2. dose-response

Question 1

Hazard

Answer 1

in North America, is the intrinsic toxic properties of a toxicant or toxicant mixture.

Question 2

Risk

Answer 2

is the probability (so statistical…) of an adverse outcome based on the exposure and potency of the hazardous toxicant(s).

Question 3

Risk assessment

Answer 3

characterization of the probability of potentially adverse health effects from human (or other animals!) exposures to hazardous agents.

Question 4

Risk management

Answer 4

process by which policy actions are chosen to control hazards.

Question 5

Hazard Identification

Answer 5

Do the chemicals/agents present cause — or have the potential to
cause — adverse health affects?

Question 6

Epidemiology data (correlative)

Answer 6

studies the patterns, causes, and effects of health and disease conditions in defined populations.

Question 7

In vitro tests

Answer 7

test how cell cultures respond to exposure)

Question 8

Structure activity modeling

Answer 8

does the chemical look like a toxicant

Question 9

bioassay experiments

Answer 9

One way to prove causation

Can be done on live animals (in vivo)

Question 10

bioassay

Answer 10

quantitative estimation of the intensity or concentration of a biologically active chemical, measured via some biological response under standardized conditions.

Question 11

Common animals used in bioassays

Test group

Answer 11

Mammals
Rats, mice, guinea pigs, monkeys
Fish
Goldfish, fathead minnows, Japanese medaka, rainbow trout
Invertebrates
Cladocerans (water fleas), oysters

Question 12

Goals of toxicity testing:

Answer 12

1. Determine the range of doses over which the
   toxic responses are produced
2. Identifythenatureoftheresponsestoa toxicant
3. Extrapolation of these results for risk assessment analyses for human exposure

Question 13

Uses of bioassays in environmental toxicology:

Answer 13

1. Determine of the most sensitive species or life stage in an
   assemblage of organisms.
2. Compare effects of different pollutants on a single organism.
3. Compare effects of other environmental factors acting with the pollutant that modify its effects.
4. Determine the maximum level of a pollutant that may occur in the environment without causing biological change (Maximum Allowable Toxicant Concentration: MATC).

Question 14

Dose-Response assessments quantify the relationships between the exposure concentration (i.e., the dose) and a defined

Answer 14

endpoint (i.e., the response).
• Often represented graphically – a dose-response curve.
• Fundamental concept in toxicology.
• Usually the first step in toxicity testing

Question 15

Endpoints can be

Answer 15

whatever we are most interested in measuring (e.g., molecular, enzymatic, organismal, etc.
• Recall adverse outcome pathways.

Question 16

What to we mean by dose?

Answer 16

We tend to give the same amount of substance per unit of body weight in bioassays (and pharmaceutical drug tests)
• The same dose of a toxicant can have a greater effect on smaller individuals or organisms
• give80mgofatoxicanttoan80kgadult…adoseof1mg/kg
• give 80 mg to a 8 kg child… that child is dosed at 10 mg/kg
• This is why we standardize doses to body weight when studying organisms!

Question 17

important for understanding the response in a test.

Answer 17

Duration and Frequency

Question 18

Acute exposures

Answer 18

means different things to different people…
– Physiologists: acute is seconds to minutes
– Toxicologists: acute is hours to a day (i.e., 24 hrs)
– BUT, acute toxicity tests for aquatic organisms are often exposures for days

Question 19

Chronic exposures

Answer 19

means different things to different people…
– Physiologists: chronic is weeks to months
– Toxicologists: chronic is months to years

Question 20

This is why we must clearly state how long an individual was exposed to a toxicant

Answer 20

For example, we did an acute toxicity test and measured what concentration would kill (endpoint) 50% of the fish in a tank over 96 hrs.
• This is the definition of the lethal concentration (LC50) or lethal dose (LD50)
• Then we should report the concentration as the 96-hr LC50.

Question 21

Graded dose-response relationships

Answer 21

use a continuous variable and occur in a single individual. They are characterized by a dose- related increase in the severity of the response.
• Examples:
– enzyme inhibition (pictured)
– changes in blood hormone levels

Question 22

Quantal dose–response relationships occur in a

Answer 22

population
• At a given dose, an individual in the population is classified as either
a “responder” or a “non-responder.”

Question 23

Often the endpoint is mortality (easy to quantify)

Answer 23

• Count how many individuals die (i.e., the responder…) in your experiment at a given concentration
• Example of a quantal dose-response relationship
-Often we want to know the dose when 50% of individuals die (i.e., the LD50 or LC50).

Question 24

Can use dose-response curves to compare relative

Answer 24

toxicity of toxicants.

• We should use the same test conditions and test species.

Question 25

toxicants can be ranked based upon their

Answer 25

LD50s into toxicity classes

Question 26

Class 6

Answer 26

Relatively harmless (Acute toxicity of chemicals in rats*)

Question 27

Class 5

Answer 27

Practically non-toxic (Acute toxicity of chemicals in rats*)

Question 28

Class 4:

Answer 28

Slightly toxic | Acute toxicity of chemicals in rats*

Question 29

Class 3

Answer 29

Moderately toxic (Acute toxicity of chemicals in rats*)

Question 30

Class 2

Answer 30

Highly toxic | Acute toxicity of chemicals in rats*

Question 31

Class 1

Answer 31

Super toxic | Acute toxicity of chemicals in rats*

Question 32

Dose-Response curves will change based on

Answer 32

“route of exposure” – Inhalation, Injection, Ingestion, Dermal (in order of effectiveness) – The speed of the response is related to how quickly a toxicant can get into the bloodstream.

Question 33

We can try to transform to linear functions if possible.

Answer 33

– Because it is hard to generate a nice sigmoidal curve without a lot of things dying The response at 50% of the population is, by definition, the population mean. Normally distributed curves have fixed standard deviations (SD) that always represent a percent of the population. For example 1 SD = 69.3% of the population. So we can swap the y-axis from cumulative response to deviations away from the mean (Probit – Probability Units).

Question 34

The y-axis gets converted to ‘probits’

Answer 34

The y-axis on a probit graph is always the same in probit plots (convenient for comparisons...) 1) the % response gets changed to the Normal Equivalent Deviation (NED 2) Add 5 to all to avoid negative numbers 3) The new probit Y-axis evenly spaces things to effectively turn the sigmoidal curve into a straight line 5 always corresponds to 50% of the population. 6 is one NED away from mean which represents cumulative 84% of the population.

Question 35

The data points can be converted from % mortality to probits by looking up the values in a chart

Answer 35

1. Convert%mortalityvaluestoprobitvalues 2. Any%mortalitybelow1or100isignored 3. Tolookupinthetable,the%moralityis rounded to the nearest 0.5

Question 36

These values will plot as a linear ‘probit plot’ when plotted vs

Answer 36

log dose | Can use this to calculate the LC50 when you don’t know it.

Question 37

ED50

Answer 37

effective dose where the drug is doing what we want it to do in 50% of the populatio

Question 38

TD50

Answer 38

toxic dose | where bad things start happening in 50% of the population

Question 39

LD50:

Answer 39

lethal dose in 50% of the population

Question 40

therapeutic index (TI)

Answer 40

is the ratio of TD50 and ED50 High values mean that the drug is relatively safe. Low values usually lead to the rejection of the drug from further clinical testing. TI = TD50 ED50

Question 41

Potency

Answer 41

the amount required to produce an effect of given intensity A is more potent than B

Question 42

Efficacy

Answer 42

refers to the maximum response achievable D has a greater efficacy than C

Question 43

NOEC

Answer 43

No Observable Effect Concentration

Question 44

LOEC:

Answer 44

Lowest Observable Effect Concentration

Question 45

to distribute the contaminant to the animals.

Answer 45

Often use a “vehicle” or “carrier”

Question 46

Chlorpyrifos

Answer 46

used on crops like strawberries, broccoli and citrus fruit as an insecticide. – Residues can harm the developing brains of small children, even in the womb. • Environmental Protection Agency (EPA) issued a proposal to ban chlorpyrifos 2 years ago. • This was blocked by newly appointed EPA Administer Scott Pruitt (a lawyer) – Has sued the EPA before, received money from the oil and gas industry, does not believe in climate change, no science background. – Should NOT be in the position to interfere with the EPA trying to protect the health of citizens.

Question 47

Dose-response curves can be

Answer 47

U-shaped or inversely U- shaped as well | – Some essential nutrients can have adverse effects at low and high doses (e.g., iron, chromium, vitamin A and D)

Question 48

Hormesis

Answer 48

can refer to some types of dose-response curves | • Compounds that are beneficial/stimulatory at low doses but toxic at high doses

Question 49

Nonmonotonic dose-response curves

Answer 49

Often observed with EDCs: toxicants that can have effects at very low levels At low levels they interact with a hormonal receptor, leading to a response At high levels, the receptor is ‘burned out’, thus the response decreases Highlights the danger of extrapolating the effects of high doses to low dose responses Basically curves that are not straight lines These indicate thresholds in the response

Question 50

Sub-lethal

Answer 50

responses are very important | Many (most) toxic events occur before the animals died...

Question 51

Can conduct a subchronic bioassay

Answer 51

at lower doses. Often with more than 1 species at different doses (i.e., 3 doses): • High dose that causes toxicity but not more than 10% fatalities • Low dose that should cause no toxic effects • An intermediate dose • Exposures for longer periods of time • e.g., 90 days

Question 52

Why do a subchronic test??

Answer 52

1. To provide information on all types of subchronic toxicity (other than carcinogenicity) that might occur – immunotoxicity, neurotoxicity 2. Establish dose regimens for chronic studies 3. Provide data which will allow an estimate to be made of the MTD (maximum tolerable dose), where there is no significant impairment of growth. 4. To develop biomarkers of exposure (e.g., expression of a gene, specific enzyme function).

Question 53

Observed during the study:

Answer 53

– Altered growth rate | – Behavioural changes

Question 54

After the exposure period, the animals are euthanized and sampled to see what deviates from ‘normal’:

Answer 54

``` – Mass – Blood chemistry (hormone levels) – Biochemical (glucose, ATP levels) – Cell membrane permeability – Enzyme activity – Organ and tissue damage (necrosis) ```

Question 55

biomarker

Answer 55

can be described as a cellular or biochemical response to a xenobiotic that is measurable in a biological system or sample. – There are biomarkers to other types of stressors, such as temperature in fish!!!

Question 56

Biomarkers can include, but are not limited to:

Answer 56

i. Enzyme activity • Certain enzymes in the blood can indicate liver toxicity • Increase in cytochrome P450 activity for detoxification • Metallothionein induction to bind heavy metals ii. Changes in cellular receptor amount and activity • Estrogen receptor in response to EDCs iii. Changes in hormone levels • Increase in cortisol (the ‘stress hormone’) iv. Increased/decreased expression of genes that respond to toxicants v. Changes in the histology of cells to detect cellular damage

Question 57

chronic bioassay

Answer 57

Can conduct a chronic bioassay to look at longer-term endpoints like cancer development (months to years). – Determine whether it is a carcinogenic compound. • Cancer can take a long time to develop, and likely will not be identified in a subchronic study.

Question 58

Carcinogens are classified based upon

Answer 58

what is known from humans (e.g., epidemiological studies) and animals (e.g., bioassays)

Question 59

Rofecoxib (trade name Vioxx)

Answer 59

is a non-steroidal anti-inflammatory drug (NSAID)