fast the toxic dose is
  delivered and by what means.
• Age, which can affect the capacity to repair damage.
• Previous exposure, which can lead to tolerance or increased sensitivity,
  or make no difference.
• State of health, medications, physical condition, and lifestyle, which
  can affect the toxic response. Preexisting disease can result in increased
  sensitivity.
• Host factors, including genetic predisposition and the sex of the exposed
  individual.

Question 49

What are the 7 physical classifications of toxic substances?

Answer 49

Gas

Vapor

Aerosol

Dust

Mist

Fume

Smoke

Question 50

Target Systems/Organs Commonly Affected by Toxins

What are the 8 target systems or organs that are commonly affected by toxins?

Hints

CNS

Hematoxic

Immune system

Cardiotoxic

Pulmonary

Hepatotoxic

Nephrotoxic

Reproductive system

Answer 50