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DOI: 10.1039/D1RP00190F (Paper) Chem. Educ. Res. Pract., 2022, 23, 100-112

Student participation in a coastal water quality citizen science project and its contribution to the conceptual and procedural learning of chemistry

J. L. Araújo *, C. Morais and J. C. Paiva
CIQUP, Unidade de Ensino das Ciências, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal. E-mail: jose.araujo@fc.up.pt

Received 15th July 2021 , Accepted 17th September 2021

First published on 20th September 2021

Abstract

The active participation of citizens in scientific research, through citizen science, has been proven successful. However, knowledge on the potential of citizen science within formal chemistry learning, at the conceptual and procedural levels, remains insufficiently explored. We developed a citizen science project – PVC: Perceiving the Value of Chemistry behind water and microplastics – which sought to involve students in monitoring the physicochemical parameters of coastal water quality, through the detection of microplastics in these waters, in addition to the qualitative identification of plastic contaminants on beaches. The project was conducted throughout the 2018/2019 school year and involved 442 middle school students (Key Stage 3 (KS3) aged 12–14, in Portuguese schools) and 9 chemistry teachers, in the northern coastal region of Portugal. The data on learning outcomes was collected through knowledge tests, applied after project conclusion, and was then compared to data collected up to six months later (retention test). In addition, interviews were conducted with participants, and researchers’ field notes were recorded and analyzed. Data analysis suggests the PVC project promoted conceptual chemistry learning related to the analysis of physicochemical water parameters (pH, temperature, turbidity, salinity, nitrate and nitrite concentrations and dissolved oxygen), as well as polymers (polymer types, formation and structure). A positive knowledge retention was registered a few months after the project conclusion. At a process level, participants learned laboratory techniques (sieving, gravity and reduced pressure filtrations and crystallization) and the handling of laboratory materials. Furthermore, teachers recognized that their students’ participation in the PVC project fostered the development of their argumentation skills, as well as their reflexive and critical thinking skills. The ability to communicate ideas and results, along with the development of students’ digital skills, was also mentioned.

Introduction

Research on chemistry learning has revealed that students often consider chemistry, in general (Cardellini, 2012; Hofstein, 2017; Gulacar et al., 2018; Irwanto et al., 2019; Prodjosantoso et al., 2019), and Organic Chemistry, in particular (Dwyer, 2017), as areas of difficult learning. Cardellini (2012) stated “the nature of the science [chemistry] itself makes it inaccessible” (p. 306). As highlighted by Czysz et al. (2020), “any model for chemical phenomena requires a description of the connections between molecular events and macroscopic observations. Explanations of any nature require symbolic representations that are mutually understood” (p. 486). In addition to the cognitive barriers to learning chemistry, some authors (Aikenhead, 2003; Osborne and Dillon, 2008, Sausan et al., 2018) argue that students consider chemistry to be an irrelevant subject, boring, detached from reality and of no interest for their future. Thus, there is an urgent need to engage students in chemistry and promote their active involvement in learning a subject that “commonly incorporates many abstract concepts, which are central to further learning in both chemistry and other sciences” (Sirhan, 2007, p. 2). The use of contexts familiar to students, as well as contemporary social problems often present in citizen science projects (NASEM, 2016), may contribute to a better understanding of the core of chemistry knowledge, as well as its potential application in preventing and solving socio-scientific problems (Hoyer et al., 2012; Nichols, 2018), such as environmental sustainability (Waard et al., 2020).

Citizen science as a pedagogical tool for Chemistry

Citizen science is a form of research collaboration that enlists the public in scientific research to address real-world problems, embracing various levels of public engagement in science: “from being better informed about science, to participating in the scientific process itself by observing, gathering or processing data” (European Commission, 2021). In this scope, citizens may act as contributors, collaborators, or project leaders, and have a meaningful role in the project (Bonney et al., 2009). Citizen science is an approach “applicable across all scientific disciplines, alongside a variety of disciplinary traditions and research methods” (ECSA, 2020, p. 3). In this regard, the literature (Follett and Strezov, 2015; Hecker et al., 2018) suggests the existence of large citizen science projects, in areas such as Ecology, Environment, Biology, Astronomy and Sociology. For Motion (2019), the predominance of citizen science projects in these areas is due to the “rich history of ‘citizen naturalists’ and a long tradition of using data from ‘amateurs’ who have participated in projects recording the population of different species, migratory patterns and behaviours”. However, according to Hecker et al. (2018) and Sammut (2015), as well as by performing a quick search on the SciStarter (2021) platform which aggregates citizen science projects, there is indication that chemistry is one of the sciences with the lowest expression. Generally, when citizen science projects involve chemistry, the latter merely emerges as a useful tool (for example, in environmental projects focused on soil or air quality monitoring) or as a bridge to enhance project interdisciplinarity (i.e., Hoyer et al., 2012). This shortage of citizen science projects in chemistry, according to Motion (2019), may be because safely handling “lab chemicals outside of specialized laboratories can be problematic” and the use of “specialist software or equipment can be prohibitively expensive or simply too unwieldy for institutions to loan out for use by schools and communities”. Despite these constraints, Nichols (2018) emphasizes that citizen science is a way of displaying the importance of chemistry to the community, since “considering the global lack of chemical expertise, helping communities address their chemistry-related concerns and challenges, especially underserved communities, is a great way for chemists [and citizens] to become more productively engaged” (p. 70). As stated by Harlin et al. (2018, p. 410), “citizen science is growing in popularity, but most attention focuses on adult volunteers and their potential contribution to science and society” and “this disregards the millions of children studying science in school as they learn the skills of citizenship”. Therefore, “connecting citizen science and schools seems like a natural step” as it allows teachers and students to get “authentic access to science in action,” and, at the same time, “scientists get many enthusiastic volunteers (students) along with team leaders and data quality filters (teachers), while also expanding public awareness of their research topics and findings” (Harlin et al., 2018, p. 411). However, the implementation of pedagogical dynamics based on citizen science, and the formal evaluation of its contributions to student training, is not yet systematized in the literature (Aristeidou et al., 2020). In this regard, there are many publications related to the evaluation of citizen science projects, although “only a few have been evaluated in terms of science and learning outcomes or directly used in formal education settings” (Aristeidou et al., 2020, p. 278). Overall, publications resulting from the evaluation of public involvement in citizen science do not evidence the full potential of these projects for participants (i.e., Braschler, 2009; Paige et al., 2010; Weckel et al., 2010; Ferreira et al., 2012; Thornton and Leahy, 2012; Nicosia et al., 2014; Savage and Jude, 2014; Sullivan et al., 2014; Scheuch et al., 2018; Wilken, 2018), since the contributions of this involvement are widely differentiated and difficult to assess (Harlin et al., 2018). Most of the examples mentioned focus on the projects’ contributions to scientific literacy and student motivation. However, Nicosia et al. (2014), Ruiz-Mallén et al. (2016) and Wilken (2018) conclude that, through participation in citizen science projects, students improve their understanding of scientific content, as they attribute higher relevance to it, by contextualizing learning with problems and issues of their daily lives. Moreover, Strasser et al. (2019, p. 63) indicate that “empirical research on the learning outcomes of citizen science has documented improvements in content knowledge”. Several authors (for example, Paige et al., 2010; Ruiz-Mallén et al., 2016; Ballard et al., 2017; Wilken, 2018; Sharma et al., 2019) further refer that citizen science projects have a positive impact on students’ learning outcomes, with the experience being described as rich and interdisciplinary. Wiggins and Crowston (2011) define citizen science projects focused on teaching and learning dynamics as educational citizen science projects.

Nonetheless, the pedagogical potential of citizen science depends on the teaching strategies and resources used by teachers, as well as their adaptation to students. Preparing materials and planning strategies are time-consuming tasks, and this often constitutes an obstacle to teachers’ willingness to take on projects. As such, during the development of citizen science projects that aim to involve students, it is crucial that support be provided to the teachers who will manage the projects in schools. Indeed, as stated by Harlin et al. (2018), “citizen science programmes need to offer relevant teaching material to ease the work of teachers in connecting them to school curriculum” (p. 413).

As a result, we considered it important to develop, implement and evaluate the pedagogical impact of a citizen science educational PVC project – Perceiving the Value of Chemistry behind water and microplastics – where chemistry was given a central position in the production of resources and implementation of strategies. In the PVC project, the citizen science model used was a collaborative model (Bonney et al., 2009). Scientists designed the project, while the students, as non-scientists, contributed to the collection and analysis of data, as well as disseminated new findings to a school community and a broader citizen science project (EarthEcho Water Challenge, 2021), in addition to learning and developing skills beyond the Chemistry curriculum. Thus, to investigate the pedagogical potential of citizen science projects, particularly in the domain of Chemistry Education, the following research question was formulated:

RQ: To what extent did students’ participation in the PVC citizen science project contribute to their conceptual and procedural learning of the chemistry content explored in the project?

Methodology

Participants

The PVC project involved the participation of 442 middle school students (208 boys and 234 girls; Key Stage 3 (KS3) aged 12–14 in Portuguese schools), from 19 Chemistry classes – 7th grade (138 students), 8th grade (279 students) and 9th grade (25 students), with an average of 13 years of age. The sample presents a relevant equitable distribution regarding the sex of the participants. The participating chemistry classes were taught by nine teachers from four different schools, who collaborated in this research by following and monitoring their students’ participation in the different PVC project phases, in close collaboration with the researchers. The purpose of exploring the Chemistry contents underlying the PVC project was, on the one hand, to consolidate some Chemistry contents already explored with students throughout their schooling and, on the other hand, to introduce the exploration of new contents to enhance the pedagogical approach of the project. Table 1 presents the chemistry contents previously explored by students in their educational process and which the PVC project intended to consolidate, as well as the chemistry contents explored for the first time, in the PVC project, and which do not integrate the KS3 Chemistry curriculum in Portugal.
Table 1 Students’ prior knowledge of chemistry from the school curriculum and chemistry contents explored for the first time in the PVC project
Chemistry contents previously explored in students’ educational process Chemistry contents explored for the first time in the PVC project
a Considering the school level and the moment of the school year when the project was implemented, for the 7th grade students, contents related to acidity of solutions and colorimetric tests were explored for the first time in the project.
– Material composition – Turbidity
– Qualitative composition of solutions – Dissolved oxygen
– Quantitative composition of solutions – Salinity
– Temperature – Polymers
– Laboratory equipment – Aciditya
– Laboratory techniques – Colorimetric testsa
– Laboratory safety

Participation in the study was voluntary. The teachers and parents of the students signed an informed consent form, which described students’ participation in the research and the activities in which they would be involved and ensured the anonymity and confidentiality of personal data.

PVC project and its implementation

An important goal of the 2030 Agenda for Sustainable Development, adopted by the United Nations – particularly Goal 14, which is to conserve and sustainably use oceans, seas and marine resources for sustainable development – is to ensure that all students acquire knowledge and necessary skills to promote sustainable development (United Nations, 2020). In light of this and considering Portugal's large coastal area and close historical ties with the sea, we found it relevant to develop a PVC project to explore the quality of coastal waters and their contamination by microplastics. This topic is current, relevant and of great importance within the scientific community (please see Wang et al., 2019; Li et al., 2020; Mercogliano et al., 2020; Pirsaheb et al., 2020; Wang et al., 2020; Zhang and Chen, 2020) and has been heavily present in the media. In this regard, participants were involved in a PVC project, which entailed “the sampling, analysis and monitoring of physicochemical parameters and detect the presence of microplastics in coastal waters from the Portuguese region of Douro Litoral” (Araújo et al., 2020a).

When preparing the schedule for the school year, teachers made sure to include students’ participation in the PVC project. Thus, some project tasks could be implemented during school hours, without compromising the teaching of the chemistry curriculum. The project was implemented in four main phases that took place in the classroom, in the chemistry laboratory, in field visits and in extra-class moments. As shown in Fig. 1, the phases of the PVC project were: (1) online tasks, such as guided searches, video visualization, interpretation and creation of posters and infographics; (2) the sampling and physicochemical analysis of coastal waters, and identification of (micro)plastics; (3) the sampling of beach plastics and their qualitative identification; and (4) project dissemination (Araújo et al., 2020b). A more detailed description of the PVC project phases, and their objectives, is displayed in Table 2.


image file: d1rp00190f-f1.tif
Fig. 1 Phases and chronogram of the PVC project implementation.
Table 2 Detailed description of the PVC project phases
Phases Brief description Duration and location Teacher involvement
I – Online tasks This phase is composed of 6 virtual and asynchronous tasks, performed on the project page, on the Moodle platform. These tasks, such as guided searches, video visualization, as well as interpretation and creation of posters and infographics, aimed to raise awareness about marine litter, especially the presence of (micro)plastics in coastal waters and its consequences; it also aimed to highlight the importance of Chemistry and its preventive role in combating these environmental scourges. PVC project phase I took place during the Autumn and Winter months, which allowed students to gradually be introduced to the contents that would be explored in the project, while also ensuring attractive weather conditions to collect safely in coastal waters (phase II). Classroom and extra-classroom occasions outside school hours: 15–60 minutes/task. Guide and monitor students’ participation.
II – Collection and analysis of physicochemical parameters and detection of microplastics in coastal waters The goal of this phase is to promote the learning of chemistry content related to water quality parameters, as well as develop laboratory skills. Its implementation took place in two separate occasions: (1) a group (3 to 5 students) sampling, in loco, of the coastal waters and analysis of some of their physicochemical parameters (pH, turbidity, temperature, dissolved oxygen, concentration of nitrates and nitrites); (2) in the laboratory, to determine the water's salinity (through crystallization) and to detect the presence of microplastics, through digital microscope observation of the solid residues of the collected coastal waters, subjected to sieving and filtration. Participants were given a portable, low-cost pedagogical kit for monitoring coastal water quality (Araújo et al., 2020a), containing all the materials needed to conduct the practical activities proposed in this phase, as well as the associated support manuals. Field visit: one morning or one afternoon outside school hours/Chemistry class. Organize the field visit to the beach. Oversee the sampling process and laboratory work.
Laboratory: two classes of 1 h 30 min/Chemistry class.
III – Qualitative identification of the plastics collected on the beaches This phase started with groups of students collecting plastics that polluted the beaches, as a matter of environmental awareness. Further, in order to explore contents related to polymer chemistry and to develop laboratory skills, the collected plastics were qualitatively identified, by applying solubility and density tests to determine the type of polymer in each sample (Kolb and Kolb, 1991; Hughes et al., 2001; Harris and Walker, 2010; Morais et al., 2021). Pedagogical kits, especially developed for the project, were also provided to students, for the qualitative identification of plastics. These pedagogical kits contained all the materials and specific resources necessary to conduct the activities of this phase. Field visit: one morning or one afternoon outside school hours/Chemistry class. Oversee the sampling process and laboratory work.
Laboratory: two classes of 1 h 30 min/Chemistry class.
IV – Communication and dissemination of results Students shared the results of the PVC project implementation in the field with both the scientific and school communities, to mobilize the acquired knowledge and to develop communication skills. The analysis of the physicochemical parameters of coastal waters was disseminated within a citizen science platform dedicated to global water quality monitoring (EarthEcho Water Challenge, 2021). Within the school community, the results obtained by students were shared through the exhibition of posters, environmental awareness infographics, and through scientific dissemination lectures organized in different schools. These lectures, conducted by invited experts from the Chemistry and Environment fields, were also attended by some students, who presented the work they developed in the PVC project. Classroom and extra classroom moments outside school hours: Oversee results sharing.
• Sharing the results on the citizen science platform: 30 min/Chemistry class. Support students in the exhibition preparation and lecture organization.
• Exhibition preparation: 3–4 hours/Chemistry class.
• Lecture: 1 hour.

Measures and procedures

Data collection procedure

A knowledge test was developed (see some examples of the questions in the Appendix) and applied as soon as the implementation of the PVC project was concluded, in order to obtain indicators related to students’ chemistry learning. The test included 23 multiple-choice questions designed to cover various chemistry contents explored within the project, namely concepts related to the physicochemical parameters of the coastal waters analysed (temperature, pH, turbidity, dissolved oxygen, nitrate concentrations and salinity), polymers, physicochemical properties of the materials and techniques, procedures, instruments and safety rules related to the practical-laboratorial activities developed throughout the PVC project.

The questions presented in the knowledge test were developed so as to cover a range of different cognitive skills, according to the revised Bloom's Taxonomy (Anderson et al., 2001). The distribution of the 23 questions, according to this taxonomy, was: questions 2, 9, 15, 21 – remembering; questions: 1, 3, 8, 10, 12, 16, 19 – understanding; questions: 4, 6, 11, 13, 14, 15, 18, 20, 23 – applying; questions: 5, 7, 10, 17, 22 – analysing. Since the knowledge test was exclusively focused on the Chemistry contents explored throughout the PVC project, we believed the learning gains observed would result from the intervention program, because, given the specificity of the questions, the students would have had to have participated in the project to be able to respond accordingly.

For content validation purposes, the test was answered, firstly, by two students, from each grade of middle school, who were not involved in the PVC project, in order to guarantee that all questions were intelligible and understandable. The test was also analysed by two teachers specialized in Chemistry Education, taking into account the project aims. The validation process showed that there was no need to promote changes in the structure/questions of the knowledge test.

The knowledge test was applied to each of the participating students, during a Chemistry class, shortly after the conclusion of the PVC project activities. The students were given 50 minutes to answer all the questions. Though literature indicates (Crossgrove and Curran, 2008; Custers 2010) that “most studies report relatively large losses for short retention intervals [four to six months]” (Custers, 2010, p. 113), we decided to apply the same knowledge test (which we called the knowledge retention test) four to six months after the conclusion of the PVC project activities. The retention test was applied after the summer holidays (a period of approximately three months), as most students would attend the following school year. It was not possible to maintain the same time interval between the application of both tests for all students, as this depended on the availability of teachers to apply the knowledge retention test, which had to be included in the school year planning. However, most students’ answers to the retention test (around 300) were collected five months after the knowledge test. Since the project was undertaken on a voluntary basis, the results from both the knowledge test and the retention test did not count towards students’ marks. The performance of students on these tests was only used as measure of success of the PVC project.

The remaining data collection methods included interviews with the supporting teachers and some participating students, as well as field notes collected by the researcher.

Data analysis procedure

The 23 test questions were scored equitably. Each question correctly answered corresponded to approximately 4.35% of the student's score on this test. Students’ responses to the knowledge tests were analysed through descriptive statistics (frequencies and means) and parametric statistical procedures (t-test and ANOVA) since the assumption of normality and homogeneity of variances were verified. An analysis of results by grade and gender (sex) of participating students was performed, as well as a comparative analysis of the results of both the knowledge and retention tests.

The contents of the interviews and field notes were also analysed. Within the scope of this article, particular emphasis is given to the criteria ‘PVC project impact on students’, related to the chemistry learning that had taken place over the course of the PVC project, as well as to the development of environmental awareness and other skills. In addition to the knowledge and retention test results, the following section presents the main results of the content analysis that are directly related to chemistry learning.

Results

Since this publication focuses on the contribution of the PVC project to students’ conceptual and procedural learning of chemistry, the results from the project dissemination phase will not be presented.

Knowledge and retention tests

As shown in Table 3, students participating in the PVC project, who answered the knowledge test, achieved an average performance of 77.8%. An ANOVA test was conducted (F2,442 = 0.811, p = 0.368), and no statistically significant differences were found between the average scores for each school grade involved in the project. Furthermore, male students achieved an average score of 78.3%, whereas the average score was slightly lower for female students. Nonetheless, the t-test (t441 = 1.235, p = 0.219) conducted revealed no statistically significant differences in this situation.
Table 3 Detailed description of student performance, by grade and gender, on the knowledge test
Student performance N M (%) SD (%)
Overall 442 77.8 8.3
7th grade 138 79.5 8.4
8th grade 279 77.7 8.2
9th grade 25 77.8 8.3
Male students 208 78.3 8.6
Female students 234 77.5 8.1

A detailed analysis of students’ answers to each question of the knowledge test (Chart 1) indicates that, in general, questions that focus on content covered for the first time in the PVC project, such as turbidity (Question 15), salinity (Question 18), water dissolved oxygen percentage (Questions 16, 17) and colorimetric tests to determine the concentration of nitrite (Question 19), exhibit average scores above 75%, for all school grades. Moreover, content about the qualitative composition of solutions (Questions 2–4), the composition of materials (Question 1), laboratory techniques (Questions 8–10) and laboratory safety (Questions 11–14), which had previously been explored in class, reveal average scores above 75%.


image file: d1rp00190f-c1.tif
Chart 1 Students’ performance on the knowledge and knowledge retention tests.

On the other hand, students presented a performance below 75% on content related to polymers (Questions 20–23) (which was new content explored within the project), acidity of solutions (Questions 6 and 7) and quantitative composition of solutions (Question 5) (these contents had previously been explored, in general, during classes).

The same knowledge test was applied four to six months after the PVC project conclusion, in order to understand the retention of knowledge after this period. However, the 9th grade students advanced to another study cycle (they started attending secondary education) and changed school. Thus, it was not feasible to apply the retention test to these students. As such, the analyses only consider the results of the 7th and 8th grade students.

Regarding the students’ answers to the knowledge retention test, their performance was poorer than the performance exhibited on the knowledge test. As presented in Table 4, in this second moment of knowledge assessment, students reached an overall average score of 57.6%, with no statistical differences between the performances of each school grade. As for gender, male students revealed a slightly higher score on this test than did female students, showing that gender is not a differentiating factor in students’ knowledge retention.

Table 4 Detailed description of student performance, by grade and by gender, in the knowledge retention test
Student performance N M (%) SD (%)
Overall 357 57.6 13.4
7th grade 117 59.0 13.3
8th grade 240 56.8 13.5
Male students 165 58.4 13.5
Female students 192 56.8 13.4

A detailed analysis of students’ answers to each question of the knowledge retention test (Chart 1) highlights a greater heterogeneity among the answers, in contrast to the results of the knowledge test. Specifically, it was observed that questions related to the water dissolved oxygen percentage (Questions 16, 17), qualitative composition of solutions (Questions 2–4), colorimetric tests to determine nitrite concentration (Question 19), acidity of solutions (Questions 6), composition of materials (Question 1), laboratory techniques (Questions 8–10), laboratory safety rules (Questions 11–14), and polymers (Questions 20, 22) exhibit a positive average classification, i.e., higher than 50%. On the other hand, questions related to turbidity (Question 15), salinity (Question 18), acidity (Question 7), quantitative composition of solutions (Question 5) and polymers (Questions 21, 23) score the most unsatisfactory results overall.

Although the comparison of students’ results in these knowledge assessments (2 tests) reveals a significant decrease in performance (t357 = −39.392, p < 0.001) from the knowledge test (M = 77.8%) to the knowledge retention test (M = 57.6%), students’ average performance on the knowledge retention test remains positive (above 50%).

Concerning specific contents of the questions, students’ exhibited a clearly positive performance on questions related to turbidity and water salinity, in the knowledge test, whereas they presented negative results (below 50%) in the knowledge retention test (there was a major difference between scores of these questions from the knowledge test and the knowledge retention test). This may indicate the learning of these contents was not as significant as expected, since students’ performance on the knowledge test had been clearly positive. Regarding the remaining questions, students’ average scores decreased from the knowledge test to the knowledge retention test, below 35%. Given the above, and since the average score on the knowledge retention test was positive (57.6%), the authors considered there was a satisfactory degree of knowledge retention (according to the Portuguese middle school performance levels – Weak: 0–19%; Unsatisfactory: 20–49%; Satisfactory: 50–69%; Good: 70–89%; and Very Good: 90–100%).

Interviews and field notes

In order to gather additional and complementary information regarding chemistry learning, the participants were invited to be interviewed, on a voluntary basis. Semi-structured interviews were conducted by the first author, with a sample of 20 students and nine teachers. The interviews were transcribed, and the first author of this study performed the initial open coding of the data collected following a content analysis technique (Bardin, 2011). Then, the other authors collaboratively discussed and validated the analysis. The interviews were conducted in Portuguese; therefore, the quotes presented in this section were translated from Portuguese to English by the first author and validated by the other two authors and a native English speaker.

Regarding the chemistry content of the PVC project, 7th grade students acknowledged that many new and difficult concepts were explored, which prepared them for future learning. As student A, from 7th grade, states “If [contents covered] were easier I think the next school year would be too hard for us and we wouldn't be able to handle it (…) Thus it won't be a very drastic change for us” (Interview A, June 13, 2019). Older students admitted having experienced fewer difficulties in learning new chemistry concepts explored in the PVC project, as an 8th grade student (Student B) claims “To be honest, at the beginning I didn't even really know what microplastics were, […] but I think concepts weren’t really difficult” (Interview B, June 13, 2019).

On the other hand, teachers considered the PVC project had a very positive impact on students, by opening up new perspectives to the world of chemistry. In the opinion of Teacher I, “It allowed us to broaden horizons, acquiring other perspectives and to consider chemistry from a different perspective” (Interview I, July 3, 2019). According to another teacher, the consolidation of chemistry concepts, through the project, helped students to assign a meaning and put their learning into practice: “I found it encouraging that they were able to practice what they have learned” (Teacher II, Interview II, July 3, 2019).

Nonetheless, views regarding the project's contribution to the learning/consolidation of the contents explored among the younger students were not so unanimous. It was mentioned that these students had an increased difficulty to follow concepts explored for the first time in the project.

These interviews also gathered students’ perceptions about the planning of the practical-laboratory phase of the PVC project and the resources produced for its implementation, namely the pedagogical kits to collect and analyse the physicochemical parameters of coastal waters, as well as to detect and perform a qualitative identification of microplastics. Regarding this matter, students from different grades mentioned the kits facilitated practical-laboratorial tasks, allowing everyone to perform the activities. As one student said: “Kits allow us to have our own materials and perform [the activity]” (Student C, 7th grade, Interview C, June 13, 2019).

Students also evidenced higher autonomy by using the pedagogical kits. In their own words: “Each of us may work independently even with no support from the teacher” (Student D, 8th grade, Interview D, June 14, 2019); “Kits made it easier, because we have guidelines, whereas, with no kits, generally the teacher has to explain it to us (…) I think those guidelines describe exactly what we had to do. I think it was interesting to perform this experience because we acquired a better perception of plastic, for example” (Student E, 8th grade, Interview E, June 14, 2019); “If we had no kits, I think it would be more difficult and we would not have the same results” (Student F, 7th grade, Interview F, June 14, 2019).

Most of the teachers interviewed also highlighted the laboratorial nature of the PVC project and its contribution to the development of students’ skills.

For example, the project helped “students to feel more comfortable in the lab” (Teacher III, Interview III, July 3, 2019), as “…the more they work in a lab, the better for them, it is easier for them to get to know the materials and acquire know-how” (Teacher IV, Interview IV, July 3, 2019). Thus, this promotes increased engagement with the proposed activities, as stated by Teacher V: “students (…) loved it, they participated and performed activities with great interest” (Interview V, July 3 2019).

Regarding the use of a digital microscope to detect microplastics and the sharing of results on an online citizen science platform, teachers emphasized students’ proficiency with digital skills. On this topic, Teacher VI said: “they mastered that [the setup/use of the digital microscope and digital citizen science platform] more easily than I did. They were the ones saying, ‘Oh teacher, do this and do that!’ They are from a different generation that has other skills” (Teacher VI, Interview VI, June 26, 2019). Globally, evaluating all activities proposed to students under the PVC project, teachers emphasize a positive impact on the development of students’ scientific skills, particularly communication, argumentation, as well as critical and reflection thinking. According to the teachers, the PVC project helped students to develop “argumentation skills. Although I did not notice it in some students, obviously. However, in most students, and some classes in particular, the effect was quite positive” (Teacher VI, Interview VI, June, 26, 2019). In addition, “the project forced them to reflect. It forced them to think. I believe that was quite important” (Teacher VII, Interview VII, June, 26, 2019).

The researcher's field notes, collected through free observation during the PVC project implementation, as well as informal conversations held with participating students and teachers, also highlighted students’ motivation and commitment to collect coastal waters, as well as analyse their physicochemical parameters indicated in the manual attached to the pedagogical kit. Students autonomously conducted the different analyses. Teachers offered a brief, complementary explanation of the procedures to be followed (or offered an example in specific cases). When students were analysing the physicochemical parameters of coastal waters, there was a strong collaboration between members of the work group, so that everyone could accomplish the task. Teachers mentioned the microplastics detection activity as the practical-laboratory activity that elicited the most motivation from students. In addition, students were also committed and motivated when exploring the pedagogical kit for the qualitative identification of plastics, because, when a group identified a plastic sample, they would freely and spontaneously repeat the analysis for another sample. Students revealed a considerable working autonomy.

Discussion

Due to its clear educational aspect (Wiggins and Crowston, 2011), the PVC project aimed to involve students in a set of pedagogical dynamics that would enhance their learning of chemistry contents explored throughout the project. Nicosia et al. (2014), Scheuch et al. (2018) and Wilken (2018) argue that engaging students in citizen science approaches not only promotes the learning of scientific content (embracing science issues relevant to the real-world context, in order to promote new learning which may go beyond those established in the subject curricula), as well as enabling the development of students' skills which, as argued by Vogelzang et al. (2020), is a major goal of science education. Therefore, the PVC project also explored contents related to water quality and its pollution by plastics that go beyond those defined in the Chemistry curriculum of each school grade. Thus, the knowledge test was applied at the end of the PVC project and then applied as a knowledge retention test, to assess students’ learning.

Students achieved a good performance on the knowledge test. The analysis of students’ answers reveals a higher difficulty, regardless of grade, in questions related to polymer chemistry, which may have contributed to the less positive results, since these contents were taught for the first time for all participating students, and because organic chemistry is considered difficult to learn (Dwyer, 2017). In addition, students revealed a lower performance average in questions related to the quantitative composition of solutions, as these questions involved the possession of mathematical skills, in which students traditionally show more difficulties (Ranga, 2018).

However, students exhibited a good performance on the knowledge test regarding other topics explored in the PVC project. These topics relate to the physicochemical parameters of coastal water quality and were not part of the curriculum of the subject, namely concepts of turbidity, salinity, dissolved oxygen, or the use of colorimetric tests to determine nitrite concentration. Thus, the analysis of students’ results on the knowledge test gathered indicators related to the PVC project. This project contributed to learning outcomes and helped consolidate chemistry contents, not only those explored in the subject curriculum, but also new contents introduced by the activities proposed in the PVC project (Nicosia et al., 2014). According to Custers (2010), students’ performance on the retention test was poorer than their performance on the knowledge test; yet, overall, their performance on the knowledge retention test was positive. This result suggests a satisfactory degree of knowledge retention and it is considered a good indicator that the learning outcomes during the PVC project participation may have been significant. However, as mentioned by Custers (2010) and Passeri and Mazur (2019), there was a significant decrease in students’ performance from the knowledge test to the retention test. Overall, the results obtained are considered quite positive, since students had no formal contact with the Chemistry subject in the period between the first and second data collection moments (they were on summer holidays), and these contents were not further addressed until the moment the retention test was applied. In particular, the large differences observed in questions related to water turbidity and salinity can be explained by the fact that these contents are not included in the Chemistry curriculum and, therefore, were not formally taught and reviewed in chemistry classes. On a procedural level, the PVC project also contributed to students’ learning and skills development, mainly through the practical-laboratory tasks. Interviews conducted with students and teachers, as well as field notes, provided indicators related to the learning of techniques, materials, and laboratory rules, as well as the development of several important skills for laboratory chemistry tasks. As Hofstein (2017) and Irwanto et al. (2019) point out, these skills are believed to boost chemistry learning and may help to explain students’ positive performance on the knowledge test and knowledge retention test. In this regard, students mentioned that the resources developed, and the activities proposed in the project facilitated the performance of practical-laboratory activities, even those that involved new techniques, giving all students in the work group the opportunity to perform activities with a high level of autonomy (Bonney, 1996; Nicosia et al., 2014). Teachers also supported the idea that students’ involvement in the project promoted the development of laboratory skills. However, they add that, for example, for younger students, the increase in autonomy was not as noticeable, since they had limited practice in laboratory work, at the start of their project participation. Furthermore, the use of computers, tablets or smartphones to display and record images of microplastics, collected using the digital microscope, as well as to share the results of the physicochemical analysis of coastal waters, on the online citizen science platform, enhanced the development of digital skills, as argued by Spante et al. (2018).

Bonney (1996), Shirk and Bonney (2018), and Strasser et al. (2019) report that citizen science is an approach that promotes the development of new scientific skills, among other features, in citizens in general, as well as in students, in particular (Nicosia et al., 2014). Thus, the PVC project helped to develop communication, argumentation, and critical thinking skills, which are fundamental skills for the education of 21st century students (Taber, 2016; Stehle and Peters-Burton, 2019).

Conclusions

In terms of conceptual learning, students’ performance on the knowledge test was quite good. In addition to questions about contents previously taught in Chemistry classes, there were also questions about Chemistry contents explored for the first time in the project. Regardless of their school grade, students revealed a greater difficulty in questions related to polymer chemistry and quantitative composition of solutions, due to a lack of mathematical skills, as often reported by students themselves. Similarly, gender did not reveal itself as an influencing learning factor for students who participated in the project.

Knowledge retention results indicate a considerably lower performance, compared with results achieved on the knowledge test. However, this performance was still positive, which is a good indicator that this educational experience contributed to increased learning outcomes that persisted even after project conclusion. Analogous to the knowledge test results, an analysis of the knowledge retention test results also suggested gender and school grade were not factors of influence.

On a procedural level, this educational experience promoted the learning of techniques, materials and laboratory rules in chemistry, also contributing to the development of essential skills, such as laboratory autonomy and teamwork, promoted by the use of teaching kits.

Students recognized their participation in the PVC project as very positive, stating that it promoted the development of skills, such as critical and reflexive thinking. Students also mentioned their motivation for the proposed activities, especially the practical-laboratorial activities, due to citizen science component, which also allowed them to contribute to the scientific community with their results. Students and teachers also highlighted the various dynamics promoted by this experience, particularly awareness activities and scientific dissemination among their communities, which fostered teamwork, reflection and communication, as well as argumentation and discussion of ideas among peers.

The evaluation of the potential of citizen science approaches, within Chemistry teaching, has not yet been explored to a great extent in literature (Harlin et al., 2018). The assessment of the PVC project was conducted so as to increase the knowledge in this field. In conclusion, students’ collection and analysis of physicochemical parameters of coastal waters, within the framework of this citizen science project, has promoted the learning of chemistry contents. Indeed, it is essential that 21st century students achieve satisfactory levels of learning retention, as well as develop various laboratory skills.

The paper concludes with specific implications directed at relevant audiences such as school teachers, teacher educators, and curriculum developers, who might use student-led citizen science for their classes, prioritizing participant learning gains.

Our results show that the PVC project is a citizen science project that provides learning opportunities for participating students. Moreover, our project has supported the idea that citizen science can be a worthy part of formal education in incorporating authentic research practices into everyday classroom practice. In this scope, it is essential to emphasize guiding and mentoring participation in citizen science projects. As such, school groups are advantageous because their teachers facilitate students' participation. Notwithstanding, this creates an important requirement for the citizen science projects: they need to be aligned to the school curricula. Citizen science projects can enlarge the real contexts, incorporating students into real-world science projects and providing motivational aspects of citizen science, such as the possibility of data collection outside the school setting.

Our study points out at least four crucial aspects that need to be considered for successful participation in citizen science projects: (1) Schools can introduce vast numbers of citizens-students to participatory science. In line with this, it is necessary to integrate citizen science into curriculum development and recognize citizen science as an educational tool in the schools' policy. (2) Teachers' and students' objectives need to be aligned with the researchers who are running the project, balancing scientific and learning outcomes within a project. Students feel more involved in their learning by participating in genuine scientific investigations that contribute to world knowledge. The citizen science projects can fit well into a curriculum and provide ready-made kits and assessment tools that match local standards. Teachers need to potentialize the experiences and outcomes of student participation, providing an opportunity to reflect on the project in a classroom: the objectives, problems related to, and experiences during the citizen science project and their relationship with the school curricula. (3) Citizen science projects can offer possibilities for teacher professional development. It is essential to support teachers, helping them see that citizen science is not an addition to their teaching demands; instead, it helps them meet their existing instructional goals and develop their professional practices and reflections. (4) Data analysis, communication, and interaction with larger communities can open further learning opportunities; a collaborative or co-created citizen science project could be developed and be more fruitful from an educational perspective.

Future projects

Given the positive results achieved with the PVC project, we believe that doors are open to pursuing PVC projects with students from secondary education (or even higher education), where contents related to water quality and polymers can be further explored. In this regard, and in line with participants’ suggestions, this project could also be extended to the public, by involving communities, particularly coastal communities, in monitoring the quality of coastal waters and/or in quantifying the presence of microplastics on beaches. Therefore, in the short term, we intend to implement some of the research proposals presented here, particularly regarding the assessment of the PVC project's impact on the affective dimension of students’ scientific literacy involved in this educational experience.

Conflicts of interest

There are no conflicts to declare.

Appendix

Knowledge test

Sample questions. 3. The water of the Dead Sea has high salinity. The water from this sea is a homogeneous mixture in which, for each litter of sea water, there are 300 g of salt dissolved. To lower the salinity in a water sample from the Dead Sea, it is necessary to:

A. Add water to the sample.

B. Add salt to the sample.

C. Boil the sample.

D. Place the sample in the sun for a long time.

6. A water sample collected from a beach in Matosinhos has a pH of 7.9 and another sample, collected from a beach in Vila Nova de Gaia, has a pH of 8.0. If the analysed waters were at different temperatures, would it be possible to predict, without more information, which beach presents the more acidic water?

A. Yes, because the pH is a measure that is not dependent on temperature.

B. Yes, despite the pH being a measure that is dependent on temperature.

C. No, because the pH is a measure that is dependent on tem perature.

D. No, despite the pH being a measure that is not dependent on temperature.

15. One of the water samples collected near a river mouth presents a turbidity of 40 JTU.

What is the reason for the turbidity of the water sample?

A. Small particles suspended in the water.

B. Small particles dissolved in the water.

C. Other liquids dissolved in the water.

D. Gases dissolved in the water.

17. Oxygen is a gas that is poorly soluble in water. However, this small amount of oxygen dissolved in water is essential for the survival of aquatic species. Consider that it is possible to dissolve, at most, approximately 10 mg of oxygen per litter of water. In the analysis of a seawater sample collected near the coast, a dissolved oxygen concentration of 8.2 mg L−1 was found.

An oxygen-saturated aqueous solution has a concentration:

A. Higher than 10 mg L−1.

B. Of 10 mg L−1.

C. Of 8.2 mg L−1.

D. Lower than 8.2 mg L−1.

20. In the laboratory, a sample of 2 g of polystyrene was mixed with 20 cm3 of acetylacetone.

Select the option that correctly completes the sentence.

From the aforementioned dissolution, it is possible to conclude that _____ is the solvent, that is, it is the _____ component of the solution; thus, _____ is the solute of the solution.

A. … acetylacetone … minority … polystyrene.

B. … acetylacetone … majority … polystyrene.

C. … polystyrene … minority … acetylacetone.

D. … polystyrene … majority … acetylacetone.

Acknowledgements

J. L. Araújo was supported by the Fundação para a Ciência e Tecnologia (FCT, Lisbon) grant: SFRH/BD/132482/2017. This work was developed in the framework of project UIDB/00081/2020, funded by Fundação para a Ciência e Tecnologia (FCT, Lisbon). The authors gratefully acknowledge the teachers and students who took part in this project and greatly contributed to its success.

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