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Validating the Hot Needle Method for Determining the Presence of Microplastics
Citation:
Robinson, S., K. Ho, M. Cashman, AND R. Burgess. Validating the Hot Needle Method for Determining the Presence of Microplastics. NAC SETAC 27th Annual Meeting, NA, Virtual, April 05 - 07, 2021.
Impact/Purpose:
Microplastics are found throughout the marine environment. Determining the presence of microplastics in water or sediment samples is expensive, time-consuming, and may require advanced training. However, the Hot Needle Method can be used to determine if a particle in a filtered sample is plastic or some other environmental material such as clam or crab shell, wood, feathers, or even salt or sand. To evaluate a particle, a heated needle is touched to its surface; a plastic particle melts and many environmental samples do not. We documented the response of a variety of known commercial plastics as well as materials collected from a beach. This simple test would be useful as an early indicator of particles made of plastic in environmental samples and could be used by citizen scientists as well as researchers. It does not provide information on more specific composition.
Description:
Microplastics are ubiquitous in the marine environment. To study their fate and effects in the environment, researchers need to isolate, extract, and identify plastics from environmental (e.g., water, sediment or tissue) samples. Differentiating a plastic fragment from natural materials such as chitin, wood, silica, or feather can be challenging. Although sophisticated analytical techniques are available for identifying microplastics, they are expensive, time-consuming, and require advanced training. This method determines plastics based on their melting and distortion after a hot needle is applied to its surface. This study documents the method and the responses of many plastics and natural materials to a heated needle. For this study, we weathered seven commercial microplastics (e.g. polyethylene, polyvinylchloride, polypropylene), and applied a heated needle to weathered, non-weathered, and beach-collected samples. We observed changes in the appearance of a variety of plastic and non-plastic materials (e.g., melted, not melted, burned) after being treated with the Hot Needle Method. We captured the response of each sample photographically and assessed the utility of the Hot Needle Method. We observed that this method melted commercial plastic samples (> 40 µm), regardless of weathering. Our findings and photographic documentation of these physical changes strengthen the applicability of the Hot Needle Method to confirm plastics found in environmental matrices.
