Developing a lesson plan on conventional and green pesticides in chemistry education – a project of participatory action research

Abstract

The debate on the use of pesticides is very current in the public media when it comes to topics such as organic farming, bee mortality, and the use of glyphosate. The broad range of pesticide applications and their potential environmental impact makes pesticides an interesting topic for science education in general and for chemistry teaching in particular. This is particularly true when conventional pesticide use is contrasted with current chemistry research efforts to develop alternatives based on the ideas of green chemistry. This paper discusses the potential relevance of pesticides for chemistry education in connection with education for sustainable development. It gives a brief outlook on pesticides in science teaching and connects the topic to socio-scientific issue-based chemistry education. A case study which developed a lesson plan for secondary school students is presented here. It defines pesticides, before focusing on the development of green pesticides as potential alternatives to current products. The lesson is focusing learning about chemistry rather than learning of chemistry in the means that the lesson introduces quite young chemistry learners (age range 15–17) to ideas of green and sustainable chemistry and how green alternatives in chemistry can be assessed and compared to traditional alternatives. Video vignettes of a scientist are used to introduce the topic to students. Finally, both glyphosate as a conventional, industrial pesticide and orange oil as an example of a green pesticide are compared using spider chart diagrams. The lesson plan was cyclically designed by a group of ten chemistry teachers using participatory action research. It was piloted with the help of secondary school chemistry student teachers and then tested in five German secondary school classes (grades 10/11). The use of the spider charts was regarded as especially helpful by the learners, most of whom felt that they had been able to understand the controversy surrounding pesticides.

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1 Introduction

In 2015, the United Nations introduced Agenda 2030 as an action plan promoting a sustainable future for the world. 193 countries worldwide agreed on a definition of sustainability containing three balanced dimensions: environmental, societal and economic sustainability. These countries reached agreement on 17 sustainable development goals (SDGs). Out of these 17 SDGs ten were recently tied to chemistry by the Global Chemicals Outlook II published by the United Nations Environmental Program (UNEP) (UNEP, 2019).

In 2015, Steffen et al. (2015) also published an updated version of their planetary boundary framework, which reflects upon (potential) human impact on the earth. One planetary boundary, which has not been quantified so far, is that of novel entities. Synthetic pesticides are novel entities which have been released into the environment by mankind for several decades now. Chemistry plays an important role in staying within planetary boundaries and achieving the above-stated SDGs. It also contributes to contemplating novel routes for obtaining, synthesizing and using chemicals (Correa et al., 2013; Matlin et al., 2015; Zuin, 2016a). Despite chemistry's importance in developing a sustainable future, chemistry lessons are often perceived as unpopular and uninteresting by many learners (Osborne and Dillon, 2008). This might be related to a lack of understanding of the relevance of chemistry education's content and contexts (Osborne, 2003). An orientation towards a more societal perspective along socio-scientific issues (SSIs) has been suggested to increase the learners' perception of the relevance of chemistry education (Hofstein et al., 2011).

One controversial SSI being currently discussed both in politics and in the public media is the use of pesticides, such as glyphosate. Some media excerpts claim that pesticides are responsible for both decreasing numbers of pollinating insects and an increase in the cases of certain cancers. Other contributions highlight the necessity of pesticides for food security and for stable worldwide food prices. A quite recent study showed that consumers from the USA associate high pesticide-related risks with conventionally grown foods (Williams and Hammitt, 2001). In Germany, for instance, pesticides also have a negative image. A majority of the public believes that the risk of using pesticides is higher than the resulting benefits (BfR, 2016a). Pesticides are a topic with a multitude of different shareholder viewpoints ranging all the way from the political arena to the economy, society, the agricultural sector, and science. For this reason any “right” decision based on cost-benefit analysis is extremely difficult to make (Hastik et al., 2013). However, such decisions still need to be made, hopefully to the benefit of society.

In this article we first discuss selected aspects of the use of conventional pesticides, potential alternatives and the implementation of this topic in science (chemistry) education. We outline links to sustainability education and SSI-based teaching to justify why pesticides are a suitable topic for chemistry education. We then describe an evidence-based curriculum design project focusing a lesson plan for secondary or undergraduate chemistry education on glyphosate (conventional pesticide) and orange oil (green pesticide). Finally, we discuss first results from the accompanying evaluation and outline conclusions for future research and implementation.

2 Background

According to the United States Environmental Protection Agency (EPA, 2019) “a pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest; use as a plant regulator, defoliant, or desiccant; use as a nitrogen stabilizer.” The European Union suggests that pesticides can be divided into plant protection and biocidal products (2009, 309/71) (EFSA, 2019): “…this Directive should apply to pesticides which are plant protection products. However, it is anticipated that the scope […] will be extended to cover biocidal products.”

Pesticides are plant protection products which can be divided according to the target organisms. They mainly include insecticides against insect pests, herbicides against unwanted plants (weeds), and fungicides against harmful fungi. A recent example is glyphosate with its massive media presence due to the extension of the approval by the EU in 2017 and ongoing trials in the USA. In contrast, alternatives such as green pesticides are hardly mentioned by the media.

Pesticides are designed to prevent, destroy, repel or mitigate pests. They act in a variety of ways, primarily by affecting metabolic processes (for more information see Copping and Hewitt, 1998 or Krämer and Schirmer, 2008). Modern pest control was first launched in the 1940s with invention of synthetic pesticides, like dichlorodiphenyltrichloroethane (DDT) which was effective and cheap in eradicating malaria-carrying mosquitoes (Unsworth, 2010). Pesticides were also part of the Green Revolution in the 1960s, which attempted to massively increase crop yields. Over time, more and more risks associated with pesticides were described and became part of the public discussion, especially after Rachel Carson's alarmist book “The Silent Spring” in 1962. Today, crop protection has a range of options. Pesticides have been modified and improved in their modes of action, as well as in their selectivity. At the same time, plants were also genetically manipulated so that they were given a natural resistance to some pesticides (Unsworth, 2010).

Conventional agriculture uses pesticides for integrated pest management. Such management focuses on different components, including pesticides, which strengthen plant growth or effect selected crop sequences. One alternative is organic agriculture, which renounces synthetic pesticides. However, according to the German Federal Ministry of Food and Agriculture (BMEL, 2017a), a complete change to organic agriculture in Germany's case would mean that the German population would need to largely refrain from meat consumption, abstain from fruits and vegetables which are produced using synthetic pesticides elsewhere, and willingly to accept higher food prices. Thus, banning synthetic pesticides is also a question of changing consumer behavior or requiring consumers to spend more on food.

Cooper and Dobson (2007) have suggested that the perceived risks of pesticides are much higher than the real-world risks. They also stated that the benefits of pesticide use are not sufficiently appreciated by the public. In Germany, for example, a national action plan says that plant protection methods are necessary, and pesticides are one component which should become less relevant over time (BMEL, 2017b). Glyphosate is such a pesticide – the aim is to steadily decrease its use. The debate about glyphosate use is controversial and not even experts can reach a general consensus. Supporters of glyphosate state that the discussion is not objective, while the opponents want to prohibit glyphosate due to (potential) consequences (Küchler and Zaller, 2018). Glyphosate was invented in the 1970s and was re-approved by the European Union in 2017 for five additional years. It is one of the bestselling herbicides worldwide, e.g. under the trade name Roundup®, and is very effective in destroying non-resistant plants, which means that it eradicates most unwanted weeds (BMEL, 2018). Glyphosate inhibits the production of aromatic amino acids (e.g. phenylalanine and tyrosine), due to its structural similarity to phosphoenolpyruvate. It has very low production costs and works reliably and effectively (Seitz et al., 2003).

Overall, the use of glyphosate has been widely criticized in several developed countries. On the one hand, the International Agency for Research on Cancer (IARC, 2016) stated that glyphosate is probably carcinogenic to humans. On the other hand, the German Federal Institute for Risk Assessment (BfR) stated that there is no increased risk using glyphosate in terms of cancer as long as it is used properly (BfR, 2016b). Both statements seem to be contradictory, but in fact the IARC tries to estimate whether a substance might eventually promote cancer, while the BfR points out how likely this case is, if the substance is applied in accordance with the suggested dosage. Long term studies from the USA examined (among others) 45 000 glyphosate-using farmers. They found that “no association was apparent between glyphosate and any solid tumors or lymphoid malignancies overall. There was some evidence of increased risk of AML among the highest exposed group that requires confirmation” (Andreotti et al., 2018, 509).

Another frequently mentioned issue in the context of the use of conventional pesticides is the decline in biodiversity, especially pollinators. A connection between modern agriculture with its use of pesticides, fertilizers and monocultures and the decline in biodiversity may be reasonable (UBA, 2018). Glyphosate is considered to be comparably insect-friendly, because the mode of action does not affect insects. However, a recent study came to the conclusion that it is likely that glyphosate damages the microbiota in honey bees (Motta et al., 2018). In any case, glyphosate can possibly impact the living environments and food sources of insects. Recently, Brillsauer et al. (2019) suggested a new cyanobacterial antimetabolite as an alternative to glyphosate, which also blocks the shikimate pathway. But, even if not every risk of glyphosate is applicable here it will also work as an herbicide in killing plants.

On the other hand, recent new regulations for the use and sale of pesticides in Brazil have been proposed, weakening current regulations and transferring their control to the Ministry of Agriculture instead of the current Ministries of Environment and Agriculture and the National Agency of Health. Brazil is already one of the main markets of pesticides and almost all of its population has been severely affected by their use (e.g., via inhalation, ingestion of contaminated water and food). Additionally, the maximum acceptable limits (MRL) for some pesticide residues in water and food in Brazil are much higher than those established by the European Union (EU), e.g., for glyphosate the Brazilian MRL in food is 10 mg kg⁻¹, considerably different to the one in the EU that is 0.05 mg kg⁻¹ (Abessa et al., 2019).

An alternative to conventional, synthetic pesticides might be green (ecological) pesticides, which are “derived from organic sources that are considered environmentally friendly and cause less harm to human and animal health, to habitats and to the ecosystem” (Rathore, 2017; 4). Using essential oils such as eucalyptus, orange or clove oil has been suggested. These are obtained from diverse plant parts like leaves, roots, peels or bark. Most of these substances are volatile, odor-intensive compounds with a variety of functional groups. Many of them are monoterpenes which can be cytotoxic to plant and animal tissue. One example is the monoterpenoid linalool which acts as an insecticide and can be found in basil or nutmeg. Linalool influences ion transport in the nervous system and thus the release of acetylcholinesterase which is an enzyme catalyzing the breakdown of acetylcholine. Another mode of action is the smell of some essential oils, which suggests “danger” to insects (Rathore, 2017). Blocking the smell also works in some cases. A further example is orange oil, which can be obtained from leftover orange peels from orange juice production. From these peels, many chemicals such as D-limonene and pectin can be extracted. The terpene D-limonene is the main component of orange oil, which has been registered in the USA as an insecticide since 1958 and as an antibacterial agent since 1971. Orange oil is a highly effective contact insecticide for ants, cockroaches, flies or silverfish. Many products (such as Orange Guard® in the USA) are on the market for domestic use. It is not very toxic, non-persistent in the environment, a good repellent and slows down the growth of some insects. Orange oil can cause a variety of symptoms in insects such as hyperactivity, loss of orientation, or paralyzed limbs. These symptoms are similar to those caused by neurotoxic substances. Problematic for mass production is the comparatively high price and issues in handling the volatility of the orange oil. Although D-limonene is allowed as an indoor insecticide, it is suspected of inducing dermatitis (Zuin, 2016b; Ciriminna et al., 2017).

3 Sustainability, chemistry education and pesticides

The connection between sustainability issues and chemistry teaching has been made for a long time by authors such as Burmeister et al. (2012), Juntunen and Aksela (2014) and Tytler (2012). Burmeister et al. (2012) named SSIs as one potential way to teach about sustainability in chemistry contexts. Even sustainability itself can be seen as an SSI (Simonneaux and Simonneaux, 2012), especially in terms of hot type SSIs, the most relevant and controversial ones which are interdisciplinary in nature and go beyond teaching conceptual knowledge (e.g. climate change) (Simonneaux, 2014). This is especially true in times where the human influence on system earth is increasing (Crutzen, 2002). This suggests that we need a new definition of sustainable development, which emphasizes the environment (Griggs et al., 2013). Dealing with sustainability topics in chemistry education can be seen in the context of Model 3 as suggested by Burmeister et al. (2012; 64) for sustainable development education: “Using Controversial Sustainability Questions for Socio-scientific Issues Driven Science Education”. It has been suggested that SSIs in chemistry education should start with societal dilemmas or controversial social issues with direct links to science (Sadler, 2004). Therefore, the starting point of an SSI cannot be purely scientific content. To understand this point of view, a helpful question was asked by Sadler (2011; 1): “What should be the goal of science education?”. Sadler's answer for school science education is preparing future citizens, so the primary goal cannot merely be pure science content.

Sadler's view is supported by that of Sjöström (2013), Sjöström et al. (2016), or Mahaffy (2015). Mahaffy (2015) even warns not to neglect that it is important for young learners to understand and make decisions, since the majority of students will not pursue a chemistry degree. This is especially true in times where various sustainability topics reach broad media attention and have high levels of coverage. Here Mahaffy (2015; 7) says that “overemphasis is often placed on providing all of the foundational pieces for the few students who major in chemistry, rather than for the majority of students who will pursue careers in health professions, engineering, or other areas”. This is even more true for secondary chemistry education as it might be for undergraduate studies. It can be concluded that an SSI approach should be interdisciplinary due to limits in chemistry and other subjects. A demand for more holistic approaches can be made (Vilches and Gil-Pérez, 2013; Zuin, 2016a). Also, Mahaffy et al. (2018) emphasized connections beyond disciplines in order for learners to face challenges like sustainable development. Zeidler (2015; 1001) summarizes potential positive outcomes of using SSIs in science education:

“Promoting developmental changes in reflective judgment, moving students to more informed views of the nature of science, increasing moral sensitivity and empathy, increasing conceptual understanding of scientific content, increasing students’ ability to transfer concepts and scaffold ideas, revealing and reconstructing alternative perceptions of science, facilitating moral reasoning, improving argumentation skills, promoting understanding of eco-justice and environmental awareness, engaging students’ interest in the inquiry of science”.

An important question is how suitable SSIs can be identified. Marks and Eilks (2009) and Stolz et al. (2013) have suggested the following criteria for fruitful SSIs in science education: authenticity, relevance, openness for evaluation with respect to a societally relevant question, inclusion of open discussions, and a basis of the topic in science (chemistry) or technology. Applying those criteria to pesticides leads to the following results:

• Authenticity: Critical discussion on pesticides use frequently occurs in public debate and the media.

• Relevance: Everyone has to decide whether to buy conventional or organic food products. Pesticides have only temporarily been authorized by the European Union. Keeping in mind the discussion about glyphosate in Europe and the USA we can conclude that decisions will affect learners’ lives both today and in the future.

• Open for evaluation with respect to a societal relevant question: There are various positions in the public debate ranging between the necessity of pesticides for a cheap, dependable food supply and protecting nature. In any case, any result is a tradeoff between these two poles.

• Open discussions: There are many realistic positions on how various pesticides should be used and in which recommended amounts.

• Connection to science and technology: Pesticides are chemicals which are invented and researched by chemists, and produced by the chemical industry.

In the past, there were some suggestions to integrate pesticides into chemistry teaching, e.g., related to analytical chemistry. Radford et al. (2013) analyzed pesticides by extraction from different products juice with undergraduate students, like juice. Davis et al. (2017) used project-based learning to find methods to quantify DDT and its degradation products in environmental samples. Other ideas focused around plant extractions to teach analytical chemistry (Hartwell, 2012). Glyphosate was also suggested for analysis in a laboratory activity using UV-Vis spectroscopy in undergraduate teaching (Felton et al., 2018). In 1999, O’Hara et al. developed a laboratory course studying pesticides in drinking water as an introductory chemistry course to foster learner motivation and interest. In another study, students were asked (among other things) to improve detection tests for three pesticides in fruits. This led to an increase in self-efficacy beliefs when performing chemistry experiments using a problem-based learning laboratory (Mataka and Kowalske Grunert, 2015). Another study focused on instructional methods (Current and Kowalske Grunert, 2016) using the above-mentioned detection of pesticides. More recently, a new module dedicated to green chemistry focused on bio-circular economy models in pre-service teacher education courses in Brazil (Zuin, 2018). This education module aims at understanding the process for design and development in the scope of transformative science education. It highlights case studies such as the bio-rational control of insects and the search for biologically active compounds closely related to human life with an eye towards sustainable agriculture.

In New Zealand, students were taught about integrated pest management using an online-based platform. This included virtual visits to a farm where they needed to decide how to protect crops against pests during a growing season (Stewart, 2014). To increase student interest and connect chemistry more closely to real-life issues, Kegley et al. (1996) used a module-based laboratory curriculum for general chemistry. Students analyzed pesticide residues in fruits and vegetables, which then lead to the discussion of two contradictory roles (environmentalist and agribusiness advocate) in a debate on regulating pesticide use in connection to food supply.

A few years ago, an interdisciplinary module was suggested, which focused on the mode of action of pesticides and the ethics of their use, in order to introduce complex mechanisms and consequences to the environment from the ethical side (Ryno and Cottine, 2018). Mandler et al. (2012) also tried to integrate real world issues into teaching. In their module “We are the world – The Carbon Cycle” they embedded the use of pesticides in the context “Our role in conversing our planet” by focusing on the story of methyl bromide. In order to reliably evaluate the scientific thinking skills of undergraduates, Harsh (2016) designed a set of tasks based on relevant real-world problems. One of them was the controversial pesticide atrazine, which is suspected of causing malformations in animals. Based on these tasks, an instrument measuring scientific thinking skills was later developed (Harsh et al., 2017). Already in 2002, Zeidler et al. referred to DDT as an example of unwitting errors of science and highlighted the importance of its social implications in education.

In the International Year of Chemistry in 2011 a monthly chemistry calendar containing videos was produced in Sweden. One focus was on more environmentally friendly pesticides, as well as the huge questions of risk vs. benefit and pesticide residues in food (Christensson and Sjöström, 2014). The question of risk and benefits was also raised for several chemical substances by Cullipher et al. (2015). They analyzed different levels of sophistication in ideas of benefit, cost and risk reasoning, based on the topic of energy resources. Among other topics, an international survey was conducted by Asada et al. (1996) on bioethics. They found that topics related to bio-ethics were more frequently taught in biology classes than in chemistry or the social sciences. They also found a need for more high-quality educational materials. In 2000, Zoller used an exam to asses learners' higher-order cognitive skills, using questions containing items about the potential impacts of pesticides for farmers. A strong focus on chemical-related environmental science was claimed for education and research, e.g., by Schaeffer et al. (2009) and Sjöström et al. (2016).

Assessing the sustainability of pesticides with students is difficult due to the inherent complexity of the issue. Sustainability assessments in science are often based on many factors that are quantified in order to make statements. Several attempts have been suggested for focusing on sustainability while researching new syntheses. These are also related to teaching about green chemistry (Ribeiro et al., 2010; McElroy et al., 2015). Ribeiro et al. (2010) introduced the “Green Star,” which is a spider chart diagram oriented around the twelve principles of green chemistry as presented by Anastas and Warner (1998). This method is, however, still complex. Its use in education might need to be limited to advanced students in higher education, since it calculates certain statistical values and requires a broad knowledge of chemistry. A search in the literature could not identify an easy-to-handle, informative tool for students at the secondary school level to assess the sustainability of a given substance or chemical process.

Most of the examples and suggestions described here focus on undergraduate chemistry education. Teaching about pesticides is, however, not really present in science education in general and in chemistry education in particular when it comes to the secondary schooling level and it is not yet part of German chemistry curricula. The same holds true if such teaching is meant to be connected to learning about green pesticides neither from a perspective of the chemistry behind green pesticides, nor as an SSI in chemistry teaching. Since the chemistry behind green pesticides is rather complicated and this lesson plan is designed for quite young chemistry learners at the end of lower and beginning of upper secondary education with a limited background in chemistry, in the following sections we suggest integrating learning about traditional and green pesticides in an SSI framework in chemistry education. The lesson plan is focusing learning about chemistry rather than learning of chemistry. That means it introduces quite young chemistry learners (age range 15–17) to ideas of green and sustainable chemistry and how green alternatives in chemistry can be assessed and compared to traditional alternatives. The central objectives of the intervention are that students get first ideas which actions chemistry is taking to replace synthetic chemicals with green alternatives and what criteria and visualization tools can be used to gain initial measures of sustainability in the lower and upper secondary classroom. The implementation of corresponding sustainability assessments is rare in secondary chemistry education in general, and for the German context in particular where the subject chemistry is generally taught as a self-standing subject from the early years of lower secondary education onwards. At the same time a connection to the sustainability debate should be established in order to introduce the topic for in-class discussions and debates. Although the focus of this intervention is more general and might be considered general science content in those countries teaching integrated science at the lower secondary level, this is not the case for Germany. In Germany, chemistry curricula for both the lower and upper secondary schooling levels ask for the teaching of evaluation competence and to operate education for sustainable development as integral parts of secondary chemistry education.

4 Research design

The lesson plan was developed using the model of Participatory Action Research (PAR) as suggested by Eilks and Ralle (2002). In the PAR design research approach, science educators and experienced teachers cyclically design teaching interventions for topics where teachers see a gap in the curriculum or pedagogy. They can then arrive at evidence-based lesson plans and the associated media (Marks and Eilks, 2010). After the design phase the lesson plan is tested in different groups of students in order to elicit student feedback. This feedback aids in further iterations while developing the lesson plan. The initial design of the lesson plan, in this case, was discussed and revised in a group of teachers in three rounds over a time span of six months. The group consisted of ten experienced chemistry teachers, some of whom have worked in this PAR group for almost 20 years (Eilks, 2018). Changes were then integrated according to the teachers’ input and feedback.

A first round of pretesting was carried out with a group of roughly 20 chemistry student teachers during a university chemistry teacher education seminar. The student teachers provided feedback in a group discussion format and a preliminary version of a questionnaire containing 5 open-ended questions and 15 Likert-scale items (4 step). The instrument that was piloted in this group was later used in the case study evaluation with school students. The feedback provided led to further slight improvements in the teaching and learning materials. The lesson plan was finally applied to five senior secondary school chemistry classes (last year lower and first year upper secondary level, age range 15–17). The intervention was comprised of three to four lessons of 45 minutes each. The slightly adjusted questionnaire from the pilot test with the student teachers was used. Feedback was provided by a total of 95 secondary school students from five classes in different schools. All of the students volunteered to provide anonymous feedback. The intervention and data collection were performed in compliance with the authors’ institute's policy on ethics and corresponding regulations for data collection in schools.

In the questionnaire, the open-ended questions related to what students perceived they had learned, the positive aspects of the learning environment, any potential changes and improvements, a reflection upon a given statement (“Agriculture without pesticides – this doesn’t work!”), and feedback on the approach of working with video vignettes from a real scientist. The Likert-based items focused on various aspects of motivation and interest, the use of contexts and pedagogies, perceptions of the teaching materials, and attitudes towards the chemical industry, government policy and green alternatives. Additionally, spider chart diagrams were filled out by the students and were also collected.

Answers to the Likert questions were subjected to descriptive statistics, which is suggested appropriate for this kind of action research-based design research, where evaluation is cyclical and aims more at understanding teaching practice improvement, than at producing hard data (Bodner et al., 1999). The open-ended questions were analyzed using qualitative content analysis according to Mayring (2000). Summarizing qualitative content analysis was used, which is a cyclical, multi-step procedure for examining qualitative data. The data was first paraphrased to inductively identify common themes and categories (Mayring, 2000). Two rounds of coding with the help of two coders were applied in order to constitute a category system, which described the content of each open-ended question. The final inter-rater reliability was almost perfect with a Cohens value of κ = 0.899.

5 Teaching intervention

The suggested teaching approach generally follows the socio-critical, problem-oriented approach to chemistry teaching defined by Marks and Eilks (2009). In contrast to this model, however, no experiments were used. The lesson plan is designed for 135–150 minutes of lessons, starting with media excerpts highlighting the controversy surrounding pesticides. One of the authors from Brazil (V.G.Z.) introduces the learners to Brazil's agricultural system and to pesticides via a short video vignette (English with German subtitles). The Brazilian context was chosen to connect chemistry learning with an authentic field of research that is operated in Brazil where it has an enormous economic importance. Additionally, literature suggests for the case of Germany that students are more interested in regions outside Europe (Hemmer and Hemmer, 2017).

Afterward, the learners start working in groups (pro and contra pesticides) to write a fictional e-mail to the researcher in Brazil, who is evaluating pesticides. The fictional e-mails are placed on an opinion scale and are connected to the use of glyphosate. The next step is to fill out a spider chart (see Fig. 1) with six categories. Spider charts are regularly suggested for visualizing certain aspects of sustainability on a soft scale (applicable – partially applicable – not applicable); e.g. (Ribeiro et al., 2010). The four criteria at the top of the diagram were inspired by the philosophy of green chemistry. The two criteria at the bottom are based on other important aspects of the use of a new compound, including its economic soundness, in particular its efficiency and availability. A new chemical agent needs to fulfill its purpose and be able to be produced in sufficient amounts within justified costs. The information to fill the spider chart is again provided through a video with an associated text and, in case it is necessary, oral explanations by the teacher. The video is stopped at several points in order to give the students time to make notes and fill out the spider chart. The students have to interpret texts and information to fill in the spider charts. For our target group of students this is not an easy task and needs competencies in evaluation and interpretation which are central to understand sustainability assessments.

Fig. 1 Simple spider chart for evaluating the use of chemicals with potential entries suggested by the authors for glyphosate and orange oil.

The weaknesses visible in the spider chart diagram on glyphosate is used by the teacher to lead to the question of potential alternatives. Here, green pesticides are introduced using another video vignette from the Brazilian context. Students list pros and cons based on the video vignette. After that, the students fill in a second spider chart diagram with help of a text about orange oil (D-limonene) as an example of a green pesticide. The spider charts filled out by the students on glyphosate and orange oil are then compared.†

The strengths and weaknesses of both of the pesticides were made visible by the spider chart diagrams, so that the students could easily compare the two pesticides. Some student results also contained extreme values, which were an important factor in a classroom discussion. For example, the idea that glyphosate cannot be produced in large amounts is definitely not correct – however, potential (negative) consequences for the environment might actually be the case. Such differing results are most valuable, because they can be compared to the results of other class members and discussed within the whole group in order to gain broad agreement.

When discussing and comparing the spider charts, it is emphasized that any solution as shown in Fig. 1 includes a certain level of uncertainty, based upon the interpretation of the information by the students. Discussion leads to the point where the whole issue becomes a topic with a high level of uncertainty. This uncertainty can then be addressed using different results from the students with regard to soft scaling. During the interpretation phase it becomes clear, for example, that glyphosate is highly efficient, can be produced in large amounts at low costs, but is not produced from renewable raw materials. In contrast, orange oil is made from a renewable resource at considerable cost, but not yet available at the large scale. Several issues in the task demanded of the students ask for an educated guess and a decision as to what level of fulfillment for a certain criterion should be considered. This spider chart purposely reveals the strong focus of environmental factors, although economic aspects are also addressed. Aspects of societal sustainability were left in this example out to limit the overall complexity. Fig. 2 presents an overview of the lesson plan.

Fig. 2 Course of the lesson plan.

6 Findings

Fig. 3 shows the results of the Likert questionnaire. In general, most of the students perceived the topic to be interesting (over 90% agreed/agreed mostly) and thought that the topic should be taught in school (over 80% agreed/agreed mostly). However, only about 40% of the participants agreed or mostly agreed that the lessons had motivated them to follow media coverage on pesticides more intensively, although another 40% agreed at least partially. Roughly 60% of the students agreed or mostly agreed that they liked the idea of using video vignettes showing scientists, with another 30% agreeing partially with the idea. The innovation connecting chemistry learning in a German school to the geographical and economic context of a country like Brazil received split support. Nearly 20% agreed and a further 35% and 30% mostly or partially supported this corresponding claim, respectively. One item was answered by only about one-third of the participants (“I liked the fact that the experts were women.”) This answer is not shown in Fig. 3 because of the low answer rate. In informal feedback, some students stated that it didn’t matter to them whether the chemistry experts presented in class were male or female. It seems that among these students, the prevalent image of a chemist is no longer male-dominated. This might be an indication that the previously prevalent stereotypical views of scientists are disappearing, at least in some developed countries (Fung, 2002).

Fig. 3 Students’ answers on the Likert items (n = 95; m = 44; f = 43; diverse = 6; no answer = 2).

The use of the spider charts was viewed positively by nearly all of the students. Most found it helpful (over 95% agreed/agreed mostly). Nearly all of the learners liked to work with them. Almost 90% of the students disagreed with statement that they had had problems following the lesson plan. A vast majority said that the material was well-designed (over 90% agreed/agreed mostly) and that they had not had any difficulties in solving the tasks. It seems that the complex issue of performing sustainability assessment based on given information was not seen as overwhelming by the students as was also reported in Burmeister and Eilks (2012).

After the module was completed, most of the students agreed that the chemical industry is important for our future. It was not seen as being one of the main reasons for environmental pollution. Here, more than 70% of the students agreed or mostly agreed that they were willing to pay more for fruits and vegetables. Slightly less students thought that green pesticides might be a good alternative. More than 60% disagreed or only agreed partially that the decision to extend the approval for glyphosate by the EU was a good decision.

Additionally, the students were asked to answer five open-ended questions: (1) name the most important aspects you have learned during the lessons, (2) describe the aspects you particularly liked during the lessons, (3) describe the aspects we should change or improve, (4) describe how you perceived “working with” a Brazilian chemistry professor, and (5) formulate a position to the following claim: “Agriculture without pesticides – this doesn’t work!”.

While answering questions most students stated that they had learned something about alternatives to conventional pesticides as well as the pros and cons of pesticides in general and glyphosate in particular. Many students named the potential effects of pesticide use on the environment and human health. About one-third of the students mentioned learning about the tension existing between specific societal needs, the (potential) negative consequences, and financial interests: “Economy and ecology are at two ends of a spectrum here – the aim should be a compromise”. In one of the groups, about one-third of the learners stated that they did not learn that much new information, which must be seen in light of the teacher who reformed the curriculum towards green chemistry.

Nearly half of all the participants referred positively to the pedagogy of the lesson plan, namely the mixture of media use, different tasks, and the constant change in work forms between individual, pair and whole class presentations. Aspects of pedagogy which the students liked most included the use of the video sequences and the inclusion of spider charts to compare different pesticides (about one-third of the students mentioned both explicitly). Some students referred to the topic and the design of the material, as well as to the comparison of glyphosate and orange oil: “I liked the interviews very much as well as our self-made diagrams (spider charts). But, overall I like the topic of green pesticides most.“ “I especially liked the use of those ‘spiderwebs’, because it was very easy to see the opinion of all others and it was also fun.”

Regarding negative aspects and suggested improvements, most students said that there was either nothing to improve or left this field blank. A few students asked for a stronger focus on the chemistry of pesticides or a deeper focus on different aspects. This occurred mostly in one group, which was an advanced course. To meet the request for a more chemistry-based view, we later designed a worksheet about the function of glyphosate for optional use. A very few other students criticized other parts of the lesson plan, saying that they would prefer to work individually rather than in groups, or that they sometimes needed more time.

Regarding the fourth question about “working with” a Brazilian chemistry professor, most students answered it in a positive way. As a reason they stated the authenticity of the involvement with a real scientist. Some of the students emphasized positively that their perspective was focused towards a Brazilian view or that the innovation of using video vignettes in class was good. Some students liked the video, but said that it was hard to understand everything due to the English language, despite the German subtitles. On the other hand, there was also thoroughly positive feedback on the video vignettes: “I thought it would be a great idea to involve someone who is professionally involved and is able to tell so much about it. It was always easy to understand her, and she made you feel like she was sitting at the other end of the classroom.” Only two students said that they were neutral regarding the videos. A few students pointed out that instead of videos a text could also be used. This might be related to the fact that a text can be taken anywhere and reread at will, whereas a video requires that proper video access and/or playback devices are available. Videos also require quick uptake and retention skills, if they are not paused frequently or the material presented is very complex or totally new.

For question five about the students' position on banning the use of pesticides in agriculture, all answers were first categorized into the responses: agree, agree partially, disagree, or no statement (no text or arguments without connection to the statement). Afterwards only the first three categories were analyzed further. About half of the students agreed to the statement in question five. They gave reasons such as a decrease in harvest yield or product quality, as well as connecting the topic to a growing world population and looking for further research. One example connected feeding the growing world population, necessary research, and to other aspects. It referred to a moderate use which can be legitimized: “I think the statement is true, because without the use of pesticides, the harvest rate would decrease, e.g. due to pest infestation. As the world population is steadily growing and more people need to be fed, a waiver of pesticides would not be beneficial. Pesticides are being researched and threshold values are set for agricultural use […]. Furthermore, there are alternatives to synthetic pesticides, which unfortunately are not as potent and are produced in smaller amounts than e.g. glyphosate. Thus, moderate use with care taken as to the dosage would be legitimate, so that the human health and the environment are not harmed.”

About one quarter of the students agreed only partially or disagreed based on similar reasons to those agreeing with the statement. Also, the disagreeing students argued that it's a difficult decision and said that harvest yield would probably decrease. None of the students disagreed without stating limitations like higher prices or decreasing harvest amounts. Interestingly, for the categories “partially agree” and “disagree” five students overall stated that a change in their consumer behavior might be of high importance for using less (or no) pesticides in future.

The filled-in spider charts for glyphosate and orange oil were also analyzed by measuring each spider chart and calculating a mean value for every criterion. Fig. 4 provides the average values from the results of the students. Clear differences between the two pesticides become immediately visible.

Fig. 4 Mean values of the students’ spider chart diagrams.

7 Discussion and conclusion

The topic of pesticides is relevant, authentic and very present in current media offerings and political debates. It can, however, only rarely be found in chemistry teaching. This paper presents a case study integrating the societal debate on pesticide use with chemistry teaching in the sense of an SSI. To our knowledge, this is the first test case which has ever contrasted the use of conventional pesticides with chemistry's search for green alternatives in order to learn about green and sustainable chemistry efforts in secondary school chemistry education. Such approaches were suggested by the recent Global Chemicals Outlook II (GCOII) published by the United Nations (UNEP, 2019, Chapter 4).

The evaluation of this case shows that most students liked the topic and the lesson plan. They agreed on the importance of dealing with the use of pesticides in school chemistry teaching. Most students felt able to comprehend the controversy and the tension between the potential risks of pesticides uses and their benefits. Most students were open to paying more for vegetables and fruits, if no pesticides were used, thus indicating the perception of relevance of the topic to students’ lives. Although this is only agreement with a Likert item, it shows the willingness of students to change something in their behavior, which can make learning about associated backgrounds relevant to chemistry education (Stuckey et al., 2013). This finding is also supported by the open-ended questions, showing that many students perceived the content learned to be relevant to them. The fact that many students linked pesticides to decreasing harvest yields, as well as the connection made by students to the growing world population, provide hints that they are developing a broader personal picture of chemistry, including the perception of the societal relevance of chemistry learning (Hofstein et al., 2011). The majority also acknowledged that the chemical industry is important for the future – also highlighted e.g. by Matlin et al. (2015) or the GCO II (UNEP, 2019).

The implemented spider chart diagrams depict the student's results in a clear and functional fashion. Interestingly, all of students received the same information and achieved more or less the same results. In only in a few cases were major differences observed. Maybe such spikes were subject to mistakes and misinterpretations. Those spikes can, however, be discussed in class in light of the idea of filtered information, the idea that the presenter of any information can influence its reliability and trustworthiness, sometimes even more than the original data behind it suggests (Eilks et al., 2014). The same might happen in daily media when journalists filter information while writing an article, making interpretations, committing mistakes, or coming to conclusions based on personal worldviews.

Although not unanimously agreed upon, there were many indications in the data that the involvement of a real scientist via video vignettes and the connection to the Brazilian context was appreciated by most of the students, at least to a certain extent. Especially the open-ended questions showed that many students named the videos as the aspect they liked most, and that involvement of the Brazilian expert was highly appreciated. The learners liked hearing from an authentic expert, but it was unimportant to them whether this was a male or female expert. This is a sign that students are starting to abstain from prevalent images of chemists, which tended to be male-dominated in the past (Fung, 2002). However, this image is still current in developing countries as Brazil, especially at the level of more experienced scientists (Santos et al., 2019).

Although only a few students named potential changes for the lesson plan in their feedback and primarily reiterated their broad positive feedback, especially regarding the videos and spider chart diagrams, there are several indications that this teaching approach is an appropriate way to introduce the complex topic of pesticide use in a limited amount of time. Based on the open-ended answers, there is hope that learning about pesticides in an SSI approach fosters student perception of the societal relevance of chemistry (Stuckey et al., 2013) by showing that there is ongoing research trying to develop alternatives to reduce risks associated with chemical use.

The case presented here is limited to the German educational context, and the senior secondary schooling level. The study was not connected to an evaluation of how this lesson plan interacted with learning the basic chemistry behind the issue of pesticides, since this was not in the focus of the lesson plan materials. This lesson plan was purposely not overloaded with too much pure chemistry content knowledge, because it focused primarily on gaining a broader understanding of the role of chemistry in students’ daily lives and in society as suggested by Mahaffy (2015). Further studies might reveal whether there is any potential for integrating more theoretical chemistry concepts or practical work, especially when the issue is implemented in advanced level courses or at the undergraduate teaching level. Already-existing examples at the higher education level such as Kegley et al. (1996) may provide guidance.

Core innovations in the lesson plan included both working with video vignettes presented by an authentic scientist and the use of spider charts for sustainability assessment. The spider charts and their use might be further modified and developed based on research so that they can be used for analyzing more complex products or processes. Further research can, for instance, evaluate their usefulness to show any gains in learners' understanding of complex chemistry issues. Also, the use of video vignettes hosted by experts from chemistry research might be further evaluated in terms of design, motivational aspects, or the most effective application of their uses. The material in German language can be found here: http://www.idn.uni-bremen.de/chemiedidaktik/materialien.php (password: Br4s1L13n)

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

We gratefully acknowledge the support by BremenIDEA and the DAAD for providing a research travel grant that made this curriculum design-project possible. The authors would also like to thank the CNPq (310149/2017-7, 421096/2016-0 and 311000/2014-2), FAPESP (18/11409-0 and 17/25015-1) and IUPAC (2013-041-3-300) for their financial support.

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Footnote

† Glyphosate is an herbicide, D-limonene is an insecticide. The two substances were chosen because of the (1) importance and authentic debate on glyphosate, and (2) for operating the chance to make the connection to authentic green chemistry research in the Brazilian context. It is suggested that independent from the different function of both substances’ general characteristics of conventional and green pesticides can be compared.

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