Lecture 22

Definition of Soil Pollution
- "The introduction of substances or organisms into the soil, resulting in a change of the soil quality, which is likely to affect the normal use of the soil or endangering public health and the living environment."
Types of Soil Pollution
- Point Source Pollution
- Refers to a single identifiable source of pollution such as a pipe or drain.
- Non-Point Source Pollution
- Also known as diffuse pollution; refers to inputs occurring over a wide area from multiple sources, e.g., agricultural lands, lawns.

18th-19th Century
- Industrial Revolution significantly accelerated pollution.
19th Century
- Initiation of large-scale mining.
Second Half of 20th Century
- Large-scale use of fertilizers and pesticides.
- Expansion of industrial production.
- Increased fossil fuel use.
- Rapid population growth led to an increase in the diversity and quantity of contaminants.

Petroleum Hydrocarbons
Pesticides
- Most widely dispersed contaminants.
Industrial Organics
- Includes solvents, BTEX (benzene, toluene, ethylbenzene, and xylene), PCBs (polychlorinated biphenyls), and other xenobiotics.

Defined as "chemicals discovered in water that previously had not been detected, or are being detected at levels significantly different than expected" (EPA).
- Examples include pharmaceuticals (antibiotics, hormones, drugs) and personal care products (PCPs, such as fragrances and ultraviolet filters).
- Also includes nanomaterials.

Pollutant Sources
- Includes surface and groundwater, soil, plants, animals, animal feed, processed animal products, and ultimately humans.
Routes of Exposure
- Ingestion, dermal contact, and inhalation.
- Factors influencing exposure: gender, age, etc.
Contamination Pathways
- Humans can be contaminated by consuming contaminated water, crops, or animal products, directly ingesting soil (especially children), or inhaling dust.
- Pollutant sources include animal and human wastes.

Pollution causes a chain of degradation processes in soil, jeopardizing its ability to provide essential ecosystem services.

Arsenic in Groundwater
Agricultural Pollution
- Impact of fertilizers contributing to eutrophication.
- Groundwater contamination by pesticides.

Historical Context
- Arsenic is associated with the "largest mass poisoning in human history" with an estimated 94-220 million people at risk (Podgorski & Berg, 2020).
- Subsurface wells from the 1970s were intended to avoid surface pathogens but later contributed to arsenic exposure, resulting in high infant mortality rates.
- Approximately 7-11 million wells exist today in contaminated areas.
Consequences
- Arsenic poisoning detected in the late 1980s with extensive exposure noted in the 1990s.
- Over 50% of wells exceeding WHO guidelines.
- A cohort study showed that more than 20% of all adult deaths in Bangladesh are attributed to arsenic.

Global Use Data
- Fertilization heavily contributes to soil contamination.
- Heavy metals like arsenic (As), cadmium (Cd), lead (Pb) added to soils.
- Contamination leads to surface water issues, primarily through eutrophication.

Nitrate Levels
- Drinking water standard level is at 10 mg/L for N-NO3-.
- Higher levels can cause methemoglobinemia and potential stomach cancers.
- Predictions indicate significant nitrate concentrations in shallow U.S. groundwater.

Bee Population Decline
- An unprecedented decline in bee populations globally since the 1990s, potentially linked to pesticide use.
- Chronic exposure to two pesticides can impair foraging behavior and increase worker mortality.
Example: DDT
- Banned in the U.S. in 1972 due to issues with biomagnification, affecting animals higher up in the food chain.
- The bald eagle population dramatically decreased between 1942-1958, but showed increases after DDT was banned (1963-2006).
Human Health Concerns
- Long-term exposure studies have linked pesticide exposure with ADHD and poorer neurodevelopment in children, particularly in communities near agricultural fields.

Treatment processes that aim to address soil contamination directly in the location of contamination (e.g., biostimulation, chemical agents).

Dig and Dump Technique
- Involves excavation of contaminated soil followed by storage in a landfill.
- This method does not provide true remediation but merely shifts contamination elsewhere.
- Historically, this has been the default remediation method for soils.

Amendments for Stabilization
- Commonly used to stabilize inorganic contaminants like lead.
Bioremediation
- Uses naturally occurring microorganisms to break down hazardous substances into less harmful or non-toxic forms, including processes such as biostimulation to enhance microbial activity.

Refers to the addition of nutrients to accelerate the degradation of oil spills.
- Exxon Valdez Oil Spill
- A study demonstrated effective microbial degradation of petroleum hydrocarbons through the addition of nitrogen (N) and phosphorus (P).

Defined as the use of green plants to remove, contain, or render harmless contaminants in soil or water.
Contaminants can be degraded, accumulated in the plants, or released in a volatile form.
Example of Phytoremediation
- Case study on arsenic contamination in Santa Fe using Pteris vittata, an arsenic-hyperaccumulator, illustrated potential for bioremediation through plant uptake.

Performance of phytoremediation is dependent on soil types, showing low efficiency in clayey soils, while sandy soils yield better results.
Process of arsenic removal is gradual and may take decades.

Soil is a finite resource taking thousands to millions of years to form.
Industrial, agricultural, and naturally occurring toxic chemicals contaminate soils, threatening ecosystems, water resources, and public health.
Sustainable remediation methods should prioritize stabilization and bioremediation, like phytoremediation, focusing on in situ treatment for chronic contamination, while acute cases may necessitate ex situ treatment approaches.
Pesticides are a significant class of pollutants impacting both ecosystems and human health.