Why is lead often detected in urban soils?

Lead is often detected in urban soils primarily due to a combination of factors related to human activity and historical practices. Urban areas are typically more industrialized and densely populated, which contributes significantly to the presence of lead in the environment.

The proximity to industrial areas contributes to lead contamination as factories and manufacturing processes historically used lead in various materials and products. Furthermore, these industries may have emitted lead into the air, which could later settle in nearby soils.

In addition to industrial contributions, the historical use of lead in fuels and paints plays a crucial role in lead presence in urban soils. Leaded gasoline, commonly used until the late 20th century, released lead contaminants into the atmosphere. As these pollutants settled over urban areas, they accumulated in the soil. Similarly, lead-based paints, used extensively in older buildings, have contributed to soil contamination through deterioration and peeling over time, with lead particles ultimately finding their way into the ground.

This combination of industrial activity and historical practices explains why urban soils tend to have higher levels of lead, making the option stating both factors as contributing causes the most comprehensive and accurate response. The other choice, which mentions only agricultural practices, does not align with the well-documented sources of lead in urban environments.