Soil Remediation Methods Part II

Some of the common methods of soil remediation: 

1. Water-treatment/filter method: not favorable for places with water shortages and water sources which are used directly without treatment.

2. Soil screening: 

•       Soils are sorted by machines (sieves), and smaller clay, slit and organic matter are removed for further treatment because most organic and inorganic contaminants tend to bind, chemically or physically to these particulates.
•       Soils can also be sorted by electrokinetics: A current is passed between the two electrodes to attract and separate heavy metal contaminated soils.

3. Soil removal and landfill disposal: This method is usually used when other remediation methods are not able to remove contaminants to acceptable levels according to land-use requirements (i.e. for residential or school uses, contaminant levels are required to be at very low levels). However, the landfill disposal infrastructure must be able to prevent pollutants from seeping into the surrounding environment, and huge disruptions are made to the original landscapes. 

4. Soil washing: after soil has undergone physical screening, chemical extraction (acid, chelating agents EDTA, surfactants) will be added to remove contaminants. Usually acids are used:

• desorption of metal cations via ion exchange or de-complexation,
• dissolution of metal compounds
• dissolution of soil mineral compounds (Fe/Mn oxides)

However, strong acids also destroy the soil structure, creates problematic waste water and there needs to be proper disposal of solid/liquid waste.

5. Phyto-remediation: uses plants certain plant species—known as metal hyperaccumulators which have the ability to extract elements (heavy metals) from the soil and concentrate them in the easily harvested plant stems, shoots, and leaves (ARS, 2014). This method is preferred as it does not disrupt the landscape as compared to other methods, but the time taken for remediation is much longer. 

There are no perfect solutions to soil remediation, and every method has its advantages and disadvantages. Therefore, it is paramount that we control and minimize soil pollution before it needs remediation. 

References: 
ARS (2014) Phytoremediation: Using Plants To Clean Up Soils. Online, Available at: http://www.ars.usda.gov/is/ar/archive/jun00/soil0600.htm

All these methods are elaborated in detail on many online videos, such as: 

Video of soil washing in London before the summer Olympics 2008.
Available at: https://www.youtube.com/watch?v=wJ8Vp_KZ4lE

Video of Phytoremediation rehabilitation hydrocarbon contaminated soils in Belgium. Available at: https://www.youtube.com/watch?v=wt0hkcHYTe0 

Soil Remediation Methods Part I

Figure shows the overall inputs of pollution and trace elements such as heavy metals into soils. Soil pollution can be due to natural or anthropogenic causes, but it is usually the anthropogenic contributions which are hazardous as excessive amounts of pollutants which cannot be remediated by soils naturally are added into soils.

In view of the risks imposed by soil pollution, remediation methods have been carried out in many developed countries such as Norway. However, although the tropical and developing countries host most of the heavy polluting industries, soil remediation is rarely carried out in these places. While these remediation methods are costly, the potential health effects may be more costly if soils continued to be polluted without control and remediation.

In the diagram below, soil remediation methods for inorganic pollutants are listed. Remediation can be classified into ex-situ and in-situ methods. Some of the common methods used are water treatment/filter, soil screening, soil removal and landfill disposal, soil washing and phyto-remediation.

References

Heavy metal in the soils of Pistol and Rifle Ranges

Outdoor pistol and rifle ranges have been under scrutiny from both the public and the state as these places have soils which are contaminated with heavy metals such as lead, zinc and antimony. Pistol and rifle ranges cannot be easily converted for other land uses due to heavy metal contamination, they have to be remediated before other usages can be deployed on these soils, especially for residential uses.

Pistol and Rifle ranges have very high possibility of accumulating Hardison, et al. (2003) examined lead contamination in shooting range soils from abrasion of lead bullets and subsequent weathering. This study showed that it is not just the weathering of lead bullets in soils which contribute to lead contamination in soils, even the abrasion of bullets in soils contributes significantly to lead contamination in soils.

Besides lead contamination, other heavy metals in bullets such as zinc and antimony (used as a hardener in bullets) also contaminate pistol and rifle range soils. These heavy metals complicate the process of soil remediation as these heavy metals are bioavailable at different environments. Lead is soluble in soils at low pH while Sb is at high pH.

Okkenhaug, et al. (2013) reported in a seminar that the largest source of pb and sb contamination (i.e. leach into the environment) in Norway is from shooting ranges. To stabilise pb and sb, they identified and used iron based sorbents to immobilise pb and sb in soils and later to be removed by mechanical means. This has been tested out in Norway, and may be useful in remediating pistol and rifle range soils for other land use purposes.

References

Hardison, D.W. Jr., et al. (2004) Lead contamination in shooting range soils from abrasion of lead bullets and subsequent weathering. Science of the total environment, Vol. 328, pp. 175-183.

Okkenhaug, G.; Amstätter, K.; Lassen Bue, Cornelissen, G.; Breedveld, G.D.; Mulder, J., Antimony (Sb) contaminated shooting range soil: Sb mobility and immobilization by soil amendments. Accepted with major revisions, Environmental Science & Technology.

Industrial lead soil pollution

Picture Taken from:
https://www.youtube.com/watch?v=dUX9kd2VjyA

While researching on lead pollution, I came across this YouTube video – ‘Asian Children Suffering from LEAD POISONING Due to Years of ENVIRONMENTAL POLLUTION’. It depicts the city of Shymkent, South Kazakhstan which is the 3^rd largest city and home to 600, 000 people with declining heavy industries. It suffered from environmental abuse under the Soviet Union and then subsequently the MNCs. As a result of pollution, researchers and urban regenerators have found that the lead in soils are more than 2000ppm, which is about 70 times the legal limit of 30ppm.

This lead came from the lead smelter – lead production plant built in 1934, which was used by S.U. for producing bullets. The plant does not have infrastructure for lead pollution prevention, releasing leaded fumes into atmosphere which is eventually deposited and accumulated in soils, posing extreme levels of lead poisoning to the surrounding suburban area. The children there have borne the brunt of lead poisoning, with growth stunned and intelligence dulled.

It has been closed down, but Kazakhmys, UK-registered copper mining company whose main assets are located in Kazakhstan, has been suspected of running the plant for the final few years. However, they have denied their operations in the plant and the company A Mega Trading, a subsidiary under Kazakhmys, has been traced to be in contract with the smelting plant. Until now, the company has not been subjected to environmental and health liabilities despite vidence that they did pollute the environment and harm the health of Shymkent children (Mayne, 2014). However, as the company only rented the place and supplied raw materials to the plant, they denied that the lead pollution was a result of their activities. In addition, the secrecy of the ultimate beneficial owners of Kazakhmys made it difficult for authorities to trace responsibility and liabilities.

Although there is no data to confirm whether the lead pollution in Shymkent is due to Kazakhmys or previous users or owners, they all have to assume responsibility of risking the possibility of increasing the already lead polluted environment.

Lead pollution in Shymknet calls for the need for better policing of lead pollution. Communities should step in to request for business transparency and environment reports, especially when they locate or utilise industrial plants are within close proximity. Governments should tighten their reign over their businesses, increase business transparency and fight for their environmental and pollution rights. Given the hazardous effects of lead pollution and its potential detrimental health impacts, there is a need give paramount attention to the lead pollution and its accumulated amounts in soils.

Reference

Mayne, T. (2014) Questions remain for Kazakhmys plc over ownership of poisonous smelter. Online. Available at: http://www.globalwitness.org/blog/questions-remain-for-kazakhmys-plc-over-ownership-of-poisonous-smelter/

Video: https://www.youtube.com/watch?v=dUX9kd2VjyA

Problem of Lead-based paints

Lead has been added into the production of paint due to its ability to speed up drying, are highly opaque, increase durability by resist moisture that causes corrosion and neutralising acidic oils in paints (Crow, 2007). Lead-based paints have a long history of usage and production. While the poisonous effects of lead have been realised since the 20^th century, efforts to regulate and ban the usage of lead-based paints have been weak. It was only until 1978 when US banned the usage of lead-based paint for all uses (Rosner and Markowitz, 2013).

Picture taken from: http://en.wikipedia.org/wiki/Dutch_Boy_Paint

The most widely used form of lead in paint is white lead or lead (II) carbonate (PbCO3). When lead-based paint flakes off or when it is removed from old buildings, lead in paint may be mixed in soils and enters into soils via weathering. As lead does not rapidly biodegrade or decay in soils, it will accumulate overtime. Soils which are alkaline retains lead in the top soils while soils which are acidic may react with hydrogen ions to form soluble compounds in soil solution. Alkaline soils with lead contamination might be more toxic when in contact due to lead concentration in top soils. However, in acidic soils, leached lead compounds may seep into and contaminate ground water and water bodies, wide-spreading the problem of lead pollution to other resources.

While lead-based paint has been outlawed in developed countries, it is still being manufactured and sold to poor developing countries. In 2013, it has been found extremely high levels of lead in numerous commercialised house paints in Cameroon. Some even have lead concentrations which exceeded the U.S. standard more than 300 times. This lead-based paint was traced to PPG Industries, an American global supplier of paints, who manufactured paints at toxic levels in Cameroon despite being educated of the dangerous consequences of lead poisoning (Kessler, 2013).

Such blatant double standards used by global paint manufacturers shows that industries can never be relied to be able to police themselves. Governments and local health authorities have to implement stringent rules to protect their own people, otherwise the bill falls back onto them when irreversible health problems emerges.

References

Crow, J. M. (2007) Why use lead in paint? Online. Available at: http://www.rsc.org/chemistryworld/News/2007/August/21080701.asp

Kessler, R. (2013) Long Outlawed in the West, Lead Paint Sold in Poor Nations. Online, Available at: http://e360.yale.edu/feature/long_outlawed_in_the_west_lead_paint_sold_in_poor_nations/2633/

Rosner, D. and Markowitz, G. (2013) Why It Took Decades of Blaming Parents Before We Banned Lead Paint. Online. Available at: http://www.theatlantic.com/health/archive/2013/04/why-it-took-decades-of-blaming-parents-before-we-banned-lead-paint/275169/

Sources of lead in soils

Lead in soils can originate from vehicle emissions, the mixing of lead-based paint in soils and lead bullets in pistol shooting ranges. In this post, I will first discuss lead in soils from vehicle emissions. 

In 1970, Motto, H. L., et al. sampled the soils along heavily travelled highways of New Jersey, Pennsylvania and Maryland and concluded that lead contents in soils tend to increase with traffic volume and decrease with distance from the highway. The lead in road soils origin from usage of leaded petrol. The lead in soils are very persistent as soil colloids bind firmly to tetraethyllead released from the combustion of leaded petrol in vehicles. If humans ingest dust particles contaminated with Pb overtime, Pb poisoning may occur. Crops grown at the vicinity of highways are also found to be contaminated with Pb. This may also result in Pb poisoning. If neighborhoods are situated near heavy traffic roads, children are especially vulnerable if they play with soils.

Picture showing the process of cleaning and recovery of
lead contaminated soils. Taken from:
https://www.youtube.com/watch?v=fFRs6xfAILY

While leaded petrol has been banned in many developed countries, developing countries have lax rules regarding leaded petrol. In 2013, British company Innospec Ltd was found to be selling tetraethyl lead to improvised countries such as Iraq and Algeria through bribery (Telegraph Reporters, 2013). There is a need to ban leaded petrol in developing countries as these countries do not have the capacity to deal with lead cleaning of soils, which is expensive and time-consuming. 

References

McCarthy, M. (2000) Lead-free petrol may be villain in mystery of demise of the world's most familiar bird. Online. Available at: http://www.independent.co.uk/environment/leadfree-petrol-may-be-villain-in-mystery-of-demise-of-the-worlds-most-familiar-bird-698469.html

Motto, H. L. (1970) Lead in Soils and Plants: Its Relationship to Traffic Volume and Proximity to Highways. Environ. Sci. Technol., Vol. 4 (3), pp 231–237. 

Telegraph Reporters (2013) British company 'selling toxic lead fuel to poor countries'. Online. Available at: http://www.telegraph.co.uk/news/earth/energy/9800019/British-company-selling-toxic-lead-fuel-to-poor-countries.html

Lead Pollution in Soils

The long distance transportation of lead is a significant source of Pb in terrestrial systems. This is because lead from mining can be attached to dust and transported by winds over long distances. Upon precipitation, lead in dust is deposited on soils and can be adsorped by soil colloids or transported by flows to water bodies.

Serious health problems such as nerve damage and vision impairment occurs from Pb poisoning as shown in the figure below. 

Figure showing the possible effects of lead poisoning. Available at: http://brickleyenv.com/what-is-lead-poisoning/

One important source of Pb poisoning is from the consumption of food which is contaminated with pb from soils. This has been postulated in China as high levels of pb were found in children’s blood and agriculture soils (Bale 2014) 

However, researchers have been in dispute over the source of anthropogenic Pb contamination in soils, as a 'generally accepted tool that would unmistakably prove the importance of air pollution relative to local geogenic sources has not been available' (Steinnes, E. et al. 2005:1399).  Reimann et al. (2001) explained the increase in Pb in the O horizons as the result of “plant pumping and organic binding” and not related to atmospheric deposition. 

Steinnes, E. et al. (2005) thus quantified pollution lead in forest soils (sodic) of Norway. This study focuses on the atmospheric deposition of pb on soils, which is determined by using the stable pb isotope. They concluded that in Norway, overwhelming part of Pb in the humus layer of natural soils is derived from air pollution, as strongly suspected from previous studies. This result directs the need to curb anthrogpogenic Pb production sources in order to reduce the Pb contamination in soils. 

However, there is also the need to include the factor of acidity when using data from Steinnes, E. et al. (2005) for studies in acidic soils, such as in China. The leaching of Pb into deeper soil horizons makes it difficult to gauge degree of Pb contamination and its potential consequences to water sources and food security issues, and that Pb found in these areas of soil depth should include anthropogenic activities as a source of pollution. 

References

Bale, R. (2014) China’s other pollution problem – its soil. Available at: http://www.revealnews.org/article-legacy/chinas-other-pollution-problem-its-soil/

Brickley Environmental (2014) What is lead poisoning? Available at: http://brickleyenv.com/what-is-lead-poisoning/

Reimann, C., G. Kashulina, P. de Caritat, and H. Niskavaara. 2001. Multi-element, multi-medium regional geochemistry in the European Arctic: Element concentration, variation and correlation. Appl. Geochem. 16:759–780.

Steinnes, E. et al, (2005) Quantification of Pollutant Lead in Forest Soils. Soil Sci. Soc. Am. J. 69:1399–1404 (2005).