Asbestos in Coloured Sand: What New Zealand’s Latest Research Means
Asbestos in Coloured Sand: What New Zealand’s Latest Research Means
Recent New Zealand research into asbestos-contaminated coloured sand has provided an important reminder: finding asbestos is not always straightforward, and a laboratory result of “not detected” does not necessarily prove that a product is asbestos-free.
The research examined whether contaminated craft sand could release asbestos fibres into the air during realistic play activities. Its findings are particularly relevant to schools, early-childhood centres, workplaces, property managers and anyone responsible for assessing an area where recalled sand may have been used.
The study does not mean every coloured-sand product contains asbestos. It also does not establish that everyone who handled an affected product received a significant exposure.
What it does show is that some contaminated loose craft sands can release identifiable airborne asbestos fibres during ordinary handling.
What did the researchers investigate?
Researchers from Auckland University of Technology and collaborating organisations tested a selection of craft and moulding sands, including products affected by recalls.
The work was conducted inside a controlled Class A asbestos enclosure. A trained technician used the products in ways intended to simulate play, including:
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pouring and scooping sand;
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moving it with toy vehicles;
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shaping and handling the material; and
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transferring it between containers.
Personal and static air samples were collected at different heights and positions. The researchers used phase-contrast microscopy, transmission electron microscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy to examine the material and air samples.
This combination of methods was important because each analytical technique answers a different question and has different limitations.
What did the study find?
Nine out of ten contaminated loose craft-sand samples released identifiable airborne asbestos during the simulated activities.
The airborne material included chrysotile and tremolite asbestos, with some fibres meeting respirable dimensional criteria.
No asbestos was detected in air during four moulding-sand scenarios. However, the researchers cautioned that the analytical detection limits were not low enough to conclude that absolutely no release had occurred.
That distinction matters.
A non-detect means asbestos was not identified above the method’s detection capability in that particular sample. It does not necessarily mean that the true concentration was zero.
The study demonstrates that airborne release can occur. It does not establish how much exposure every user received, how frequently release occurs across all products or what an individual’s resulting health risk may be.
Why the analytical method matters
One of the most practically important findings involved the testing of the sand itself.
Several samples reported as “not detected” using polarised-light microscopy were subsequently found to contain asbestos when examined using transmission electron microscopy. In one case, a purple sand sample reported as negative by PLM was reported as containing 1.64% chrysotile by TEM.
PLM remains an established and valuable method for identifying asbestos in many building materials. However, very fine asbestos fibres, low concentrations and complicated mineral matrices can make some materials difficult to assess using PLM alone.
Electron microscopy can examine considerably smaller particles and provide additional information about their morphology and composition.
This does not mean TEM should automatically replace PLM for every asbestos survey sample. It means the selected method must be appropriate for the material, the suspected contamination and the decision that needs to be made from the result.
Why air monitoring results also need careful interpretation
Phase-contrast microscopy is widely used for occupational asbestos air monitoring and clearance work in New Zealand. It is useful for counting fibres that meet specified dimensional rules, but it cannot determine whether an individual fibre is asbestos.
Non-asbestos fibres may therefore be included in a PCM count. Equally, asbestos structures outside the applicable PCM counting rules may not be represented in the reported concentration.
Electron microscopy can identify asbestos structures, but its results cannot automatically be compared with a PCM clearance result. The analytical magnification, counting rules, fibre dimensions and reporting units may differ.
The sand study also encountered heavy dust loading, shortened sampling durations and reduced pump flows. These factors affected the sensitivity of some samples.
This is why an asbestos air-monitoring report should not be reduced to a single number. The sampling duration, air volume, filter condition, analytical sensitivity, sampling position and method must all be considered when interpreting the result.
What does this mean for schools and workplaces?
WorkSafe New Zealand’s advice remains precautionary.
Recalled or suspected affected sand in a workplace should be treated as friable asbestos-containing material until proven otherwise. Its assessment, removal and clearance must be undertaken using the appropriate asbestos controls and competent people.
If suspect sand has been spilled or extensively used, an assessment may need to consider more than the product remaining in its original container. Depending on the circumstances, the investigation could include:
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floors, carpets and nearby surfaces;
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storage areas and activity tables;
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cleaning equipment and vacuum cleaners;
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footwear and movement routes;
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adjacent rooms or spaces;
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settled dust; and
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secondary transfer of the material.
Disturbance testing should not be improvised inside an occupied room. Deliberately handling suspect material to “see whether fibres become airborne” could create additional contamination and exposure.
Any release assessment needs controlled conditions, suitable containment and a defensible sampling strategy.
Five practical lessons from the research
1. Appearance cannot confirm whether sand contains asbestos
Colour, texture, packaging and supplier information are not substitutes for suitable laboratory analysis.
2. One sample may not represent the entire product
Loose mineral products can be heterogeneous. Different containers, batches, colours or areas of the same container may not contain identical material.
3. “Not detected” does not mean “zero”
The result must be interpreted alongside the method, detection limit, sample size and representativeness.
4. PCM cannot identify asbestos fibres
PCM is useful for established air-monitoring purposes, but it reports fibres meeting its counting criteria rather than confirming that every counted fibre is asbestos.
5. A good assessment considers how contamination may have spread
Testing only the remaining sand may be insufficient where the product has already been poured, played with, cleaned up or transported through other areas.
Should current asbestos practice change?
The research reinforces existing precautionary practice rather than replacing it.
It does not establish a new clearance limit, invalidate New Zealand’s prescribed PCM methodology or create a new legal test for determining whether an area is safe to reoccupy.
It is also important to recognise that the paper remains a preprint and has not yet completed peer review. The controlled simulation involved a limited selection of products and cannot reconstruct every real-life exposure.
However, the combination of bulk-material testing and airborne-fibre identification provides credible evidence that contaminated loose craft sand can release asbestos during normal handling.
For asbestos consultants, the practical message is clear: select the analytical method according to the material and purpose of the investigation, design sampling around realistic contamination pathways, and state the limitations of every non-detect result.
Independent asbestos advice in New Zealand
If recalled or suspect coloured sand has been found at your school, workplace or property, avoid disturbing or attempting to clean it until the situation has been properly assessed.
Asbestos Safe Consultancy provides independent asbestos inspections, sampling, air monitoring and clearance services across Hawke’s Bay, Gisborne, Taupō and Manawatū.
Contact us for practical advice before disturbing suspect material or arranging remediation.