Biochar - Remediation of acidic and compacted soils

Biochar refers to organic matter which has undergone thermal decomposition of biomass in oxygen-limited conditions. In other words, it is charcoal which has been plough into soils to increase the soil quality for agricultural purposes. It has been experimented by soil scientists in poor agriculture soils - i.e. acidic, compacted and waterlogged soils, and found to be effective in improving the soil quality and subsequently harvest. 

Flow diagram of Biochar production and uses. Taken from Tang, J.C. et al. (2013)

Biochar is not a new invention, it is a traditional agricultural practice in many countries such as India and Japan. Recently, much attention has been given to biochar as the ploughing of biochar into soils increase soil fertility, porosity, acidity and subsequently harvest. These positive effects have been met with enthusiasm as biochar is an inexpensive form of soil remediation, organic waste can be well utilized and carbon can be stored in soils. 

Tang, J.C. et al. (2013) examined the organic matter and temperatures used in the production of biochar as these two factors are seen to cause a difference in biochar quality. According to the paper, biochar produced by rice straws at higher temperatures have larger surface areas which will improve soil sorption of nutrients for plants. Zargohar and Dalai (2008) improved the sorption capacity of biochar by steam activation, however, this is not a choice for poor farmers. In fact, most poor farmers may not even be able to afford biochar because of the costs involved to employ techniques which are not polluting are high.  Further research and development into environmentally friendly economical production of biochar necessary for promoting the use of biochar to substantial farmers. 

References
Tang, J., Zhu, W., Kookana, R., & Katayama, A. (2013). Characteristics of biochar and its application in remediation of contaminated soil. Journal of bioscience and bioengineering, 116(6), 653-659.
Azargohar, R., & Dalai, A. K. (2008). Steam and KOH activation of biochar: Experimental and modeling studies. Microporous and Mesoporous Materials,110(2), 413-421.

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). 

Aluminium toxicity and magnesium uptake in spruce forest

In response to the problems in quantifying the effects of aluminium in plant nutrient uptake and growth as mentioned in the previous post, De Wit et al. (2010) specifically measured the effects of dissolved al on mg uptake in Norway spruce forests, in a long term field manipulation experiment from 1996.

Table from De Wit et al. (2010) showing the changes to BS after the addition of dilute aluminum carbonate into soil. 

The sites chosen were homogeneous-sandy soils with low al and n concentrations and Norway spruce stand. Dilute aluminium carbonate was added to 12 adjoining plots during snow and frost free seasons. Frequent measurements of soil at O horizon, pine needles and bark samples, crown density and color were observed and taken for analysis.

BS at O horizons were found to have significantly decreased while exchangeable al increased after 3 years of treatment. Mg in needles were also found to be reduced as compared to the control.

However, De Wit et al. (2010) found no significant impact of al on tree volume, crown, density annual increment and height increment. Plant root growth was not affected as hypothesized by many researchers. Only reduced mg uptake was significant, and this is not due to fluctuations in mg in soils. This mg deficiency has been reported in Lehstenbach, Germany by Alewell et al. (2000) but in nutrient poor soils.

Despite reports of al toxicity, it seems that spruce trees are more tolerant to acid deposition than previously thought. Similar experiments should be carried out in other areas to verify al toxicity levels in plants. However, this is a challenge to tropical areas as the vegetation is much more heterogeneous in a given area. Field experiments will need to be aided with laboratory experiments to test al sensitivity for all types of vegetation in a given area in order better quantify the effects of al in tropical regions.

References:

De Wit, H.A., Eldhuset, T.D. and Mulder, J. (2010) Dissolved Al reduces Mg uptake in Norway spruce forest: Results from long-term field manipulation experiment in Norway. Forest Ecology and Management. Vol. 259, pp. 2072-2082.

Alewell, C., Manderscheid, B., Gerstberger, P., Matzner, E., 2000. Effects of reduced atmospheric deposition on soil solution chemistry and elemental contents of spruce needles in NE-Bavaria, Germany. Journal of Plant Nutrition and Soil Science—Zeitschrift Fur Pflanzenernahrung Und Bodenkunde 163, 509-516.

Discussing dissolved aluminium in soils

Studies have shown that dissolved aluminium in soils are a threat to forest health. Aluminium in soils occur naturally as aluminium is one of the most abundant metals in the earth’s crust. Upon acid deposition, aluminium is dissolved and mobilised from clays as the negative clay sites are replaced by hydrogen ions. In the soil solution, aluminium ions hydrolyse and are taken up by plants, inhibiting nutrient uptakes and plant root growth. Nutrient deficiency in trees have been found to be present at sites with high aluminium in soil solutions (Alewell et al. 2000).

Picture showing controlled experiment of plant root growth in different aluminium concentrations. Taken from http://www.summitfertz.com.au/research-and-agronomy/soil-ph.html

However, there are also healthy trees found under similar aluminium concentrations (Huber et al. 2004). There is no direct relationship between forest/tree health with acid deposition or dissolved aluminium toxicity in soils. Some researchers have thus used bases such as calcium, magnesium and potassium to aluminium ratio as a predictor of forest vitality (De Vries et al. 2003). However, as different types of vegetation, soils and ecological environments have different sensitivities to dissolves aluminium in soils, it is difficult to determine a threshold of base to aluminium ratio. Laboratory experiments of aluminium toxicity have been disputed by whole-ecosystem experiments as well. Laboratory experiments have been criticised for using potentially toxic levels of aluminium in controls and the amount of nitrogen added will have influence on root growth. Whole-ecosystem experiments are inconclusive about the role of aluminium in reducing root growth and nutrient uptake due to the presence of multiple variables (De Wit et al. 2001).

There is a need to reconcile both methods, in order to prove a direct, unambiguous relationship of nutrient uptake and root growth with aluminium toxicity.

References

Alewell, C., Manderscheid, B., Gerstberger, P., Matzner, E., 2000. Effects of reduced atmospheric deposition on soil solution chemistry and elemental contents of spruce needles in NE-Bavaria, Germany. Journal of Plant Nutrition and Soil Science—Zeitschrift Fur Pflanzenernahrung Und Bodenkunde 163, 509– 516.

De Vries, W., et al. (2003) Intensive monitoring of forest ecosystems in Europe2: atmospheric deposition and its impacts on soil solution chemistry. Forest Ecology and Management 174, 97–115.

De Wit, H.A. et al. (2001) Aluminium: the need for a re-evaluation of its toxicity and solubility in mature spruce stands. Water Air and Soil Pollution: Focus 1, 103–118.

Huber, C., et al. (2004) Response of artificial acid irrigation, liming, and N-fertilisation on elemental concentrations in needles, litter fluxes, volume increment, and crown transparency of a N saturated Norway spruce stand. Forest Ecology and Management 200, 3–21.

Soil Acidification and Heavy Metal Contamination in Soils

Soils are acid/base systems which have the ability to absorb and release metals which have been introduced into the soil by anthropogenic or natural means. Soils are naturally acidic or alkaline based on their bedrock and climatic conditions. This measure of acidity or alkalinity in soils is important as it directly affects the growth of plants and the leach of heavy metals into soils which will cause crop contaminations.

In alkaline soils, i.e. sodic soils, plant growth is poor due to competition of sodium ions with other important ions such as magnesium and potassium for uptake in plant roots. However, alkaline soils have excesses of base cations which can bond with oxidised heavy metals (metal oxides) to fix heavy metals in soil. Alkaline soils thus are less likely to cause health problems when contaminated with heavy metals, but this is dependent on the type of metal oxides present in soil solution. However, these soils are too salty for crop growth. 

Picture showing Sodic Soils. Taken on 2 October 2014 in Inner Mongolia, China. Sodium salt levels are very high, with salts crystallizing to form a white layer on top. Nearby lake is salty as well. 

In acidic soils, the problem of heavy metal contamination is more serious than in alkaline soils due to the release of metals bonded on soil surfaces into the soil solution. In places where acid rain from nearby polluting factories acidifies soils, aluminium is leached into soils when pH<4. Aluminium ions are toxic to plants and retards plant root growth (Krstic et al. 2012). Besides, as aluminium has 3 free electrons for bonding, after being leached out, negative soil surface adsorbs other metal ions available and causes nutrient deficiency in plants. However, addition of hydrogen ions also replaces metal ions in soils and releases metals, but the overall effect of adsorption is higher as aluminium has 3 free electrons for bonding as compared to a hydrogen ion which only has one. 

Thus, places in the south - the southern part of China where acidic soils and acid rain are both present, aluminium toxification levels are high. For some crops, they will fail to grow, but crops with higher tolerance levels can bioaccumulate aluminium and pass on aluminium in the food chain. 

Krstic, D. et al. (2012) Aluminium in Acid Soils: Chemistry, Toxicity and Impact on Maize Plants. Collected in Food Production - Approaches, Challenges and Tasks. Aladjadjiyan, A. eds. InTech,  Croatia. 

Acid Rain - Soil Interactions (n.d.) Available at: http://www.elmhurst.edu/~chm/vchembook/196soil.html

Soil Pollution in China

According to BBC, ‘Almost a fifth of China's soil is contaminated, an official study released by the government has shown’. Decades of poor environmental management problems and rapid industrialization has repercussions in the environment. However, even in the capital Beijing, these problems have not been given critical importance.

Photo showing extreme eutrophication problems in Beijing, China. Photo taken on 26 October 2014.

Soil quality standards have been implemented in China, but these standards are outdated (1996) and have been criticized by environmentalists for being irrelevant. There has been attempts to establish new soil quality standards, especially in farmlands, but "almost no major country has set a unified national standard” (Chen, quoted in Caixin, Chinese news). China has to set up and implement her own standards instead of relying on foreign help, as no other developed western countries had such critical levels of pollution in farmland. This has proved to be difficult, given the diversity of soil types in China. Critics of the new soil standards have mentioned the need to match the standards of soils to the soil type present in order for standards to be met.

This poses a serious problem to food security in China. Pollution from the soils contaminates the food produces and accumulates in the food chain. Reports have suspected that the outbreak of cancer deaths is linked to the pollution (Wong 2013). Lead in children’s blood may be due to heavy metal soil pollution as well. These are dire consequences resulting from poor pollution control and land use planning. Many farms in China operate in the vicinity of heavy metal polluting industries, resulting in undesirable effects on human health.

There is a need to spread the awareness of soil pollution. Soil is not dirt, it supports lives.

BBC (2014) Report: One fifth of China's soil contaminated. Online news, 18 April, Available at: http://www.bbc.com/news/world-asia-china-27076645

Wong, E. (2013) Pollution Rising, Chinese Fear for Soil and Food. Online news. The New York Times, 30 December. Available at: http://www.nytimes.com/2013/12/31/world/asia/good-earth-no-more-soil-pollution-plagues-chinese-countryside.html?pagewanted=all&_r=0 

Zheng, C. (2015) Gov't Digs Into Soil Pollution Problem with Proposal for New Standards. Online, Available at: http://english.caixin.com/2015-01-27/100778811.html

The different types of soils

Soils differ in nature mainly due to the type of bedrock (lithology) and the climatic conditions. The nature of soils must be understood in order to determine the influence of pollutants in the soil. For example, the impact of acid rain on acidic soils with heavy metal pollution in southern China will be different from the impact on sodic soils – salty/alkaline soils with heavy metal pollution in northern China.

Soils can be classified in many different ways, according to their colour, texture, chemical properties, percentage of clay, etc. One of the easiest and common way of classifying soils are according to their colour. A soil Munsell colour system is usually used to determine the redness/yellowness of the soil, and this categorisation gives us a basic idea on the acidity/alkalinity of the soil, and thus its climatic or paleoclimatic conditions.

The percentage of clay is also usually examined in order understand the extent of sorption which may take place. In soils, clay colloids are very important as they are where the chemical process of sorption takes place, which usually refers to the exchange of metal ions in the soil solution with clay colloids (usually negatively charged, variable). This affects the toxicity of metals in soils as it is the free metal concentration in soil solutions which is polluting and affects plants and humans.

Other factors such as soil structure and detailed chemical composition also affects the impact of pollutants on soils and their toxicity to the biosphere, hydrosphere and atmosphere. 

The Importance of Soils

Soils are complex, living and dynamic systems that are at the interface of four 'environments' - lithosphere, biosphere, atmosphere and hydrosphere. Any changes to these 4 environments will affect soils. The biosphere, atmosphere and hydrosphere are the main contributors to the pollution of soils. However, the climatic conditions of the situated environment and lithosphere controls the main characteristics of soils. The characteristic of soils will in turn determine the extent of impact of the pollutants. 

The heterogeneity of soils makes it difficult for the impact of pollutants on soils be quantified. As a result, soils often treated as a black box. Besides, since soils are good absorbents, they have been treated as stores for pollutants with no considerations for its sustainability. Usually, when soils start to leach their pollutants into the groundwater, soils have been too contaminated for effective treatment and they will have to be disposed at landfills. This will then greatly disrupt the carbon budget as soils are important carbon stores. Therefore, there is a need to promote the awareness for soil sustainability. 

Soils are important as they are 

1. Mediums for Plant Growth
2. Regulators of Water Supply
3. Assistants in the Recycling of Nutrients and Waste (N and C cycles)
4. Habitats of Organisms
5. Engineering Mediums