Presence of Lead in drinking water can adversely affect the human health. The…

Concept — why lead has specific target systems. Lead (Pb) is a cumulative heavy metal that behaves inside the body like a divalent cation. It substitutes for calcium (Ca2+) and zinc (Zn2+) at their binding sites and it latches on to the sulfhydryl (–SH) groups of enzymes. Toxicology therefore predicts the damage: the systems whose normal working depends most on those cations and on those enzymes are hit first and hardest, and they are called the critical, or most sensitive, target systems.

Applying that idea to the five systems listed in the question.

• Nervous system — neurotransmitter release and neuronal development are calcium-driven, so lead standing in for calcium blocks synaptic transmission and disturbs brain development; loss of cognitive ability in children and, at high dose, encephalopathy follow.

• Blood-forming (haematopoietic) system — lead attacks the haem-synthesis pathway at two points: it displaces the zinc of delta-aminolaevulinic acid dehydratase (ALAD), and it also inhibits ferrochelatase, the iron-sulfur-cluster enzyme that inserts iron into protoporphyrin; haem synthesis therefore stalls and anaemia with basophilic stippling of the red cells appears.

• Renal system — lead-protein complexes are taken up by endocytosis into the epithelial cells of the proximal tubule, so the metal accumulates in exactly the cells that do the reabsorbing and injures them, giving a Fanconi-type reabsorption defect early and chronic lead nephropathy later.

Cross-check the two systems that are left out.

• Cardio-vascular system — sustained lead exposure genuinely does raise blood pressure, but that effect emerges later and at a higher cumulative body burden, so it is not counted in the classical most-sensitive triad.

• Respiratory system — lead taken in through drinking water is absorbed from the gut, not inhaled, and lead produces no characteristic lung lesion, so on this exposure route the lungs are not a target organ at all.

Result. The three systems most sensitive to lead are therefore the nervous system, the renal system and the blood-forming system — that is, statements (A), (C) and (E) of the list in the question. The WHO lead-poisoning fact sheet and the ATSDR toxicological profile for lead name the same three systems as the principal targets of lead toxicity.