Table 2 Publications most cited for the hot needle test method in the present systematic review
Reference | # citations (% of papers reviewed) | Description (and references where given) |
|---|---|---|
De Witte et al. 2014 [17] | 42 (32%) | “Each plastic fragment was verified as plastic with a hot needle.” |
Devriese et al. 2015 [18] | 26 (20%) | “The hot point will make the plastic sticky and leave a mark.” |
Campbell et al. 2017 [14] | 8 (6%) | “application of a heated needle tip to each plastic to confirm that it would melt. Although characterization using Raman spectroscopy would have been helpful in identifying the nature of the plastics, budgets did not allow this.” |
Lusher et al. 2017 [46]a | 8 (6%) | “Perhaps the simplest technique is the use of a hot needle to observe melting points [6, 17, 18, 70]. While both cheap and fast, this method does not allow for the accurate identification of the polymer; however, the temperature range at which melting occurs does provide a specific range of potential plastics.”d |
Karlsson et al. 2017 [36] | 5 (4%) | “On occasion the hot needle test, where a hot needle is pushed against the particle to test if/how the material melts, was also used.” |
Barrows et al. 2017 [3]b | 5 (4%) | “The Hot Needle Test (based on [17]: In the presence of a very hot needle, plastic pieces will melt or curl…When using this technique, be sure your needle is very hot and held as close as possible to the piece in question (without blocking your view). If the needle is not hot enough, you will see no movement, even if the piece is plastic. This test should be used in conjunction with knowledge of other characteristics of plastic pieces.” |
Silva et al. 2018 [67]a | 5 (4%) | “the use of a heated needle tip to each plastic particle to ascertain whether the suspected particles melt when subject to heat. Nonetheless, this method has the drawback of not allowing for the identification of the polymer in question, although it remains a viable approach, particularly when more expensive equipments, such as spectroscopic analysers, are not available [14].” |
Hanke et al. 2013 [26]c | 4 (3%) | “In cases where the identification of plastic by visual inspection is ambiguous, i.e. for smaller items, confirmation might be sought by spectroscopy, e.g. FT-IR or Raman, or the “hot needle” technique may be employed." [in context of monitoring litter ingestion by fish, > 1 mm size] |
Norén, 2007 [56] | 4 (3%) | “In the laboratory, the particles showed the following properties: They were not dissolved in ethanol, acetone or xylene. The particles melted after having been heated gently on a microscope slide with a spirit burner. They emitted a distinct smell of plastics, as they were melting (smell of melted plastic rope end). Furthermore the plastic resolidified after having cooled and could easily be scratched with a sharpened glass needle.” [in context of particles > 80 micron from water] |