Morphology and Size Distribution of Naturally Occurring Asbestos using TEM in Landscape Rock in Parks

Abstract BackgroundAsbestos is a silicate mineral that is naturally generated by geological processes in the Earth's crust. The six types of commercially used asbestos each display the asbestiform crystal habit that is characterized by fibrous aggregates of extremely long, thin crystals. This study provided data that can be used to discriminate asbestiform and non-asbestiform amphiboles contained in landscaping rocks in parks. MethodIn five of the 21 parks, two or more landscaping rocks were found to contain asbestos. These five were selected for additional study. The length and width of fibers being at least 5 ㎛ long and with a minimum aspect ratio of 3:1 were measured using a Transmission Electron Microscope(TEM) and compared to a standard asbestos sample.ResultsThe park samples were thicker than 1 ㎛(average 1.9 ㎛) while the Health and Safety Executive(HSE) reference sample averaged 0.3 ㎛ in width with 100 % thinner than 1.0 ㎛. The average aspect ratios were 7.1 for the park samples and 67.1 for the HSE reference sample. The actinolite contained in the landscape rocks of the five selected parks did not show the typical asbestiform structure that was observed in the standard asbestos sample.ConclusionsBased on these distributions, the amphibole fibers in sampled landscape rocks were found to be thicker and lower aspect ratio than those of the standard sample. The result of this study can contribute to the public policy for managing and controlling of landscaping rocks containing naturally occurring asbestos(NOA) and also to communicate about the possible health risk resulting from NOA contained in landscaping rocks.