| Abstract: | Synthetic Polymers, commonly known as plastics, have been entering the marine environment in quantities paralleling their level of production over the last half century (Thompson). However, during the last decade of the 20th Century, the deposition rate accelerated exponentially (Copello, Ogi). Thirty years ago the prevailing attitude of the industry was that “plastic litter is a very small proportion of all litter and causes no harm to the environment except as an eyesore” (Derraik). Plastics became the fastest growing segment of the U.S. municipal waste stream between 1970 and 2003, increasing nine-fold (U.S. EPA), and marine litter is now 60–80% plastic, reaching 90–95% in some areas (Derraik). While undoubtedly still an eyesore, plastic debris today is having significant harmful effects on marine biota. Albatross, fulmars, shearwaters and petrels mistake floating plastics for food and few, individuals of these species remain unaffected; in fact, 44% of all seabird species ingest plastic. Sea turtles ingest plastic bags, fishing line and other plastics, as do 26 species of cetaceans. In all, 267 species worldwide are known to have been affected (Derraik). The numbers of fish, birds, and mammals that succumb each year to derelict fishing nets and lines in which they become entangled cannot be reliably known, but estimates in the millions have been made (Moore). Marine plastic debris can be divided into two categories; macro, >5mm and micro, <5mm. While macro debris may sometimes be traced to its origin by object identification or markings, micro debris, consisting of particles of two main varieties, degraded pieces broken from larger objects, and resin pellets and powders, the basic thermoplastic industry feedstocks, are difficult to trace. Ingestion of small plastics by filter feeders at the base of the food pyramid is known to occur (Moore, Thompson), but has not been quantified. Ready ingestion of degraded plastic pellets and fragments (U.S. EPA) raises toxicity concerns since they are known to sorb hydrophobic pollutants (Moore, Takada). The potential bioavailability of compounds added to plastics at the time of manufacture, as well as those sorbed from the environment is a complex issue that merits more widespread investigation (Andrady). The physiological effects of any bioavailable compounds desorbed from plastics by marine biota have not been directly investigated, but Ryan et al. found that the mass of ingested plastic in Great shearwaters was positively correlated with PCBs in their fat and eggs. Field and laboratory studies of the physiological effects on seabirds that ingest plastic resin pellets are in progress (Takada), and a fish study to examine possible xenoestrogenic activity of ingested plastics has been designed by Michael Baker of the UC San Diego Department of Medicine. “Studies by Gregory, Zitko and Hanlon have drawn attention to … small fragments of plastic …derived from hand cleaners, cosmetic preparations and airblast cleaning media” (Derraik). The quantities and effects of these contaminants on the marine environment have yet to be determined, but in a study conducted on the Los Angeles and San Gabriel Rivers in 2004-2005, 2 billion plastic particles of all types, <5mm, were found to flow toward the ocean in three days of sampling (Moore). Colonization of all plastic marine debris by alien species poses one of the greatest threats to global marine biodiversity (Barnes). “There is also potential danger to marine ecosystems from the accumulation of plastic debris on the sea floor … The accumulation of such debris can inhibit the gas exchange between the overlying waters and the pore waters of the sediments …”(Derraik). The extent of this problem and its effects, have yet to be investigated, but based on resin sales in the United States, a little more than half of all thermoplastics will sink in seawater (U.S. EPA). |
