Hazardous Pesticide Contamination in Soils

Primary reference(s)

FAO, 2000. Assessing Soil Contamination: A reference manual. FAO Pesticide Disposal Series 8. Food and Agriculture Organization of the United Nations (FAO). Accessed 29 October 2020.

Additional scientific description

Human activities over thousands of years have left a legacy of polluted soils worldwide. Much of it is local soil contamination, which frequently occurs in connection with past and present industrial activities, waste management and disposal, including remnants of hazardous materials such as obsolete pesticides. The unsustainable application of pesticides in agricultural fields has also contributed to the spread of diffuse pollution in many areas (FAO, 2018).

Half a million tonnes of obsolete pesticides are scattered throughout the developing world. These toxic chemicals, often stored outdoors in leaking containers, are seeping into the soil and water. Eliminating these dangerous stocks is a development priority. Rural communities cannot hope to develop if the soil and water are contaminated with pesticides. People cannot hope to prosper if they are suffering from severe illnesses caused by pesticide poisoning. The Food and Agriculture Organization of the United Nations (FAO) Programme on the Prevention and Disposal of Obsolete Pesticides is working to inform the world about the dangers of obsolete pesticide stocks. It collaborates with developing countries to prevent more obsolete pesticides from accumulating and assists them in disposing of their existing stockpiles (FAO, no date a).

Obsolete pesticides include insecticides, fungicides, herbicides, larvicides, acaricides, rodenticides, molluscides, nematocides, and aphicides. Around a thousand active ingredients are used to manufacture the wide array of pesticides in countries all over the world. Pesticide ingredients come in many thousands of different formulations. All these formulations degrade over time although some are more persistent in the environment than others. The chemical by-products that form as the pesticide deteriorates can be more toxic than the original product (FAO, no date b).

Once pesticides enter soil, their fate depends on the physico-chemical characteristics of the soil, such as moisture, texture, and soil organic matter content, as well as the pesticide properties. A relatively small amount of spilled pesticides can therefore create a much larger volume of polluted soil. For example, approximately 30 tonnes of pesticides buried at a site in Yemen in the 1980s contaminated over 1500 tonnes of soil. This can pose a serious health and environmental threat to nearby communities (FAO, no date c).

Every site is different. First, the extent of the contamination and the impact on the local environment must be determined. This requires an understanding of the chemical properties of the pesticides and the characteristics of the soil. Often the quantity of pesticides is unknown, and soil samples must be analysed. Depending on the results of the chemical analysis and risk assessment, there are three ways of dealing with polluted soil and water: (i) removing the contamination by excavating the soil and pumping-up of groundwater; (ii) containing the contamination by covering polluted soil with buildings, asphalt or another impermeable layer, and preventing contaminated groundwater from flowing downstream; and (iii) preventing human contact with the contamination by covering the polluted soil with clean soil, fencing-off polluted areas and closing contaminated wells (FAO, no date c).

Removing pollution is more expensive than containing it, which in turn is more expensive than taking protective measures. Additionally, excavated polluted soil represents a hazardous waste that needs to be properly managed to avoid the pollution being transferred to other areas. Containment and protective measures are effective only for as long as they are maintained, and their proper maintenance may be difficult to ensure over a long period of time (FAO, no date c).

The FAO has published a reference manual for assessing soil contamination to help developing countries make sound decisions about how to deal with the problem in the most cost-effective manner. The FAO is also working to develop cost-effective methods for dealing with pesticide contaminated soil in developing countries (FAO, 2000).

Wherever pesticides are used, there are discarded pesticide containers. These old containers can be as dangerous as the pesticides themselves. In developing countries, they are often used to store food or water. The FAO’s Programme on the Prevention and Disposal of Obsolete Pesticides assists developing countries in dealing with these toxic containers (FAO, no date c).

Despite the identification efforts conducted in many regions of the world to estimate the extent of soil pollution, the lack of a global assessment presents an obstacle to the mobilisation of economic resources to minimise soil pollution and to achieving public and private commitment to combating soil pollution. Stronger linkages between scientific evidence and decision-making processes are required to support actions to prevent, control and remediate soil pollution (FAO, 2018).

Contaminated land is assessed in the context of national or state methods for deriving soil guidance values. There is no international standard. For example, Jennings (2013) compared the range of American standards with standards used elsewhere in the world. 5949 guidance values for 57 elements were identified across the US regulatory authorities and it was established that guidance values have also been published in at least 71 other United Nations member states.

Metrics and numeric limits

No globally agreed metrics have been identified.

Examples of drivers, outcomes and risk management

The roles of soils in food production and food quality, in climate regulation and in the provision of raw materials and services is vital. Notwithstanding the enormous scientific progress made to date, protection and monitoring of soil condition at national and global levels still face complex challenges impeding effective on-the-ground policy design and decision making (FAO, 2018).

The FAO has prepared a manual on assessing soil contamination which focuses on pesticide disposal. It aims to help the user determine if pesticide spills have caused soil or groundwater contamination and, if so, whether or not that contamination implies risks for human health (FAO, 2000). Not every spill of pesticides implies health risks. Some important factors determining the risks of a spill are: (i) the characteristics of the stored pesticides; some pesticides are more toxic than others, some degrade rapidly into harmless compounds, while others are more persistent; (ii) how much of a pesticide has been spilled and for how long the spillage has been occurring. It takes time for contamination to reach the high levels at which health risks may occur; and (iii) the physico-chemical characteristics of the soil matrix, such as the type and content of clay, the content of soil organic matter, the soil moisture, or the diversity of soil microorganisms, which are involved in the degradation of pesticides and their by-products. Taking these and other relevant aspects into account, this manual provides users with a simple method for reaching three conclusions: whether it is likely that the soil or groundwater in the surroundings of the storage facility are contaminated; whether such a possible contamination is a risk for human health; and what measures can be taken to reduce these risks (FAO, 2000).

As an example of the FAO programme on hazardous pesticide contamination in soils, they reported that large amounts of pesticides were shipped to Africa for desert locust control from the 1950s, but some did not arrive at the correct site or time, and so became obsolete. Stockpiles of these pesticides have created a serious problem. A site-specific remediation plan was developed for each location on the basis of analytical data and environmental surveys. Remediation typically involved the addition of organic matter and land-farming to enhance local biodegradation of pesticides. In cases where a high environmental risk existed and the contaminants were considered too persistent to be left in situ, the contaminated soil was isolated in treatment cells.

The principle of all treatments was to facilitate and, where possible accelerate the natural degradation of the pesticides in the soil. In the case of organophosphate and carbamate insecticides, this has been very successful. However, organochlorine insecticides are persistent and degrade very slowly. Where these are present in high concentrations and pose a high risk, the soil has been isolated, adsorbent carbon barriers (made from local activated charcoal) have been used and in some low risk cases, the soil has been left in place. All sites were regularly monitored and encouraging results have been obtained (FAO, no date d).

Remediation of polluted soils is essential, and research continues to develop novel, science-based remediation methods. Increasingly expensive physical remediation methods such as chemical inactivation or sequestration in landfills are being replaced by science-based biological methods such as enhanced microbial degradation or phytoremediation (Rodríguez-Eugenio et al., 2018). Maintenance of soil health and the prevention and reduction of soil pollution are possible through promoting sustainable soil management practices, environmentally friendly industrial processes, reduction of waste generation, recycling and reuse of goods, and sustainable waste storage (FAO, 2018).

A key outcome of the global symposium on soil pollution Be The Solution To Soil Pollution (FAO, 2018) was a recommendation for the active and effective implementation of the Voluntary Guidelines for Sustainable Soil Management, which were developed through an inclusive process and endorsed by the 155th session of the FAO Council (Rome, 5 December 2016). Their implementation is important in order to progress with the accomplishment of several of the sustainable soil management objectives, such as: to ensure that the availability and flows of nutrients are appropriate to maintain or improve soil fertility and productivity, and to reduce their losses to the environment; to reduce soil salinisation, sodification and alkalinisation; to ensure that water is efficiently infiltrated and stored to meet the requirements of plants and ensure the drainage of any excess; to ensure that contaminants are below toxic levels, i.e., those which would cause harm to plants, animals, humans and the environment; to guarantee that soil biodiversity provides a full range of biological functions; and to undertake soil management (FAO, 2018).