Final answer:
Controlled substances returned to the pharmacy should be destroyed via high-temperature incineration to prevent ecotoxic activity, with careful handling of the residual ashes to protect the environment.
Step-by-step explanation:
The destruction of controlled substances which are returned to the pharmacy must be carried out with caution to ensure there is no pharmaceutical or ecotoxic activity. The recommended method for this process is incineration at high temperatures above 1000 degrees Celsius. This high level of heat is sufficient to break down the compounds and reduce the risk of their becoming environmental pollutants.
However even after such a thorough process, the residual ashes must be managed responsibly to avoid any detrimental environmental impact. In many European countries, systems are in place for the take-back and proper disposal of pharmaceutical residues but in the United States such systems are often voluntary and localized. To reduce environmental pollution, it is important to prevent improper disposal of these substances such as flushing them down the toilet or sink, as studies have shown this can contribute to contamination.