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Low probability and great potential damage – statistical comments
on
biomonitoring
Carsten Lüring
Kiel - 2010
www.bbe-moldaenke.de
Why use Biomonitors?

Fast and online detection of toxic substances

Detection of known as well as unknown or unexpected toxic substances

Massive reduction of efforts for chemical analysis

Detection of rare events

Prevention of high damage
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Statistical proof of God’s existence
Blaise Pascale (1623 - 1662)
Belief in God
No belief in God
God exists
God does not exist
+ ∞ (heaven)
-C
- ∞ (hell)
0
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The statistics of biomonitoring
(2010)
Monitoring
No monitoring
Toxic event
No toxic events
+ ∞ (heaven)
-C
- ∞ (hell)
0
-> consider the use of biomonitoring
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Organisms and Biomonitors

daphnids

algae
 luminescent bacteria
 mussels
 fish
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Performance of a water monitoring instrument:
Toxic event
No toxic events
Alarm
98%
0.1%
No Alarm
2%
99.9%
Question:
What is the probability of a toxic event if an alarm is indicated?
1.
ca. 99,9%
2.
ca. 98%
3.
ca. 5%
4.
ca. 2%
5.
I don’t know
6.
Nobody knows
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Performance of a medical test:
You are travelling to a tropical country.
After returning, you notice that some travellers - let´s say 1 of 1000 - are infected by a painful sickness.
To check whether you are infected or not, a diagnostic test with the following performance is conducted:
Test result:
Infected
Not infected
Test: infected
99%
2%
Test: not infected
1%
98%
infected
How high is the probability of infection?
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Performance of a medical test:
Infected
Not infected
Test: infected
99%
2%
Test: not infected
1%
98%
Your personal test result: infected
How high is the probability of real infection?
1.
ca. 99%
2.
ca. 98%
3.
ca. 5%
4.
ca. 2%
5.
I don’t know
6.
Nobody knows
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Result of the medical test:
Your personal test result: infected
How high is the probability of real infection?
1.
ca. 99%
2.
ca. 98%
3.
ca. 5%
4.
ca. 2%
5.
I don’t know
6.
Nobody knows
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Result of the medical test:
Example:
Number of travellers:
100,000
Number of not infected travellers
99,900
Number of infected travellers
Number of not infected travellers
100
with a false positive test
Number of infected travellers with a positive test
99
Number of infected travellers with a false negative test
Probability:
2,000
99 of 2,099 -> ca. 5%
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1
Consequence: Redo the test
Your personal second test result: infected
How high is the probability of real infection?
1.
ca. 99%
2.
ca. 98%
3.
ca. 70%
4.
ca. 35%
4.
ca. 15%
5.
I don’t know
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Consequence: Redo the test
Example:
Number of travellers with a positive test:
2,099
Number of not infected travellers with a positive test:
2,000
Number of infected travellers with a positive test:
99
Number of not infected travellers with a second false positive test
40
Number of infected travellers with a second positive test
98
Number of infected travellers with a false negative test
1
Probability:
98 of 138 -> ca. 70%
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Performance of a test:
To answer the questions of the probability of being infected, 3 pieces of information are required:
•Error of the test showing an infection although there is none
•Error of the test showing no infection although there is an infection
•A priori probability of the population
Infected
Not infected
Test: infected
99%
2%
Test: not infected
1%
98%
A priori probability
1/1000
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Performance of a water monitoring instrument:
Toxic event
No toxic events
Alarm
98%
0.1%
No Alarm
2%
99.9%
Question:
What is the probability of a toxic event if an alarm is indicated?
1.
ca. 99.9%
2.
ca. 98%
3.
ca. 5%
4.
ca. 2%
5.
I don’t know
6.
Nobody knows
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Performance of a single biomonitor
at a river:
Toxic event
No toxic event
0.9900000
0.0000100
0.0100000
0.9999900
0.0000100
Alarm
No Alarm
A Priori
Measurements per year
Measurements per hour
Number of correct alarms
Number of false alarms
Quota
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100000
11.416
0.990
1.000
0.497
Performance of 10 biomonitors in a drinking water supply system:
Toxic event
No toxic event
0.9900000
0.0001000
0.0100000
0.9999000
0.0000010
Alarm
No Alarm
A Priori
Measurements per year
Measurements per hour
Number of correct alarms
Number of false alarms
Quota
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100000
11.416
0.099
10.000
0.010
Consequences for biomonitoring:
•Double check in case of an alarm
•Reduce the number of alarms although there is no toxin by enhancing the instrument
Toxic event
No toxic event
0.9900000
0.0000100
0.0100000
0.9999900
0.0000100
Alarm
No Alarm
A Priori
Measurements per year
Measurements per hour
Number of correct alarms
Number of false alarms
Quota
100000
11.416
0.990
1.000
0.497
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Realization in bbe biomonitoring instruments:
Reduce the number of alarms although there is no alarm by enhancing the instrument by:
•using special alarm detection algorithms
•using more than on parameter to detect an alarm
- DaphTox / FTOX:
2-3 of the behavioural parameters need to be suspicious
- ToxProtect:
Activity and “swimming in the top row”
•supervising the hardware for illegal states
- Temperature
- Flowrate
- Function of heating / cooling devices
- Status of the organisms
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Double check in case of an alarm:
Using 2 instruments of the same type
BioMonitor A1
BioMonitor A2
-> expensive
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Double check in case of an alarm:
Using 2 instruments with different organisms
Detecting a wider range of toxins
Not usable for a double checking
BioMonitor A
BioMonitor A
BioMonitor B
BioMonitor B
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Realization in bbe biomonitoring instruments:
Double check in case of an alarm:
DaphTox / FTOX:
ToxProtect:
Two chamber systems with parallel alarm evaluation
Alarm evaluation by switching off the light
Algae Toximeter:
Redo the measurement 2 or 3 times
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The bbe Daphnia Toximeter verification mechanism
- current subjects of research  Using the phototaxis of the daphnia for
a second test
 Additional alternating blue light on the
left and right side in case of alarm
 Horizontal distribution
of daphnia by adding
5µg/l Pyrethrum
PyrethrumZugabe 5µg/L
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Ende
PyrethrumZugabe
Take home message:
The lower the probability of a toxic event the more important is the use of a biomonitor with an automatic double check of the alarm.
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Special thanks to:
Dr. Hans-Hermann Dubben:
Der Hund, der Eier legt
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Many thanks for
your attention
www.bbe-moldaenke.de
bbe MOLDAENKE GmbH
Wildrosenweg 3
24119 Kiel-Kronshagen
GERMANY
Service-Hotline: ++49-431-380 40-40
Telefax: ++49-431-380 40-10
[email protected]
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