Management of toxic waste released by incorrectly discarded batteries in Brazil

1 Introduction

In Brazil, about three billion units of batteries are produced annually for domestic use. According to the Brazilian Association of Electrical and Electronics Industry (ABINEE) (2006), 800 million batteries are produced in the country, of which 70 % are dry cell batteries, or zinc–carbon, and the other 30 % are alkaline batteries.

Batteries are sources of electric power that work through a spontaneous oxidation-reduction reaction, or redox reaction, responsible for generating the electric current. They are composed of two electrodes, positive and negative, and by an electrolyte, an ionic conductor that surrounds the electrodes (Bocchi et al., 2000).

The main difference between a dry cell battery and an alkaline one is the composition of the electrolyte. In zinc–carbon batteries, the electrolyte is a paste formed by mixing ammonium chloride and zinc chloride, while in alkaline batteries, the electrolyte is an aqueous solution of concentrated potassium hydroxide containing a certain amount of zinc oxide, hence the name alkaline for this battery (Agourakis et al., 2006).

Batteries are considered electronic waste. “Waste from Electrical and Electronic Equipment (WEEE), or simply electronic waste, are terms used to designate all electrical and electronic equipment when their parts and accessories have been discarded with no intention of reusing them.” (Ecycle, 2022)

Duracell, one of the manufacturers of batteries in Brazil, states that, “Duracell is committed to technologies that provide more energy and are less dangerous than regular zinc–carbon batteries.” (Duracell). However, they are only truly safe as long as their internal materials are protected and contained in the casing. With the activity of external factors (corrosion, degradation, oxidation), this casing can be damaged, resulting in the leak of potentially toxic materials into the environment.

Leaching is portrayed as being “the extraction or solubilization of the chemical elements of a rock, mineral, soil or sedimentary deposit by the action of a percolating fluid”. In other words, it is related to the entrainment process of the mineral salts present in the soil. In general, it occurs in soils without the coverage of vegetation, such as landfills, and leads to a decrease in its natural fertility over time (Azevedo, 2022).

Batteries are constituted of numerous substances, and, among them, it is possible to find potentially toxic metals such as zinc, manganese, lead, mercury, cadmium, nickel, copper, and chromium, which can be present either as impurities or as additives to improve the efficiency of batteries. Some of these metals have been highlighted by EUCHEMS, as well as other organizations, as scarce elements with growing threats due to their increased use (EuChemS Periodic Table, 2023). Besides, even after a battery is exhausted, it can still contain 30 % zinc (Zn) in its composition, showing that the redox reaction does not occur completely (Vatistas et al., 2001).

2 Objectives

This project was designed by students in their 2nd year of High School (aged 16–17 years old), with the goal of participating at the Olimpíada Estadual de Química de São Paulo [State Chemistry Olympiad of São Paulo] – in which the group was among the 150 winners and moved on to the second phase of the Olympiad.

After observing and analyzing the problem of the incorrect disposal of batteries, and the understanding that they contain potentially toxic substances, the following questions regarding the topic comes to mind: The incorrect disposal of batteries can origin the rupture of their casing, thus making their chemical substances leak into the environment? If so, how? What factors can cause this rupture? And finally, how are these substances capable of impacting the ecosystem and living beings that come into contact with them?

From these questions, added to general knowledge acquired in class, the students arrived at the following hypotheses: if the batteries are disposed of incorrectly, in regular garbage bins, their destination will be a landfill where they will be subjected to mechanical impacts, and especially to the action of external agents such as rain. The oxidation of the casing can then occur from rainwater – possibly acidic due to pollution of urban areas – thus causing the rupture of the battery. And as for the substances coming into contact with the environment and living beings, they will impact the proper functioning of their health.

3 Materials and methods

The following materials were used for this experiment: Three beakers, four zinc-carbon batteries, coarse and fine sand, fertilized soil, rainwater, a Pasteur pipette, & an acid-base indicator.

In order to simulate the terrain of a landfill, fertilized soil was used in the first beaker with a weight equivalent to 514 g, while in the second and third beakers were placed, respectively, fine sand with a weight of 835 g, and coarse sand (more porous than fine sand) with a weight of 1026 g. To present a clearer visualization of possible substances leaked from the batteries, all weight measurements account only the weight of the soils, disregarding the weight of the beakers. Two batteries were placed in the beaker with fertilized soil and one in each of the other two beakers, with sand, totaling four batteries, with an approximate weight of 16.7 g. Then, a Pasteur pipette, with a total capacity of 3 ml, was used to drip rainwater onto the batteries, previously collected by the students in an urban area of the city, to simulate a situation closer to reality. To replicate a day-to-day basis in the region of Sorocaba, São Paulo, the rainwater was dripped according to the days with rain in that month, so the experiment could resemble the natural environment in that region.

The pH level of the fertilized soil was measured before the addition of the batteries and at the end of the experiment, as well as the pH level of the rainwater. In all, the experiment was carried out for about 30 days, requiring it to be monitored weekly to observe the leaking of waste.

4 Results and discussions

Initially, the pH level of rainwater was read between 5.0 and 6.0, that is, being slightly acidic, since rainwater contains chemical substances derived from the pollution of burning fuels, generated by automobiles and industries. Among the main substances that cause this change in pH levels is sulfuric acid (H₂SO₄), which is formed when sulfur dioxide (SO₂), released by industries, comes into contact with water vapor in the clouds (Sousa, 2022). Presenting a more acidic pH, its corrosive potential is also higher. Over time, it was possible to notice the oxidation of the batteries along with dark and orange-colored substances, especially in the beakers with sandy soils. It is possible to observe such findings as shown in Figure 1.

Figure 1:

Rusty battery in soil. Note. Photo taken by students themselves.

At the end of the experiment, the pH of the fertilized soil, the main target of the study, was measured and compared with its pH level from the beginning of the experiment. The change was from the initial value of approximately 6.0 to a more basic pH level, between 7.0 and 8.0, which also differs from the acidic pH of the rainwater used.

After a few simulations of rain on the samples, it was observed that by dripping water from a certain height using the Pasteur pipette, the sandy soils eroded and buried the batteries, which, in an external natural environment, hinders the ability to locate the discarded batteries, also preventing a possible collection of them from the environment. In addition, the beakers with sandy soils also presented, as expected, more noticeable results of battery oxidation. After a few days of the batteries’ regular exposure to rainwater, it was possible to note a faster oxidation reaction around the casing, especially at their terminals. In many cases, the theory and underlying electrochemical principles of batteries is all that students learn about in their curriculum.

Although the oxidation process was gradual, it occurred relatively quickly due to the slightly acidic pH of the rainwater, indicating that it would not take long for the casing to degrade and release the toxic zinc and manganese compounds into the environment. The degradation due oxidation of its casing can also ease the external interference for the rupture of the battery. It should be considered that, in a landfill, the battery may undergo physical interference due to the accumulation of garbage on it and/or due to a garbage compressor, resulting in the rupture of its body.

Regular dry cell batteries are composed of zinc, carbon, and manganese dioxide. These elements tend to have higher pH values (basic) at the upper parts of the soil in certain preparation systems (Teixeira et al., 2003). This explains the fact that the pH level of the fertilized soil was identified as being more basic than normal. It is worth mentioning that all the tests performed were qualitative, and that the pH levels of rainwater can vary between regions, as it is affected by different factors.

Regarding the harm caused to the ecosystem and living beings that may come into contact with these substances from the batteries, it has been found, through studies and research, that this is a matter to be taken seriously because there is a diversity of risks to health. Starting from the fact that just one battery can contaminate about 1 m² of area with its toxic waste, getting larger according to the number of batteries in the area. In addition, these residues can contaminate the local flora and reach the groundwater, contaminating the water that living beings, including humans, can ingest (Roa et al., 2009). All the experiments carried out by the students, as described in this article, can help students introduce concepts of environmental, sustainable and green chemistry (Celestino, 2023).

Among the health problems that can be affected to humans by ingestion of zinc–carbon battery materials are, for high amounts of zinc (Zn): hematological changes, lesions on the lungs and respiratory system, gastrointestinal disorders, and pancreatic lesions; And for high amounts of manganese (Mn): brain and neurological system dysfunction, and renal, hepatic, respiratory and teratogenic dysfunctions (Ribeiro et al., 2022).

What is more, not only harm to the life of living beings and the ecosystem, but the improper disposal of batteries may even develop considerable economic problems. According to GM&C’s institutional relations coordinator, Henrique Mendesma, this company from São José dos Campos, SP, recycled about 6 thousand tons of electronic waste and created about 140 direct jobs and another 380 indirect jobs in 2022 alone. However, according to data from the United Nations (2022), about 3 % of all electronic waste in Latin America was in fact officially recycled in 2019. Then, looking at Brazil, it could reach a figure of at least R$ 800 million to R$ 8 billion, creating about 42 thousand direct jobs and another 110 thousand indirect jobs. Currently, being part of the current 3 % of the continent, Brazil generates around R$ 24 million to R$ 240 million (Agência Paulista de Promoção de Investimentos e Competitividade 2023).

Regarding its educational purposes, this project proved to be practical and easy to reproduce, so that students can observe concepts that are normally seen only theoretically in the classroom, providing an environment of creativity and scientific research since it is necessary active participation from students, both in research and monitoring the tests, allowing greater autonomy from students, as well as an active role inside the classroom. In general, teacher and students agree that this practical activity brought results beyond the expected, since the students were really interested in the topic and its investigation, favoring satisfactory results.

It is therefore necessary to have multidisciplinary knowledge on the subject of e-waste, since it has different compositions and properties, so that this problem can be tackled properly in different regions of Brazil and the world (IUPAC|International Union of Pure and Applied Chemistry).

5 Conclusions

The conclusion of the experiment is that batteries, having their degradation due to oxidation by contact with acidic rainwater, released a relative amount of their internal chemical composition of zinc, carbon, and manganese oxide into the soils in each beaker, indicated by the change of the pH levels of the fertilized soil to basic, despite acidic interference from rainwater.

Given all the information previously provided about the harmful power of toxic materials present in batteries and the experiment carried out to prove the rapid degradation of batteries, culminating in the leaching of these materials into the environment when they are disposed of inappropriately, the ideal way to discard these materials will be pointed out, aiming at the preservation of the environment and human health. After use, batteries are electronic waste and, as other types of waste of the same classification, can be recycled and have their materials reused by their manufacturers, since, as provided by Brazilian legislation, companies must have extraction points for customers to properly discard their products, that is, a reverse logistics (Art. 33 da Lei n.12.305, de 2 de agosto de 2010, 2020). In addition, by correctly discarding batteries, the revenue it can generate for the country is considerably high, creating many direct and indirect jobs that would help Brazilian families who work in the sector to have more income and jobs where work is just – factors that considerably improve the country’s human and economic development.

Batteries should not be disposed of in regular organic bins, as they will be sent to landfills, polluting the soil. However, they should also not be disposed of in the common recyclable bins (for paper, plastic, metal, and others) because, as electronic waste, they must be separated and sealed with resistant material, so as not to have contact with moisture and avoid leaks, and then be taken to an electronic waste recycling plant or even electronics stores, so that they are sent through reverse logistics. Only back to the manufacturers to be recycled properly and reduce the leaching of these materials, consequently mitigating risks to the ecosystem and public health (Ecycle, 2022).