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Flashcards in Principles of toxicology 1 Deck (13):

what is a toxicant ?

man made/ synthetic chemical that has the potential to cause harm


what is a xenobiotic ?

a chemical that is foreign to life
- any chemical that is not part of the metabolic processes that maintain life
- includes both toxicants and toxins


what is the most common relationship between exposure and response to chemicals ?

most produce a hyperbola
the range of exposure is generally very large


what does response mean in the response exposure relationship ?

it is a measure of organisms in a sample that show a toxic effect
- show signs of toxicity and it is expressed as a percentage
- it is a quantal response in which it is an all or nothing response - either toxic effects are shown or not


what do toxicologists do to the response exposure graph ?

they produce a log to the base 10 of exposure to prevent data clumping together
- transforms graph into distinct regions= threshold region, linear region and plateau region to the maximum response


what is the threshold region ?

it is the first points at which a response is detected
- it is these organisms which are the most vulnerable


what is the TD 50 ?

its used to determine the median toxic dose
- it is the level of exposure that produces the toxic effects in 50% of the population


what is the LD50 ?

it is the median lethal dose
-the dose at which is lethal to 50% of the population


how is potency calculated using the log10 exposure response graphs ?

the toxin furthest to the left is the most potent- it has the smallest TD50 so it is the most potent
if the TD50s of different chemicals are divided by each other, their relative potencies can be determined


what does NOAEL stand for ?

No Observed Adverse Effect Level
- it is the highest level of exposure that does not produce any adverse effects


what does LOAEL stand for ?

Lowest Observed Adverse Effect Level
- lowest level of exposure thats produces a significant level of toxicity
- greater than this there is increasing toxicity


what does POD stand for ?

Point Of Departure
- initial curve linear threshold region stops and turns into a linear region


why is it important to look at the slope of the exposure response curve ?

important to look at when carrying out a risk assessment
- the slope of the graph can be very steep (organophosphate nerve agents) this almost represents an all or nothing response, therefore for a very narrow range of exposures there is a large increase in toxicity which is more dangerous
- a very steep slope can often indicate that the chemical has only 1 molecular target