Nitrogen (N2) gas is used in controlled atmospheres are effective in causing insect death within 2-6 weeks, as shown by measuring insect respiration before and after treatment. For Nitrogen/Argon treatment to work, the oxygen levels are reduced to 0.1-0.3%. The oxygen deprivation causes a disruption in the glucose production within insect bodies, resulting in weight loss and eventual insect death. Rates of death vary with temperature, relative humidity, exposure time, and species type. Increasing the temperature helps reduce the exposure time for both gases because insect respiration is increased with higher temperature, causing rapid water loss. (Valentín 1993). Argon is 25-50% faster than nitrogen at killing insects. Additionally, argon kills some fungal tissue while nitrogen permits the same fungi to survive anoxia (Koestler, Tavzes, Pohleven 2004). Modified atmospheres using nitrogen and argon are usually continuous-flow systems with soft or hard walled, vapor impermeable chambers. The continuous flow of gas initially purges the chamber of oxygen, and then maintains low oxygen levels to compensate for leaks.

What collections materials can be treated this way?

Almost all collections can be treated with nitrogen or argon.  Exceptions include:

• One study showed that minerals such as litharge (PbO), cinnabar (HgS), and sienna (mostly Fe2O3) do experience color change in the absence of oxygen (Arney, Jacobs, and Newman 1979), so care must be taken if this is a concern with artifacts or pigments. Prussian blue and ultramarine initially change, but the color comes back. Changes are not noted when pigments are in mixtures, e.g., in paint films. Textiles may be the most likely to change (temporarily).
• Wet artifacts have the potential to reduce the effectiveness of treatment due to insect adaptation to use anaerobic respiration, although this is generally unlikely for the types of pests typically encountered for museum and library pests (Selwitz 1998).

General procedures

An anoxic atmosphere requires an enclosure, gas, and gas monitoring devices. Uses low-oxygen gas (less then 1000ppm of O2). Enclosures must be constructed of vapor impermeable materials such as and polypropylene films.

Pros of this treatment

• No chemical residue on artifacts.
• Appropriate for a wide variety of collection materials.
• Argon gas has the additional benefit of preventing bio-deterioration by microorganisms like fungi and bacteria (Valentín 1990).
• More time-efficient than CO2 gas.