Therefore , proof of dioxins as causative factors has been difficult .
In occupational settings many symptoms have been seen , but exposures have always been to a multitude of chemicals including chlorophenols , chlorophenoxy acid herbicides , and solvents .
Proof of dioxins as causative factors has been difficult .
In occupational settings many symptoms have been seen , but exposures have always been to a multitude of chemicals including chlorophenols , chlorophenoxy acid herbicides , and solvents .