Palygorskite (Attapulgite)

Palygorskite, also sold as attapulgite, is a fibrous clay mineral made of magnesium, aluminum and silica. It is mined for absorbents such as cat litter and floor-sweep, drilling muds, and fillers. It is not asbestos, but its fibers have been studied for cancer risk, and IARC treats long and short palygorskite fibers differently.

Origin

Palygorskite is named after a locality in the Ural Mountains of Russia, and attapulgite after Attapulgus, Georgia, where large deposits are mined; the two names were later recognized as the same mineral. The palygorskite name is now preferred in mineralogy, while attapulgite remains common in industry.

Significance in Asbestos Context

Palygorskite comes up in asbestos cases in a few ways. Workers in drilling, absorbent and filler industries handled it, and its fibers can be counted as fibers on an air sample analyzed by phase contrast microscopy, which cannot tell one mineral from another. In its review of silicate fibers in the late 1990s, IARC classified long palygorskite fibers (longer than about 5 micrometers) as possibly carcinogenic to humans and short fibers as not classifiable, reflecting animal studies that pointed to fiber length. Most commercial palygorskite consists of short fibers. In product cases, it may also matter whether a clay-based product was contaminated with true asbestos, which needs electron microscopy to confirm.

Example Sentence

The drilling mud additive was mainly attapulgite clay, so the expert used TEM to check whether any of the fibers on the filter were asbestos.

Related Terms

Sepiolite, Drilling Mud, Mineral Fiber, IARC Classification, Fiber Length, phase contrast microscopy (PCM), Mineral Filler

Notes

• If an air test from a clay-handling job reports fibers, ask whether the fibers were identified by electron microscopy.
• Note product names and suppliers for clay absorbents or drilling additives you used; these can matter later.