Science for curatorial safety: Detecting toxic heavy metal pesticides on museum collections

By National Services Te Paerangi

Toxic mercury or arsenic biocide treatments were extensively used on museum collections in the 19th and 20th Century to counteract insect damage and mould growth on textiles and natural environment collections.

While collection managers and curators are aware of the necessary health and safety precautions required for handling chemically treated collections, often a lack of information identifying past toxic treatments mean staff may be handling collections which are potentially hazardous without protective gear.

Dr Karyne Rogers from GNS Science, a scientist-in-residence at Te Papa, has been investigating the Botany collections at Te Papa and a range of Māori textiles and objects held at MTG Hawke’s Bay, Napier to determine if they have undergone chemical treatment and assess whether the collections are hazardous.

Karyne using the portable XRF to scan a kākahu in its storage drawer to minimize disturbance and damage. Photo supplied by Dr Karyne Rogers

Karyne uses a portable X-Ray Fluorescence (XRF) machine which analyses the elements on the periodic table from magnesium through to uranium. Traditional toxic treatments typically include mercuric chloride, lead arsenate and lead, copper or zinc salts. These were liberally applied, often in multiple applications over the course of decades or centuries. For some objects which have undergone specific taxidermy treatments, these levels can be even higher.

In May 2018, Karyne responded to an enquiry from Collections Coordinator Sara Perrett from MTG Hawke’s Bay, Napier. With an upcoming Māori cloak exhibit later in the year, the MTG Hawke’s Bay collections team wanted to assess whether there were toxic treatments on their cloaks before undertaking the intensive handling required to set up the exhibit.

Each XRF scan takes around two minutes to complete and the levels of each element are reported in ppm (where 10,000ppm = 1%). Karyne found most Māori cloaks in the MTG Hawke’s Bay collections had low levels of contaminants (especially paru-dyed kaitaka), but some cloaks, particularly kakahu (feather cloaks) had higher levels of contaminants. While no mercury was found on the cloaks, arsenic (up to 155ppm) was found on a child’s kakahu. On the other cloaks, various levels of lead and zinc were found to a maximum of 1020 ppm, although many had levels around 100 to 360 ppm.

Carved wooden taonga were also investigated and had much higher levels of arsenic (up to 650 ppm), lead (up to 7500 ppm) and zinc (up to 2200 ppm), while a taxidermy kiwi had arsenic levels over 1000ppm, and a huia bird had arsenic levels around 50,000 ppm.

XRF testing of the Pou Whakairo at MTG Hawke’s Bay. Photo supplied by Dr Karyne Rogers

Read the full report from the MTG Hawke’s Bay collection toxic treatments assessment

Meanwhile some mounted plant specimens from the Te Papa botany collections were also scanned and found to have mercury levels up to 2600ppm, and arsenic up to 1170ppm, along with higher levels of lead, copper and zinc salts, although these contaminants were mostly found in the old paper mounts, not the specimens themselves.

As far as we are aware, there are no official guidelines to classify safe or dangerous levels of toxic treatments on museum objects, nor official protocols for handling contaminated objects apart from wearing nitrile gloves. However measuring contamination levels does allow precautions to be put in place, and allows staff handling the toxic treated object to be more informed and make better decisions. Karyne has devised a traffic light system to guide collection care of contaminated objects. Objects with toxic elements less than 10 ppm are classed as green (no risk), between 10 and 100ppm are classed as yellow (low risk) and above 100 ppm are classed as red (handle with caution).

Testing Kevin the Kiwi using the XRF machine. Photo supplied by Dr Karyne Rogers

Where higher contamination levels exist, protection gear such as gloves and laboratory coat (and if dust particles are likely to be stirred up, a mask) should always be worn to avoid toxic chemical transfer by adsorption through the skin or accidental ingestion by touching the mouth with contaminated hands. If staff will have prolonged handling of contaminated collections for exhibits or more intensive collections handling, blood tests should be offered before and after handling events, to ensure baselines are monitored and do not change after handling. Caution about these unseen toxic treatments should also be considered when collections are used for public events and loans.

The original purpose of many taonga were as adornments or for practical use. It is understandable to want to physically engage with collection objects, and they are often irresistible in terms of texture and beauty, yet there should be a good understanding of toxic treatments before any object is loaned or publicly used.

The technology behind the XRF machines ensures it is sensitive to heavy metal contaminants and the machines are highly portable and non-destructive, so well adapted for scanning museum collections, without the need for disturbance of fragile items or removal from drawers.

XRF testing on a small kākahu from the MTG collection. Photo supplied by Dr Karyne Rogers

Although the portable XRF machine requires specialist training to operate and a radiation licence to operate because of the dangerous x-rays that it emits, Karyne is able to work with collections teams to undertake scanning of collections.

For more information about XRF scanning contact Karyne at GNS Science via k.rogers@gns.cri.nz