HLSC 4P04 - Soil Contamination

Lecture 4

What are the four major components of soil?

Mineral matter, organic matter, water, and air.

What ecological functions does soil serve?

• Transformer of energy

• Recycler of materials

• Purifier of water

• Ecosystem component

What is a soil profile?

A vertical arrangement of soil layers (horizons) seen by digging a trench.

What are the three main soil horizons?

• Topsoil: Rich in humus and organisms

• Subsoil: More inorganic material

• Parent material: Reflects characteristics of the rock that formed it

What environmental factors affect soil formation?

Temperature and precipitation – Warmth and moisture speed decay; rainfall causes leaching.

What is soil contamination?

The presence of pollutants above a safe level that deteriorate or destroy soil functions.

What are common soil contaminants?

• Petroleum hydrocarbons

• Solvents

• Pesticides

• Lead and heavy metals

What are common sources of soil contamination?

• Ruptured storage tanks

• Pesticides

• Landfill leaching

• Industrial waste discharge

What are the 3 main ways soil contaminants enter the human body?

• Ingestion (eating soil)

• Inhalation

• Dermal (skin) absorption

Who is most at risk from ingesting contaminated soil?

Young children under 3, due to frequent soil ingestion and higher absorption of toxins (e.g., lead).

What happens when contaminants are ingested?

Some are absorbed in the mouth or digestive system, then processed by the liver; excess overwhelms detox systems.

How does inhalation of contaminated soil particles affect health?

Small particles can lodge in the lungs and may enter the bloodstream with repeated, long-term exposure.

What is dermal absorption and what contaminants are most dangerous this way?

Absorption through the skin, especially of volatile organic compounds.

• Some heavy metals like Cr(VI) and inorganic mercury can also penetrate skin.

How can soil contaminants indirectly affect humans?

• Entering drinking water

• Taken up by plants/livestock and entering the food chain

• Examples: Dioxins, cadmium in crops, arsenic in water

What are heavy metals and why are they a concern?

Elements with metallic properties (or metalloids) that can be toxic at high levels, especially in contaminated soils.

Where do heavy metals in soil come from?

They occur naturally in rocks, but levels vary depending on geology and human activity.

What are key industrial uses of arsenic?

• Wood preservatives, glass, pharmaceuticals, pigments, agrochemicals, electronics

How many people are at risk of arsenic-related diseases in Southeast Asia?

An estimated 30 million people.

What are early symptoms of chronic arsenic exposure?

• Skin pigmentation changes

• Lesions, hard patches on hands and feet

What long-term health effects are linked to arsenic exposure?

• Neuropathy, GI symptoms, diabetes, renal & liver damage, bone marrow depression,

• High BP, cardiovascular disease, cancer (skin, bladder, lungs, possibly kidneys/liver/prostate)

How does arsenic affect pregnancy and children?

• Increases risk of miscarriage, stillbirth, pre-term birth

• In utero exposure increases risks of lung cancer and disorders

What are natural sources of arsenic in the environment?

• Volcanic activity

• Mineral dissolution into groundwater

• Plant exudates

• Windblown dust

What are human sources of arsenic contamination?

• Mining, smelting, fossil fuel combustion

• Pesticide production/use

• Timber preservatives

• Remobilization of old sources (e.g., mine drainage)

• Well drilling into arsenic-rich geological deposits

How is cadmium behaviour in soil influenced?

Primarily by soil pH – it becomes more mobile and bioavailable in acidic soils.

How can cadmium bioavailability be reduced in soil?

Lime the soil to raise pH (make it less acidic).

What are health effects of cadmium exposure?

• Kidney damage (proteinuria)

• Skeletal damage (osteoporosis, fractures)

• Carcinogenic effects

What are main sources of cadmium exposure in non-smokers?

Food, especially crops like rice, cereals, and shellfish.

Who is most at risk of cadmium exposure?

• Vegetarians

• People with high rice/shellfish intake

• Pregnant women with low iron or zinc

• Smokers

• Residents near industrial sources

What are environmental sources of lead?

• Petroleum

• Industrial processes

• Paint

• Solder in canned food and water pipes

• Leaded gasoline (historical)

How does lead affect children’s health?

• Lower IQ

• Developmental delays

• Higher physiological uptake than adults

• Greater vulnerability due to developing systems

What is the estimated IQ impact of lead exposure?

IQ drops by 1–3 points per 10 μg/dl of blood lead.

What is the most harmful form of mercury to human health?

Methylmercury

How does methylmercury exposure affect humans?

• Impaired brain development

• Reduced IQ and earning potential

• Risk of cardiovascular disease in adults

What are the main sources of mercury exposure in humans?

• Eating contaminated fish

• Direct soil ingestion by children

• Burning of fossil fuels

Why is asbestos in soil dangerous?

• Can become airborne by wind or disturbance

• Inhalation causes lung cancer and mesothelioma

Who is at greatest risk from asbestos exposure?

• Residents near mines or asbestos plants

• Workers with occupational exposure

• Nearby communities exposed to disturbed contaminated soil

What happened in Seveso, Italy in 1976?

A chemical factory accident released toxic dioxins (including TCDD) over 15 km², affecting 37,000 people. Studies showed increased rates of cancer, circulatory and respiratory diseases, and diabetes.

What makes dioxin exposure assessments difficult after incidents like Seveso?

Lack of appropriate exposure assessments hampers long-term health impact studies.

What are Persistent Organic Pollutants (POPs) in soil?

• PCBs

• Polybrominated biphenyls

• PCDFs

• PAHs

• Organophosphorus & carbamate insecticides

• Herbicides

• Fuels (gasoline, diesel)

• Pharmaceuticals and metabolites

Which cancers are linked to pesticide exposure?

• Non-Hodgkin lymphoma

• Leukemia (especially in children)

• Breast cancer

• Kidney and pancreatic cancer

• Prostate cancer

What neurological condition is linked to occupational pesticide exposure?

Parkinson’s disease

What are other health effects of pesticide exposure?

• Nervous system changes

• Birth defects

• Chromosomal damage (genotoxic effects)

What are common sources of solid waste?

• Animal waste

• Industrial & hazardous waste

• Food and household waste

• Non-infectious medical waste

• Mining and construction debris

What are key public health concerns of solid waste?

• Odour and aesthetics

• Groundwater contamination

• Disease-spreading vectors (rats, flies, etc.)

What are the two main disposal methods for collected waste?

• Landfilling or incineration

• Recycling or composting (waste diversion)

What problems are caused by un-diverted waste?

• Habitat destruction

• Ground and surface water pollution

• Air pollution (toxins and greenhouse gases)

What vectors breed in organic waste or refuse dumps?

• Rats (leptospirosis, plague)

• Flies (fecal-oral infections)

• Mosquitoes (Aedes, Culex – dengue, Zika, etc.)

• Sandflies (leishmaniasis)

• Reduviid bugs (Chagas disease)

What makes garbage dumps attractive breeding grounds for Aedes mosquitoes?

Discarded items like cans, jars, tires collect rainwater and provide breeding habitats.

What are types of medical waste?

• Sharps (needles, blades)

• Contaminated materials (bandages, cotton)

• Organic waste (e.g. placentas)

How should sharps be disposed of in health centers?

In sturdy, closed containers with a small opening, placed in a deep waste disposal pit with a locked superstructure.

What precautions should health workers take when handling medical waste?

• Wear protective clothing

• Use appropriate tools

• Keep incinerators and disposal pits secure and fenced off

What is the average waste generation in North America per person per day?

Around 2.5 kg/person/day

What factors increase waste generation in developed countries like Canada?

• Urbanization

• High income and consumption

• Lifestyles promoting disposable culture