Figure 2. Pellets Found during an EPA Harbor Studies Program Survey in Houston, Texas.
[Table of contents | Executive Summary | Sections 1 · 2 · 3 · 4 · 5 · Glossary | Tables | References ]
Plastic pellets are among the smallest items of debris discharged into the aquatic environment. They are, therefore, not as visible (aesthetically displeasing) or as obviously harmful as larger forms of debris, such as discarded fishing gear, medical wastes, etc. This is evidenced by their exclusion from debris inventories reported from the annual beach cleanups (i.e., CMC, 1989, 1990) and from all but one of the National parks studied by Cole et al. (1990). However, these small plastic pellets are often mistaken for food by aquatic animals, particularly seabirds.
3.1 Geographical Distribution
Although plastic pellets are one of the least noticeable forms of plastic pollution, they are ubiquitous in the oceans and on beaches. They have been reported in the sediments and the surface waters of coastal areas and oceans throughout the world (Table 5); data are limited regarding the presence of pellets in rivers, streams, and lakes. The ubiquity of pellets is demonstrated by their presence in remote areas of the world, such as beaches of the South Pacific (Gregory, 1977) and Hawaii (EPA, 1992b). Among the earliest records of pellets in the environment were the studies by Carpenter et al. (1972) and by Carpenter and Smith (1972). These studies reported pellets in the Atlantic Ocean along the southern coast of New England and in the Sargasso Sea, respectively. Several other authors also have reported pellets in the Atlantic Ocean (e.g., Colton et al., 1974; Hays and Cormons, 1974; Morris, 1980; van Franeker and Bell, 1988; Ryan et al., 1988). In the Pacific Ocean, pellets have been reported in northern waters (e.g., Wong et al., 1974, as cited in Pruter, 1987; Dahlberg and Day, 1985; Day et al., 1990) and in southern waters (Gregory, 1977). Pellets have been reported along the coasts of the Mediterranean Sea (Shiber, 1979, 1982, 1987), and the Gulf of Mexico and Caribbean Sea (Carr, 1987; Cole et al., 1990). Most pellets found in marine waters have been identified as polyethylene (PE), polypropylene (PP), or polystyrene (PS) (CEE, 1987).
Table 5. Pellet Observations and Suspected Pellet Sources.
(PE: polyethylene; LDPE: low-density polyethylene; HDPE: high-density polyethylene;
PS: polystyrene; PP: polypropylene)
Geographical Area of Study / Observations / Source(s) Discussed
ATLANTIC OCEAN
Southern New England
(Carpenter et al., 1972) PS pellets (0.1- to 2-mm dia) common in Niantic Bay, Buzzards Bay,
Vineyard Sound, Rhode Island Sound, Great Salt Pond, Long Island Sound, and Block Island
Sound; average 0.01 to 1 pellet per cubic meter. Pellets in several fish. Effluent from
plastics manufacturers or PS producers in southern New England.
Sargasso Sea
(Carpenter and Smith, 1972) 50 to 12,000 particles per square kilometer (mean: 3500 particles
per square kilometer); lowest concentrations near the Gulf Stream. Waste dumping from cities
or cargo ships.
Cape Cod to Cape Canaveral and areas south
(Colton et al., 1974; Colton, 1974) PS and PE pellets (<5-mm dia); 61 to 148 pellets per square
kilometer south of Cape Canaveral, and 8318 pellets per square kilometer between Cape Cod and
Cape Canaveral. Wastewater discharge from plastics plants. Most PS and PE pellets entered open
coastal waters between Block Island and eastern Long Island.
South Atlantic Bight from North Carolina to Cape Canaveral
(van Dolah et al., 1980) Percent occurrence of PS pellets on each cruise ranged from 15% to 34 %.
Tar and pellets were widespread throughout study area. Shipping traffic and entrainment from
other areas via currents.
Eastern Canada and Bermuda
(Gregory, 1983) In Bermuda, PE pellets averaged 5000 pellets per linear meter of beach,
(occasionally >10,000 pellets per linear meter). In eastern Canada, a maximum of 10 PE
pellets per linear meter. Lifetime of pellets suspected to be as low as 3 years. Pellets encrusted
with pseudoplanktonic biota. Released at dump sites or spillage along Atlantic seaboard, spillage
during storage, handling, and transportation activities.
Bermuda, Bahamas, and Martha's Vineyard, MA
(Wilber, 1987) >75% of neuston tows in north Sargasso Sea contained pellets. High concentrations
(2000 per square meter) on Bermuda and Bahamas beaches, where they are deposited by ocean currents.
Pellets often embedded in tar balls ("plasto-tarballs"). Spillage and loss at coastal manufacturing
and shipping sites.
Cape Basin area of South Atlantic
(Morris, 1980) White PE or PP pellets (3- to 5-mm dia) between 1333 and 3600 pellets per square
kilometer; pellets and tarballs most common contaminants in area. No immediate source known other
than through cargo loss.
Southwestern Cape Province, South Africa
(Ryan, 1988b) Predominance of PE and other polyolefin pellets, most of which were <10 mg. Pellets
may be lost during handling and released into the sea via drainage lines. Pellets lost during
transport or by manufacture of user products in industrial areas; may enter South Africa via oceanic
circulation from the South Atlantic.
PACIFIC OCEAN
North Pacific
(Wong et al., 1974, as cited in Pruter, 1987) Round, colorless pellets (1-5-mm dia) in 64% of tows
along 35ø N longitude. Plastics industry. Manufacturer outfalls; spillage from trucks, ships, and
trains while loading or unloading; and when used as ball bearings to move cargo.
North Pacific Ocean
(Day et al., 1990) Pellets found in 6% of total stations and 10% of stations with plastic. Collected
primarily in transitional and nearshore waters east of Japan. Highest density was 6500 per square
kilometer north of Hawaiian Islands. Not discussed.
New Zealand
(Gregory, 1977) PE and PP pellets, ovoid and spheruloid (greater than or equal to 5-mm dia); 10,000
to 40,000 pellets per meter on beaches in narrow zone along driftline or spread across the back beach
and washover flat. Spillage at ports or via streams and storm water drainage after spills at inland
processing plants.
Alaska
(Day, 1980 and Jarrell, pers. commun. as cited in Day, 1980) Substantial amounts of pellets; PE common
but PS unknown. Also reported approximately 500,000 lb of PP pellets were dumped into the ocean during
a dock strike in Costa Rica. Effluent of plastic manufacturers and during loading and unloading of ships
at ports.
North Pacific Ocean
(Day et al., 1986) Highest densities of plastic debris along 40ø N; pellets comprised 0.5% of all
plastic debris and occurred at nearly 4% of the stations. Not discussed.
North of Hawaii
(Dahlberg and Day, 1985) Pellets in neuston samples collected along latitudes 31ø N and 34ø N; densities
must be relatively high to have been collected at all. Not discussed.
North Pacific Ocean and Bering Sea
(Day and Shaw, 1987) Very low concentrations of pellets in the subarctic Pacific, especially near the
Alaskan coast. Not discussed.
MEDITERRANEAN SEA
Beaches of Lebanon
(Shiber, 1979) PE, PS, and polymethyl methacrylate pellets fairly common on most beaches. Predominant
pellet shape was oval to round (2- to 5-mm dia). Waste disposal by several plastics factories or cargo
lost at sea.
Beaches of Costa del Sol, Spain
(Shiber, 1982) Pellets (2.7 to 4.5 mm) present on all beaches sampled (13); abundant on four beaches and
common on most others. Mostly LDPE (87%), HDPE (8%), and ethylvinyl acetate (4%). Encrusting biota absent
on pellets, indicating recent introduction to marine environment. Careless disposal practices at seven
nearby plastics factories, or loss during sea shipment and cargo unloading.
Coast of Spain
(Shiber, 1987) Spherules in great variety of shapes and colors, often tar-covered, abundant on most beaches.
Pellets found were predominantly PE. Some correlation between abundance and location of 190 plastics factories
in area; cargo loss during transport in Atlantic Ocean and Mediterranean Sea.
GULF OF MEXICO AND CARIBBEAN SEA
Costa Rica and Caribbean Sea
(Carr, 1987) Large numbers of pellets on green sea turtle nesting beach in Costa Rica. Industrial wastewater.
Padre Island National Seashore
(Cole et al., 1990; Miller, pers. commun.) All pellets were white and the same size and shape; 73% of plastic
debris and 69% of all debris were pellets. Unclear whether from single or multiple discharges or from a spill.
ESTUARIES, HARBORS, AND OTHER COASTAL AREAS
Harbors of the United States
(Trulli et al., 1990; EPA, 1990b, 1992a,b; Redford et al., 1991) Many different resins in assorted sizes,
shapes, and colors found in all harbors studied except Mayagüez, PR. Hundreds to hundreds-of-thousands of
pellets in each harbor. Industrial and municipal storm water and CSO discharges.
Kahana Bay, Oahu, Hawaii
(EPA, 1992b) Average of 105 pellets per m2 were present between low and high tide lines, concentrated mostly
among other anthropogenic and natural debris near high tide lines. Pellets appeared clean but weathered,
likely polyethylene. Commercial shipping or carried by ocean currents from distant land-based sources.
Sanitary systems in Philadelphia, PA and Boston, MA
(EPA, 1992c) Many pellet types collected in storm water outfalls and in scum samples from sewage treatment plant.
All clean, PE pellets collected at one storm water outfall. Storm water discharges from plastics industry.
Sewage outlet pipes at factories near Long Island, NY
(Hays and Cormons, 1974) 1- to 13-mm-dia PS pellets found as far as 1.1 km downstream of one industrial outfall.
PE pellets also found near outfalls in MA, CT, and NJ. Industrial effluent.
Bristol Channel, UK
(Morris and Hamilton, 1974) 0 to 20,000 PS pellets per square meter unevenly distributed in sediments. PS beads
incorporated into polychaete tubes, and becoming common in plankton samples. Effluent from a PS manufacturer.
Severn Estuary and Bristol Channel, UK
(Karter et al., 1973, 1976, as cited in Pruter, 1987) In 1973, 1-mm PS pellets found in mud, sand, and on cooling
water intake screens at nuclear power plants. Many polychaete worm tubes constructed almost entirely of pellets.
PS spherules found in some flounder. By 1976, pellets virtually absent in all locations noted in 1972 and 1973.
Effluent from plastics industry.
source: http://www.epa.gov/owowwtr1/OCPD/PLASTIC/5-geog.html 12apr03
Under the ongoing Harbor Studies Program, the Environmental Protection Agency (EPA) has conducted studies of floating aquatic debris in harbors along the coastal United States since October 1988 (EPA, 1990b, 1992a,b; Trulli et al., 1990; Redford et al., 1992). The debris was collected by conducting net tows at the water surface to a maximum depth of 0.5 m. Over 200 different types of manmade debris were counted. By the end of 1991, sampling had been conducted in 13 cities and the Mid-Atlantic Bight during a total of 20 surveys.
Plastic pellets were among the most common items found during the Harbor Studies Program, comprising approximately 94% (by number) of all debris collected. The pellets were generally ovoid, cylindrical, square, discoid, or irregularly spherical in shape, and were approximately 5 mm or less in diameter (see Figure 2 below). Most of the pellets were clear, white, or off-white, but several other colors (such as black, green, yellow, amber, orange, blue, etc.) were also observed in the samples. Visual assessments made by a polymer chemist confirmed that a variety of pure polymers and additive-containing pellets were found in the samples (Mr. Elmer Bradbury, Battelle Memorial Institute, personal communication, February 1991). The descriptions are also consistent with EPA's description of PE and PP pellets (EPA, 1990a).
Plastic pellets were found in the harbors of 13 of the 14 cities surveyed and in the Mid-Atlantic Bight (Table 6), and in 29 of the 32 sampling areas (two to four areas were sampled within each city). Mayagüez, Puerto Rico, was the only major study area in which pellets were not found. Pellets were not found in Hampton Roads, Norfolk, or in the Weymouth/Neponset Rivers, Boston, but they were found in other areas in these harbors.
Table 6. Pellets Found during EPA Aquatic Debris Programs. [Adapted from EPA (1990, 1992a,b,c), Trulli et al. (1990); and Redford et al. (1992)
Survey Area Sampled Number Percent Harbor Studies Program (a) Boston I Charles River 2,684 30 Chelsea River 0 0 Mystic River 7 2 President Roads 10 6 Weymouth/Neponset Rivers 0 0 Charles River 453 23 Boston II Chelsea River 2 1 Mystic River 45 6 President Roads 0 0 New York I Manhattan Island 2,039 25 The Narrows and Lower Bay 461 8 Manhattan Island 617 21 New York II The Narrows and Lower Bay 548 27 Staten Island 7,601 78 Schuylkill River 461 32 Philadelphia Delaware River - Camden 197 23 Delaware River - Philadelphia 219 42 Mid-Atlantic Bight Wilmington Canyon to 1 5 (b) Norfolk Canyon Baltimore I Inner Harbor 600 20 Middle Harbor 110 12 Patapsco River 70 15 Baltimore II Inner Harbor 2,625 46 Middle Harbor 524 27 Inner Harbor 1,972 23 Baltimore III Middle Harbor 698 19 Patapsco River 7 4 Norfolk Elizabeth River 135 2 Hampton Roads 0 0 Miami River 56 3 Miami l Dodge Island 51 11 Little River 7 1 Miami River 68 3 Miami II Dodge Island 173 18 Nearshore Atlantic 1 2 Upper Ship Channel 106,759 98 Houston I Middle Ship Channel 352,790 99 Lower Ship Channel 15,660 98 Houston II Upper Ship Channel 38,199 96 Middle Ship Channel 186,936 97 Seattle Duwamish Waterway 20 8 Lake Union Ship Channel 4 1 Tacoma I Commencement Bay 13,834 178 San Francisco San Francisco Bay 1297 19 Oakland San Francisco Bay 279 18 Mayagüez Bahia de MayagUez to 10 10 Puerto Real San Juan San Juan Harbor 1714 23 Honolulu Honolulu Harbor 181 5 Ala Wai Canal 2 <1 Philadelphia Combined Sewer Overflow (CSO) Studies Program (c) Philadelphia Combined Sewer Overflow 1 13 Stormwater Discharges 1,898 65 NE Sewage Treatment Plant(d) 3,420 3 SE Sewage Treatment Plant(d) 49,500 24 SW Sewage Treatment Plant(d) 24,880 6 Boston Combined Sewer Overflow 981 11 Deer Isl. Sewage Trmnt Plant(d) 810 4 Chelsea St.Headworks(Bar Screen)(d) 0 0 Ward St.Headworks(Bar Screen)(d) 0 0 (a) EPA (1990,1992ab); Tr ulli et al. (1990); Redford et al. (1992). (b) items were collected in the Mid-Atlantic Bight. (c) EPA (1992c). (d) Numbers of pellets present in 100% of each facility's solid wastes, based on collection and analysis of 10% of the solid wastes at each. source: http://www.epa.gov/owowwtr1/OCPD/PLASTIC/6-wa31.html 12apr03
Figure 2. Pellets Found during an EPA Harbor Studies Program Survey in Houston, Texas.
Plastic pellets were the most common item (by number of items) in eight cities (Houston, New York, Tacoma, Baltimore, Boston, Oakland, Philadelphia, and San Juan), and were among the ten most common items in three additional cities (San Francisco, Miami, and Seattle) and in the Mid-Atlantic Bight. [Note: In all, only 20 debris items were collected in the Mid-Atlantic Bight, and the percent composition should be considered with caution.] Pellets were the 14th most common item in Norfolk.
Of all cities surveyed, the greatest number, variety, and percentage of pellets were collected in the Houston Ship Channel at Houston, Texas. Over 700,000 pellets were collected during the Houston surveys combined (approximately 98% of all Houston debris). One sample alone contained more than 225,000 pellets. Although pellets of many colors and shapes were collected, most of the pellets from Houston were clear, white, or off-white and ovoid. Notably, Houston has one of the greatest concentrations of plastics industries in the United States and several pellet industries are located along the Houston Ship Channel. Most of the pellets were found in Buffalo Bayou, which is inaccessible to shipping traffic.
A high percentage of aquatic debris collected in Tacoma, Washington, was pellets (78%). Unlike the pellets from the Houston Ship Channel, those from Tacoma were similar to each other in size, shape, and color. Most of the Tacoma pellets (2732 pellets out of 3834 pellets) were found in a single sample. These observations suggest that the pellets may have originated from a single source.
The New York/New Jersey Harbor complex, ranked second by number (11,266 plastic pellets) and third in percentage of plastic pellets (39%). In samples collected from the Hudson and East Rivers around Manhattan Island, pellets varied considerably in color, shape, and condition, indicating possibly several sources of entry into the environment. Some pellets from these areas were embedded in grease, tar, or other organic matter (including fecal matter), which might be expected to accumulate on debris flowing from combined sewer overflows (CSO). In samples collected from the Kills (the water mass separating Staten Island from New Jersey), pellets were of a more uniform size, shape, and color.
Immediately following a February 1992 survey of the harbor at Honolulu, Hawaii, the presence of pellets was studied at the beach along Kahana Bay on the northeastern coast of Oahu. Most of the pellets collected at Kahana Bay were white or off-white, and many were weathered or discolored. Several black pellets were also found in each sample. Based on enumerations along three transects, the average number of pellets on the beach at Kahana Bay was 105 pellets per m2 (range: 88 to 115 pellets per m2). The pellets were found interspersed with other manmade debris, including light sticks, net floats, plastic food containers, and plastic pieces, and natural debris such as driftwood and seaweed, and were concentrated in the portions of the transects that were farthest from the water. According to the Chief Scientist, many more pellets and types of pellets were present on the same beach in 1989 than were present during the survey (Mr. David Redford, EPA, personal communication, February 1992). The decreased numbers of pellets may have been due to heavy storm activity during the two weeks prior to the survey, which would have resuspended beached pellets in rough surf conditions at high tide.
Two additional pellet-related items, plastic powder and flattened pellets, were found in several cities. Plastic powder, an intermediate form of the raw material used to make pellets and molded products, was observed floating on the water's surface and was collected in considerable volume along with other debris. In Houston, this powder was initially thought to be grain dust from nearby grain elevators, and was discarded as natural debris (i.e., not anthropogenic in origin); Figure 3 shows plastic powder collected in Houston. However, during the pellet producer site visits conducted under the present study, the investigators recognized the powder, and plastics industry personnel verified that the material was plastic powder. For additional verification of these conclusions, the investigators removed some of the material from the Houston samples and heated the material in a metal spoon. The grains melted and subsequently solidified into an amorphous mass after cooling. The mass appeared to be plastic, although this was not confirmed by chemical analysis. Survey scientists do not recall collecting this powder in other cities, but again the material may have been overlooked as natural debris.
Figure 3.
Not Available: http://www.epa.gov/owowwtr1/OCPD/PLASTIC/fig03.gif
Thin, irregularly shaped plastic disks approximately 1 cm in diameter (see Figure
4 above) were identified in samples collected from several different harbors. At the time, these disks could not be identified, and they were subsequently counted and recorded as miscellaneous plastic pieces. However, several disks identical to ones collected during the surveys were found during a site visit to a pellet producer. The plastic disks, found among plastic pellets, were scattered along railroad tracks and beneath hopper cars in the loading and cleaning areas of the producing facility. Plastics industry personnel identified the disks as plastic pellets that had been flattened by rail hopper cars.
Figure 4.
Not available
http://www.epa.gov/owowwtr1/OCPD/PLASTIC/fig04.gif
3.2 Sources Identified in the Literature
Several researchers have suggested possible sources of pellets to the aquatic environment (Table
5 above), including
Direct discharges and improper waste water disposal by the plastics industry
Waste disposal and sewer discharges by cities
Spillage from trucks, trains, and ships during loading, transport, or unloading
Improper use of pellets, such as for packing material, for insulation, and for bearings to facilitate the movement of cargo boxes and other heavy objects.
Unfortunately, most studies focused on reporting pellet distributions and abundances, and the source identifications were based mostly on empirical evidence rather than on direct evidence. As presented in Section 3.2.1, the recent EPA studies of U.S. harbors (EPA, 1990b, 1992a,b) and CSOs (EPA, 1992c) have provided some direct evidence that storm sewers, CSOs, and direct spillage into the waterways are sources of pellets to the aquatic environment.
3.2.1 EPA's Harbor Studies Program
As discussed in Section 3.1, EPA has conducted studies of floating aquatic debris in selected harbors of the United States. One objective of the EPA Harbor Studies Program was to identify potential sources of floatable debris collected during the surveys. Several possible sources of pellets were identified based on field observations and conversations with local authorities; these sources were CSOs and storm sewers, storm-water runoff, and spillage from loading docks.
The results of surveys in New York, Boston, and Houston, for example, indicated that CSOs and storm sewers were sources of pellets in the aquatic environment. In the Kills area of New York Harbor, the cleanliness and uniform size, shape, and color of the collected pellets (as in Tacoma), indicate a possible single source. Because the pellets were mixed with other debris typically discharged from storm sewers or CSOs, storm sewers and CSOs are likely the discharge points for pellets released by the plastics industry and related transporters.
In Boston, the majority of the pellets was collected from the Charles River on the freshwater side of the locks near the Museum of Science. There is no commercial shipping on the River and there are no known pellet industries along the banks of the River. This suggests that pellets are entering the environment through storm sewers or CSOs that receive storm-water runoff and other drainage from pellet industries.
As previously discussed, extremely large numbers of pellets were collected from every area of the Houston Ship Channel. Large numbers of pellets were found above or west of the turning basin in Buffalo Bayou, where there is no commercial shipping and tidal fluctuations are minimal (<0.5 ft). Because of the lack of shipping and the unlikely transport of pellets by tidal currents, pellets found in Buffalo Bayou were most likely discharged from storm sewers (Houston has no CSOs) or carried into the Channel directly by storm-water runoff.
The results of surveys in Tacoma and Houston indicated that spillage at loading and shipping docks is another source of pellets in the aquatic environment. In Tacoma, a local resident reported that a crate of pellets was spilled into the harbor 2 months prior to the Tacoma survey, thereby establishing the possibility that a single discharge was a possible source of the collected pellets (Mr. David Redford, EPA, personal communication, March, 1989). An-other resident stated that pellets were regularly observed on local beaches; this would indicate that pellet spills may be common to the Tacoma area. In addition, the fact that people are noticing pellets during recreational activities indicates that pellets are frequently present in large numbers; large numbers would make the pellets more obvious and easier to distinguish from natural debris.
In Houston, pellets also were collected in massive numbers in the middle area of the Houston Ship Channel (areas below or east of the turning basin). These pellets probably entered the channel through several sources, including spills at the loading dock, spills aboard ship, or spills at industrial sites where pellets are carried by rain water into the storm sewers or are blown into waterways. Pellets discharged into Buffalo Bayou would also be transported to areas east of the turning basin. Discussions with a local longshoreman indicated that during ship loading operations pellet packaging often was punctured by forklift tines. When the pellets were transferred from the dock to the ships, thousands of pellets would spill onto the dock and directly into the Channel. He also indicated that pellets spilled onto the docks were swept directly into the Channel during routine maintenance of the area.
3.2.2 EPA's CSO Studies Program
In older cities of the northeastern United States, CSO discharges of raw sewage and street litter are common during heavy rainstorms. Studies conducted under the EPA-sponsored CSO Studies Program examined the types and amounts of floatables discharged from selected CSOs and storm sewers, as well as floatables captured by bar screens and settled out in the scum of sewage treatment facilities in Philadelphia and Boston. Final data show that pellets are present in the sewage treatment plant scum (small-sized, floating material at the surface of the settling tanks) samples (Table 7), in CSO samples of both cities, and in the storm sewer samples collected in Philadelphia (Table 6). No storm sewers were sampled in Boston. [Note: One pellet was found in the CSO discharge in Philadelphia; these data should be viewed with caution because it was not determined that the CSO had discharged during the study.] The data from this study indicate that pellets are entering municipal sewerage systems from land-based sources, and are subsequently entering the aquatic environment through CSO and storm sewer discharges.
Table 7. Pellets Collected Each Day at Sewage Treatment Facilities in Philadelphia and Boston [EPA (1992c)]
Number Number
Location Day 1(a) Day 2(a)
Philadelphia
Northeast WPCP 2,110 1,310
Southeast WPCP 22,820 26,680
Southwest WPCP 5,520 19,360
Boston
Ward Street HW 0 0
Chelsea HW 0 0
Deer Island STP 650 160
WPCP: Water Pollution Control Plant
HW: Headworks
STP: Sewage Treatment Plant
(a): Daily totals calculated based on the analysis of 10% of the screenings and
scum present each day at each facility.
3.3 Fate and Impacts
There are several documented accounts describing pellet and other plastic debris ingestion by wildlife, most notably by seabirds and sea turtles (Table 8). Generally, impacts or biological effects of the pellets have not been clearly defined in most wildlife, and, to date, direct correlations between pellet ingestions and effects have not been demonstrated conclusively. This may be attributable to the fact that the studies typically use stranded and beached animals, and most animals that die at sea either sink to the bottom or are consumed by predators before they are found by humans (Laist, 1987).
Table 8. Pellet Ingestions and Potential Effects.
Geographical Location / Species Reported / Description of Ingestion or Effects BIRDS Alaska (Day, 1980) Northern fulmars, sooty shearwaters, short-tailed shearwaters, red-legged kittiwake, thick-billed murre, Cassin's auklet, parakeet auklet, tufted puffin, horned puffin, fork-tailed storm-petrel, Leach's storm-petrel, northern phalarope, glaucous gull, black-legged kittiwake, and least auklet. Ingestions likely due to pellet resemblance to natural prey, and will increase as annual plastics production and use of pellets increase. Some particles embedded in gizzard walls; mean residence time in gizzards may be approximately 15 months. Hydrocarbon pollutants associated with the pellets may decrease reproductive ability of seabirds. California (Chu, pers. commun., as cited in Day et al., 1985) Sooty shearwaters Ingestions Galapagos Islands (Anon., 1981, as cited in Day et al., 1985) Blue-footed booby Secondary ingestion of raw plastic. Monterey Bay, CA (Baltz and Morejohn, 1976) Northern fulmars, pink-footed shearwaters, sooty shearwaters, short-tailed shearwaters, Heermann's gull, and black-legged kittiwake. Ingestions of PE pellets in stomachs of 6 seabird species. New Zealand (Imber, pers. commun., as cited in Day et al., 1985) Great-winged petrels, kerguelen petrels, Cook's petrels, blue petrels, broad-billed prions, antarctic prions, fairy prions, Parkinson's petrels, white-faced storm-petrels, salvin's prions, and sooty shearwaters. Ingestions in low to high numbers. Chatham Islands and Gough Island (Bourne and Imber, 1982) Broad-billed prions and white-faced storm-petrels. Pellets normally found in the gizzard, and birds containing pellets often lacked food in the proventriculus. Difficult to determine whether pellet ingestion is a cause or an effect of starvation. Secondary ingestion by great skuas that consume old, pellet-containing prions. Eastern Canada (Brown et al., 1981, as cited in Day et al., 1985) Greater shearwaters and sooty shearwaters Ingestions reported. South Africa (Furness, 1983, as cited in Day et al., 1985) Greater shearwaters PS spheres ingested. Dutch coast (van Franeker, 1985) Fulmars >50% of stomachs contained pellets; toxic additives in pellets may be assimilated by birds. Midway Island and Oahu Island, Hawaii (Fry et al., 1987) Wedge-tailed shearwaters 60% of birds contained pellets (majority were PP and PE) and plastic fragments; toxicity of additives and organochlorine pollutants may be less significant hazard than obstruction/impaction of the gut of seabirds; risks to chicks may differ from risks to adults. Scottish colonies (Furness, 1985) Procellariiform seabirds (Leach's petrels, Manx shearwaters, and fulmars) Fulmars and Leach's petrels select debris according to their preference for particular prey sizes. Only equivocal statistical evidence for an influence of ingested plastic on body mass. Pellets not found in British storm petrels. Laboratory experiment. (Ryan, 1988a) Chickens Even under ideal feeding conditions, plastic-loaded birds cannot forage as efficiently as plastic-free birds. Large loads of plastic impair feeding by reducing meal size, which may, therefore, limit accumulation of fat reserves essential for reproduction, migration, and molting. Antarctica (van Franeker and Bell, 1988) Wilson's storm petrels, southern fulmars, and Cape petrels. Pellets comprised 73% of all ingested particles (combined for all species); plastic particles remaining in the gizzards of petrels may persist for months or years if not regurgitated. Decrease fitness is a likely consequence of ingestion by chicks and adults. Most plastics originate in wintering areas outside the Antarctic. South Africa and Southern hemisphere (Ryan, 1987) Blue petrels, great shearwaters, white-faced storm-petrels, pintado petrels, thin-billed prion, antarctic prion, salvin's prion, sooty shearwater, grey phalarope, arctic skua, Cory's shearwaters, grey-backed storm-petrel, broad-billed prion, kerguelen petrel, subantarctic skua, soft-plumaged petrel, great-winged petrel, Atlantic petrel, and white-chinned petrel. Three factors determine the rate of pellets (and plastic) ingestion: foraging technique, dietary specialization, and density of pellet (pollutants) in the foraging area. Procellariiform seabirds exhibit the largest plastic loads owing to foraging patterns at the sea surface. Secondary ingestion of plastic through contaminated prey is uncommon and was found only in subantarctic skua which preys on small petrels containing plastic particles. Gough Island, South Atlantic Ocean (Ryan et al., 1988) Great shearwaters (females only) Positive correlation between polychlorinated biphenyl (PCB) and plastic loads in the species; PCBs likely were derived from ingested plastic particles, and these PCBs contribute significantly to the total body load of PCBs in great shearwaters. Long Island Sound (Hays and Cormons, 1974) Gulls and terns PS pellets found in tern and gull pellets (regurgitated indigestible food). Southern Indian Ocean (Ryan and Jackson, 1987) White-chinned petrels PE pellets lost 1% of their mass after 12 days (half-life equal to at least 1 year); no instances of intestinal obstruction or physical damage to the birds; ingested plastic seldom impairs digestive efficiency in seabirds. Hawaii (Sileo et al., 1990)) Seabirds 80 species, or approximately 25% of all seabird species, are known to ingest plastic debris. Bodega Harbor, CA (Connors and Smith, 1982) Red phalaropes 6 of 7 birds contained plastic particles, most of which were PE pellets. Plastic ingestion may be producing physiological effects that threaten successful migration and breeding in regions remote from the pollution sources. Galapagos Islands and South Atlantic Ocean (Wehle and Coleman, 1983, as cited in Wallace, 1985) Blue-footed boobies, short-eared owls, broad-billed prion, and South Polar skua. Secondary ingestion of pellets from food source: blue-footed boobies and short-eared owls consumed fish containing pellets, and broad-billed prion consumed a skua containing pellets. TURTLES Texas coast (Plotkin and Amos, 1990) Loggerhead, green, hawksbill, and Kemp's ridley turtles. Pellets were ingested by eight turtles, and comprised 7% of all ingested debris. Texas coast (Amos, pers. commun., as cited in Balazs, 1985) Green turtle PE spherules in mouth of stranded, dead sea turtle. South Africa (Hughes, 1970, 1974, as cited in Balazs, 1985) Loggerhead turtles 6% of stranded posthatchlings contained pellets in stomach. Florida (Meylan, 1984, as cited in Balazs, 1985) Hawksbill turtles PS pellets and other manmade materials in stomachs. Florida East Coast and Caribbean Sea (Carr, 1987) Loggerhead and green sea turtles Resemblance to Sargassum floats may account for ingestions; young sea turtles vulnerable during open-ocean associations with Sargassum rafts; large numbers of pellets found on green sea turtle nesting beach. Hawaii and worldwide (Balazs, 1985) Sea turtles Marine turtles eat a wide variety of synthetic material, including pellets. Effects of toxic chemicals released by these materials and physical obstruction of the digestive tracts are two possible adverse impacts. Mediterranean Sea (Gramentz, 1988) Loggerhead turtles Pellets, crude oil, and tarballs apparently are ingested and excreted. Texas coast (Plotkin and Amos, 1988) Loggerhead, green, and hawksbill sea turtles PE pellets ingested by 9% of necropsied turtles; high probability that sea turtles inhabiting Texas coast will come into contact with debris. Texas coast (Shaver, 1991, pers. commun.) Kemp's ridley sea turtles 2% (2 out of 101 turtles) contained pellets; one turtle was wild and one was reared in captivity. FISH AND INVERTEBRATES Severn Estuary (Karter et al., 1973, as cited in Shiber, 1982 and Pruter, 1987) Flounder and polychaetes Ingestions by flounder. Polychaetes incorporate pellets into dwelling tubes. New York Bight (Steimle, 1991 (pers. commun.) Lobster and winter flounder Low numbers of pellets ingested, and more common in lobsters than in winter flounder. Southern New England (Carpenter et al., 1972) Grubby, winter flounder, white perch, and silversides (fish), and one chaetognath (arrow worm) PS pellets in stomachs of 8 out of 14 species of fish and one chaetognath; speculated that pellets could cause intestinal blockage in smaller fish. OTHER BIOTA North American waters (Walker and Coe, 1990) Baleen whales Suggested that filter-feeding makes baleen whales vulnerable to incidental debris ingestion; stomachs of stranded baleen whales should be examined. Canada and Bermuda (Gregory, 1983) Epibionts Epibionts on pellets include coralline algae, bryozoans, calcareous annelids, and foraminiferans. Caribbean Sea and waters off Florida (Winston, 1982) Epibionts Plastics (including pellets) encrusted with bryozoan (Electra tenella); success of this species on the east coast attributed to its colonizing of drifting smooth-surfaced plastic. ESTHETIC AND ECONOMIC EFFECTS New Zealand (Gregory, 1977) Humans Concentrations ranged from <1 pellet per meter of beach to >20,000 pellets per meter, and may lead to esthetically displeasing plastic sand beaches. Worldwide (Wallace, 1985) Humans Pellets have a negative effect on recreational activities; economic impact due to loss of raw materials that must be replaced. Bermuda (Wilber, 1987) Humans Beachgoers shocked by the presence of high numbers of pellets; pellets and plastic fragments embed in tarballs and become plasto-tarballs. United States (Klemm and Wendt, 1990) Humans Labeled combination of plastic debris and pellets beach confetti. source: http://www.epa.gov/owowwtr1/OCPD/PLASTIC/8-biol.html 13apr03
3.3.1 Birds
The ingestion of pellets by seabirds has been reported worldwide (Table 8), and seabirds ingest plastic pellets more frequently than do any other taxon (Ryan, 1990). Sileo et al. (1990) reported that 80 species, or approximately one-quarter of all seabird species, are known to ingest plastic debris. Pellets are the most common form of plastic debris ingested by seabirds (EPA, 1990a; Ryan, 1990). Day (1980) estimated that polyethylene pellets remain in the digestive tracts of birds for 10 to 15 months (see Figure 5).
Figure 5.
not available
http://www.epa.gov/owowwtr1/OCPD/PLASTIC/fig05.gif
Several factors affect the vulnerability of a seabird population to the presence of pellets.
Frequency of regurgitation - Birds with a limited ability to regurgitate are most likely to be effected by pellet ingestion. Debris loads in birds are a function of the ratio of the rates of ingestion and regurgitation (Ryan, 1990).
Foraging habits - Birds that feed by pursuit diving are the most likely to ingest pellets, and birds that feed by plunging and piracy are the least likely to ingest pellets (Day et al., 1985).
Pellet color - Seabirds are more likely to ingest pellets that are light-colored (e.g., white, tan, brown, yellow) than those of any other color (Sileo et al., 1990; Day et al., 1985). This color preference has been attributed to the pellet's similarity to common food sources, such as fish eggs, crustaceans, etc. (Day et al., 1985).
Prey type - Pellets pose the greatest threat to plankton-feeding species, such as shearwaters, petrels, prions, phalaropes, and auklets (Fry et al., 1987).
Proximity to pellet sources - Logically, the closer that a seabird is to a release point, the more likely it is to encounter and ingest pellets (EPA, 1990a; van Franeker and Bell, 1988).
Proximity to areas where pellets accumulate - Species that feed at the ocean surface are more likely to ingest plastic, most probably because they are more likely to be exposed to floating plastic (Sileo et al., 1990).
The effects on seabirds of ingested pellets and other plastic debris were summarized recently by Ryan (1990) at the Second International Conference on Marine Debris (Shomura and Godfrey, 1990). Ryan (1990) stated that anthropogenic debris may have three specific effects on seabirds: (1) diminished foraging ability or a decreased foraging efficiency, (2) physical damage (e.g., intestinal blockage), and (3) physiological effects from the absorption of toxic chemicals associated with the pellets.
Diminished foraging ability appears to be the most serious effect of pellets on seabirds. The presence of pellets in the stomachs of seabirds may create false feelings of satiation, decrease the storage volume of the stomach, and reduce foraging. Ultimately, this will reduce the ability of the seabirds to accumulate the energy (fat) reserves necessary for migration, reproduction, molting, and survival of adverse environmental conditions (Day et al., 1985; Ryan, 1988a, 1990). These effects would occur most likely in procellariiform seabirds, which, compared to other seabirds, experience the highest incidence of plastic ingestion (Ryan, 1988a). However, a few pellets in a bird's stomach are not likely to have an adverse affect, primarily because many seabirds retain indigestible materials in their stomachs to aid in digestion (Furness, 1985; Ryan, 1988a, 1990), although Wallace (1985) believed that the birds could be chronically stressed. Studies to determine a critical pellet volume have not been reported.
Studies of potential impacts caused by pellet ingestions generally have indicated that physical damage probably occurs in only a small number of seabirds. Day (1980) reported that ingestions increased the gizzard volumes of some auklets, resulting in the full distension of the gizzards and a potential reduction in hunger. Where individuals that had ingested large numbers of pellets, the pellets were found embedded in sockets in the gizzard wall, but no effects (good or bad) were noted. Day et al. (1985) subsequently reported that ingested pellets reduce the storage volume of seabird stomachs.
In a controlled study of the effects of large numbers of PE pellets in white-chinned petrels, Ryan and Jackson (1987) reported no significant changes in digestive efficiency between test and control birds. Several authors have document lacerations by sharp debris (e.g., Day et al., 1985; Fry et al., 1987, Ryan and Jackson, 1987); however, because pellets are generally round and smooth, it is unlikely that pellets lacerate stomach linings in seabirds.
Finally, plastic pellets in the environment may contain chemicals that are toxic to seabirds. These toxic substances may be additives that were intentionally mixed into the resin to achieve specific properties, or contaminants that were adsorbed by the pellets from the environment. Carpenter et al. (1972) reported the adsorption by pellets of organochlorine compounds from ambient seawater. Day (1980) noted a decreased ability to reproduce in pellet-ingesting birds, which he attributed to the hydrocarbon pollutants associated with plastic. Ryan et al. (1988) provided the only direct evidence of a correlation between plastic loads and PCBs in seabirds, but Ryan (1990) speculated that paint chips and tar balls may contribute more significantly than do pellets to the total toxic chemical load in seabirds.
Further studies are needed to determine if pellet ingestion leads to poor bird condition or if poor bird condition leads to pellet ingestion (Connors and Smith, 1982; Bourne and Imber, 1982; Ryan, 1987, 1990).
3.3.2 Turtles
Balazs (1985) found that marine turtles ingest many items of floating debris, including plastic pellets (e.g., unfoamed polystyrene beads). Evidence suggested that plastic material passes through the digestive tracts and are voided naturally. However, Balazs (1985) also reported that ingested debris may cause potentially serious problems in sea turtles, such as lost nutrition, reduced absorption of nutrients, and adsorption of plasticizers. In addition, small plastic fragments may adversely affect turtles during digestion when pellets or fragments are ground together by muscular contractions, and pinocytotic absorption of the resulting microscopic plastic particles could occur. The latter phenomenon was suggested to occur also in albatrosses [Pettit et al., 1981, as cited in Balazs (1985)].
Balazs (1985) suggested several explanations for ingestion by turtles.
Marine organisms encrusting plastic debris may be a desirable food source or may mask the artificial nature of the debris, thereby inhibiting a rejection reflex by the sea turtles.
Under conditions of extreme hunger when available food stocks are limited, sea turtles may feed on items that they would not normally eat.
Prey that has consumed debris is ingested by a predator. Balazs suggested that the increasing volumes of plastic particles in the oceans make this mechanism distinctly possible.
Balazs concluded that additional research is needed in regard to incidence and effects of plastic ingestions by sea turtles.
Carr (1987) discussed the significance of nondegradable debris, including pellets, to sea turtles during early developmental stages. Because manmade and natural debris and planktonic organisms accumulate along convergences, Carr concluded that young, advanced pelagic-stage sea turtles are vulnerable to the presence of pellets in the oceans owing to the turtles' close association with the convergences. The findings of Plotkin (1988) and Plotkin and Amos (1990) support Carr's conclusion.
3.3.3 Other Biota
Although most of the published literature describing ingestion and biological effects of pellets concerns seabirds and sea turtles, a few studies have discussed associations between pellets and other organisms, including fish [(Carpenter et al., 1972; Karter et al., 1973, 1976; Colton et al., 1974; Mr. Frank Steimle, National Marine Fisheries Service (NMFS), personal communication, August 1991)], several invertebrates (Carpenter et al., 1972; Karter et al., 1973; Mr. Frank Steimle, National Marine Fisheries Service (NMFS), personal communication, August 1991), and, potentially, baleen whales (Walker and Coe, 1990). Secondary ingestions of pellets by seabirds were reported by Wehle and Coleman (1983, as cited in Wallace, 1985); the investigators reported that the birds had consumed other birds and fish that had ingested pellets.
A few investigators have reported colonization on pellets by biological organisms that are normally epibionts on Sargassum floats and other floating organisms. The epibionts reported include hydrozoans and diatoms (Carpenter and Smith, 1972; Winston, 1982; Gregory, 1983), bryozoans, coralline algae, coiled calcareous annelids and other calcareous worm tubes, and foraminiferids (Gregory, 1983). Accumulations of organic matter and tar or oil have also been observed on pellets (Wilber, 1987; Redford et al., 1992); the presence of these materials could increase the possibility that an animal might confuse the pellets with its natural food sources. Finally, one study reported that pellets might be useful to some species: Karter et al. (1973) found that polychaete worms used pellets to build dwelling tubes.
3.3.4 Aesthetic and Economic
Several authors have documented the human aesthetic (Gregory, 1983; Wallace, 1985; Wilber, 1987; Klemm and Wendt, 1990) and economic (Wallace, 1985) impacts of pellets in the environment. Although plastic pellets may not be as aesthetically displeasing as other items of debris, such as sewage-related and medical-related debris, the quantities present and their persistence in the environment are cause for notice. Gregory (1977) speculated that someday man will sunbathe on plastic sand beaches; Klemm and Wendt (1990) labeled the combination of pellets and plastic fragments beach confetti, but believed its presence was not a celebration. The aesthetic impacts of pellets to recreational areas were discussed by Wallace (1985) and CEE (1987).
A final impact of pellets in the environment may be measured in terms of economic costs. The loss of feedstock and the costs of replacing the feedstock may be offset only if the pellets are recaptured and recycled instead of replacing them (Wallace, 1985). The economic incentive to recycle spilled pellets was evident during the site visits of the present study, where several of the companies were already actively collecting and recycling waste pellets and other plastic scrap.
source: http://www.epa.gov/owow/OCPD/PLASTIC/sec3-.html 12apr03
February 11, 1997
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