1.1. Pesticide Use and Impacts
Farmers around the world apply pesticides to mitigate the impacts of crop pests. Insects and fungi can cause crop damage that affects the farmers’ income [
1]. Several studies indicate that the behavior of farmers, external circumstances (i.e., political and economic issues) and technological factors (i.e., agricultural environment and equipment conditions) can influence pesticide usage [
2].
In 2008 the usage of pesticides was estimated at two million tonnes worldwide. The USA, Europe and the rest of the world consume 24%, 45% and 25% of the total amounts of pesticides, respectively [
3]. Global pesticide application has increased from 2.3 million tonnes of active ingredient, in 1990, to 4.1 million tonnes in 2016 [
4]. In the US, pesticide usage particularly organophosphates has decreased since 1992 by more than 40%, but the used pesticides have become more potent. At the same time, worldwide, pesticide (herbicides in particular) use seems to have an upward trend [
5]. Despite the doubling of Plant Protection Products (PPP) since 1980, their environmental impact is significantly reduced due to the use of more specialized PPPs and more advanced application technologies [
6]. According to the Food and Agriculture Organization (FAO), more than 500,000 tonnes of unused and obsolete pesticides need proper management.
When pesticides are used on crops, a considerable part of residues remaining in soil is absorbed by plants [
7]. Less than 0.1% of the pesticides applied on plants finally reach their target. Thus, a considerable amount of those potentially hazardous chemicals, are transferred to the environment where they can be a hazard to public health and to environmental compartments such as soil, surface, ground water and the atmosphere [
8].
Pesticides in the soil move through drainage, leaching or runoff, increasing the extent of pollution [
9]. The United Nations Environment Protection (UNEP) reports that 9 out of the 12 most persistent organic pollutants (POPs) are pesticides [
10].
The substantial use of pesticides causes severe negative environmental impacts [
1]. Health problems on farmers [
11], environmental deterioration [
12], resistance to pests [
13] and presence of residues on agricultural products [
14] are the most important of those impacts. Moreover, pesticides could be hazardous to birds, fish and non-harmful insects. Studies have reported that 76 pesticide residues are found in topsoil around Europe. Around 83% of the European soils contained one or more pesticide residues [
15]. Pesticides have been also found in surface water, rivers and lakes throughout Europe rendering them a threat to aquatic organisms [
16].
Humans are exposed to pesticides through different environmental pathways (soil, water, air and food). Pesticides can enter the body via inhalation, ingestion and skin contact causing serious deterioration to human health, such as diabetes, reproductive disorders, neurological dysfunction, cancer and respiratory disorders [
17]. There is a need to keep farmers aware of the safety measures to be employed during the use of pesticides. Environmental organizations, farmers and pesticide manufacturers must take initiatives to reduce the hazard of pesticides. At the same time, governments should apply stricter regulations for the efficient and targeted application of pesticides [
16].
Several review papers have investigated the associations between pesticide exposure and cancer risk [
18]. In 2012, 193,460 fatalities were recorded across the world due to pesticide poisoning. The International Code of Conduct on Pesticide Management (‘Code of Conduct’) provides best practices of pesticide use to decrease risks to human health and the environment [
4]. The FAO publishes manuals on how to prevent accumulation of the disposed pesticides and the resulting empty containers. It is costly to clean up obsolete pesticide disposal sites, as the management cost seems to range from USD 3 to 5 per kg or L of pesticide. Management methods include repackaging, transportation, incineration and landfilling [
19].
1.2. Wasted Plastic Pesticide Containers’ Management Worldwide
This work will focus on the plastic wasted pesticide containers, as this is the majority of the containers. According to the European Waste Catalogue (EWC), WPPC is a packaging waste and is listed as a hazardous waste that belongs to the 15 01 10* category, that is “packaging containing residues of or contaminated by hazardous substances”. An important source of polluted water with pesticides is the rinsate produced after cleaning empty pesticide containers. Therefore, a suitable treatment of the Wasted Plastic Pesticide Containers (WPPC) is necessary to prevent generation of such polluted wastewater. Reusing WPPC for domestic purposes has been identified as a health risk especially in developing countries. WPPC represent the end of the life cycle of agrochemicals and need to be well rinsed [
20] prior to treatment/disposal. However, farmers are often unwilling to clean and destroy empty containers, due to lack of knowledge. In addition, the uncontrolled disposal of the rinsate could be an additional environmental threat.
Farmers can return WPPC to chemical companies for reuse but this option does not appear to be financially feasible. Therefore, reuse of pesticides, high-temperature incineration, chemical treatment and landfilling are possible disposal methods according to the International Group of National Associations of Manufacturers of Agrochemical Products. As several pesticides are being either banned, withdrawn or restricted, container reuse seems to be unfeasible [
21]. At the same time, burning empty pesticide containers in open fires or dumping empty containers should be prohibited. On the other hand, safe incineration techniques and safe landfilling require adequate knowledge of pesticide chemistry and local hydrology, respectively [
22].
With regard to soils contaminated with pesticides, bioremediation seems to be the most efficient approach [
23]. A biological process to degrade pesticides and decontaminate empty pesticide containers could be a proper WPPC management method. In developing countries, farmers dispose of pesticide containers in water canals, streams or nearby vegetation. For example, a study in Pakistan reported that a great proportion of farmers (53%) disposed of WPPC into the environment uncontrollably. At the same time, 18% of those WPPC were reused for household purposes. Similarly, 44% of the farmers in Papua New Guinea dispose of WPPC into fields and bushes, 12% bury them in the ground, 9% discard them into streams, 9% burn them in open fires, 6% reuse them for home purposes and the rest reuse them for other purposes. A total of 14% of the farmers in Costa Rica and 19% in Uganda simply discard pesticide residues into rivers and reuse the WPPC to wash clothes, carry vegetables and even store water [
24]. East Africa Rift (EAR) zone countries, such as Ethiopia, Tanzania, Kenya, and Uganda, carry obsolete pesticides to Europe for incineration [
19]. In Ghana, 53% of the farmers burn WPPC, 25% bury them and the rest find alternative uses [
25]. In Greece, 30.2% of the farmers dump WPPC (and any residual remaining in the container) next to the crops, 33.3% dispose of them near or into irrigation canals and streams and 17.9% burn WPPC in open fires [
22]. Additionally, in some developing countries, empty WPPC may be used for storage of fuel or even food and water [
21].
Table 1 presents the different WPPC management practices in some countries.
Ineffective management for the disposal of obsolete pesticides has been reported in China, India [
26] and in most developing countries. Incineration seems to be the prevalent management option for disposal of obsolete pesticides [
27], but the releases of toxic chemicals such as hexachlorobenzene (HCB), dioxins and furans is detrimental to the environment. Cement kilns could be an environmentally sound alternative to controlled incineration for obsolete pesticides in developing countries [
28]. According to the WHO and the Food and Agriculture Organization (FAO), the most appropriate management method would be to return WPPC back to the manufacturer for destruction through high-temperature incineration [
24]. In Ethiopia, 1000 tonnes of obsolete pesticides, including WPPC, have been transported over the period 2006–2007 to incineration facilities in England and Germany [
29].
The efficiency of the management system of WPPC depends on training, control and traceability [
30]. As technologies for waste management are improving, it is necessary to assess the most optimal forms of treatment of WPPC [
31]. The European Crop Protection Agency has proposed triple rinsing of WPPC as a special waste management practice prior to container treatment and disposal. It is a simple and effective method and aims to keep the contents of the active substance of the residual liquid in the container below the threshold limits. The contaminated rinsate is returned back to the spraying tank and is applied again on the crops. WPPC that contains residual pesticide with a very toxic active substance at a concentration higher than 0.1% of its total weight (residual liquid + container), then it is listed as a hazardous waste [
32]. If low levels of the active substance of the pesticide are achieved after triple rinsing, then the WPPC would likely belong to the 15 01 02 (plastic packaging) category of the European Waste Catalogue.
A large number of methods and tools for assessing environmental impacts have been developed. Life cycle assessment (LCA) started to be applied on waste around 1990 [
33]. LCA investigates the environmental aspects and potential impacts throughout a product’s life (i.e., from cradle to grave) [
34]. LCA is widely used as a decision support tool (DST) for effective waste management aiding to find the most appropriate alternative waste management methods [
35]. A reliable LCA can be performed only when system boundaries and inventory data are well understood and acquired. For a successful implementation of the LCA models, accurate inventory data (ideally local data) and system boundaries must always be carefully considered [
31].
For example, LCA was used as a decision support tool in the State of Rio de Janeiro to evaluate the management of lubricating oil plastic containers, comparing recycling to incineration with energy generation (waste-to-energy). Incineration is a treatment widely used in many countries, as an alternative management to landfilling [
36].
The chemical residuals contained in empty WPPC is a necessary knowledge when performing LCAs. Such information does not exist in the international literature and for this reason residual analyses were performed here to determine the remaining pesticide residues in the rinsed WPPC [
37]. This analytical methodology could be employed in routine analysis, thus supporting a proper evaluation of the agricultural solid waste according to EU regulations.