- Soil contamination: Lead can be present in soil due to historical industrial activities, such as lead smelting or mining, or from the use of lead-based pesticides or fertilizers. When contaminated soil is used for gardening, lead can be absorbed by plants.

- Lead-based paint: Lead-based paint is a common source of lead contamination in older homes. When lead-based paint chips or flakes, it can release lead dust that can settle on soil and plants.

- Water contamination: Lead can leach from old lead pipes and fixtures into drinking water. If contaminated water is used for irrigation, it can introduce lead into the garden soil and plants.

- Compost: Compost made from materials that contain lead, such as food scraps from homes with lead-based paint, can also introduce lead into garden soil.

- Fertilizers: Some fertilizers may contain lead as an impurity. Using fertilizers that contain lead can contaminate garden soil and plants.