Chapter 12. Status of soil pollution in sub-Saharan Africa
Spatial distribution of soil pollution in sub-Saharan Africa
In order to identify critical areas that may be polluted with contaminants that represent a high risk to human health, international organizations have assisted countries to identify stockpiles of persistent organic pollutants and obsolete pesticide. Through its Toxic Sites Investigation Programme (TSIP), Pure Earth has created a database of polluted sites including some in sub-Saharan Africa.1 South Africa and Nigeria have national initiatives for monitoring soil. Both of these systems largely depend on voluntary reporting. The Nigerian system has been created for spill reports specifically related to the oil industry while that for South Africa covers all activities that can be sources of a specific list of contaminants. These initiatives are discussed in further detail in section 12.3.3. As there is not a harmonized soil pollution monitoring system available for the region or for the different sub-regions, this section discusses examples of different approaches to the issue. In the region, land is often considered the same as soil and therefore land contamination will be discussed under the concept of soil pollution.
12.3.1. Soil pollution caused by trace elements
In sub-Saharan Africa, the most widely reported group of soil pollutants in published scientific literature, are trace elements. In contrast to this, there are currently no databases, maps or reports available on the extent of trace metal pollution across the region. It has been stated that, globally, artisanal and small-scale mining (ASM) is the largest emitter of mercury with estimated annual emissions of 1 400 tonnes. Annual emissions from this sector in Burkina Faso are estimated at 35 tonnes (Fritz et al., 2018). Pure Earth’s TSIP database includes 75 sites in sub-Saharan Africa that have been registered as being polluted by mercury (Fritz et al., 2018). It is estimated that these sites adversely impact 2.4 million people.
Although mining is a major source of trace element contamination in the region, several other activities are also responsible for the presence of elevated trace element concentrations in soil. These activities include the region’s rapid urbanization that is accompanied by industrialization and ineffective solid waste management (Yabe, Ishizuka and Umemura, 2010). Other regional activities that are sources of soil pollution by trace elements are the recycling of e-waste (Daum, Stoler and Grant, 2017), and the use in agriculture of manure (Malan et al., 2015) and wastewater irrigation (Mapanda et al., 2005). These activities are often present in very close proximity to each other and this increases the complexity of determining a source-receptor pathway in soil pollution studies.
There are also other challenges to reporting and monitoring the extent of trace elements pollution in soil. This includes the consideration of the fractionation of trace elements to determine exposure risk as large fractions of the total concentrations are immobile. It is also complicated by the presence of high natural background concentrations of trace elements in countries such as South Africa (Davies and Mundalamo, 2010; Elsenbroek and Neser, 2002) and the Santiago island of Cabo Verde (Cabral Pinto et al., 2015).
Pure Earth’s TSIP has assessed sites for soil pollution mainly from point sources in low- and middle-income countries since 2009. It verifies the pollution status of suspected areas by using either portable x-ray fluorescence spectroscopy equipment (XRF) or the laboratory analysis of soil samples. In order to be more effective in the widespread detection of soil pollution, the programme trains local partners to assist the organization with site assessments.
Through the TSIP, Pure Earth has already identified sites in sub-Saharan Africa that are polluted with trace elements. These include arsenic, cadmium, chromium (both hexavalent and total), lead, mercury and uranium (Pure Earth, 2019b). Sites with toxic lead concentrations are the most prevalent of the trace element polluted sites. Countries where lead pollution has been detected by the TSIP includes Ghana, Kenya, Madagascar, Nigeria, Rwanda, Senegal, Uganda and the United Republic of Tanzania. The high lead concentrations in soil originate from a wide range of activities. These activities include lead battery recycling, transport, weapons manufacturing, tanneries, wastewater treatment plants, power plants that use coal or oil, mining and ore processing, smelters, vehicle repair workshops and medical waste.
Soil pollution with arsenic has been identified on sites in Ghana, Kenya, Senegal and the United Republic of Tanzania. The activities responsible for the pollution includes tannery operations, ship-breaking, e-waste recycling, industrial and municipal waste sites, artisanal and small-scale mining and agriculture. An area in the northern province of Yatenga and Lorum in Burkina Faso has naturally high levels of arsenic that are toxic to human health.
Sites polluted with elemental mercury have been identified in seven countries in the region: Ghana, Guinea, Kenya, Mozambique, Senegal, Uganda and the United Republic of Tanzania. The sources of this pollution include mining and ore processing as well as artisanal and small-scale mining, industrial and municipal dumpsites.
Soil polluted with cadmium has been identified in areas in Ghana, Kenya, Nigeria, Rwanda, Senegal, South Africa, Togo, the United Republic of Tanzania and Zimbabwe. The sources have been identified as agriculture, e-waste recycling, transport, industrial facilities and waste sites. Sites that have been identified as being polluted with other trace elements include: in Niger, soil pollution with uranium from mining and ore processing; in both Madagascar and Zimbabwe tanning activities have caused pollution with hexavalent chromium.
12.3.2. Soil pollution caused by pesticides and organic contaminants
Through the commitments indicated in Article 7 of the Stockholm Convention, each of the Parties is obliged to submit a National Implementation Plan (NIP) that includes inventories of the POPs present in their country. The Stockholm Convention’s official website indicates that NIPs have been submitted by 45 of the 48 countries and makes them available for download (Stockholm Convention, 2019). The inventories of POPs were largely based on the scrutiny of records to identify the presence of old transformers, capacitors and pesticides. In most cases these were corroborated with some form of physical inventory. Where soil polluted with POPs was identified, it was noted in the NIP but generally there was no comprehensive assessment of soil polluted by POPs. The continued use and storage of POPs chemicals or equipment containing POPs poses a risk of leakage and subsequent soil pollution.
An example of the details submitted as part of the NIPs, is the National Implementation Plan for the Stockholm Convention on Persistent Organic Pollutants for Zimbabwe submitted in April 2013 (Government of Zimbabwe, 2013). The strategy used included the sampling of oil from 505 transformers of which 39 samples contained PCB. It further indicated that decommissioned capacitors and transformers are stored inappropriately and cause soil pollution through leakage. The theft of transformer oil and its subsequent sale for use in welding machines or as cooking oil has been reported in the Zimbabwean NIP. Other African countries have submitted similar National Implementation Plans including POPs inventories and action plans to address the different POPs groups.
Recent reviews of the contamination by and exposure to PCDD/PCDF in Africa showed that only a handful of studies have evaluated the pollution of environmental matrices with PCDD/Fs and dl-PCBs (Pius et al., 2019; Ssebugere et al., 2019). Sources of these organic contaminants were identified as obsolete pesticides in the United Republic of Tanzania and burning of wastes at dumpsites in Senegal, Ghana and Kenya as well as industrial areas and human settlements in South Africa. The dry cleaning industry can pose a risk for soil pollution from perchloroethene if unwanted chemicals and wastes from the process are disposed of inappropriately. Although there is no production of organochlorine chemicals in Africa, there are sites that are currently or were previously used for the formulation of pesticides. These sites, as well as any sites that were used for the landfill of wastes that originated from them should be considered to be potentially polluted with pesticides and by-products such as PCDD/PCDFs.
The World Bank has reported that in 2013, approximately 50 000 tonnes of obsolete pesticides have been identified across the African continent (World Bank Group, 2020). The extent of pesticide pollution in Africa, including those classified as POPs, was determined by 2010 under the Africa Stockpiles Programme (FAO, 2020). With funding from the Global Environment Facility’s (GEF) POPs programme, bilateral trust funds, FAO, UNEP and CropLife International, most countries in the region have implemented projects that have eliminated the historic stocks of POPS and other obsolete pesticides. The projects have generally included components that strengthen capacity in sound pesticide management and sustainable agricultural practice that reduces reliance on pesticides. As the mandate of the GEF is to support the elimination of POPs, the funding was focused on the elimination of the pesticides themselves rather than other polluted media. Exceptionally, as there was evidence of grossly polluted soil, the projects in Botswana and Mozambique included components for its remediation.
Unfortunately, some countries continue to accumulate obsolete pesticides. This is largely as a consequence of weaknesses in regulation and enforcement capacity, needs assessments, procurement practices, and stock management. The new obsolete pesticides are generally less toxic and less persistent, but still pose a pollution risk to soils through leakage and inappropriate disposal.
Soil polluted with pesticides have also been identified by the TSIP (Pure Earth, 2019b). The countries where these sites have been identified are Benin, Cameroon, Ethiopia, Ghana, Kenya, Senegal, Somalia and the United Republic of Tanzania. The main pesticides as well as the estimated number of people that may have been exposed to health risks as a result of this pollution, are presented in Table 1.
Table 1. Pesticide contamination and the estimated number of people at exposure risk (data source: Pure Earth, 2019b)
12.3.3. Soil pollution monitoring: the example of Nigeria and South Africa
Nigeria and South Africa are two of the region’s largest economies whose main industries include the extractive industries, agriculture, tourism and manufacturing to a smaller extent. Both of these countries have voluntary systems for reporting pollution, however they follow different approaches for the data collection.
In Nigeria, the activities of the petroleum industry and sabotage of its infrastructure by third parties, are a major cause of soil pollution. In order to monitor the extent of the oil spills, the National Oil Spill Detection and Response Agency (NOSDRA) is tasked to implement the National Oil Spill Contingency Plan for the country (NOSDRA, 2020). The website of NOSDRA provides report templates for oil spill reporting that can then be captured on their database. It encourages anyone, including concerned or affected citizens to report incidents of pollution and provides contact details for emergency notifications. The database is available a separate website (Nigerian Oil Spill Monitor, 2020) where the data can be evaluated both on an interactive map and summarized in table format. The data indicates that already 11 spills have been reported since the onset of 2020, totalling 16 cubic metres of oil. Respectively in 2018 and 2019, there were 643 and 626 reports of spill incidents, totalling 4 100 cubic metres and 5 800 cubic metres of oil.
Although the Nigerian Oil Spill Monitor provides data on the number of oil spills, it does not provide quantitative data on the contamination levels of soil, groundwater, surface water or biota (Figure 10). The Environmental Assessment of Ogoniland report was the result of a two-year project commissioned by UNEP that included that analysis of soil samples from 780 boreholes across 69 sites (UNEP, 2011). It provides detailed information on the extent of soil contamination at each site. The Assessment provides data from 67 of the sites including: the size of area investigated; the number of soil samples collected; the maximum TPH level measured in soil; and the volume of soil above the intervention value of 5 000 mg/kg TPH as set by the Environmental Guidelines and Standards for the Petroleum Industry in Nigeria.
Figure 10. Screenshot of the Nigerian oil spill monitoring platform.
The voluntary site reporting system in South Africa makes provision for any activity that is causing or has caused soil pollution with contaminants as listed in the National Norms and Standards for the Remediation of Contaminated Land and Soil Quality that forms part of the National Environmental Management: Waste Act No. 59 of 2008. These norms and standards provide soil screening values for a range of contaminants including trace elements, alkanes, monocyclic aromatic hydrocarbons, aromatics and other organic contaminants. Some of the organic contaminants listed include chlorobenzene, chlorophenol, trichlorobenzenes, PCBs and cyanide (Department of Environmental Affairs, 2019a).
In order to avoid paying a fine, business and land-owners can voluntary report the presence of soil pollution on their properties. This registry of contaminated sites are available online and include the address of the properties, the coordinates of its location as well as the industry within which it operates and the nature and origin of contamination (SAWIC - Department of Environmental Affairs, 2019). The list does not include the extent of the pollution plume or the number of people that are at risk of exposure. Some of the contaminants reported include arsenic’ asbestos, fluoride, manganese, PAHs, petroleum products and zinc. However, the levels measured for each of the contaminants as well as the volumes of soil contaminated, are not indicated in this registry. Fuel stations (including refuelling depots) are the main source of pollution in the current list while other sources reported include manufacturing of paint, leather cloth and coatings. Industrial manufacturing has also been reported as a source of soil pollution with chlorinated solvents, mercury, phthalates and volatile organic compounds amongst other contaminants.