**Core Concept**
Methyl mercury is a toxic form of mercury that can accumulate in the body, particularly in the nervous system and kidneys. When ingested, it undergoes enterohepatic recirculation, allowing nearly complete absorption from the gastrointestinal tract.

**Why the Correct Answer is Right**
Methyl mercury is absorbed from the gut due to its lipophilic nature, allowing it to easily cross the intestinal epithelium. Once inside the body, it is bound to cysteine residues in proteins, facilitating its transport and distribution to various organs. The enterohepatic circulation of methyl mercury enables its reabsorption from the bile back into the bloodstream, resulting in nearly complete absorption from the gut.

**Why Each Wrong Option is Incorrect**
**Option A:** 20% is an underestimation, as methyl mercury's lipophilic nature and enterohepatic circulation contribute to its high absorption rate.
**Option B:** 50% is still too low, given the efficient absorption mechanisms at play.
**Option C:** 80% is close but still incorrect, as the actual absorption rate is nearly complete.

**Clinical Pearl / High-Yield Fact**
Methyl mercury is a potent neurotoxin that can cause irreversible damage to the nervous system, particularly in developing fetuses and young children. Its high absorption rate from the gut makes it a significant public health concern, particularly for individuals consuming contaminated fish or other seafood.

✓ Correct Answer: D. 100%