Lecture 1-Environmental Toxico

8/13/2019 Lecture 1-Environmental Toxico

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Environmental Toxicology

Lecture-1

Introduction to Environmental Toxicology (EnTox)

EnTox is a young (1965) and interdisciplinary science that uses both

basic and applied scientific knowledge to understand natural and

anthropogenic pollutants, life cycle and their ipacts upon structure and

functions of biological and ecological systes!

"esearch in EnTox includes both laboratory experients and field

studies! EnTox wants to answer two ain #uestions

(1) $ow the release of a pollutant causes harful effects%

(&) 'hat can we do to preent or iniise risk to biological and

ecological syste%

EnTox obectie can be broken down into a 5*steps understanding process

useful for research+regulation!

"elease of pollutant into the enironent Transport and fate into biota (with+out cheical transforation)

Exposure to biological and ecological syste

-nderstanding responses and+or effects (olecular to ecological systes)

.esign experients, reediation, iniisation, conseration, and risk

assessent plans

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To understand, eliinate, preent or predict enironental and huan

health pollutions situations!

The EnTox confusion

/eople isunderstand EnTox as a scientific discipline that only focus on

cheicals into the enironent! 0ot true!

That represents enironental cheistry and cheodynaics! The rich

fabric of ideas, core concepts, literature body, technology and ideologies

that erge together to deelop EnTox is rather a dissiilar process

through ost educational institutions!

This ay be the point in case that EnTox is a young interdisciplinary

science and controersy regarding what to include in a curriculu is an

on going atter of discussion!

How to identify the blur lines interconnecting basic concets

"eading the obecties for each discipline that erge into EnTox should

decrease the confusion

2lassical toxicology protects huan (subcellular to indiidual) fro

toxic substances at concentration that are harful!

Ecotoxicology (ecology 3 toxicology) wants to protect any indiiduals,

populations, counities and ecosystes fro exposure to toxic

substance at concentration that are harful!

Enironental science is an interdisciplinary science that studies the

earth, air, water, liing enironents and social coponents!

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Enironental cheistry and cheodynaics is the study of cheical

sources, reactions, transports, effects and fate in the enironent!

EnTox ebraces both disciplines classical toxicology and

ecotoxicology!

4urther, it includes other sciences to ake a ore logical approach to

understanding and soling real and coplex pollution probles that

society faces today or will encounter in the future!

The interdisciplinary core of EnTox borrows heaily fro a range of

disciplines such as enironental science, enironental cheistry and

cheodynaics, analytical cheistry, organic cheistry, biocheistry,olecular genetics, cell biology, genoics, pharacology, pharaco*

and toxico*kinetics, physiology, atheatics and statistics, coputer

odeling, risk assessent, soil science, geology, ecology, eteorology,

arine biology and oceanography, linology, and wildlife biology!


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The science of toxicology is based on the principle that there is a

relationship between a toxic reaction (the response) and the aount ofpoison receied (the dose)!

!ose "esonse "elationshi

o s n iportant assuption in this relationship is that there is

alost always a dose below which no response occurs or can beeasured! second assuption is that once a axiu response

is reached any further increases in the dose will not result in any

increased effect!

7ne particular instance in which this dose*response relationship does not

hold true is in regard to true allergic reactions!

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llergic reactions are special kinds of changes in the iune syste

they are not really toxic responses!

The difference between allergies and toxic reactions is that a toxic effect

is directly the result of the toxic cheical acting on cells!

llergic responses are the result of a cheical stiulating the body to

release natural cheicals which are in turn directly responsible for the

effects seen! Thus, in an allergic reaction, the cheical acts erely as a

trigger, not as the bullet!

4or all other types of toxicity, knowing the dose*response relationship is

a necessary part of understanding the cause and effect relationship

between cheical exposure and illness!

s /aracelsus once wrote, :The right dose differentiates a poison fro a

reedy!: ;eep in ind that the toxicity of a cheical is an inherent

#uality of the cheical and cannot be changed without changing the

cheical to another for! The toxic effects on an organis are related to

the aount of exposure!

#easures of Exosure

Exposure to poisons can be intentional or unintentional! The effects ofexposure to poisons ary with the aount of exposure, which is another

way of saying :the dose!:

-sually when we think of dose, we think in ters of taking one itain

capsule a day or two aspirin eery four hours, or soething like that!

2ontaination of food or water with cheicals can also proide doses of

cheicals each tie we eat or drink!


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=oernent tolerance liits for arious poisons usually use these

abbreiations! "eeber that these are extreely sall #uantities!

4or exaple, if you put one teaspoon of salt in two gallons of water theresulting salt concentration would be approxiately 1,>>> pp and it

would not een taste salty?

Table 1$@easureents for Expressing Aeels of 2ontainants in 4ood and 'ater!

!ose %bbrev$ #etric e&uivalent %bbrev$ %rox$ amt$ in water

parts per

illionpp

illigras per

kilograg+kg 1 teaspoon per 1,>>> gallons

parts per

billion ppb

icrogras per

kilogra ug+kg

1 teaspoon per 1,>>>,>>>

gallons

!ose Effect "elationshis

The dose of a poison is going to deterine the degree of effect it

produces! The following exaple illustrates this principle!

>*proof whiskey to the water eery fie inutes until all the fish get

drunk and swi upside down! /robably none would swi upside down

after the first two or three shots! fter four or fie, a ery sensitie fish

ight!

fter six or eight shots another one or two ight! 'ith a dose of ten

shots, fie of the ten fish ight be swiing upside down! fter fifteen

shots, there ight be only one fish swiing properly and it too would

turn oer after seenteen or eighteen shots!

The effect easured in this exaple is swiing upside down!

Bndiidual sensitiity to alcohol aries, as does indiidual sensitiity to

other poisons!

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There is a dose leel at which none of the fish swi upside down (no

obsered effect)! There is also a dose leel at which all of the fish swi

upside down!

The dose leel at which 5> percent of the fish hae turned oer is knownas the E.5>, which eans effectie dose for 5> percent of the fish tested!

The E.5> of any poison aries depending on the effect easured! Bn

general, the less seere the effect easured, the lower the E.5> for that

particular effect!

7biously poisons are not tested in huans in such a fashion! Bnstead,

anials are used to predict the toxicity that ay occur in huans!

7ne of the ore coonly used easures of toxicity is the A.5>! The

A.5> (the lethal dose for 5> percent of the anials tested) of a poison is

usually expressed in illigras of cheical per kilogra of body weight

(g+kg)!

cheical with a sall A.5> (like 5 g+kg) is ery highly toxic!

cheical with a large A.5> (1,>>> to 5,>>> g+kg) is practically non*

toxic! The A.5> says nothing about non*lethal toxic effects though!

cheical ay hae a large A.5>, but ay produce illness at ery

sall exposure leels! Bt is incorrect to say that cheicals with sall

A.5>s are ore dangerous than cheicals with large A.5>s, they are

siply ore toxic!

The danger, or risk of aderse effect of cheicals, is ostly deterined

by how they are used, not by the inherent toxicity of the cheical itself!

The A.5>s of different poisons ay be easily copared howeer, it is

always necessary to know which species was used for the tests and howthe poison was adinistered (the route of exposure), since the A.5> of a

poison ay ary considerably based on the species of anial and the way

exposure occurs!

C


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B

highly toxic

.0=E"*

/7B less than &>>a few drops to

a teaspoon

BBoderately

toxic

'"0B0= 51 to 5>> &>> to &,>>>oer 1teaspoon to 1

ounce

BBB

slightly toxic2-TB70 oer 5>> oer &,>>> oer 1 ounce

BF

practically

non*toxic

none re#uired

Toxicity assessent is #uite coplex, any factors can affect the results

of toxicity tests! > to 1,>>>

ties less than the 07EA to proide a wide argin of safety for huans!

The TAF (threshold liit alue) for a cheical is the airborne

concentration of the cheical (expressed in pp) that produces no

aderse effects in workers exposed for eight hours per day fie days per

week! The TAF is usually set to preent inor toxic effects like skin or

eye irritation!

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Fery often people copare poisons based on their A.5>Gs and base

decisions about the safety of a cheical based on this nuber! This is an

oer*siplified approach to coparing cheicals because the A.5> is

siply one point on the dose*response cure that reflects the potential of

the copound to cause death!

'hat is ore iportant in assessing cheical safety is the threshold

dose, and the slope of the dose*response cure, which shows how fast the

response increases as the dose increases!

'hile the A.5> can proide soe useful inforation, it is of liited

alue in risk assessent because the A.5> only reflects inforation

about the lethal effects of the cheical!

Bt is #uite possible that a cheical will produce a ery undesirable toxic

effect (such as reproductie toxicity or birth defects) at doses which

cause no deaths at all!

true assessent of cheical toxicity inoles coparisons of

nuerous dose*response cures coering any different types of toxic

effects!

The deterination of which pesticides will be "estricted -se /esticides

inoles this approach!


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The knowledge gained fro dose*response studies in anials is used to

set standards for huan exposure and the aount of cheical residue

that is allowed in the enironent!

s entioned preiously, nuerous dose*response relationships ust be

deterined, in any different species! 'ithout this inforation, it is

ipossible to accurately predict the health risks associated with cheical

exposure!

'ith ade#uate inforation, we can ake infored decisions about

cheical exposure and work to iniise the risk to huan health and theenironent!

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Lecture 1-Environmental Toxico

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