Final answer:
The radon tester should inform the homeowner about the health risks of high radon levels and the importance of mitigation, even if they cannot force action. Documentation of this communication is recommended.
Step-by-step explanation:
If radon measurements in a home confirm radon concentrations in excess of 4 pCi/L and the homeowner refuses mitigation, the radon tester's ethical responsibility is primarily to ensure that the homeowner is well informed about the risks associated with high radon levels. This includes explaining that radon exposure is a leading cause of lung cancer in non-smokers and that prolonged exposure to levels above 4 pCi/L carries significant health risks, comparable to smoking a carton of cigarettes a day. While the radon tester cannot force mitigation, they should provide detailed information and recommend action be taken to reduce radon levels to protect the occupants' health. Documentation of the communication and the homeowner's decision is also advisable in case of future legal implications.