What does it mean when a chemical residue is biologically inert despite being technically present in the soil?

Answer

It is too tightly bound to particles to be absorbed by plant roots

A chemical can linger long enough to be detected by sensitive laboratory tests, but if it is tightly associated with organic matter or clay, it is biologically unavailable to interact with soil life or be absorbed by plants.

What does it mean when a chemical residue is biologically inert despite being technically present in the soil?
environmentpersistencesoildegradationtoxin