the relevance of the noael concept and related parameters in defining pollution thresholds for...
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The Relevance of the NOAEL concept and related parameters in defining pollution thresholds for
cultural heritage collections.
Jens Glastrup
The National Museum of Denmark
Articles to discuss:
• Studies of Lead Corrosion in Acetic Acid Environments(1).– Jean Tétreault, Jane Siriois and Eugénie Stamatopoulou
• Studies in Conservation 43 (1998) 17-32.
• Corrosion of Copper and Lead by Formaldehyde, Formic and Acetic Acid Vapours(2).– Jean Tétreault, Emilio Cano, Maarten van Bommel,
David Scott, Megan Dennis, Marie-Geneviève Barthés-Labrousse, Léa Minel and Luc Robbiola
• Studies in Conservation 48 (2003) 237-250.
Experiments:
• Experimental conditions:– Copper or lead plates, 2.5 (or
2) x 5 cm
– Room temperature
– Varying RH (I discuss 54%).
– Different acetic or formic acid concentrations.
Graph from (2)
Weight increase of copper over 135 days at varying formic acid koncentrations - Logarithmic x
-1
0
1
2
3
4
5
6
0,1 1 10 100 1000
ppm
g/m2
The NOAEL concept(No Observable Adverse Effect Level)
• From (1):
• Lead: ”As observed in……., when the acetic acid concentration is below 0.43mg/m3(175ppb), insignificant weight gains on lead were detected”
• From (2):
• Copper: ”A significant weight gain for copper samples is seen when the formic acid concentration is higher than 2ppmv(2000ppb or 3,8mg/m3)
The NOAEL conceptThe figures
• The balance minimum detection limit is 0.1 mg
• However, in the figure, 1-2 (difference between the ”same” weight is equalling a difference in weighing of 0.5mg, 3-2 is 0.6mg on the balance.
• This means that on a 25cm2 plate we cannot see a corrosion layer less than 128nm/year.
• This is at least 128 Cu(Ac)2 molecules
Weight increase of copper over 135 days at varying formic acid koncentrations
-0,2
0
0,2
0,4
0,6
0,8
1
1,2
0 2 4 6 8
ppm
g/m2
1
2
3
The size of things
Question 1?
• Is a minimum detection level of 128nm satisfactory to define a No Observable
Adverse Effect?
The NOAEL concept (No Observable Adverse Effect Level)
• Tétreault (2003): The NOAEL approach relies on thermodynamic limitations (Brimblecombe 1994)
• But then:• If the concentration shall have no effect, the rate
of reaction must approach 0 at low concentrations.
• Is this true in this case?
Graph from (1)
Weight increase of lead over 4 months at varying acetic acid koncentrations
Logarithmic x
0
1
2
3
4
5
0,01 0,1 1 10 100
ppm
g/m2
What is the rate of reaction?Constant
Linear increase of corrosion
01234567
0 50 100 150
ppm
g/m2
What is the rate of reaction?Decreasing with increasing conc.
Loogarithmic decrease of corrosion rate
0
2
4
6
8
0 50 100 150
ppm
g/m2
What is the rate of reaction?Increasing with increasing conc.
Exponential increase of corrosion rate
01234567
0 50 100 150
ppm
g/m2
Graph from (1)
Weight increase of lead over 4 months at varying acetic acid koncentrations
Logarithmic x
0
1
2
3
4
5
0,01 0,1 1 10 100
ppm
g/m2
Graph from (1)
Weight increase of lead over 4 months at varying acetic acid koncentrations
Linear x
0
1
2
3
4
5
0 10 20 30 40
ppm
g/m2
Graph from (1)
Weight increase of lead over 4 months at varying acetic acid koncentrations
-2
-1
0
1
2
3
4
5
0 10 20 30 40
ppm
g/m2
Graph from (2)
Weight increase of lead over 135 days at varying formic acid koncentrations - Logarithmic x
-0,5
0
0,5
1
1,5
2
0,01 0,1 1 10 100
ppm
g/m2
Graph from (2)
Weight increase of lead over 135 days at varying formic acid koncentrations
Linear x
-0,5
0
0,5
1
1,5
2
0 5 10 15
ppm
g/m2
Graph from (2)
Weight increase of lead over 135 days at varying formic acid koncentrations
-0,5
0
0,5
1
1,5
2
0 5 10 15
ppm
g/m2
Graph from (2)
Weight increase of copper over 135 days at varying formic acid koncentrations - Logarithmic x
-1
0
1
2
3
4
5
6
0,1 1 10 100 1000
ppm
g/m2
Graph from (2)
Weight increase of copper over 135 days at varying formic acid koncentrations
Linear x
-1
0
1
2
3
4
5
6
0 50 100 150
ppm
g/m2
Graph from (2)
Weight increase of copper over 135 days at varying formic acid koncentrations
-1
0
1
2
3
4
5
6
0 50 100 150
ppm
g/m2
Own results:Removal of acetic and formic acid by lead.
0,0
500,0
1000,0
1500,0
2000,0
2500,0
0 20 40 60 80 100
Days
Acet
ic a
cid
(µg
/m3)
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
Fo
rmic
aci
d (
µg
/m3)
Acetic acid Formic acid
Question 2?
• Does a “No Observable Adverse Effect Level” exist?
My conclusions:• It is easy to set standards in air:
• But is it the best possibility?
• NOAEL is dangerous because of the “specific design” parameter.
• NOAEL does not exist, or only to a very limited degree
• We are the chemists, the readers are the curators, therefore, our standards should be defined with great, great care.
Source of data (from Hatchfield 2002): Organic pollutants, limit: NARA, Archives II Formaldehyde 4ppb Dutch government Acetic acid, HCl, formaldehyde, best technology Tétreault 1998 (CCI) Carbonyl compounds < 100µg/m3
My conclusions 2:
• If we continue to• - define thresholds based on NOAEL and NOAED.
– we risk to give acceptance to corrosion layers as thick as 1µm/10year.
– we risk to give the impression to curators that at certain low concentrations everything is safe.
– we “miss the focus”, by pinpointing a concentration in air, but what about highly desorbing/reacting materials in areas with high ventilation rates? As shown above, at lowest concentrations we probably have the the highest reaction rates.
• LIMITS IN AIR SHOULD BE BASED ON FLUX FROM SURROUNDING MATERIALS
My conclusions 3:
• Future research should focus on:– Establishing specific reaction rates for different
materials in contact.– FAST methods to evaluate materials.– Defining maximum desorbing flux from
materials.
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