What are pesticides?

Pesticides are poisons or toxins used to kill pests by entering the organism through dermal contact (skin), oral ingestion (mouth), or inhalation (nose or mouth). Commonly, pesticides are divided into organic and inorganic pesticides according to their main chemical component.

Organic pesticides
Organic pesticides are carbon-based compounds that include pesticides such as Naphthalene and Paradichlorobenzene (PDB), two chemicals commonly known as mothballs. Naphthalene and PDB are applied as a solid (in mothball and flake form) and sublimate, acting as a fumigant. The fumes from these materials kill insects and work best in tightly closed spaces. The pesticide residue is expected to evaporate over time. Old collections often smell of these pesticides and it is not clearly understood how long it takes for the chemicals to completely sublimate in the museum environment.

Inorganic pesticides
At NMAI, “inorganic pesticides” refers to compounds that include heavy metals such as arsenic or mercury. Arsenic was commonly used as arsenic trioxide (As2O3) or arsenous acid and mercury as mercuric chloride (HgCl2). Inorganic pesticides were often used in powder, paste, or dip form. The pesticide residue stays on the object and continues to be an effective insect killer for a long time.

Within the types of pesticides used on museum collections, botanicals such as tobacco and camphor are generally mildly toxic and are not persistent. Organic compounds such as DDT can be toxic and more persistent, Naphthalene and PDB can result in skin and respiratory problems or allergies. Inorganic pesticides such as arsenic and mercury are generally the most persistent and most dangerous compounds and can have the most deleterious effects on human health.

Why were pesticides used?

Collections made of animal or plant materials such as leather, feathers, plant fibers, and textiles represent an excellent food source for many insects. Pesticides including herbicides and fungicides were used by collectors and in museums in order to prevent or destroy pests and to preserve the collections.

How were pesticides applied to objects?

Application methods of pesticides are as varied as the pesticides, herbicides, and fungicides that have been used on collections throughout the decades. Understanding the different application methods is important in order to evaluate past methods of care, visible chemical alterations, and possible health hazards. One pesticide might have been applied in many different ways with a variety of individual preparations and recipes at different museums. It is often difficult to obtain information on preparation and application of the pesticide in question, since these treatments were probably considered standard procedure at the time and were often not recorded or documented. Also prior to 1972 (When the Federal Insecticide, Fungicide and Rodenticide Act was passed) the use and application of many pesticide chemicals was unregulated. The pesticide chemical may be formulated in oil concentrate, emulsifying concentrate, wet able powder, dust, baited or resin pest strip. The chemicals might have been applied through dipping, spraying, aerosol bombing, misting, dusting, or fumigation techniques. Objects might have been completely filled or covered with a chemical over long periods of time. As the pesticide formulations changed over time, the application methods developed as well. Examples of application techniques include:

The pesticide is applied through immersing the material into the liquid solution of the pesticide, such as gasoline.

Residual sprays
A residual spray is applied and remains active for a long period of time. Most household pesticide sprays are not residual and usually become inactive and lose their toxicity within a matter of hours. Other pesticides, such as organochlorides and organophosphates, can remain active for many years. Residual sprays are applied to skirting boards, cracks, and crevices within the area being treated. When the liquid carrier evaporates, the pesticide remains on the surface, where it is picked up by insects or ingested by insects during grooming.

Misting, dusting, or aerosol bombing
A pesticide chemical is applied to an area as a mist or aerosol or is dusted over the area.

Fumigation allows the pesticide to penetrate areas that would not be affected by other applications. The fumigant, which could be one of many toxic chemicals, is released inside a chamber, or under a gas-tight tarpaulin. Fumigants are generally broad-spectrum pesticides, which kill a wide variety of insects and animals.

What are current pest management techniques?

With growing environmental concerns, museums have become aware of non-chemical pest control methods for their collections. Integrated pest management (IPM) refers to the methods and techniques used to prevent pests in museums and how to take appropriate pest control measures to mitigate the problem. Today the focus in museums is on the monitoring of insects through the use of traps, practice of good housekeeping and maintenance of the building interior and exterior areas, and the development of a plan for the occasional active infestation. Pest eradication methods are usually non-chemical and include freezing, high heat, and low oxygen (anoxic) environments. For more information visit

Repatriation and pesticides

The advent of repatriation legislation in the United States, including the National Museum of the America Indian (NMAI) Act of 1989 and the Native American Graves Protection and Repatriation Act (NAGPRA) of 1990, introduced a different aspect to the dilemma of pesticide residues on collections for museums actively involved in repatriation efforts, and for the Native American recipients of culturally sensitive materials: objects repatriated to Native communities and individuals by museums for ceremonial use may pose potential human health hazards.

It is not advisable to make assumptions on appearances alone about whether or not an artifact is likely to be contaminated with hazardous residues. If an artifact has evidence of prior infestation, this does not mean it is free of pesticide residues—it may have been treated with pesticides as a result of that infestation. Likewise, it is possible that an object in excellent condition has not been treated with pesticides. Objects in museum collections may have a long history of prior owners, any of whom could have used pesticides. The only way to know with any certainty if pesticides or other hazardous residues are present on an item is through chemical analysis.

The NMAI strongly encourages the testing of items considered for repatriation, specifically for the presence of arsenic and mercury compounds. Information gathered from testing may help the tribe determine the object's future use and disposition. However, some people may view the testing of an object to be invasive or culturally inappropriate. The decision to conduct testing of an object requested for repatriation rests with the official representatives of the affiliated tribal community. The tribe must consider both the ramifications of the testing results and the compatibility of this activity with traditional protocol.