Which organs are responsible for destroying old red blood cells?

Spleen is also known as the graveyard of RBC, if it helps u 

1.Stem cells in bone marrow make all blood cells. RBC lives about 120 days. 
RBC are destroyed in Spleen. This process takes place as: 
- RBCs are ruptured. 
- Heme and globin portions separated. 
- Globin > amino acids. 
- Iron transferred in transferrin into the blood > into bone marrow for reuse. 
- Heme > Biliverdin > Bilirubin > liver >small intestine. 

2.Reticuloendothelial cells participate in the destruction of senescent RBC's. The spleen is a well suited site of RBC destruction given that cells must course through 2-3 micron apertures in the walls of splenic sinusoids, which is an ultimate test of cell pliability. Rigid cells are entrapped and phagocytosed. Intra-erythrocyte inclusions are removed during splenic circulation. 
Destruction of RBCs happens within reticuloendothelial cells – NOT in the circulation. Globin and heme get recycled, porphyrin is degraded to bilirubin which is conjugated by the liver and excreted in the gut. Rate limiting step is conjugation. Indirect (unconjugated) bilirubin is result if this doesn’t happen. 
Normally ~10% RBCs lyse while in circulation Þ Hgb gets released into circulation and rapidly disassociates into alpha and beta dimers which are bound by haptoglobin. The Hgb/haptoglobin complex is transported to the liver. If haptoglobin is depleted, free Hgb circulates and is filtered by the kidney. Free Hgb is either reabsorbed by renal tubular cells or excreted as free Hgb in the urine. 

3. Another site reported that 
RBC destroyed in liver and spleen, by macrophages. 2 million destroyed per second. 
Hb is released and iron is recovered and returned to bone marrow.

The answer is nucleic acid