Chapter 11. Status of soil pollution in North America
Main human health problems associated with soil pollution in North America
In order to assess the population exposure to contaminants, Canada conducts regular surveys on environmental chemicals in Canadians as an ongoing national health programme called the Canadian Health Measures Survey (CHMS), first launched by Statistics Canada in 2007. Currently, biomonitoring of environmental chemicals and their metabolites occurs through blood, urine and hair samples analyses of the participants. In the last cycle of data collected between 2016-2017, about 5 800 Canadians aged 3–79 years at 16 sites across Canada participated and included an analysis of 99 environmental chemicals (Health Canada, 2019b).
The US EPA constantly updates and monitors the exposure to environmental contaminants through 12 Report on the Environment indicators. These indicators are based on health and nutritional status data collected by the US Centers for Disease Control and Prevention, National Health and Nutrition Examination Survey (NHANES). The indicators monitored by EPA are blood cadmium, blood lead, blood mercury, serum cotinine, serum persistent organic pollutants, urinary pesticides and urinary phthalates (US EPA, 2018e).
It is understood that the route of exposure from soil-to-human can lead to human health problems. The following are some well-documented examples of soil contaminants in the region as well as success stories of how policies around this issue have impacted human health.
11.4.2. Health problems associated with trace elements
11.4.2.1. Lead
Although lead-based paint and dust in the home environment continue to be the predominant sources for lead exposure in children, exposure also occurs from lead in air, soil, water, and nontraditional sources including foods, folk remedies, and consumer products. Over the past 40 years, the percentage of United States of America children with blood lead levels of 10 μg/dL or more declined from 88.2 percent to less than 1 percent (US Centers for Disease Control, 2013). This substantial decrease in population lead exposure was due mainly to national policies aimed at controlling sources of exposure in gasoline, paint, and consumer products. However, there are still at least 500 000 children 1 to 5 years of age, or 2.5 percent of the population of children in that age range, above the CDC blood lead reference value. This estimate does not include younger or older children or other groups at high risk for adverse effects of lead exposure such as pregnant and lactating women or workers exposed on the job. In Canada exposure from lead-based paint and paint polluted soil is also a health concern (Health Canada, 2010), but there has historically been a less rigorous regulatory response than that seen in the United States of America (O’Grady and Perron, 2011).
While removing lead from the environment had been deemed a success story, the 2017 lead pollution of drinking water supplies in Flint, Michigan and soil in East Chicago, Indiana reignited concern over lead in the environment (Santucci and Scully, 2020; US DHHS, 2018). A 2018 United States of America Government Accountability Office report estimated that 6.1 million lead service lines remain in use across the United States of America (Government Accountability Office, 2018) with Canada facing a problem of similar magnitude (Mendoza, 2019). A 2019 meta-analysis of the lead exposure assessment literature showed that: mean lead in residential soils is three times higher for urbanized versus non-urbanized areas; mean estimate of lead in produce reported in the literature (e.g. home, community or urban garden) is approximately three orders of magnitude greater than commercially-sourced raw produce; mean estimate of lead in soils from shooting ranges is two times greater than non-residential lead polluted Superfund sites; and research reporting environmental lead concentrations for school and daycare sites is very limited (Frank et al., 2019). While significant strides have been made in reducing the impact of soil lead on human health, much work remains.
11.4.1.2. Arsenic
For the past 15 years, the Canadian Federal and Northwest Territories governments have been engaged in remediation of the former Giant gold-mining complex. When the mine ceased operations and was declared abandoned in 2005, 237 000 tonnes of arsenic trioxide smelter by-product were left behind in 15 underground vaults (Thomson, 2018). The size and scope of the project has required 15 years of planning with the site being maintained until remediation could proceed. September 2020 final regulatory approval was granted moving the project into active remediation (Government of Canada; Indigenous and Northern Affairs Canada, 2020).
While arsenic in soil remains a widespread problem especially at known polluted sites, the United States of America also has many areas with naturally high arsenic levels in soil (Figure 13). This complicates human exposure standards and site remediation. To assist in determining whether arsenic present in soil is natural or due to anthropogenic inputs the United States of America Geological Survey has developed a soils geochemistry atlas showing arsenic concentrations (USGS, 2020c).
Figure 13. Arsenic concentrations of surface soils in the conterminous United States.
Additionally, in 2017 the US EPA determined that there was sufficient scientific data to validate a soil arsenic bioaccessibility method for soil and a bioaccessibility/ bioavailability correlation (also available for lead) (US EPA, 2020e). In standard human health risk assessment equations, the default for arsenic soil bioaccessibility is 100 percent, but can be as low as 2.7 percent for mine wastes (Rodriguez et al., 1999). Application of bioaccessibility in risk assessment allows for more precise remediation plan development and efficient use of scarce financial resources.
11.4.2. Health problems associated with organic contaminants in soil
11.4.2.1. Polycyclic aromatic hydrocarbons
The toxic legacy of manufactured gas plant (MGP) soil pollution continues to be addressed, but the work is slow as the clean-ups are often extensive and costly (US EPA, 2020c). MGPs operated from the early 1800s through the mid-1900s producing gas from coal or oil. This process produced waste tar, sludges and other hydrocarbon products that contain high concentrations of PAHs, and other metal and organic waste. There are an estimated 3 000 MGPs across the United States of America largely found in inner areas of older cities (US EPA, 1999). MGP sites in Canada have not been catalogued.
Recently coal-tar based asphalt paving sealants have been recognized as significant polycyclic aromatic hydrocarbons (PAH) sources in both soil and sediment (Baldwin et al., 2017). Coal-tar based sealants are 20-35 percent coal tar pitch, a by-product of the steel manufacturing industry, which is 50 percent or more PAHs by weight and require application every few years. Individual states, counties, cities and towns have been enacting bans on coal-tar sealants and although the US EPA is aware of the issue no national regulations have been enacted (US EPA, 2018b). Similarly, Canada has proposed that coal tars may be hazardous to human health, but no regulatory action has yet occurred (Health Canada, 2016).
11.4.2.2. Dioxins
Dioxin is not produced or used commercially in the United States of America or Canada. Since the 1980’s regulatory and voluntary actions have dramatically reduced the amount of dioxins released into the environment and the amount of dioxins to which people are exposed. Based on recent measures it appears that levels in people are decreasing. However, when current body burdens in the population are compared to the levels of concern derived from animal and human studies it is clear that it is desirable and necessary to further reduce human exposure. According to US EPA’s 2006 Dioxin Inventory of Sources Report man-made emissions, including backyard and household trash burning, dominated releases in the United States of America (US EPA, 2006). The report also acknowledges the need for more data on natural sources, such as forest fires, that can form dioxins.