What is a key concern regarding the use of persistent herbicides?

The key concern regarding persistent herbicides is that they may contaminate groundwater. These herbicides have a tendency to remain in the environment for extended periods, which can lead to runoff or leaching into groundwater supplies. This is particularly concerning because once these chemicals enter the water supply, they can affect not only agricultural and recreational water sources but also drinking water quality. The potential for long-term environmental effects and impacts on non-target plant and animal life makes the issue of groundwater contamination a significant consideration when using these herbicides in landscape and turf management.

The other options, while important in different contexts, do not address the primary concern associated with persistent herbicides. Frequent applications may indicate a different category of herbicides, specific targeting of weeds is typically a desired characteristic, and claims of having no residual effects contradict the very nature of persistent products.