Consequences of the incorrect disposal of electronic waste when growing flower seedlings

1 Introduction

The consumption of portable electronic devices has increased in the last decades, causing a gradual increase in demand and use of batteries (Aumento do Lixo Eletrônico Afeta Saúde de Milhões de Crianças, Alerta OMS, 2021). Due to its large consumption, it is imperative to pay attention to its disposal methods because if inadequate, it leads to the release of chemical substances containing potentially toxic metals such as zinc, manganese, lead, mercury, cadmium, nickel, lithium, copper and chromium, causing environmental problems as well as damage to living beings. It is important to bear in mind that a battery, even after its exhaustion, can still contain 30 % zinc (Zn) in its composition (Vatistas et al., 2001).

The problem is that when they are discarded and the capsule that envelops them suffers deformations (by being kneaded or bloated) they may leak a toxic liquid from their interior. This liquid accumulates in nature and represents one of many non-biodegradable wastes, not being decomposed or dissolved naturally over time. The contamination reaches the soil and over time the groundwater, damaging agriculture and affecting potable water. A battery, when discarded inadequately, can contaminate the equivalent of twenty thousand liters of water, causing harm to human health such as kidney and neurological disorders, genetic mutations, changes in metabolism, damage to the nervous system, cancer, memory loss, insomnia, vomiting, among many other complications (Varejão, 2014).

Due to the serious damage that can be caused, the disposal of these materials cannot be done in regular trash bins or containers. There are laws nowadays that bind manufacturers to receive their batteries back and thus dispose of them properly. It would be ideal if all companies also added clear warnings to product packaging, informing possible risks caused by incorrect disposal of this material (Carvalho et al., 2019).

With the expansion of the electronics market and easy access to these devices for the population, more and more electronic waste will be produced in the coming years. On the other hand, the electronics recycling market is a very productive branch in expansion, and it is proving to be very profitable. Batteries are discarded, commercially, having their metals burned in high temperature industrial furnaces, equipped with filters that prevent the emission of polluting gases. With this process, salts and metal oxides are obtained, which are used in industrial refractory, glass, paints, ceramics, and chemistry in general, without risk to people or the environment (Schneider, 2009).

The ideal option is undoubtedly the use of rechargeable batteries. In Brazil, they still occupy a small niche, no more than 5% of the market. They are more expensive than ordinary ones, but their lifespan is much longer, meaning that they can be reused hundreds of times, and they are more environmentally friendly (Varejão, 2014).

Batteries are devices that work by a spontaneous oxidation-reduction reaction, or redox reaction, which is responsible for generating its electric current (Bocchi et al., 2000). One of the most used batteries is alkaline, and the main difference between a common battery and an alkaline one is the composition of the electrolyte. In alkaline batteries the electrolyte is a concentrated aqueous solution of potassium hydroxide containing a certain amount of zinc oxide, hence the denomination alkaline. According to reaction (1), an alkaline battery has metallic zinc and manganese dioxide, as well as a basic substance such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). The redox reaction occurs in a way that zinc (Zn) is oxidized, and manganese (Mn) is reduced. Therefore, Zn is the reducing agent, losing electrons, and MnO₂ is the oxidizing agent, gaining electrons (Matsubara et al., 2007).

Therefore, it is important to highlight that the material used throughout the research process of this work were alkaline batteries, since they are easier to access and commonly used.

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]. With that in mind, to demonstrate what can be inflicted to the environment by the improper disposal and recycling of batteries, microcosm tests were carried out to investigate the damage that a discarded battery would cause to the soil and plants.

3 Materials and methods

The following materials were used for this experiment: two alkaline batteries; two plant seedlings of the same species; two beakers; 300 ml of rainwater; & a pH indicator.

Two calandiva plants, or Widow’s-thrill, were used, which were replanted in two separate beakers each. Then, two alkaline batteries (one Panasonic and one Rayovac) were placed in one of the beakers only, while the other had only the plant for the purpose of comparison with the first plant exposed to the batteries. It is worth mentioning that the selected batteries already had been used for a certain amount of time prior to the experiment. This species of plant, the calandiva, required it to be watered once a week. Using the rainwater previously collected by the students, both plants were watered over the course of one month, and the whole process was photographed to observe the gradual difference between the beakers.

4 Results and discussion

In the first week of the experiment, the plants did not show signs of any relevant differences. However, from the last week on, changes became noticeable on the plant in the beaker with batteries, since it began to wither faster and the flowers to die; whereas the other plant, with no batteries, managed to maintain its initial appearance. This result could be due to batteries degradation due to contact with soil and water or to an interference between batteries and soil and affect the plants negatively. Figure 1 shows the degradation process of the plant over the one month.

Figure 1:

Plants with batteries, in the first week and last week of the experiment. Note: Photo taken by students themselves.

There are several possible reasons for damage to plants, such as the leaching of substances from batteries, the occurrence of weak currents, are some factors that may have contributed to this result. Subsequently, the pH of the soil was measured, which presented a value between 7 and 8, thus having slightly basic characteristics. The soil without batteries kept its slightly acidic pH level, probably because of the rainwater, which is already slightly acidic due to pollution nowadays. On the other hand, the soil exposed to the batteries had a considerable increase in pH, that was probably because the batteries were alkaline. This increase was only not greater because of the short period of time in contact with the batteries and some of its basic characteristics must have been neutralized by the acidity of the rainwater. It is worth remembering that pH tests were not carried out using technological equipment, but only using a universal pH indicator, but as future analysis more precise measurements can be carried out, as well as analysis of substances present in the soil and in the plant, before and after the experiment.

The solubility of potentially toxic metals is determined primarily by the physical and chemical characteristics of the soil properties. Among soil properties, pH is one of the most influential parameters in metal adsorption and desorption. In general, the neutral and slightly alkaline pH favors the adsorption of metals in the soil (Antonio Augusto Soares Paulino, 2018).

According to studies (Minerals and Agriculture GmbH – Bertha-von-Suttner-Str), plants absorb zinc more intensely in basic soils than in acidic soils. As previously stated, the soil analyzed presented slightly basic characteristics, therefore, the absorption of zinc is expected to be more intense. Zinc toxicity causes the inhibition of root development and chlorosis in younger leaves, as well as induces iron deficiency. As zinc is a component of a variety of enzymes, it affects many metabolic processes of the plant (Minerals and Agriculture GmbH – Bertha-von-Suttner-Str). It’s also worth noting that although zinc can harm plant growth when absorbed, Zn and Mn are necessary elements for plant growth, but not as Zn²⁺ ion as released by batteries, the way they are found in batteries. In fact, a Finnish industry recovers Zn and Mn from alkaline batteries to be used as fertilizer for the soil. Again, as the battery is treated and these materials are separated beforehand, the way they are used to fertilize the soil may have different results to those observed (TRACEGROW grow with us). This initiative serves as an example and inspiration for a good disposal and use of electronic waste.

It should be noted that all tests performed were qualitative, and that the rainwater pH levels may vary from region to region, as it is influenced by different factors. It is worth remembering that one of the biggest challenges of this work was in relation to time, since the degradation time of a stack is slow. Another aspect that would be interesting, would be to carry out an analysis of soil and plant and also detect if some metals were released from batteries. The analysis of these factors only exalts the importance of discarding this type of material appropriately. It also demonstrated that with easily accessible materials it is possible to carry out significant experiments and understand, in a practical and visual way, the impact that the improper disposal of batteries can cause over the years to the environment and, consequently, to human health. Experiments undertaken and led by students as described in this current article can help introduce students to the concepts of environmental, sustainable and green chemistry (Celestino, 2023).

5 Conclusions

Taking into consideration everything that has been discussed so far, it is possible to conclude how beneficial recycling these materials is, since they have chemical properties and components that need special attention when disposing of them. In addition, from the experiments, it was possible to identify in a short period of time that the soil and the plant were contaminated by the presence of batteries. The tests were carried out in a controlled environment, but the objective is to highlight that in a landfill the number of discarded batteries will be much greater, posing risks not only to the soil and plants, but also to groundwater, highlighting once again the importance of adequate disposal and recycling of these materials.