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Stakeholders' Perspectives on Microplastics in Sludge Applied to Agricultural Land


Abstract and Figures

Microplastic (MPs) inputs to agricultural lands from wastewater and sewage sludge reuse in Europe have been estimated to be between 65,000 and 230,000 tons/year making the farm environment one of the major receptors and, possibly, environmental reservoirs of MPs. In Sweden there have been ongoing discussions since 1994 about environmental and health effects of sewage sludge application to agricultural lands. This debate on sludge use focused initially on metals, then moved on to pharmaceutical residues and currently has turned to MPs. In spite of the limited scientific information about environmental impacts of MPs in soils, governmental approval in Sweden to allow increased spreading of sludge on productive agricultural lands is moving forward. To study individual perceptions of the potential risks, interviews were conducted in 2020 with Swedish stakeholders who in some way work with the issue of sludge management. The results of these interviews provide an indication of not only how environmental risk information is interpreted by representatives from different sectors but also the degree to which perceived risks may shape environmental policy.
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published: 21 February 2022
doi: 10.3389/fsufs.2022.830637
Frontiers in Sustainable Food Systems | 1February 2022 | Volume 6 | Article 830637
Edited by:
Paula Alvarenga,
University of Lisbon, Portugal
Reviewed by:
Nicolas Beriot,
Wageningen University and
Research, Netherlands
Juan José Alava,
University of British Columbia, Canada
Dennis Collentine
Specialty section:
This article was submitted to
Waste Management in
a section of the journal
Frontiers in Sustainable Food Systems
Received: 07 December 2021
Accepted: 13 January 2022
Published: 21 February 2022
Zilinskaite E, Futter M and Collentine D
(2022) Stakeholders’ Perspectives on
Microplastics in Sludge Applied to
Agricultural Land.
Front. Sustain. Food Syst. 6:830637.
doi: 10.3389/fsufs.2022.830637
Stakeholders’ Perspectives on
Microplastics in Sludge Applied to
Agricultural Land
Emilija Zilinskaite, Martyn Futter and Dennis Collentine*
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences Sveriges Lantbruksuniversitet
(SLU), Uppsala, Sweden
Microplastic (MPs) inputs to agricultural lands from wastewater and sewage sludge
reuse in Europe have been estimated to be between 65,000 and 230,000 tons/year
making the farm environment one of the major receptors and, possibly, environmental
reservoirs of MPs. In Sweden there have been ongoing discussions since 1994 about
environmental and health effects of sewage sludge application to agricultural lands. This
debate on sludge use focused initially on metals, then moved on to pharmaceutical
residues and currently has turned to MPs. In spite of the limited scientific information
about environmental impacts of MPs in soils, governmental approval in Sweden to allow
increased spreading of sludge on productive agricultural lands is moving forward. To
study individual perceptions of the potential risks, interviews were conducted in 2020
with Swedish stakeholders who in some way work with the issue of sludge management.
The results of these interviews provide an indication of not only how environmental risk
information is interpreted by representatives from different sectors but also the degree to
which perceived risks may shape environmental policy.
Keywords: agricultural soil, circular economy, MPs, sewage sludge, stakeholder interviews/analysis
Microplastics (MPs), or plastic particles smaller than 5 mm, are one of the most discussed
environmental issues of the twenty-first century. They were first reported in the Sargasso Sea
(Carpenter and Smith, 1972) but it was not until much later that the issue began to attract
widespread scientific and popular attention (Thompson et al., 2004). Much of the early focus was
on marine systems, but more recently, attention has expanded to include freshwater (Wagner et al.,
2014; Eerkes-Medrano et al., 2015; de et al., 2018; Li et al., 2018) and terrestrial environments
(Huerta Lwanga et al., 2016; de Souza Machado et al., 2018; Rillig and Lehmann, 2020; Baho
et al., 2021). Microplastics are ubiquitous in the environment. They are produced through primary
and secondary emission pathways. The former occurs when MPs are introduced directly into the
environment via, e.g., domestic and industrial effluents, spills, sewage or indirectly via, e.g., run-off.
Secondary MPs emissions are driven by the breakdown of larger plastic particles already present in
the environment. Once in the environment, MPs can be further broken down to form nanoplastics
(1–100 nm).
The presence of MPs in the terrestrial environment was first reported in 2012 (Rillig, 2012).
Terrestrial MPs originate from multiple sources including atmospheric deposition (Allen et al.,
2019; Klein and Fischer, 2019), leaching from landfills (He et al., 2019), tire wear (Knight et al.,
2020), breakdown of agricultural mulch (Huang et al., 2020; Zhang et al., 2020) and application of
sewage sludge to agricultural land (Nizzetto et al., 2016a,b; Crossman et al., 2020). Despite multiple
lines of evidence suggesting that terrestrial ecosystems are major MPs sinks, microplastic research
Zilinskaite et al. Stakeholders Perspectives on Microplastics in Sludge
in the terrestrial environment is still at an early stage (see, e.g.,
Baho et al., 2021 for a recent review).
Wastewater treatment plants (WWTPs) typically remove a
large fraction of MPs in influent water (Carr et al., 2016).
However, they can still be a significant source of MPs to the
environment (Murphy et al., 2016; Edo et al., 2020). Multiple
studies have documented elevated levels of MPs in receiving
waters of WWTPs (e.g., Sun et al., 2019; Schell et al., 2021) as well
as in sludge (e.g., Crossman et al., 2020; Edo et al., 2020). When
sludge from WWTPs is used either as compost or as a fertilizer for
agricultural soils, the MPs removed during wastewater treatment
re-enter the environment. Sludge application to agricultural
land may add between 63,000–430,000 and 44,000–300,000 tons
MPs each year to European and North American farmlands,
respectively (Nizzetto et al., 2016b).
The issue of spreading sludge on agricultural land has been
actively debated in Sweden over the last 30 years without
reaching a definite conclusion (Bengtsson and Tillman, 2004;
SOU, 2020:3). Early debates concerned the presence of metals
(primarily cadmium) in sludge. This was followed later with
new concerns when it was recognized that pharmaceutical
residues were also present in sludge. In the last five years
the debate has now expanded to include concerns about MPs
(Ljung et al., 2018). The primary opposition to spreading with
respect to these concerns has come from agricultural producers
(Wallenberg and Eksvärd, 2018; Ekane et al., 2021). In response
to a lack of guidelines which would ensure that these issues
were addressed and that spreading sludge would be accepted by
agricultural producers, a national network of WWTPs (Swedish
Water) developed a certification program REVAQ in cooperation
with the Federation of Swedish farmers (LRF), an agricultural
supplier cooperative (Lantmännen) and Swedish grocery chains
(L’Ons et al., 2012; Persson et al., 2015). The REVAQ program
supplies stakeholders not only with information regarding the
composition of REVAQ-certified sludge it also sets guidelines
for continuous improvement in the quality of wastewater and
sludge with respect to metals and other prioritized substances.
However, this voluntary program has not been able to sufficiently
resolve the question of whether sewage sludge is deemed to be
safe enough to be used as a source of recycled phosphorus (P).
In 2018 the Swedish Government commissioned a study to
explore relevant concerns around sludge management with a
particular focus on the recycling of P from sludge. In their remit,
the committee was assigned several tasks including:
“(to) formulate proposals on the spreading of sewage sludge, with
possible exceptions, in order to prevent hazardous substances,
pharmaceutical residues and microplastics from entering the
ecocycle and to steer toward a non-toxic environment” (SOU,
2020:3, p. 31).
With respect to this question, the committee offered
two alternatives:
“ban on spreading of sewage sludge on or in soil through (1)
a complete ban on spreading with very limited exceptions, or
(2) a ban on spreading on the basis that possible risks are to
be managed and addressed—under this option exceptions are
permitted for sanitized and quality-assured sludge to be spread
on productive farmland” (SOU, 2020:3, p. 32).
While SOU, 2020:3 acknowledged that the presence of MPs had
an effect on whether or not sludge spreading should be permitted
due to possible risks, the only direct conclusion was that there
is a need for more research to determine to what extent MPs
have an effect on biota and ecosystems. If the first alternative, a
complete ban on spreading, were to be accepted then this would
mean that concerns about MPs in sludge would no longer be a
high priority for continued research. However, under the second
alternative, there is a significant possibility that spreading of
sludge, consistent with REVAQ guidelines, would be permitted.
Under the current REVAQ guidelines there is no specific analysis
required for MPs. On the basis of a study commissioned by the
consortium behind the REVAQ program (Ljung et al., 2018),
the conclusion was that it was not necessary to establish a
threshold value for MPs in their guidelines. Therefore, if the
second alternative is adopted by the government, there is a high
probability that the sludge will be spread on agricultural land and
that this sludge will contain MPs.
Environmental policy is usually informed by scientists but
decided on by elected politicians. However, policy is informed not
only by opinions from both of these groups but also shaped by
input from interested stakeholders. Since the fate of MPs in the
environment is a relatively recent area of interest and research,
there is a great deal of uncertainty with respect to risks (see, e.g.,
SAPEA, 2019; Völker et al., 2020; Zhou et al., 2020; Catarino
et al., 2021; Thiele and Hudson, 2021) and risk communication
(Wardman et al., 2021). To date, there have been a number of
studies of stakeholder perspectives and attitudes toward MPs
(summarized in Garcia-Vazquez and García-Ael, 2021). Most
of these studies have focused on specific groups, e.g. university
students (Chang, 2015; Raab and Bogner, 2021) or consumers of
personal care products (Anderson et al., 2016) and have targeted
MPs impacts on the marine environment.
Thiele and Hudson (2021) conducted an on-line survey on
the subject of MPs risks in general with both lay and “topic-
experienced” respondents. They found that the topic-experienced
group expressed a greater concern than the lay group. They
reported that this was not consistent with previous findings that
persons with expertise in an area usually assigned a lower risk
than the general public (e.g., Persson et al., 2015). Additionally,
their survey found that “almost 1/3 of people—including topic-
experienced ones—were affirmative about existing evidence or
links despite evidence gathered to date suggesting that no proven
health effects for humans from microplastics exists.”
Other studies have been conducted on public perceptions
of risks associated with MPs. Henderson and Green (2020)
conducted focus groups composed of both the general public and
people with a special interest or knowledge about MPs. However,
as the primary focus of the media has been on MPs in the marine
environment, this was the context which respondents used in
discussions. Catarino et al. (2021) investigated public perception
with respect to the impact of MPs on human health and Deng
et al. (2020) wanted to know how willing the public was to take
actions to reduce the amount of MPs in the environment.
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We are not aware of any studies specifically dedicated to the
study of stakeholder perspectives with respect to risks associated
with MPs in sludge spread on agricultural soil. However, there
have been studies of Swedish stakeholder perspectives on sludge
spreading (Bengtsson and Tillman, 2004; Oberg and Mason-
Renton, 2018; Ekane et al., 2021).
To better understand Swedish stakeholders’ perspectives on
the environmental risk from MPs in sludge applied to agricultural
soil, in Spring 2020 a survey was planned as part of the
IMPASSE research program (Nizzetto et al., 2021). Interviews
were designed around the following two central questions:
i) How much is known with respect to the risk from MPs in
terrestrial environments?
ii) Are MPs a concern when permitting sludge applications to
agricultural soil?
Stakeholders were first identified based on organizations with an
interest in the broad field of sludge management from WWTPs.
This identification included politicians, government authorities,
sector organizations, interest organizations (environmental
NGOs and a farmer association) and research organizations.
Based on initial organizational contact, individuals in these
organizations were selected for future contact. Finally, when
these individuals were contacted some of them suggested
including other persons with an interest in the survey. In
total 103 stakeholders, representing 37 organizations in Sweden,
were contacted and asked to participate. One-third of the
contacted individuals, representing twenty-six organizations in
five stakeholder categories, agreed to take part in the survey.
The interview protocol was based on our earlier work
(Žilinskaite et al., 2021). Interviews were conducted online,
using ZOOM and Skype, between late March and early June
2020. Thirty-one interviews were conducted in Swedish and
two interviews in English. Each interview lasted between 30
to 90 mins. The limited number of participants allowed the
survey to be designed as a series of open-ended questions. The
final questionnaire consisted of 25 questions organized into four
blocks: MPs in the environment (three questions), contaminants
in wastewater sludge (six questions), MPs in agricultural soil (10
questions), sludge regulation and management (six questions).
In the following text citations from interviews are presented in
italics (the transcriptions and translations from Swedish into
English are available on request from the corresponding author).
Interviews were analyzed using Grounded Theory as a
qualitative data analysis research design (Creswell, 2013). When
using Grounded Theory, the collected data is combined with a
qualitative content analysis to generate consistent results based
on empirical material (Glaser and Strauss, 2008). The first step
consisted in analyzing each interview separately, identifying the
stakeholders’ main concerns and issues they raised during the
interviews. The answers to the questions were then organized
in Excel sheets, where each sheet represented one of the five
stakeholder categories. Afterwards, the answers were organized
into stakeholder categories where each block of questions
was analyzed for each one of the five stakeholder categories.
Then sub-categories were identified and organized into tables
presenting the overall picture by not only stakeholders as a group
but also as by stakeholder categories.
In order to better contextualize responses, interviewees were
asked to identify their primary area of focus at the beginning
of the interview. At this time, stakeholders usually described
their current working duties and other relevant projects or
tasks they are currently involved with or they have been
dealing with in the past. These self-identified focus areas were
sorted into seven classifications (Figure 1): sludge management,
waste pollutants, pharmaceutical residues, agriculture, waste
management, environment and water management. There was
considerable overlap between these classifications, e.g., a person
with a focus on sludge management would also be likely to have
a focus on waste management. However, using the classification
did provide a broader picture of the self-identified focus areas for
the five stakeholder categories (Figure 1).
No stakeholder group identified all seven categories as
primary focus areas, but reported between four and six different
areas of interest. However, each of the categories, with the
exception of public authorities (Government), had one focus area
that dominated. Politicians were predominantly focused on the
environment which is not surprising as their tasks often include
a broader interest. That sludge management was the dominant
interest among researchers reflected the fact that individual
expertise (research) in that area was a criterion for selection
of people to interview. What is more surprising is that no one
in this category identified environment as a focus area which
also perhaps reflects not only the individuals asked but also
a need to focus on a narrow subject as a researcher. Finally,
people from both interest and sector organizations identified
waste treatment as their major focus area although both groups
included additional areas.
In the following sections, each block of questions is represented
by one or more central questions. Since the interview format was
based on open-ended questions each block had a central theme
and the questions included in the block were either central or
complementary to the topic area. The complementary questions
were included to deepen the responses in order to allow for a
more in-depth understanding of each answer when analyzing
the results. The complete set of questions is included in the
Supplementary Material. In the sections below each block is
introduced and then followed by a categorization of the responses
to the relevant central questions. The responses were analyzed
from two perspectives, as a share of total respondents and as a
share within each category. In the text, the share is described
as a percentage. For several of the questions responses could
be multiple therefore the sum of percentages may be greater
than 100%.
MPs in the Environment
The first series of questions related to how stakeholders were
affected by the issue of MPs in the environment and their
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FIGURE 1 | Proportion of stakeholders (n=31) in each main category and their self-reported primary focus areas.
FIGURE 2 | Stakeholder descriptions of how the microplastics issue affects them. Percentages reported represent the frequency with which an issue was mentioned
across all stakeholders responding (n=33).
assessment of current scientific and societal knowledge with
respect to the presence of MPs in the marine and terrestrial
environments. The first central question for stakeholders was
“How do MPs issues affect you?.” The responses to this question
were distributed across four categories (Figure 2).
Almost half (46%) of stakeholders stated that MPs issues affect
them directly in their work tasks. An additional 15% expressed
that they are in other ways involved in MPs issues, they chose
to participate in the interview because of their own general
interest in the potential impact of MPs; 24% answered that MPs
issues are not a major concern or focus in their work and/or
that the issue is not a major focus area for them professionally.
The remaining 15% stated that they lacked knowledge on MPs
issues. Respondents working in the public sector (Government)
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Zilinskaite et al. Stakeholders Perspectives on Microplastics in Sludge
answered that they were mainly affected through their work
although a small fraction stated that they were not affected that
much. Politicians had a greater general interest in MPs issues,
with the remaining groups divided evenly between the other
possibilities. The greatest share of researchers answered that they
were affected daily in their work with only a small number
expressing that they had general interest. As noted above, this
reflects that a particular group of researchers participated and
that as for most researchers they have a narrow research focus
on area of expertise. People associated with Interest and Sector
organizations were also affected primarily through their work.
The second central question in this series “Why is there so
little focus on MPs in the terrestrial environment compared
to the marine environment?” was asked to get a sense of why
there was divergence in societal interest between the marine and
terrestrial environments. Responses are reported separately for
the marine (Figure 3) and terrestrial (Figure 4) environments.
With respect to MPs in the marine environment, types of
explanation were offered (Figure 3). A general belief held by
35% of the stakeholders referred to MPs being harmful for the
marine environment, in particular they highlighted the risks
that marine mammals ingest MPs or getting stuck in plastic
and die. The next largest group, 23%, highlighted that MPs
are very visible in the marine environment and therefore get
more attention. Another 14% mentioned that in the marine
environment it is methodologically easier to measure and collect
macro- and MPs. Answers from 10% of the participants stressed
the greater political priority the marine environment has while
8% of respondents said that this is a well-known issue and that
is why it gets attention continuously. The remaining 8% talked
about a possible stronger emotional connection with the marine
environment rather than with the terrestrial environment.
Government and politician respondents mainly referred to
MPs being harmful for the marine environment, reflecting
considerations such as political priorities, visible impacts and the
relative ease of measuring and analyzing their impact. Just a small
fraction of respondents mentioned that MPs is a known issue and
that people may have an emotional connection with the marine
environment. A similar small fraction of researchers noted MPs
are a known issue and talked about an emotional connection.
In general, researchers emphasized the visible impact and the
harm MPs are believed to cause to marine life, as well as the ease
of measuring and analyzing MPs impacts. Sector respondents
reasoned mainly that visible impacts were important, giving the
same weight to concerns to political priorities, harm to marine
life, emotional connection and the ease of measurement and
analysis. Interest organization respondents highlighted that MPs
in the marine environment is a known issue and that it is easy to
measure and tackle while also being concerned about the harm to
marine life.
There were seven main explanations for the lower focus
on MPs in the terrestrial environment (Figure 4). Lack of
knowledge/research was identified by 30% of the participants as
a reason for less interest in MPs in the terrestrial environment.
There were also 17% who argued that the lower level of
focus might be due to the fact that it is hard to analyze
soil environments while another 17% referred to the higher
degradation rate of MPs in soils compared to in water. The lower
emotional connection to soil than to water was also a reason
mentioned by 13% of respondents while another 17% suggested
that the lack of focus might be because land animals are better
able to adapt to MPs in soils. One respondent referred to the
soils buffering ability, or the ability of absorbing nutrients, and
another pointed out the lack of shared responsibilities, stating
that it is unclear which authorities are responsible for the relevant
environmental issues.
Responses from government and politicians both point to a
lack of knowledge/awareness as the major reason for a lower
interest in the terrestrial environment. This view was shared,
though to a lesser degree, by researchers and people in the
wastewater sector though both of these also were the only groups
who believed that the degradability of MPs in soil may also be
an explanation. Respondents from interest organizations differed
from the other four categories by being the only group to
assigning importance to the buffering ability of the soil and lack
of shared responsibilities.
Pollutants in Wastewater Sludge
The second series of questions focused on stakeholder knowledge
and perspectives on pollutants present in sludge. The first
question was about pollutants in general (Figure 5) while the
second question took up how much was known about the
presence of MPs in sludge specifically (Figure 6).
Responses to the first question “What is known about
pollutants in sludge?” were separated into two categories:
good knowledge and uncertain knowledge. Over half of the
respondents (56%) believed there was good knowledge about
pollutants in sludge, primarily because there had been a long-
term interest in the spreading of sludge on agricultural land in
Sweden and that over a 30 year period there had been many
studies related to pollutants in sludge (Figure 5).
The 44% of respondents (14) that were uncertain about the
level of knowledge reflected the many unknown and/or new
pollutants which add complexity to sludge analysis, with possible
cocktail effects. Some in this group specifically referred to the
lack of a systematic way to measure pollutants, questioning their
limit values and how the different ways in which concentration
boundaries are defined. Some of these respondents also argued
that sludge composition had changed over time, differing from
the product it had been in the past.
Four stakeholder categories were relatively evenly divided,
with around half believing that there was good knowledge and
half believing there was uncertain knowledge, the researcher
category was exceptional as this group expressed the view that
the existing knowledge was good. As noted above, since there
have been studies performed on pollutants in sludge over a long
period of time, these respondents may have believed that the
existing knowledge was conclusive and that any effects of changes
in sludge composition were not an important factor (Figure 5).
Responses to the second question in this series “What is
known about MPs in sludge?” were divided into six categories
(Figure 6). Of these, 27% of the interviewees highlighted the
general lack of knowledge on the topic while 34% talked about
methodological limitations, of which more than half mentioned
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FIGURE 3 | MPs in the marine environment by category of stakeholder. Percentages reported represent the frequency with which an issue was mentioned across all
stakeholders responding (n=46).
FIGURE 4 | Stakeholder perspectives on MPs in the terrestrial environment. Percentages reported represent the frequency with which an issue was mentioned across
all stakeholders responding (n=28).
the lack of standardized methods to detect MPs, noting that MPs
analysis in general is not easy and it is harder to do so in sludge.
A few interviewees (12%) referred to high removal rates of up
to 98% in WWTPs. A small number (10%) noted that MPs are
everywhere anyway while one respondent answered that other
contaminants might be more important.
Most answers from Government representatives referred
to methodological limitations for detecting MPs. Some of
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FIGURE 5 | “What is known about pollutants in sludge?” By category of stakeholder. Percentages reported represent the frequency with which an issue was
mentioned across all stakeholders responding (n=22).
them referred to MPs being cleaned by WWTPs and a
small fraction referred to the lack of knowledge. Politicians
stated that they had a lack of knowledge about MPs in
sludge, with some of them specifying they had no notion
about it while others mentioned that MPs are anyway
present everywhere. Interviewees from research organizations
highlighted the methodological limitations in detection and
analysis. Some interviewees from this group pointed out the
lack of knowledge and the remainder answered they did not
know. The distribution of answers from interest organization
representatives was split equally between lack of knowledge,
methodological limitations, knowing that MPs are cleaned by
WWTPs and the notion that MPs are everywhere anyway.
Sector representatives mainly talked about the methodological
limitations while also highlighting a current lack of knowledge,
the notion that MPs are everywhere anyway, the belief that it is
more important to evaluate other contaminants and not knowing
about MPs.
MPs in Agricultural Soil
The third series of questions specifically addressed stakeholder
perceptions of risks associated with sludge spread on agricultural
soil. The central question in this series was “How can
MPs in sludge affect the environment when applied to
agricultural land?.” Responses were categorized into eleven
possible environmental risks in five risk groups (Table 1).
The first risk group was associated with possible soil processes
including breakdown of MPs into smaller sizes and further
transport throughout the soil over time. Multiple respondents
thought that MPs would end up in the aquatic environment
or accumulate in soil or biota. Possible toxic effects were also
mentioned. There were also respondents who claimed not to have
any knowledge about possible risks. Although the largest number
of respondents were concerned about MPs effects in agricultural
lands there was no specific environmental risk which a majority
of stakeholders believed to be the most important.
The next question elicited stakeholder views on public
awareness, “How aware is the public of MPs in sludge which is
applied to agricultural land?.” From the answers it would seem
that the general belief is that the public is not very aware of this
issue (Figure 7). Only 10% of respondents answered that they
thought the public was aware while another 23% considered the
public to be somewhat aware. Close to two-thirds of respondents
believed the public was not aware. Politicians all held the view
that there is a great lack of public awareness. The four other
stakeholder categories all indicated that they thought the public
was to some degree aware of this issue.
MPs in Sludge Regulation and
In the Swedish regulatory environment, guidelines for spreading
sludge have existed for more than 30 years. The need for new
guidelines has been the subject of a recent national governmental
study (SOU, 2020:3). This series of questions focused on
stakeholder perceptions of how sludge is managed and regulated.
One of the questions in this series asked was “What are the
current guidelines for contaminants in sludge?.” Approximately
one quarter (24%) of interviewees referred to the existence of
guidelines. However, more than half (52%) highlighted that
although guidelines exist, they are incomplete while 12% referred
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FIGURE 6 | “What is known about MPs in sludge?” By category of stakeholder. Percentages reported represent the frequency with which an issue was mentioned
across all stakeholders responding (n=33).
TABLE 1 | Environmental risks associated with MPs in agricultural land (n=48).
Group Factor Times
Soil processes Degradation 6
Spread 5
Contamination of aquatic
Marine habitats 1
Runoff to surface waters 4
Leaching to groundwater 3
Accumulation in soil or biota Accumulation in soil 2
Effects on soil structure 3
Accumulation in crops and plants 5
Accumulation in soil biota 5
Toxins and pathogens Toxic effects 5
Viruses 1
No knowledge 8
specifically to the Swedish certification system REVAQ as an
example of upstream work while the remaining 12% said they did
not know (Figure 8).
Government, sector, research and interest organizations
participants were all aware of the existence of guidelines but
believed them to be incomplete. Stakeholders from research
organizations also mentioned the Swedish certification system
REVAQ as an example of upstream work and, although most
of the politicians answered that they were not aware of existing
guidelines, some respondents also referred to the REVAQ
certification (Figure 8).
A second core question in this series was what stakeholders
thought the issue might look like in the future “How do you
think MPs in the sludge will look in 20 years from now?.” The
answers were separated into five different categories (Figure 9).
Most (66%) thought that in 20 years there would be a minimum
use of plastics and that this would lead to less accumulation of
MPs. Future research was another area of interest (17%) with
respondents believing that the gathering of important knowledge
on how plastics and MPs affect humans the environment would
take place. A few (7%) answered that other contaminants (e.g.,
perfluorinated substances) will be seen as more problematic than
MPs, while a similar number raised the concern that outdated
regulations would not help MPs to vanish from either industrial
production or accumulation in the environment. Both those that
thought other contaminants were more important and those that
were concerned about outdated regulations thought there would
be a positive future outcome if the issue of contaminants collected
in sludge from WWTPs was addressed with improved systems.
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FIGURE 7 | “How aware is the public of MPs in sludge applied to agricultural land?” Percentages reported represent the frequency with which an issue was
mentioned across all stakeholders responding (n=30).
FIGURE 8 | “What are the current guidelines for pollutants in sludge?” Percentages reported represent the frequency with which an issue was mentioned across all
stakeholders responding (n=33).
Respondents from all stakeholder categories believed
that the usage of plastics would diminish in the next 20
years (Figure 9). Participants from interest organizations
thought that in the future there would be improvements in
systems of management for WWTPs. Politicians thought
that in addition to reduced plastic use, there would also
be more research into the impacts of MPs on people
and the environment. Other sectoral and government
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FIGURE 9 | “How do you think MPs in the sludge will look in twenty years from now?” By category of stakeholder. Percentages reported represent the frequency with
which an issue was mentioned across all stakeholders responding (n=29).
stakeholders raised the possibility of other contaminants
overshadowing MPs.
The purpose of this study was to survey stakeholder perspectives
on two questions related to the issue of MPs in sludge spread
on agricultural soil in Sweden. Stakeholders were representative
of the public sector (politicians and government bodies), branch
organizations (primarily associated with wastewater treatment),
environmental NGOs and researchers. The most common
association with MPs among all those interviewed was through
their work (Figure 1).
The first of the two research questions was about respondent’s
views on their own and the public’s level of knowledge with
respect to risks connected to MPs in the terrestrial environment.
Our results confirm that more attention is currently placed on
MPs in the marine environment. Interviewees offered multiple
reasons for this focus. The most common reason offered was
that MPs are harmful for the marine environment. However, as
Thiele and Hudson (2021) note, most information on MPs in the
marine environment is likely to have been obtained from media
sources that “often deviate from the currently existing scientific
knowledge about microplastic pollution.” This view was more
prevalent politicians and Government stakeholders. In contrast,
the stakeholder categories that work most directly with sludge
and MPs (branch organizations and researchers) and that may be
expected to have access to more scientific knowledge, believed the
main reason for concern about MPs in the marine environment
could be attributed to their higher visibility. This higher visibility
was not only due to media coverage and an emotional connection
There is a fascination that it should be untouched. The sea should
be untouched; you should not destroy” but also because it is easier
to find methodologically, it is easier to collect both ordinary plastic
and micro plastics from the aquatic environment1”.
Responses that directly concerned the level of knowledge
about MPs in the terrestrial environment did not reveal a
clear common thread. Stakeholders were evenly divided between
those that believed there was a lack of knowledge or that it
was hard to analyze MPs and those that believed that MPs
were not really a concern in this environment (Figure 4). This
evenly divided belief on the concern about MP impacts was
also reflected in opinions about the current state of knowledge
with half believing there was good knowledge about pollutants
in sludge and half believing that knowledge was uncertain
(Figure 9). Although around one-third believed there was too
little information available, the remaining answers were evenly
divided among four general views, three of which were related
to the perceived greater adaptability and buffering capacity of
the terrestrial environment: “degradation should be better in soil
environments with greater variation in decomposers of organic
material” and “there are organisms that are incredibly adapted
to disperse in different particles of different shapes.” The fourth
view was the difficulty in analyzing MPs in soils. Politicians
and government representatives were the groups who felt most
strongly that the reason for a lack of interest in MPs was a lack of
knowledge or awareness. For these same two group, this finding
1All citations in italics in this section are transcriptions and translations from
the interviews.
Frontiers in Sustainable Food Systems | 10 February 2022 | Volume 6 | Article 830637
Zilinskaite et al. Stakeholders Perspectives on Microplastics in Sludge
is similar to the one described above that assigns importance to
the role of the media in shaping more interest in MPs in the
marine environment.
The second research question which this study focused
on was to try and determine if stakeholders were concerned
about MPs when permitting sludge applications on agricultural
land. Interviewees identified many possible environmental risks
but there was no clear consensus on which risk area was
most important. Concerning the knowledge of risks associated
with pollutants in sludge in general, stakeholder views were
split between considering the current knowledge good and
considering it to be uncertain. Notably, within the group
that would likely have greatest access to scientific studies
(i.e. researchers), almost all of the participants perceived the
level of knowledge as good. However, with respect to MPs in
sludge specifically, knowledge and perceptions on the issue were
greatly fragmented. While all groups referred to the lack of
knowledge, the most common reason for this was attributed
to “methodological limitations.” Surprisingly, for some, in spite
of the lack of knowledge, MPs are not a priority “we see
other substances that should have higher attention, as PFAS and
antibacterial silver where we think we (. . . ) should continue to
monitor. But microplastics we do not see that it is the biggest
challenge from scientific point of view.”
This lack of consensus about risks associated with MPs in
sludge spread on agricultural land is perhaps related to the earlier
questions about the level of knowledge and the agreement among
respondents that this knowledge needed to be improved. Some of
the risks mentioned by respondents indicated that the fate of MPs
in soil is still an important open question there is a possibility
of runoff or that they move through macropores in the ground,
“it (MPs) accumulates in the soil and can potentially spread to
the recipient, “spread in the environment, and ends up in the
groundwater” and “can accumulate in agricultural land, and are
broken down into nanoplastics.”
When asked if they believed society to be aware of the presence
of MPs in sludge applied to agricultural land and any associated
risks, the most common view expressed was that society is not
aware. A smaller fraction of interviewees referred to society
being either informed or somewhat informed, with some of its
members interested and knowledgeable and others not interested
at all.
The last series of questions were designed to elicit stakeholder
views about current guidelines and what the issue may look like
in the year 2040. Almost all the participants were aware of the
existence of regulatory guidelines. It is important to note that
more than half of the interviewed stakeholders referred to the
existence of incomplete guidelines for managing contaminants
in sludge applied to agricultural land (Figure 8). This opinion
was reported by all groups except politicians. Politicians and
researchers specifically referred to the REVAQ certification
system as one of the existing tools to reduce upstream MPs
inputs. Finally, when talking about the future of MPs, a few
interviewees believed that not much will change and that other
contaminants will probably overshadow MPs. Almost all the
other stakeholders believed that there will be a reduction in the
use of plastics while pointing out that knowledge will be greater
and more mature.
In conclusion, while the majority of interviewed Swedish
stakeholders believe current national guidelines related to sludge
application to agricultural land are incomplete it is not clear
that this is based on a concern about MPs. As noted in the
introduction, one of the two sludge management alternatives
currently under consideration in Sweden would in all likelihood
allow sludge with MPs to be spread on agricultural soil. For
the stakeholders interviewed in the study the low level of
concern about the presence of MPs in sludge may reflect a lack
of agreement on a single risk, or set of related risks, which
was currently identified as important from an environmental
perspective. Respondents’ answers about the level of knowledge,
ranging from insufficient to good, may be closely related to the
general low level of concern. Paradoxically, a belief that there
is sufficient knowledge may lead to a low concern based on
available evidence just as insufficient knowledge may also lead to
a low level of concern based on the lack of evidence. Although
stakeholder perceptions of risks associated with MPs in soils was
included in the stakeholder survey, the purpose of this study
was not to evaluate respondents’ judgement of the scientific
evidence of specific risks but to focus on if they believed the
current level of knowledge was sufficient for decision-making.
While there was a recognized need for more research, if MPs
are allowed to be spread under new guidelines this research may
be no longer on controlled application trials but on observed
environmental impacts.
The raw data supporting the conclusions of this article will be
made available by the authors, without undue reservation.
EZ, MF, and DC: conceptualization. EZ: investigation. MF:
supervision. EZ and DC: writing—original draft. MF and DC:
writing—review and editing. All authors contributed to the
article and approved the submitted version.
This study was financed by FORMAS, the Swedish Research
Council for Sustainable Development (contract no. 2017-00029)
under the umbrella of the JPI-Water IMPASSE project.
The Supplementary Material for this article can be found
online at:
Frontiers in Sustainable Food Systems | 11 February 2022 | Volume 6 | Article 830637
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Conflict of Interest: The authors declare that the research was conducted in the
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Frontiers in Sustainable Food Systems | 13 February 2022 | Volume 6 | Article 830637
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Communicating scientific evidence to decision makers and other stakeholders is an important task for scientists (SAPEA, 2019a, SAPEA, 2019b; Environmental and Health Risks of Microplastic Pollution, 2019). In this context, and specifically referring to recent evidence reviews on microplastics (SAPEA, 2019b, World Health Organization, 2019). Leslie and Depledge (2020) argue that both SAPEA (a consortium of European academies, part of the European Commission’s Scientific Advice Mechanism) and the UN’s World Health Organisation make the mistake of “assuming risk is absent in the absence of evidence”. In what follows, we reflect on their criticism and raise some broader issues about communicating science on an emerging issue. We make four points. Of the four, the first two reply directly to Leslie and Depledge. The third point briefly discusses the philosophical issue of whether, and to what extent, an absence of evidence constitutes evidence of absence, a topic whose origins can be traced back to the Enlightenment philosopher Locke (1689/1823). The fourth point provides a broader perspective on science communication for policy. We focus largely on Leslie and Depledge’s criticisms of the way the SAPEA report on microplastics (SAPEA, 2019b) was communicated, although we expect that similar responses might be made to their criticisms directed towards the WHO. Our effort is of course undertaken in Locke’s spirit of “the common offices of humanity and friendship in the diversity of opinions” (Locke, 1689/1823).
Microplastics are emerging pollutants that threaten marine resources globally today. Being difficult to see for the human eye, their public perception and risk perception depend upon the information given to citizens. Since the psychosocial theory postulates the importance of knowledge, attitude, and perceived control to undertake pro-environmental behaviors, in this review we have analyzed relevant literature in order to look for solutions of psychosocial nature to stop microplastic emissions. We employed qualitative contingency statistics and clustering analysis of relevant terms. The consumer's knowledge about microplastics was central and directly connected with the willingness to adopt a pro-environmental behavior, while risk perception and perceived control were less important. Significant geographical gaps and differences between cultures were identified. Based on our analyses, the following measures are recommended: 1) Create baselines of knowledge about microplastics to design ad-hoc interventions for their control; 2) Explore the role of environmental values as mediators between knowledge and behavior against microplastics; 3) Enlarge the geographical scope of present studies, at least to include African countries; 4) Undertake intercultural studies to determine the scale of interventions for public awareness about the problem; 5) Study the perspective of the industry, politicians and journalists; 6) Improve scientific communication about this new threat; 7) Introduce the topic in formal and non-formal education settings.
Microplastics (MPs) are considered to be ubiquitous contaminants in freshwater ecosystems, yet their sources and pathways at the river catchment scale need to be better determined. This study assessed MP (55-5000 µm) pollution in a Mediterranean river catchment (central Spain) and aimed to identify the importance of wastewater as an environmental pathway. We sampled treated and untreated wastewaters, and raw and digested sludge from five WWTPs during two seasons. River water and sediments were sampled at three locations with different anthropogenic influences during three seasons. On average, 93% (47 - 99%) of MPs were retained by WWTPs. Concentrations in river water and sediment ranged between 1-227 MPs/m³ and 0-2630 MPs/kg dw, respectively. Concentrations strongly depended upon land-use, with pollution levels increasing significantly downstream of urban and industrial areas. Seasonality influenced the observed MP concentrations strongly. During high flow periods, higher water but lower sediment concentrations were observed compared to low flow periods. We estimate that 1×10¹⁰ MPs are discharged into the catchment via treated and untreated wastewater annually, which constitutes up to 50% of the total MP catchment discharge. Thus, we conclude that the wastewater system represents a major environmental pathway for MPs into Mediterranean rivers with low dilution capacity.
Microplastic (plastic particles measuring < 5mm) pollution is ubiquitous. Unlike in other well-studied ecosystems, e.g., marine and freshwater environments, microplastics in terrestrial systems are relatively understudied. Their potential impacts on terrestrial environments, in particular the risk of causing ecological surprise, must be better understood and quantified. Ecological surprise occurs when ecosystem behaviour deviates radically from expectations and generally has negative consequences for ecosystem services. The properties and behaviour of microplastics within terrestrial environments may increase their likelihood of causing ecological surprises as they: (a) are highly persistent global pollutants that will last for centuries, (b) can interact with the abiotic environment in a complex manner, (c) can impact terrestrial organisms directly or indirectly and (d) interact with other contaminants and can facilitate their transport. Here, we compiled findings of previous research on microplastics in terrestrial environments. We systematically focused on studies addressing different facets of microplastics related to their distribution, dispersion, impact on soil characteristics and functions, levels of biological organization of tested terrestrial biota (single species vs. assemblages), scale of experimental study and corresponding ecotoxicological effects. Our systematic assessment of previous microplastic research revealed that most studies have been conducted on single species under laboratory conditions with short-term exposures; few studies were conducted under more realistic long-term field conditions and/or with multi-species assemblages. Studies targeting multi-species assemblages primarily considered soil bacterial communities and showed that microplastics can alter essential nutrient cycling functions. More ecologically meaningful studies of terrestrial microplastics encompassing multi-species assemblages, critical ecological processes (e.g., biogeochemical cycles and pollination) and interactions with other anthropogenic stressors must be conducted. Addressing these knowledge gaps will provide a better understanding of microplastics as emerging global stressors and should lower the risk of ecological surprise in terrestrial ecosystems.
Microplastic pollution has sparked interest from researchers, public, industries and regulators, due to reports of extensive microplastics presence in the environment, household dust, drinking water, and food that indicate chronic exposure to organisms within ecosystems and in human living spaces. While exposure to microplastics is evident, negative effects from microplastics appear to be minimal in most studies on biota and no risk assessments have been completed for microplastics on human health. Despite current evidence that indicates that microplastics present low risk to biota, there is public perception that microplastics are a serious environmental and human health risk, and this perception has motivated political action. The discrepancy between scientific evidence and public risk perception has generated debate amongst researchers within the natural and social sciences. Here, we review the evidence on the risks of microplastics to ecosystem and human health, and consider the relation between evidence and public perception of microplastics risk.