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.