An analysis of marine 

debris in the US

Drawing on decades of experience in marine and coastal pollution 

research, Australia’s Commonwealth Scientific and Industrial Research 

Organization (CSIRO) undertook a collaborative project with Ocean 

Conservancy (OC) and the National Oceanic and Atmospheric 

Administration Marine Debris Program (NOAA MDP) to better understand 

marine debris within the United States.

OCEANS AND ATMOSPHERE 

www.csiro.au
How much marine debris 

is there on US shores? 

We estimate there are somewhere between 20 million and 

1.8 billion pieces of plastic along the coastline of the United 

States, with the number likely at the upper end of the range.

These estimates are based on data from the NOAA MDP 

Marine Debris Monitoring and Assessment Project (2009 

- 2016), the OC’s International Coastal Cleanup (ICC) data 

(2010 - 2015) and CSIRO’s own assessment (2016).

There are a number of variables that affect the amount 

of debris found at a site. Some of these include the level 

of urbanization, land use type, back-shore vegetation, 

accessibility to the site, population density, socioeconomic status, and inputs from local watersheds.

We included these variables in our statistical models 

to better understand the patterns in the data. We also 

incorporated additional variables to remove sampling bias. 

What do the data tell us?

Figure 1a (next page) shows the pattern of debris 

density data for the west coast, based on NOAA MDP’s 

accumulation dataset and correcting for sampling bias.

We expected to find high debris loads near major urban 

centres, and indeed, San Francisco has significantly 

higher debris than less-populated regions such as 

Washington state and the northern coast of California. 

To determine what debris patterns would look like without 

the influence of large population centers and other drivers 

(e.g. land use, socio-economic status), we incorporated these 

variables into our modelling. We see the leftover spatial 

pattern in the data in the ribbon plot in Figure 1b. Areas 

to the north of Cape Mendocino have noticeably higher 

debris loads, while in most areas south of the California/

Oregon border we see relatively low debris loads. 

The California Current is the dominant ocean current system, 

and moves north to south along the west coast of the United 

States. Interestingly, the sites with less debris than expected 

(south of Cape Mendocino), have a slightly south-westerly 

orientation, while the coastline with higher loads (north of 

Cape Mendocino) has a north-westerly orientation. Given 

the strong component of northerly winds on the west coast, 

these differences could be influenced by onshore transport 

driven by both the coastal orientation and wind direction.

Sampling bias can include: the number of 

people that carried out the survey, the size 

of the survey area, and how long people 

spend searching for debris. For example, 

surveys with six people participating 

may find more litter than surveys with 

four people, but this may not necessarily 

mean there is more litter at that site. Our 

standardization takes this information 

into account to get a ‘true’ representation 

of the amount of debris at each site. 

1 An analysis of marine debris in the US 
Where are 

the national 

hot spots?

The International Coastal Clean-up 

(ICC) (Figure 2 below) shows us that 

Texas, Idaho, Illinois and many of 

the urbanized mid-Atlantic states 

stand out as having particularly 

high debris loads, along with 

several states on the Gulf coast.

In some states, such as Texas, this 

is driven by the coastal portion 

of the state. In other cases, there 

is a significant contribution from 

inland waterways and lakes. 

The coastal current in the Gulf 

of Mexico may move material 

from the US Gulf coast southwesterly along the coast and 

onto the Texas coastline. 

These marine debris transport 

explanations could be a good 

focus of future investigation.

0

Site

Standardized 

Model

Interpoint 

Distance 

Seattle

Portland

San

Francisco

Los Angeles

San Diego

Cape 

Mendocino

7

6

5

no surveys

Log pounds

per mile

Pounds per mile

DC

TX

CO

LA

AR

MS

MO

AL GA

SC

NC

TN

VA

MD DE

NJ

RI

CT

MA ME

VT

NH

NY

PA

OH

MI

INIL

WI

MN

KS

NE

UT CA

FL

MT

WY

NV

AZ NM

ND

SD

OK

IA

KY

WV

ID

WA

OR

0 1000 2000 3000 4000

Model

Seattle

Portland

San

Francisco

Los Angeles

San Diego

Cape 

Mendocino

1a: Corrected for 

sampling bias - log 

pounds per mile

1b: Remaining spatial 

pattern - log pounds 

per mile

Figures 1a and 1b: Shoreline debris load based on NOAA MDP accumulation 

data. The ribbon on the left shows the relative amount of debris after 

accounting for sampling bias, while the ribbon on the right shows the 

remaining levels of debris after accounting for sampling bias, population 

density and other drivers, possibly indicating a greater offshore component to 

the debris north of Cape Mendocino.

Figure 2: Statewide debris load based on ICC data after correcting for sampling bias. Values represent the average weight of debris 

per mile for all debris surveys across each state 2
Which items were 

most abundant?

Using the NOAA MDP Accumulation and ICC data, we 

calculated the most common items in each survey.

Cigarette butts, food wrappers, plastic beverage bottles, 

and lids are all very common items in both the NOAA MDP 

and ICC datasets. However, there are distinct differences 

in relative abundance, with cigarette butts reaching 

nearly 25% of all items in the ICC data, while they are 

only 6% in the NOAA MDP data. The most abundant 

items in the NOAA MDP data set are fragments of hard 

plastic, filmed plastic, foamed plastic and plastic rope.

Why the NOAA MDP and ICC 

results do not match

There are a number of differences in how 

surveys are carried out including where data 

are collected (sample site), survey protocol, and 

survey effort (number of people participating 

and how much of an area is surveyed).

ICC Data

NOAA MDP 

Accumulation data

Glass Beverage Bottles

Balloons

Straws

Cutlery/Cups (Plastic)

Plastic Bags

Alumimum Cans

Food Wrappers (Plastic)

Plastic Beverage Bottles

Other Plastic

Lumber

Cigarettes

Lids

Filmed Plastic

Plastic Rope/Net

Fishing gear (all)

Foamed Plastic

Hard Plastic

Which items pose the most risk to wildlife? 

Based on recent CSIRO and OC research, fishing 

gear, plastic bags, balloons, plastic beverage 

bottles, and cigarette butts were most harmful 

to sea birds, marine mammals, and turtles.

In this study we found that fishing gear was particularly 

common on the coast of Texas, the northern Atlantic, 

southern Florida and the northern part of the Pacific. 

We found balloon litter was fairly constant 

across the whole of the continent. 

Cigarette butts were relatively high along the coastal eastern 

US, and the southern and northern ends of the US west coast.

Plastic bags were relatively common across the country, 

but we found the most in Texas and southern California.

Ballons were 

found across 

the continent.

Beverage 

containers made 

up a smaller 

percentage of 

debris collected 

in states that 

had Container 

Deposit 

Legislation 

(CDL) (see 

next page).

3 An analysis of marine debris in the US 
How effective is legislation?

Do bottle bills work? 

Based on NOAA MDP’s data, beverage containers 

made up a smaller percentage of the debris collected 

in states that had Container Deposit Legislation (CDL) 

– California, Hawaii and Oregon – compared to states

that do not provide a cash incentive for recovery of

beverage containers – Alaska, Virginia and Washington.

Maybe people in certain states are thirstier?

We also calculated the ratio of lids to containers. Many 

beverage containers (with the exception of aluminum 

cans) are produced with lids, so this means that both 

lids and containers are able to enter the waste stream. 

CDL is based on returning containers, not lids, so the 

ratio of lids to containers left behind can also shed light 

on the effectiveness of container deposit legislation. 

PROPORTION OF CONTAINERS PROPORTION OF LIDS

States without CDL States with CDL

AK CA HI OR VA WA

0

0.2

0.4

0.6

0.8

AK CA HI OR VA WA

0

0.04

0.08

0.12

0.16

Overall, our findings provide very strong evidence that CDL reduces 

the chance of beverage containers becoming marine debris.

4
Understanding the different sampling methods

NOAA MDP implements a comprehensive sampling 

regime across a relatively small set of representative 

beaches, at regular time intervals. Trained volunteers 

collect trash and quantify the debris type per unit area.

In contrast, OC’s International Coastal Cleanup is an 

annual citizen science event held at thousands of 

sites each year (typically in September). People with 

no formal training clean up an area of shoreline over 

the course of a 1.5-2 hour community participation 

event and count individual items of trash collected. 

CSIRO’s approach differs again, focusing on stratified 

designed surveys conducted by trained professionals 

at sites selected by a random sampling design. 

While it is possible to use data from any of these 

monitoring programs to understand debris baselines, 

drivers, and changes, combining them was a challenge.

Surveys using CSIRO’s method found much higher debris 

densities. One major difference is that CSIRO surveys 

include items as small as 1-2mm where as NOAA MDP and 

OC do not record any items smaller than an inch (25mm).

The differences between the data sets at 

shared locations suggest that thorough survey 

design is important to reduce variability 

among survey approaches and locations.

This balance is key for engaging participants, 

but implies some compromises from a survey 

design and data quality perspective. 

Due to the large area of the United 

States, finding a balance between 

rigorous scientific research and 

citizen science participation is key.

5 An analysis of marine debris in the US 
Recommendations 

and next steps

1. DEVELOP A NATIONAL BASE-LINE

A survey incorporating recommendations presented 

by CSIRO would require relatively little time and cost, 

and would provide a useful baseline on which to build.

2. CONTINUING COASTAL CLEAN-UPS

Although it is time consuming to compile data on 

types of items collected during volunteer clean-ups, 

these data provide a rich source of information. 

Volunteer data helped us identify the effectiveness of 

policies, hotspots for items that have a large impact 

on wildlife, and areas to prioritize engagement 

with industry and consumers. Clarifying some 

potential biases, such as how sites are chosen, 

and how volunteers search during a clean-up will 

significantly improve the value of volunteer efforts. 

3. INVESTIGATE THE CAUSES OF MARINE DEBRIS

Socioeconomics, site accessibility, population density, 

and other factors affect local marine debris loads. 

Further analysis would provide useful information 

for both understanding how these factors influence 

debris loads on the coast and inland waterways, 

as well as targeting specific actions such as cleanups, outreach, incentives, and regulation.

4. UNDERSTANDING THE LINKS BETWEEN LAND-BASED 

ACTIVITIES AND MARINE DEBRIS

Most marine debris originates from land-based 

litter. By combining the available coastal data 

with our knowledge of how debris is transported 

on land, we can gain a better picture of the 

important processes and possible intervention 

points before litter becomes marine debris.

5. ESTABLISH A NATIONAL MONITORING PROGRAM

Designing a national monitoring system would allow 

NOAA MDP to periodically re-survey the coastal US 

for debris, with a clear idea of the likely person-hours 

required, the expected data structure and sampling 

design. This would be supported by a pre-existing 

analytical design and data management system. This 

approach would deliver cost-effective monitoring 

and result in an interpretable data set, despite 

potentially using different providers over time.

6
Publications

Hardesty, BD, J Harari, A Isobe, L Lebreton, N Maximenko, J 

Potemra, E van Sebille, AD Vethaak and C Wilcox. Using numerical 

model simulations to improve the understanding of micro-plastic 

distribution and pathways in the marine environment. Fronts in 

Marine Science. https://doi.org/10.3389/fmars.2017.00030 

Willis, K., BD Hardesty, L Kriwoken and C Wilcox. Differentiating littering, 

urban runoff and marine transport as sources of marine debris in coastal 

and estuarine environments. Scientific Reports. DOI: 10.1038/srep44479 

Hardesty, BD and C Wilcox. 2017. A risk framework for tackling 

marine debris. Analytical Methods. DOI: 10.1039/C6AY02934E. 

Hardesty BD, TJ Lawson, T van der Velde, M Lansdell, G Perkins 

and C Wilcox. 2016. Estimating quantities and sources of marine 

debris at a continental scale. Frontiers in Ecol and the Enviro. 

http://onlinelibrary.wiley.com/doi/10.1002/fee.1447/full 

Roman, L, QA Schuyler, BD Hardesty and KA Townsend. 2016. 

Anthropogenic Debris Ingestion by Avifauna in Eastern Australia, 

PLoS One, 30, 2016 http://dx.doi.org/10.1371/journal.pone.0158343 

van der Velde, T., Milton, D.A., Lawson, T.J., Lansdell, M., Wilcox, C., Davis, 

G., Perkins, G., & BD Hardesty. 2016. Is citizen science data worth our 

investment? Biol Cons. http://dx.doi.org/10.1016/j.biocon.2016.05.025 

Vince, J and BD Hardesty. 2016. Plastic pollution challenges 

in the marine and coastal environments: from local to global 

governance. Rest Ecology. http://doi/10.1111/rec.12388/ 

Wilcox, C and BD Hardesty. 2016. Biodegradable nets are not a panacea, 

but can contribute to addressing the ghost fishing problem. Animal Cons. 

19; 322-323. http://onlinelibrary.wiley.com/doi/10.1111/acv.12300/pdf

Wilcox, C, E van Sebille, BD Hardesty. 2015. The threat of plastic pollution 

to seabirds is global, pervasive and increasing. Proc of the Nat’l Acad 

of Sciences. Vol. 112 no. 38 http://doi:10.1073/pnas.1502108112 

van Sebille, E, C Wilcox, L Lebreton, N Maximenko, BD Hardesty et al. 2015. 

A global inventory of small floating plastic debris. Enviro. Res Letters. 

http://iopscience.iop.org/article/10.1088/1748-9326/10/12/124006

Schuyler Q, C Wilcox, C Wilcox, K Townsend, K R Wedemeyer-Strombel, 

G Balazs, E van Sebille and BD Hardesty 2015. A global risk analysis for 

turtles and marine debris. Glob Change Bio. http://doi:10.1111/gcb.13078. 

Wilcox, C. N Mallos, GH Leonard, A Rodriguez and BD Hardesty. 2015. 

Using expert elicitation to estimate the impacts of plastic pollution on 

marine wildlife. Mar. Pol. http://dx.doi.org/10.1016/j.marpol.2015.10.014

Jambeck, JA, R Geyer, C Wilcox, et al. 2015. Plastic waste input to the oceans 

from land. Science. 347(62230):768-771. http://DOI:10.1126/science.1260352 

Hardesty, BD, T Good and C Wilcox. 2015. Novel methods, new results 

and science-based solutions to tackle marine debris impacts on wildlife. 

Ocean and Coastal Mgmt. doi:10.1016/j.ocecoaman.2015.04.004

Hardesty BD, D Holdsworth, A Revill and C Wilcox. 2015. A biochemical 

approach for identifying plastics exposure in live wildlife. Methods in Ecology 

and Evolution. http://onlinelibrary.wiley.com/doi/10.1111/2041-210X.12277/pdf 

Vegter A,... BD Hardesty, ... C Wilcox, et al. 2015. Global research priorities 

for the management and mitigation of plastic pollution on marine wildlife. 

End. Species Research, 25: 224-247. http://DOI:10.3354/esr00623 

Wilcox C, G Heathcote, J Goldberg, R Gunn, D Peel and BD 

Hardesty 2014. Understanding the sources, drivers and impacts 

of abandoned, lost and discarded fishing gear in northern 

Australia. Cons Bio. http://DOI:10.1111/cobi.12355 

Reisser J, J Shaw, G Hallegraeff, M Proietti, D Barnes, M Thums, C 

Wilcox, BD Hardesty and C Pattiaratchi. 2014. Millimeter-sized marine 

plastics: a new pelagic habitat for microorganisms and invertebrates. 

PLoS ONE 9(6): e100289. http://doi:10.1371/journal.pone.0100289.

Reisser J, J Shaw, C Wilcox, BD Hardesty, M Proietti, M Thums, C Pattiaratchi 

2013. Marine plastic pollution in waters around Australia: characteristics, 

concentrations and pathways. PLOS One. 8(11): http://www.plosone.

org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0080466 

Schuyler, Q, BD Hardesty, C. Wilcox and K Townsend 2013. 

A global analysis of anthropogenic debris ingestion by sea 

turtles. Cons Bio. 28:129-139. http://DOI:10.1111/cobi.12126. 

Wilcox, C, BD Hardesty, R Sharples, DA Griffin, TJ Lawson and R Gunn. 

2013. Ghost net impacts on globally threatened turtles, a spatial risk 

analysis for northern Australia. Cons Lett, DOI: 10.1111/conl.12001.

Schuyler, Q, K Townsend, BD Hardesty and C Wilcox. 2012. To 

eat or not to eat: debris selectivity by marine turtles. PLOS 

One 7(7): e40884. DOI:10.1371/journal.pone.0040884.

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FOR FURTHER INFORMATION

CSIRO Oceans and Atmosphere 

Dr Denise Hardesty

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