EFFECTS OF PLASTIC RESIDUES ON THE ENVIRONMENT AND ON THE FAUNA
There are some reports of the effects of debris from terrestrial habitats, for example ingestion by the endangered California condor, Gymnogyps californianus (Mee et al. 2007). However, the vast majority of the work describing the environmental consequences of plastic waste comes from marine environments and more work is needed in terrestrial and freshwater habitats. Plastic debris causes cosmetic problems and also poses a danger to maritime activities, including fishing and tourism (Moore 2008; Gregory 2009). Discarded fishing nets result in ghost fishing which can result in commercial fishing losses (Moore 2008; Brown & Macfadyen 2007).
Floating plastic debris can be rapidly colonized by marine organisms and, as it can persist on the sea surface for considerable periods, can subsequently facilitate the transport of non-native or “exotic” species (Barnes 2002; Barnes et al. 2009; Gregory 2009) . ). However, the issues that attract the most public and media attention are those that cause wildlife ingestion and involvement. More than 260 species, including invertebrates, turtles, fish, seabirds and mammals, have been reported to ingest or become entangled in plastic debris, resulting in reduced movement and feeding, reduced reproductive capacity, lacerations, ulcers and death ( Laist 1997; Derraik 2002; Gregorio 2009). The limited follow-up data we have suggests that entanglement rates have increased over time (Ryan et al. 2009). A wide range of species with different feeding modes, including filter feeders, reservoirs and detritivores, are known to ingest plastic. However, ingestion is likely to be particularly problematic for species that specifically target plastic items because they mistake them for their food. Consequently, the incidence of ingestion can be extremely high in some populations. For example, 95% of dead lightning strikes washed ashore in the North Sea have plastic in their guts, and significant amounts of plastic have been reported in the guts of other birds, including albatrosses and prions (Gregory 2009). There is very good data on the amount of waste ingested by seabirds recorded on dead bird carcasses. This approach has been used to monitor temporal and spatial patterns in the abundance of plastic debris on the sea surface on a regional scale in Europe (Van Franeker et al. 2005; Ryan et al. 2009).
One area of particular concern is the abundance of small pieces of plastic or microplastics. In some marine habitats fragments as small as 1.6 µm have been identified and it seems likely that there are even smaller fragments below current detection levels. A recent seminar convened in the United States by the National Oceanic and Atmospheric Administration concluded that microplastics should be defined as pieces <5 mm with a suggested lower size limit of 333 µm to focus on the microplastics that will be captured using conventional sampling approaches (Arthur et al. 2009). However, we believe it is important that the abundance of even smaller fragments is not overlooked. The plastic fragments appear to be formed from the mechanical and chemical deterioration of larger objects. Alternative routes for microplastics to enter the environment include direct release of small pieces of plastic that are used as abrasives in industrial and household cleaning applications (e.g. shot blasting or scrubbers used in patented hand cleaners) and the spill of plastic granules and powders which are used as raw materials for the manufacture of most plastic products. Data from the coasts, open ocean and debris ingested by seabirds indicate that the amount of plastic fragments is increasing in the environment and that the amount on some coasts is substantial (> 10% by weight of plastic material). Barnes et al. 2009). Laboratory experiments have shown that small pieces such as these can be ingested by small marine invertebrates, including filter feeders, reservoirs and detritivores (Thompson et al. 2004), while mussels have been shown to retain plastic for more than 48 days (Browne et al. 2008). ). However, the extent and consequences of the ingestion of microplastics by natural populations are not known.