Which unit is often used to express low levels of radioactivity in wastewater?

The unit commonly used to express low levels of radioactivity in wastewater is the picocurie per liter. The picocurie is a sub-unit of the curie, which quantifies radioactivity. Specifically, one picocurie represents one trillionth (10^-12) of a curie, making it more suitable for measuring low levels of radioactivity that might be found in environmental samples, such as wastewater. This sensitivity is crucial in environmental monitoring and compliance since even small amounts of radioactive material can have significant implications for public health and safety.

Using a larger unit such as curie per liter would not provide a practical measure for low levels of radioactivity commonly encountered in wastewater. Similarly, millirem and rem per liter are units of radiation dose rather than radioactivity, and thus are not applicable for quantifying the levels of radioactive material in a fluid context like wastewater. This distinction is critical in understanding the appropriate measurements used in environmental science and radiation safety.