A new cause of microplastics fragmentation in Hong Kong waters

Microplastic collected from different environments vary in composition due to the variation in sources and factors that brought these pieces to a particular location. In order to characterize the types of microplastics present in Hong Kong waters, microplastics (size of 1 - 5 mm) were collected from 11 beaches. Out of more than 6000 pieces of microplastics analyzed, 56% (by pieces) were plastic fragments with a predominance of white or transparent (42%) and blue (28%) in color. More importantly, a special type of fragment which has not been reported before is revealed. These fragments, composing about 10% of the fragments collected, are interestingly triangular in shape with at least two of the three sides being characteristically straight and resembling ad cut made by compression, often coupled with signs of tearing. Objective measurements and observation from some special pieces have made apparent differences between these "trimmed fragments" and those triangular fragments that were fracture randomly as the plastic degraded. Therefore, we proposed that this type of "trimmed fragment" was formed by biological causes, presumably by biting of macrofauna, instead of natural weathering. Preliminary tests with the bite mark of some local fish species have given some clue on the causes of these trimmed fragments. The finding here could therefore have wide implications on current ecotoxicological and modeling studies for microplastic since the active biting of large plastic debris has generally not been considered as a factor of microplastic fragmentation.