What type of radiation effects are observed with exposure to low doses over longer periods?

The correct choice highlights the nature of radiation effects associated with prolonged exposure to low doses. Stochastic effects are those that occur by chance and their probability increases with exposure to radiation, but the severity of the effect is not dependent on the dose. These effects, such as cancer and genetic mutations, may occur many years after exposure and do not have a threshold level; meaning that even low doses can contribute to the risk.

In contrast, deterministic effects are those that have a threshold dose level, and their severity increases with the dose. Acute effects typically arise from high doses of radiation received over a short period, resulting in immediate symptoms. Direct effects refer to the immediate chemical changes in cells caused by radiation hitting cellular components, which can also lead to deterministic effects.

Understanding that stochastic effects arise primarily from long-term exposure to low doses helps clarify why this is the correct answer in this context. The gradual accumulation of exposure is what makes stochastic effects significant, particularly for health risks associated with radiation over a lifetime.