Anthropogenic debris pollution in peri-urban mangroves of South China: Spatial, seasonal, and environmental drivers in Hong Kong.

Excessive mismanaged debris along tropical coasts pose a threat to vulnerable mangrove ecosystems. Here, we examined the spatial, seasonal and environmental drivers of anthropogenic debris abundance and its potential ecological impact in peri-urban mangroves across Hong Kong. Seasonal surveys were conducted in both landward and seaward zones, with identification, along belt transects, of macrodebris (>5 mm) based on material type and use. Our results indicate spatial variability in debris abundance and distribution, with plastic being the predominant material type identified. Both plastic and non-plastic domestic items covered the most surface area. Debris aggregation was highest at the landward zones, consistent with the literature. In the dry season, more debris accumulated and covered greater surface area in both seaward and landward zones. These results confirm that land-derived debris from mismanaged waste, rather than debris coming from the Pearl River, is the primary source of anthropogenic debris pollution threatening Hong Kong's mangroves.

Fate of plastic in the environment: From macro to nano by macrofauna.

Plastic ingestion has been widely investigated to understand its adverse harms on fauna, but the role of fauna itself in plastic fragmentation has been rarely addressed. Here, we review and discuss the available experimental results on the role of terrestrial and aquatic macrofauna in plastic biofragmentation and degradation. Recent studies have shown how biting, chewing, and stomach contractions of organisms shatter ingested plastic along their digestive tracts. Gut microbial communities can play a role in biodegradation and their composition can shift according to the type of plastic ingested. Shifts in molecular weights, chemical bond forming and breaking, and changes in thermal modification detected in the plastic debris present in the faeces also suggest active biodegradation. A few studies have also shown interactions other than ingestion, such as burrowing, may actively or passively promote physical plastic fragmentation by fauna. We suggest that further investigations into the role of fauna in physical fragmentation and chemical degradation linked to active ingestion and gut associated microbiota metabolism, respectively, should be conducted to better evaluate the impact of these mechanisms on the release of micro- and nano-plastic in the environment. Knowledge on macrofauna other than marine invertebrates and terrestrial soil dwelling invertebrates is particularly lacking, as well as focus on broader types of plastic polymers.