The Relevance of the NOAEL concept and related parameters in defining pollution thresholds for...

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.