Transcript TOXICOLOGY V

WATER
as
A Resource
1
Drinking Water
2
Water Contamination
 How
do we know what is “clean water?” In
other words, how do we know if water is
“safe” for humans and wildlife?
 Use “Water Cards” put in order from
unsafe  safe drinking water.
 Read “The Dose Makes the Poison,”
answer questions #1-6 on your paper.
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Water Contamination
 How
do we know what is “clean water?” In
other words, how do we know if water is
“safe” for humans and wildlife?
 Charity Water Video
 Let’s look at Water Quality Indicators
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Units for Measuring Water
Quality
PARTS PER MILLION
Most dissolved substances
found in water are measured
in parts per million (ppm) or
even smaller amounts. This
means that for every one
million parts (units) of water
there is a certain number of
parts of the substance.
It is also expressed as milligrams
per liter. There are 1000 milliliters
in a liter and 1000 milligrams in a
gram. For example, a dissolved
oxygen reading of 8 ppm means
there are 8 milligrams of oxygen
for every 1000 milliliters of water.
8/1000 gram  1000 milliliters =
8/1,000,000 (8 parts per million)
Concentrations of certain
substances are also measured
in parts per billion, parts per
trillion and so on. These are
very small amounts but certain
substances can be harmful
even at these very low
concentrations.
Water Quality Indicators
We will now take a look
at some water quality
indicators.
“Water quality” can refer
to quality for a healthy
“environment” and/or
healthy for human
consumption
TEMPERATURE
Temperature is measured in
Fahrenheit and Celsius degrees.
(Temperature, of course, is not a
“dissolved substance”)
Most aquatic organisms live
within a temperature range of
32º F (+0º C) to 90º F (32º C).
TEMPERATURE
Rapid temperature change and
temperature extremes can stress
aquatic organisms.
pH
pH is the measure of the hydrogen
ion (H+) concentration.
The pH scale is zero to 14. Seven
is neutral, below seven is acidic,
and above seven is basic (or
alkaline).
Most aquatic organisms exist
within a pH range of 5.5 to 9.5.
pH
pH is usually not a major problem
for aqutic organisms or drinking
water except in certain situations
(acid mine drainage etc.)
Salinity
Salinity refers to the salt
concentration in water,
mostly sodium chloride.
Salinity is historically
measured in parts
per thousand (ppt)
or grams per liter.
Salinity
Salinity of the ocean is
about 33-38 ppt. The
maximum considered
safe for drinking water is
1 ppt (1,000 ppm)
Salinity
Saltwater can cause drinking water
problems when it replaces fresh
groundwater near the coastal
areas.
DISSOLVED OXYGEN
Dissolved oxygen is a
product of
photosynthesis and
diffusion.
Diffusion: The movement of molecules, for example oxygen molecules,
from an area of higher concentration (e.g. the leaf) to an area of lower
concentration (e.g. the water).
Typical range 0 – 14 ppm
“Quality” water >6 ppm
DISSOLVED OXYGEN
Most aquatic
organisms that
respire using
oxygen need at
least 5 or 6 ppm
of oxygen in
order to survive.
BACTERIA
Most bacteria are important in
nutrient and other organic cycles.
Excess nutrients
cause algal blooms.
As algae die and
decay, the high
bacterial load
rapidly consumes
dissolved oxygen.
TURBIDITY
Turbidity refers
to water clarity.
Sediments
suspended in
the water
increase
turbidity.
Certain types of bacteria
indicate animal and human
waste pollution.
Escherichia coli are coliform
bacteria found in the intestines
of warm-blooded organisms.
Most strains are harmless but
one E. coli strain can cause
severe diarrhea and kidney
damage.
Bacteria
The goal for drinking water is
“zero” however this is often
impossible.
Therefore, U.S. laws require that
drinking water is treated with a
disinfectant.
Drinking water is periodically
tested for bacteria
NITRATE
Nitrate is a primary
plant nutrient.
Nitrate is water
soluble and moves
easily from surface
to groundwater.
Excess nitrate causes algal
blooms that reduce water quality.
Under normal conditions, the
nitrogen cycle keeps the amount of
available nitrogen in balance with
the demands.
However, excessive use of fertilizers
and nutrient rich sewage release
have created a surplus of nitrate.
The result is eutrophication from
excess algae and bacteria with
reduced dissolved oxygen.
PESTICIDES / HERBICIDES
These chemicals are very
complex.
Effects on aquatic
organisms – Moderately
to highly toxic to
mammals, mollusks,
aquatic insects,
amphibians and fish.
TOXIC CHEMICALS
Toxic chemicals usually come
from industry and energy
production.
The effects are often not known
until years after they have entered
the environment.
Some toxic chemicals include
petroleum products (oil), heavy
metals (lead, mercury etc.), and
organic compounds (DDT,
PCB).
Stop: Activity
 Use
“Water Cards” put in order
from unsafe  safe drinking
water.
BIOASSAYS
 Dose/Response



Bioassays are used to:
Estimate toxicity to humans.
Estimate maximum concentrations of specific
chemicals allowed to discharge into bodies of
water.
Investigate hazardous waste sites.
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Bioassay Species
3



organisms are often used
Daphnia
Duckweed
Lettuce Seeds
 Expose
organisms to chemicals and
measure how they respond.
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Bioassay Species
 Lettuce



Seeds
In Petri dishes with test samples
Sensitive to pesticides, solvents and organic
compounds
After 5 day check for:
• germination
• radicle length
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CONCENTRATION VS. DOSE
 LD50 the
Dose that is Lethal for 50% of the
test organisms.

Used for Daphnia
 TC50 the
Concentration that causes a 50%
drop in growth or health of the test
organisms (Toxic Concentration).

Used for seeds (they may not die, just not
sprout)
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An Introduction To Experimental Design
 The
Treatments in an experiment
represent the factor that you vary while
keeping everything else constant.
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An Introduction To Experimental Design
 The
control is the untreated group, used
for comparison with the treatment groups.
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An Introduction To Experimental Design
 Replicates
are groups of organisms
exposed to identical conditions.

The more replicates the better.
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INTERPRETING BIOASSAY RESULTS
do interpret LD 50’s and LC 50’s?
 What conclusions are valid about
environmental impacts of the compounds
being tested?
 How
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INTERPRETING BIOASSAY RESULTS
 Bioassays
DO NOT specify what
chemicals are present in the samples.
 They measure the combined toxicity of
whatever is in the sample.
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INTERPRETING BIOASSAY RESULTS
 Bioassays
give us a standard technique to
compare:
 Samples taken at different times and
places.
 Samples of environmental samples to
known samples.
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TIPS FOR PLANNING AN
EXPERIMENT

GO TO
 http://ei.cornell.edu/student/exptdesign.asp
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