There are thousands of polluted sites in both countries of varying size and significance in settings ranging from abandoned buildings in inner cities to large areas polluted with toxic materials from past industrial or mining activities.
Polluted lands include:
Many sites, particularly the largest and most severely polluted, are tracked at the national level, but many others are tracked only at state/ provincial or local levels. Sites are categorized in a variety of ways, often based on the level and type of contamination and the regulations under which they are monitored and cleaned up. The United States of America Environmental Protection Agency (US EPA), Environment and Climate Change Canada (ECCC) are the primary national environmental regulatory agencies. As of 2017, US EPA and its state partners reported overseeing approximately 640 000 to 1 319 100 facilities to prevent releases into communities (US EPA, 2015a). These only encompass sites currently producing possible contaminants and not legacy sites or areas polluted from non-point sources. As of July 2019, there are 23 663 known and suspected federal sites listed on the Canadian Federal Contaminated Sites Inventory, with 16 845 sites listed as closed because remediation is not feasible (Environment and Climate Change Canada, 2019a).
The US EPA annual Report on the Environment1 and Toxics Release Inventory (TRI)2, and the National Pollutant Release Inventory (NPRI)3 in Canada are excellent sources of information on soil pollution (Environment and Climate Change Canada, 2019; US EPA, 2018a, 2019a).
Under current Canadian and United States of America regulations naturally occurring compounds are not considered contaminants requiring remediation. However, naturally occurring trace elements can be found in potentially toxic background levels throughout North America and must be accounted for when determining remediation scope.
Canada provides guidance on how background soil contaminants can be determined (Canadian Council of Ministers of the Environment, 1996), as well as some provincial level datasets (British Columbia Ministry of Environment and Climate Change Strategy, 2017) and a federal geologic atlas from which geogenic soil metal ranges can be estimated (Government of Canada, 2016).
The United States Geologic Survey (USGS) has invested considerable effort to map the natural background soil levels of the surface, A, and C soil horizons of the conterminous United States of many elements including those commonly found at polluted sites (e.g. lead, arsenic, chromium, cadmium, etc.) (Figure 2). These maps are continually updated as new datasets become available (USGS, 2017a).
Canada is the global leader in the production of potash and ranks among the top five global producers for cadmium, cobalt, diamonds, gemstones, gold, graphite, indium, nickel, niobium, platinum group metals, salt, titanium and uranium. Canada also accounts for a significant proportion of the global production of primary aluminum from imported bauxite and alumina. Canada’s 200 mines and 6 500 sand, gravel and stone quarries produced CD 47.0 billion in 2018 (Natural Resources Canada, 2018). Canada is also home to abandoned mines which are being documented for eventual remediation (Crown-Indigenous Relations and Northern Affairs Canada, 2019; NOAMI, 2020).
Canada is the fourth largest producer and third largest exporter of oil in the world with 98 percent of proven reserves located in the oil sands of Alberta (Natural Resources Canada, 2017). Canada’s oil sands contain tarry bitumen mixed with sand that is mined from underneath the boreal forest. In most parts of Alberta, bitumen is extracted through wells, but north of Fort McMurray, the bitumen layer is close enough to the surface to be strip mined in open pits.
The United States of America has a wide-ranging mining industry producing an estimated USD 86.3 billion of raw materials in 2019 (USGS, 2020a). In 2019, United States of America production of crushed stone, cement, construction sand and gravel, gold, copper, industrial sand and gravel, iron ore, lime, salt, zinc, soda ash, phosphate rock, and molybdenum were each valued at more than USD 1 billion. The mining industry disposes of the largest amount of waste primarily in the form of on-site land disposal (US EPA, 2020a).
From 2007 to 2018 on-site land disposal increased by 28 percent (from 0.91 to 1.18 billion kg). In 2018 the metal mining sector accounted for 70 percent of total land disposal quantities (Figure 3). Most of the land disposal quantities from the metal mining sector were made up of either lead (44 percent) or zinc compounds (26 percent) (US EPA, 2018c).
In addition to active mines, abandoned mines are also a significant soil pollution problem. There are an estimated 23 000 abandoned mines in the state of Colorado alone (Colorado Geological Survey, 2020). This problem is of sufficient magnitude that in 2020 the USEPA opened an office dedicated solely abandoned mine remediation (US EPA, 2020f).
In 2017, the Canadian facilities responsible for the largest contaminant releases to land were those supporting air transport activities, followed by hardware manufacturing, scheduled air transport, wastewater and sewage distribution systems, and metal mining (Table 1) (Environment and Climate Change Canada, 2019c).
The Canadian National Pollutant Release Inventory collects and publishes information on a number of listed contaminants that may pose a risk to the environment and health but is not a comprehensive list of all compounds released. In the case of land and soil, ethylene glycol, used as antifreeze and de-icing agent for cars and airplanes, was the contaminant with the highest levels recorded. For ammonia, copper, phosphorus and zinc, smaller but substantial amounts were recorded (Table 2) (Environment and Climate Change, 2019c).
The US EPA TRI tracks and provides an overview of the types and quantity of contaminants released into the environment by industrial activities for 16 persistent bio-accumulative toxic (PBT) chemicals and 5 PBT chemical compound categories. In 2017, it was reported that approximately 1.72 billion kg of contaminants were released into all environmental compartments (e.g. soil, air and water) by industrial activities. The main contaminants were lead (35 percent), followed by zinc (23 percent), arsenic, manganese, barium, copper and others.
The TRI also identified on-site and off-site land disposal by different industries. Metal mining is responsible for the vast majority of waste generated although other industries also create significant waste (Figure 4).
By 1977, concern over the impact of PCBs on the environment led to a North American ban on manufacturing and importing PCBs (Health Canada, 2004). The ban did not cover PCBs that were already in use in electrical applications, but these are being phased out, and there are strict regulations for the handling, storage and disposal of PCBs. Trace levels of PCBs in the environment (air and water) are found all over the world, including remote areas of North America. Some of this was caused by accidental releases and improper disposal practices in the past, but today, pollution is due primarily to the long-range transport of PCBs by global air currents.
Extensive soil per- and polyfluoroalkyl substances (PFAS) pollution from consumer product and industrial waste disposal and use and production of PFAS-containing firefighting foam has caused massive drinking water pollution at over 2 230 sites in 49 states including drinking water systems serving an estimated 110 million people (Environmental Working Group, 2019a; Hu et al., 2016; Kary and Cannon, 2018; SSEHRI, 2019). PFAS chemicals are used for their waterproof, greaseproof, and non-stick properties in many consumer goods, in manufacturing processes, and airports and military installations that use firefighting foams. They are persistent in the environment and can accumulate in living tissues, causing serious health issues (Agency for Toxic Substances and Disease Registry, 2018). While exposure is typically from polluted drinking water, people can be potentially exposed to perfluorinated chemicals from polluted air, surface and ground water, polluted foods, in certain occupational settings, and from the possible release of perfluorinated chemicals during the normal degradation or possible use of commercial products that contain them (Health Canada, 2007). In 2019, Canada promulgated soil screening values for PFAS compounds to provide guidance for site investigations (Health Canada, 2019a). US EPA has been developing PFAS analytical methods and providing states guidance as they develop PFAS regulatory standards (US EPA, 2016).
The most severe pollution is found at PFAS production sites (e.g. Chemours Washington Works, Parkersburg, West Virginia; 3M Cottage Grove, Minnesota; Chemours GenX Fayetteville, North Carolina) (Eichmann, 2017; Lerner, 2015; Oliaei et al., 2013; SSEHRI, 2017). It is estimated that PFAS legal and clean up expenses will exceed USD 10 billion restore to natural resources but not including damages for personal injuries (Bellon, 2018; DePass, 2019). Airports (military and commercial) are also significant sources of PFAS pollution in both countries. Thirty airports in Canada are known to have soil polluted with PFAS due to federal firefighting training. However, the Canadian federal government has thus far been unwilling to provide clean up funding due to the compounds not being “contaminants of concern” when individual airports were transferred to municipal ownership (Vandongen, 2020).
Environmental concerns surrounding soils and agriculture are predominantly focused on excess soil nutrient movement into surface and groundwater. However, there are few key soil pollution drivers associated with agriculture that are important for the sustainable management of this sector. These include irrigation, agro-plastics, the use of agrochemicals (pesticides and fertilizers), land spreading of municipal biosolids as fertilizer and the use of pharmaceuticals in livestock production.
In Canada, the agricultural industry generated CD 143 billion (7.4 percent of GDP) and provided one in eight jobs in Canada (Agriculture and Agri-Food Canada, 2020). Agriculture and Agri-Food Canada (AAFC) Science and Technology Branch conducts applied agricultural research to conserve soil resources.
AAFC calculates a series of agri-environmental indicators (AEIs) as key measures of environmental conditions, risks and changes resulting from agriculture and of the management practices that producers use to mitigate these risks (Treasury Board of Canada Secretariat, 2020). Soil nitrogen and phosphorus levels are monitored on a national level (Figure 5) but regulated on the provincial level for their potential to pollute surface and groundwater. The Indicator of the Risk of Water Contamination by Pesticides (IROWC-Pest) estimates water pollution from pesticide runoff across agricultural areas in Canada (Clearwater, Martin and Hoppe, 2016). The Soil Erosion Risk Indicator assesses the risk of soil erosion by water, wind and is considered when assessing water quality issues such as the risk of water pollution from phosphorus and pesticides due to the transportation of soil-borne particles to water bodies (AAFC, 2020). A model has also been developed to estimate the national trend of soil pollution by trace elements (arsenic, cadmium, copper, lead, selenium, and zinc) from the application of fertilizers, manure and municipal biosolids to agricultural soils. The model found that the geographical distribution of trace elements reflected the intensity of agriculture and suggested that after 100 years of sustained inputs, concentrations of some trace elements are estimated to be three times higher than natural background levels (Sheppard et al., 2009).
US agriculture, food and related industries generated USD 1.05 trillion in 2017 (USDA ERS, 2019). Within the United States of America Department of Agriculture (USDA), the National Resource Conservation Service (NRCS), the National Institute of Food and Agriculture (NIFA), and Agricultural Research Service (ARS) implement coordinated programs of field and laboratory research protect and maximize agricultural soil resources.
The Agricultural Fertilizer Indicator, included in the US EPA 2018 Report on the Environment (ROE), showed a 215 percent increase in fertilizer usage compared to 1960 (US EPA, 2018a). Regulation of nutrient application is conducted primarily at the state level with varying regulations. The NRCS provides technical guidance on nutrient loss reduction, but stipulates that state regulations supersede its guidance (NRCS, 2020).
The Health Canada Pest Management Regulatory Agency (PMRA) is responsible for pesticide regulation in Canada to ensure they pose minimal risk to human health and the environment. The PMRA works with provincial, territorial and federal departments in Canada to help refine and strengthen pesticide regulation across the country (Health Canada, 2005).
Pesticide regulation in the United States of America is overseen by the US EPA under the Federal Food, Drug, and Cosmetic Act (FFDCA) and the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) (US EPA, 2013a, 2013b) with states having complementary individual pesticide regulatory programs. The pesticide industry under FIFRA only has to demonstrate that its products “will not generally cause unreasonable adverse effects on the environment,” which is partially defined as “any unreasonable risk to man or the environment, taking into account the economic, social, and environmental costs and benefits of the use of any pesticide…”. The FFDCA was amended in 1996 to strengthen the safety threshold in setting food residue tolerances to a “reasonable certainty of no harm” for pesticide exposure to humans through food, water and home uses (US EPA, 2015b). However, harm to plants, animals, the broader environment, and harm to humans from occupational exposures remains largely a cost-benefit analysis (Donley, 2019).
Pesticide usage in the United States of America peaked in 1981 with 285 million kg applied. The amount applied decreased to 234 million kg in 2008 due to increased use of genetically modified seeds and conservation agricultural practices (USDA ERS, 2019). The United States Geological Survey maintains data on estimated annual American pesticide usage (USGS, 2020b). In addition to pesticides currently registered for use, banned and cancelled pesticides now known have long lasting environmental impacts can be found in soil decades after application and can remain hazardous (Figure 6) (National Pesticide Information Center, 2020).
Plastic films used as crop mulches are composed typically of low-density polyethylene, or LDPE, and play an essential role in fruit and vegetable production. Short-term benefits provided to growers by plastic film mulches include fewer weed problems, reduced soil water evaporation, earlier and higher yields, and higher-quality produce (Brodhagen et al., 2017).
Canada has included the use of plastics in agriculture in its Action Plan for Zero Plastic waste (CCME, 2020). Canadian farming organizations have also identified that agroplastics need to be more effective managed and have undertaken recycling and waste characterization initiatives (Cleanfarms, 2020).
US farmers currently use 57 million kg of plastic mulch and 191 million kg of plastic containers annually. In addition, plastic irrigation tubing, feed bags, and greenhouse plastic add to the growing volume of waste. However, the United States of America has no policies to require or encourage recycling agricultural plastics and knowledge about the long-term effects of plastic residues in agroecosystems is sparse (Rillig, 2012; Steinmetz et al., 2016).
Biosolid application as fertilizer can present a direct contaminant route to soil (Figure 7). Biosolid application in Canada is regulated but at the same time allows certain amounts of potentially toxic trace elements (Canadian Council of Ministers of the Environment and Biosolids Task Group, 2013). As these elements tend to remain where they are applied over time the metal content of the soils increases. PFAS are also recognized as potentially present in biosolids, but allowable limits have yet to be set.
Although biosolids are regulated by the US EPA, potentially toxic contaminants are allowed within regulatory guidelines (US EPA, 2020d) and over 400 contaminant compounds have been identified as potentially present in biosolids (US EPA, 2020b). While some of these will break down to harmless components other such a lead, arsenic, per- and polyfluoroalkyl substances (PFAS) and other metals will continue to accumulate in the soil. Recent research has shown that biosolids produced using industrial wastewater have higher levels of PFOS (Mills, 2020).
Given the significant environmental impacts of coal combustion, in 2018 Canada committed to phase out traditional coal-fired electricity by 2030. Currently 10 percent of Canada’s electricity is produced by coal combustion with the provinces of Alberta, Saskatchewan, New Brunswick, and Nova Scotia being the largest producers (Environment and Climate Change Canada, 2017a).
In 2017, the US Department of Energy produced a baseline report summarizing key environmental quality issues for the energy sector including land use, water pollution, ecological impacts, human health, and environmental justice. One aspect of energy production with high potential impact to soil is the management of combustion residuals (coal ash) at coal fired power plants. In 2014, coal fired power plants generated 118 million tonnes of coal ash which includes, fly ash, bottom ash, boiler slag, and flue gas desulfurization material (US EPA, 2014b). While flue gas desulfurization material can often find beneficial reuse as a soil amendment (Koralegedara et al., 2019) the other material types frequently have elevated levels of potential toxic trace elements and are stored at the energy facility or disposed of in landfills permitted to accept toxic waste. Coal ash reuse is regulated at the state, not federal, level in the US.
Following large scale releases of coal ash into the environments at Kingston, TN, (2008, 4.1 million m3) and Eden, NC (2014, about 32 000 tonnes), the EPA developed the 2015 Coal Ash Disposal Rule, which created the first national standard for coal ash disposal by adding requirements for coal ash surface impoundments and landfills (Mast, 2018; US EPA, 2019e). In 2018 rule changes gave states flexibility in using alternative contaminant standards and establishing groundwater standards. The 2018 changes also included enhanced reporting requirements which showed that more than 95 percent of the coal ash ponds in the United States of America are unlined and 91 percent of the plants pollute groundwater with contaminants at levels above federal safety standards (Earthjustice, 2019).
In Canada, many municipalities, provinces, territories, recycling councils, waste management associations and private businesses measure residual municipal solid waste (MSW) disposed in Canadian landfills on some level, but in 2019 the federal government commissioned the National Waste Characterization Report to survey the country as a whole and provide uniform methods guidance (Environment and Climate Change Canada, 2020). In 2016, Canadians generated approximately 34 million tonnes of municipal solid waste (Figure 8). About 40 percent of the waste generated originated from residential sources and 60 percent from non-residential sources. Of this total, 25 million tonnes (73 percent) was sent for disposal in public and private landfills.
US EPA began collecting and reporting data on the generation and disposition of waste more than 35 years ago (Figure 9). The total generation of MSW in 2018 was 265 million tonnes or 2.2 kg per person per day. Of the MSW generated, approximately 133 million tonnes of MSW were landfilled in the United States of America (Figure 10). Food was the largest component at about 24 percent. Plastics accounted for over 18 percent, paper and paperboard made up about 12 percent, and rubber, leather and textiles comprised over 11 percent. Other materials accounted for less than 10 percent each.
In Canada and US, small arms firing ranges (SAFRs) are a smaller yet still significant soil pollution sources. SAFRs include government, commercial, and recreational rifle, pistol, trap, skeet, and sporting clay ranges (Figure 11). Small arms firing ranges are those ranges accepting 12.7 mm or smaller ammunition. SAFRs may contain lead, antimony, copper, zinc, arsenic, and polycyclic aromatic hydrocarbons (PAHs) from nonexploding (nonenergetic) bullets and fragments, bullet jackets, and related sporting material (e.g., clay targets); however, lead is the primary risk driver. Canada has over 800 outdoor SAFRs where approximately 5 000 tonnes of lead is discharged annually (Environment and Climate Change Canada, 2018). The United States of America Department of Defense (US DoD) oversees more than 3 000 active SAFRs as well as the closure, or pending closure, of 200 more. In all, US DoD expends more than 2 million pounds of lead annually at SAFRs. In addition to DoD facilities, there are an estimated 9 000 nonmilitary outdoor ranges in the United States of America (US EPA, 2005). USEPA estimates that 4 percent of the 73 000 tonnes of lead produced in the United States of America during the late 1990s was made into bullets and shot.
Canada’s military has developed a strategy to minimize its environmental impact from past and future operations (National Defense Canada, 2020). As part of this plan and under CEPA the military is charged with cleanup of its sites listed on the Federal Contaminated Sites Inventory. To date, CD 250 million have been allocated to former military site remediation (Royal Military College of Canada, 2015). However, some legacy installations, notably radar stations in the artic and subarctic regions, were insufficiently remediated may continue to cause problems especially for First Nation peoples (Reyes, Liberda and Tsuji, 2015).
The US DoD has extensive environmental management responsibilities at its multitude of facilities throughout the United States of America and around the world. The DoD Environmental Management Directorate receives approximately USD 3.6 billion annually to protect the environment and health of bases, personnel and surrounding communities (US DOD, 2019, 2020). Of recently concern is the realization of widespread PFAS pollution at DoD facilities due to extensive use of PFAS-containing fire suppression foam. PFAS cleanup within the DoD system is estimated to cost in excess of USD 2 billion (Beitsch, 2019).
While Canada housed some United States of America owned nuclear weapons systems during the Cold War and mined some uranium for weapons production, it does not have any known nuclear weapons polluted sites.
The United States of America Department of Energy’s (DOE) Office of Environmental Management (EM) manages one of the largest groundwater and soil remediation efforts in the world primarily due to past development and production of nuclear weapons as well as management of civilian nuclear reactor waste (US DOE, 2020; US EPA, 2018d). The inventory at the EM sites includes 6.5 trillion liters of polluted groundwater, an amount equal to about four times the daily United States of America water consumption, and 40 million cubic meters of soil and debris polluted with radionuclides, metals, and organics. Their complex site cleanups often require the development of entirely new remediation and site characterization technologies. The US DOE receives approximately USD 6.6 billion annually for environmental remediation (US DOE, 2018).
In addition, the United States of America conducted approximately 1 054 nuclear tests, primarily at the Nevada Test Site (NNSS/NTS) and the Pacific Proving Grounds in the Marshall Islands while it was a United States of America territory. The testing NNSS/NTS caused soil pollution at 2 000 sites across the 3 500 km2 facility which have almost all been remediated (US DOE, 2019). Marshall Island sites were also remediated, but concerns linger over islander exposures to polluted soil and fruit (Abella et al., 2019).