An Introduction to the

Concepts of ToxicologyConcepts of ToxicologyUsed in APESAPES

(Building off your knowledge of (Building off your knowledge of pesticides to lead into environmental pesticides to lead into environmental

hazardous chemicals as a whole)hazardous chemicals as a whole)

Toxicology Basics

PPM – Parts per million (1 in per 1,000,000 , 10-6 )

PPB – Parts per billion (1 part in 1,000,000,000 , 10-9 )

PPT – Parts per trillion (1 in 1,000,000,000,000 , 10-12 )

Since parts-per notations are quantity-per-quantity measures, they are known as dimensionless quantities; that is, they are pure numbers with no associated units of measurement.

Units Used to Measure Chemicals

in the Environment

Consider A simple cube 1 cubic meter in

volume

1m

1m

1m

formed of 1,000,000 cubes1,000,000 cubes,

1 cubic centimeter each

100cm

100cm

100cm

100cm x 100cm x 100cm =1,000,000

ccIn 1 m3

block 1cc = 1ppm

1 inch in 16 miles 1 minute in two years 1 cent in $10,000 1 ounce of salt in 31 tons of potato chips

1 bad apple in 2,000 barrels of apples

One part per million is

NOW…Divide each 11CCCC block into 1,000 blocks 0.1cM on

a side

1cm

1cm

1cm

0.1cm x 0.1cm x0.1cm = 0.001cm3

In 1 m3 block 0.001cm3 = 0.001cc or

1/1000 of a cc =

1ppb

1 inch in 16,000 miles 1 second in 32 years 1 cent in $10,000,000 1 pinch of salt in 10 tons of potato chips

1 lob in 1,200,000 tennis matches 1 bad apple in 2,000,000 barrels of apples

One part per billion is

Next, divide each 0.1cc block into 1,000 into 1,000 blocksblocks 0.01cm on a side

0.1cm

0.1cm

0.1cm

0.01cm x 0.01cm x 0.01cm =

0.000001cm3In 1 m3

block .000,000,001m3 =

0.000,001cc or

1/1,000,000 of a cc = 1ppt

1 postage stamp in the area of the city of Dallas

1 inch in 16 million miles (more than 600 times around the earth)

1 second in 320 centuries 1 flea on 360 million elephants 1 grain of sugar in an Olympic sized pool

1 bad apple in 2 billion barrels

One part per trillion is

On the left side of the decimal point ( . ) 1 trillion is bigger than 1 billion 1 billion is bigger than 1 million 1 million is bigger than 1 thousand…

On the right side of the decimal point ( . ) 1 part per trillion is smaller than 1 part per billion

1 part per billion is smaller than 1 part per million

1 part per million is smaller than 1 part per thousand

Important Concept

For water at STP (standard temperature [23oC] and pressure [15 psi])

1 cc = 1ml = 1g

Important Relationship

(1000 ml or cc ) 11 liter of water = 1 kg liter of water = 1 kg (1000 g)

(1/1000 g) 1 mg / kg 1 mg / kg (1000 g) = 1 ppm1 ppm

(1/1000 cm3 ) 1 mm 1 mm33 / liter / liter (1000 cm3 ) = 1 ppm1 ppm

(1/1000 g) 1 mg / liter 1 mg / liter (1000 g) = 1 ppm1 ppm

……Which means Which means that

LD50

The amount (dose) of a chemical which produces death in 50% of a population of test animals to which it is administered by any of a variety of

methods

SubstanceSubstance (1/1000 g) mg/kg mg/kg (1000 g) body body weightweight

Normally expressed as milligrams of substance substance per kilogram of animal body weight body weight (same as ppmppm)

Measures of Toxicity:The Median Lethal Dose

PPM Visualization Worksheet

Your Turn!

There are three primary routes by which organisms are exposed to pesticides

OralDermal

Inhalation

Primary Routes of Exposureto Pesticides

Any exposure to pesticide which occurs when the chemical is taken in through the mouth and passes through the gastrointestinal tract

During oral exposure, although carried within the body, the pesticide is is still outside of the body proper still outside of the body proper until it passes through epithelial cellular membranes.

Primary Routes of Exposure: Oral Oral Exposure

Exposure of the skin to a pesticide

Most common route of human exposure

With proper hygiene this type of exposure is generally not serious unless there is a specific, rapid toxicological effect (often eye effects) which is of concern

Primary Routes of Exposure:

Dermal Dermal Exposure

Occurs when a pesticide is breathed into the lungs through the nose or mouth

Significant route of exposure for aquatic organisms

Not of toxicological concern until it crosses from the lung into the body (unless the chemical is corrosive)

Primary Routes of Exposure:

InhalationInhalation Exposure

For pesticidespesticides – less is more when dealing with toxicity The less you need to cause a toxic effect – the more toxic the substance is

Thus an LDLD5050 of 25 mg/kg is more toxic than is one of 7,000 mg/kg

Remember –

The relative acute toxicity of a pesticide is reflected on the label in the form of

a “signal wordsignal word”

The (toxicologically) appropriate signal word MUST appear on every pesticide label

The three possible signal words are

CAUTIONCAUTIONWARNINGWARNING

DANGERDANGER

Signal Words

“WarningWarning” reflects an intermediateintermediate degree of relative toxicity

All pesticides with an LD50 of greater than 50 and less than 500 mg/kg must display this word on their label

Pesticides in this category are classed as

“Moderately toxicModerately toxic” (>50 but <500 mg/kg)

Signal Words:WARNINGWARNING

“DangerDanger” reflects the highest degree of relative toxicity

All pesticides with an LD50 of less than 50 mg/kg must display this word on their label

Pesticides here are classed as

“Highly toxicHighly toxic” (< 50 mg/kg)

Signal Words:DANGERDANGER

Legally defined term – not just anything you don’t like

Any pesticide with an LD50 of 50 mg/kg or less Labels must reflect this classification Label must have the signal word “DANGER” plus the word “POISON”

Label also must display the skull and crossbones icon

POISON!!!

YES!YES!All are toxic to some quantifiable degree

SugarSugar has an LD50 of 30,000 mg/kg

EthanolEthanol, a party favorite, has an LD50 of only

13,700 mg/kgWaterWater has a recognized LD50 of slightly greater than 80,000 mg/kg

Relative Toxicity:Are all substances

toxic?