What substances are prohibited in embalming fluids due to their poisonous effects?

The correct choice identifies heavy minerals and metallic substances as prohibited in embalming fluids due to their toxic effects. Such substances can pose significant health risks to both the embalmer and the environment. Heavy metals like lead, mercury, and others have been known to be harmful, potentially causing various health problems, including organ damage and environmental contamination.

The prohibition of these substances underscores the importance of safety in the embalming process, ensuring that the chemicals used do not pose additional risks to human health or ecological systems. Regulations are often in place to make sure that only safe and effective compounds are utilized in the embalming process to protect those involved and the public at large.

Other substances mentioned in the options may have their own concerns, but heavy metals and minerals are particularly notable for their acute toxicity and long-term environmental impact, which is why they are explicitly prohibited.