Soil characteristics and soil pollution

Prof. Xuyin YuanCollege of Environment

Outline

• Major characteristics of soils• Sources of soil pollutants• Environmental and ecological effects of soil pollution• Risk assessment of soil pollution• Prevention and remediation of soil pollution

Major characteristics of soils

• Soil formation• Soil compositions• Soil properties

Soil formation

• Soil has two important functions. One is a precious source, which can be used as an agricultural basis for food production. The other is a substance with the assimilation and metabolism ability.

• The weathering process makes rocks break up and the broken rocks form structural loose matter, which is defined as parent matter. The parent matter undergoes climate changes, biological action and other physiochemical actions to form soils .

                    

Brown soil profile

                    

Podzolic soil profile

                    

Red soil profile

                    

Yellow soil profile

Soil compositions

• Soil minerals• Soil organic matter• Soil water• Soil air• Insects• Microorganism• Plant litter

Chemical compositions of soil minerals

岩石圈和土壤的主要化学组成（重量％）

元素 岩石圈 土壤 元素 岩石圈 土壤

O

Si

Al

Fe

Ca

Na

K

47.2

33.0

8.8

5.1

3.6

2.64

2.6

49.0

27.6

7.13

3.8

1.37

0.63

1.36

Mg

S

Mn

P

N

Cu

Zn

2.1

0.09

0.09

0.08

0.01

0.01

0.005

0.6

0.085

0.085

0.08

0.1

0.002

0.005

Soil organic matter

• Soil organic matter is comprised of plant root, stalk , leaf, soil animal body and organic fertilizer.

• Humus is dominated in soil organic matter , which includes the plant and animal residual, humic acid and fulvic acid.

• Humus has strong adsorptive ability, buffer ability and complexing ability, which take significant effects on soil structure, soil properties and soil quality.

Soil water and soil air

• Soil water originates from atmospheric precipitation, snow and surface runoff, and sometime from groundwater.

• Soil air exists the pore without water, which reveals less proportion oxygen, more proportion CO2 compared to atmospheric air. Soil air is also comprised of CH4, H2S,H2 and NOx.

Soil particle composition

我国土壤质地分类

颗粒组成（％）

质地组 质地名称 砂粒

（0.05-1 mm）

粗粉粒

（0.001-0.05mm）

粘粒

（<0.001 mm）

砂土 粗砂土

细砂土

面砂土

>70

60-70

50-60

- <30

砂粉土

粉土

>20

<20 >40

粉壤土

粘壤土

>20

<20 <40

壤土

砂粘土 >50 -

>30

粘土 粉粘土

壤粘土

粘土

- -

30-35

35-40

>40

Soil Texture Terminology Refects Paricle Size Not Mineralogy

Sources of soil pollutants

Industrial source

Transport source

Agricultural source

Domestic source

Pollutants in soils mainly come from industrial

emissions, fertilizer, pesticides, urban sewage, waste.

Soil pollutants

Industrial discharge, Wastewater irrigation

Pesticides, fertilizer, agricultural waste

Tail gas

Household garbage, domestic sewage

Inorganic pollutants

Organic pollutants

Harmfulmicroorganism

Classification of soil pollutants

Heavy metals, nonmetals, radioative

elements, inorganic acids and alkalis.

Pesticides, antibiotics, hydrocarbon compounds, phenols

Polluted microorganism, pathogenic bacteria

Environmental and ecological effects of soil pollution

Harmfulness of soil pollution

• Reduction of crop production• Decline in food quality• Health hazard of human being through food web• Other environmental issues(Atmospheric quality,

surface water quality, groundwater quality, ecological

degeneration)

Some guidelines of heavy metals for non-pollution vegetables in China(maximum residue limit)

重金属 最高残留限量 （mg/kg ）

汞 0．01

砷 0．5

铅 0．2

镉 0．05

Degeneration of soil quality

Soils, Agriculture and Desertification

1. Soil degradation is mainly caused by agricultural

plowing breaking up soil structure and increasing

erosion rates.

2. Deterioration of soil quality can lead to desertification.

3. Destruction of rainforests leads to release of soil

organic carbon as atmospheric carbon dioxide.

4. Over-pumping of groundwater for irrigation depletes

this resource and causes subsidence.

5. Farming methods, such as drip irrigation and

minimum tillage planting, can lead to less water usage

and soil conservation.

Soil Degradation Varies Around the World

Soil Erosion

Soil particles sizes are carried relatively easily by streams.Vegetation, especially root structures, hold soils together.Cutting down natural vegetation (e.g., trees to clear land for

farming increases erosion rates).Plowing of soils further breaks up soils allowing erosion.Irrigation can enhance normal erosion rates.

Loss of vegetation leads to decreased stability

Excess erosion caused by agricultural runoffCentral Valley, CA

Desertification• Extended periods of drought can lead to

desertification.

• Over-grazing by cattle and sheep can also

destroy existing vegetation and decrease

soil quality.

• Over-cropping, planting too many times

per season, in semi-arid land can turn

them into arid lands.

Desertification of farmland –Danakil Depression, Egypt

Extent sub-Saharan desertification

Barren Fields Buried Under Windblown Soil

Deforestation of Amazonian rainforest nearMaraba, Brazil

Risk assessment of soil pollution

Environmental risk of soil pollution

• Risks related to one soil pollutant• Ecotoxicological risks• Biological availability• Combination effects

Environmental risk assessment of soil pollution

Ecological risk assessment of soil pollution

Remediation of polluted soils

Classification of remediation techniques for polluted soils

Based on restoration site

In-situ remediation

Ex-situ remediation

In-situ treatment

Ex-situ treatment

Based on restoration principle

Phytoremediation technique

Microorganism technique

Chemical technique

Physical technique

www.themegallery.co Company Logo

www.themegallery.co Company Logo

www.themegallery.co Company Logo

www.themegallery.co Company Logo

www.themegallery.co Company Logo

www.themegallery.co Company Logo

www.themegallery.co Company Logo

Hyperaccumulation plants of heavy metals

1)Strong tolerance to high level heavy metals2)Accumulating high concentrations of heavy metals3)Fast growth ratio4) Higher biomass5) Well developed root system

Species of hyperaccumulation plants

Chemical washing remediation of polluted soils

Injecting the leacheate into contaminated soils and dissolving pollutants like heavy metals. Then extracting the liquids with pollutants from soils.

www.themegallery.co Company Logo

Remediation of organic pollutants in soils

Microorganism remediation of organic pollutants in soils

①Microorganism degradation of petroleum pollutants

② Microorganism degradation of pesticides

③ Microorganism degradation of polycyclic aromatic hydrocarbon

④ Microorganism degradation of pentachlorophenol

Bioremediation

① Phytoremediation of organic pollutants

② Combined remediation of plant and microorganism for organic pollutants

Other remediation techniques

① In-situ washing technique② In-situ soil vapor extraction technique③ Photochemical degradation technique④ In-situ covering technique

www.themegallery.co Company Logo

Contour Plowing/Planting Impedes Water Flow

Terracing Creates “Steps” of Shallower Slope

That is all for this lecture

Thank you for your attention