Ingestion of Plastics by Marine Organisms

Abstract

Many marine organisms ingest plastic items, providing a potential mechanism for the transfer and accumulation of hazardous chemicals associated with plastics. This chapter summarises the range of organisms known to ingest plastic items and the factors influencing the amount of plastic in their digestive tracts. Ingestion can be direct (primary ingestion) or indirect (secondary ingestion via contaminated prey), with direct ingestion being either deliberate (plastic items mistaken for prey items) or accidental (plastics consumed passively by, e.g. filter feeding). Ingestion rates can be summarised as the proportion of individuals to contain ingested plastic (frequency of occurrence = incidence) as well as the average plastic load per individual (expressed by number, mass or volume of items). The amount of plastic in the digestive tract of an organism is a balance between its intake rate and removal via excretion and/or regurgitation. Individual-level variation in plastic loads typically is large and strongly right skewed. Numerous factors probably account for this variation, including age-specific and individual differences in the likelihood of plastic ingestion and retention times, as well as temporal and spatial differences in plastic exposure. Retention times are poorly known for many groups of marine animals, and may be influenced by particle size, shape and type of plastic, as well as phylogenetic and age-related differences in how animals handle indigestible prey remains. Three categories of organisms can be recognised: species that regurgitate most plastic (e.g. gulls, terns and skuas), those that excrete most plastic shortly after ingestion (e.g. fur seals) and those that store plastic in their digestive tract for protracted periods before eroding them to the point where they can be excreted (e.g. petrels, phalaropes and some auks). Turtles probably lie between the last two groups, excreting most plastic, but retaining it far longer than prey items. Further information is needed on the importance of the retention time in the digestive tract of an animal for transfer of hazardous chemicals, but it is likely that long retention times enhance chemical uptake, at least for compounds included in plastics during manufacture. Species with broad, generalist diets that retain indigestible prey items in their digestive tracts for extended periods, such as petrels, storm petrels, phalaropes and turtles, probably are most likely to obtain large body burdens of hazardous chemicals from ingesting plastic items.