DOI: 10.5061/dryad.47d7wm3c2
title: Spatial-temporal growth, distribution, and diffusion of marine microplastic research and national plastic policies

description: Plastic accounts for 80% of material waste in the ocean. The field of
 marine microplastic research is relatively new and is growing rapidly, in
 terms of published papers as well as institutions and countries conducting
 research. To combat plastic pollution, there is sufficient evidence that
 policies can lead to reduced plastic production and consumption both
 locally and globally. We aim to understand how marine plastics research
 and policies have grown and spread. Specifically, we used scientometric
 and spatial diffusion methods to best explain how ideas (in this case
 science and policy) clustered and spread geographically through time. We
 performed systematic literature searches to determine the spatial and
 temporal growth of marine microplastic publications and national plastic
 policies from 1900-2019. We found that more countries adopted national
 plastic policies than those that have conducted marine plastic research.
 Doubling times of each temporal growth rate analyzed (research paper,
 institution, country, and national policy) ranged from 1.1 – 4.05 years.
 Further, each temporal growth rate had a break point where doubling time
 changed significantly. Marine microplastic research has grown
 exponentially since 2006, and the topics of inquiry have increased
 steadily. Marine microplastic publication spread at the institution level
 is best explained by a hybrid of expansion and relocation diffusion while
 national plastic policy spread is best explained by expansion diffusion.
 Marine microplastic research activity was not a good indicator of a
 country’s resources or motivation toward national plastic policies.
description: <strong>Marine plastic peer reviewed paper
 selection</strong>: Growth of marine microplastic (MP) publications
 was compared to other types of plastic research by performing a systematic
 literature search of peer-reviewed papers from Scopus, Elsevier’s abstract
 and citation database, in April 2020. The search used five sets of
 keywords: marine AND plastic*, marine AND “plastic bag*”, marine AND
 “single use plastic*,” marine AND microbead*, and marine AND
 microplastic*. The asterisk at the end of a word ensured both the singular
 and plural forms were considered. Within each of these sets of keywords
 the “analyze search results” feature was used in Scopus to record the
 quantity of papers published annually and cumulative number of papers
 published by country for 1900-2019. We note that many early papers
 studying mussel feeding physiology used poly-microbeads since the 1980s
 but were not included in any of the keyword searches. Papers were randomly
 spot-checked to ensure they fit within the keywords, if they did not, they
 were removed from our selection. Metadata from marine
 MP papers were collected from a systematic literature search of
 peer-reviewed papers from Web of Science in April 2020. The search
 criteria used were the keywords marine AND microplastic* and all years
 (1900-2019), the same as the Scopus search. Publishing date, institution
 of lead author (including latitude and longitude), country of lead author,
 journal, and title were collected. Papers addressing non-marine MP topics
 (e.g. table salt or freshwater), highlights, commentary, news features,
 correspondences, opinion, and review papers were removed. Each marine MP
 paper was categorized based on focus topic: chemistry, environment,
 organism, policy, or review. If a paper studied multiple focus topics,
 only the predominate one was recorded. Organism papers were further
 categorized into functional groups: bacteria, fungus, invertebrate, small
 vertebrate, large vertebrate, macroalgae, phytoplankton, and zooplankton
 (includes fish larvae). If a paper studied multiple organisms, all were
 categorized by functional group and included.
 <strong>National plastic policy selection</strong>:
 To evaluate plastic policy growth and diffusion, a systematic literature
 search for national plastic policies implemented through 2019 was
 conducted. Policy data was collected from Xanthos and Walker (2017),
 Schnurr et al. (2018), Lam et al. (2018), Plastic Policy Inventory from
 Duke’s Nicholas Institute for Environmental Policy Solutions (2020), and
 news articles from Wikipedia’s “phase-out of lightweight plastic bags”
 page (April 2020). Country, implementation year, type (plastic bag,
 microbead, single use plastic; SUP), and level (levy, ban) were recorded.
 All policies were cross-validated with an internet news search and
 policies that failed cross-validation were not included. Voluntary
 national plastic levies and bans were not included. Policies were
 evaluated at a national level, where countries with multiple levels or
 types of policies were only counted once in analyses.