Step 1: Saturnine gout is a rheumatologic manifestation of chronic lead poisoning. The term "saturnine" derives from Saturn, the alchemical name for lead.
Step 2: Lead impairs purine metabolism and reduces renal excretion of uric acid, leading to hyperuricaemia and gouty arthritis.
Step 3: A classic source is illicitly distilled alcohol (moonshine) contaminated with lead from the apparatus, plus old lead plumbing and paints.
Step 4: Cadmium causes itai-itai disease and renal tubular damage, beryllium causes berylliosis, and mercury causes neurological and renal toxicity, none of which produces saturnine gout. Hence the metal is lead.