What is the cause for the difference in pH between NaCl and Ringer Lactate

"Normal saline contains approximately $$\pu{154mM}$$ of each $$\ce{Na+}$$ and $$\ce{Cl-}$$ with average pH of 5.0 and osmolarity of $$\pu{308mOsm/L}$$. LR solution has electrolytes $$\pu{130mM}$$ of $$\ce{Na+}$$, $$\pu{109mM}$$ of $$\ce{Cl-}$$, and $$\pu{28mM}$$ of lactate. The Average pH of LR is 6.5 and is slightly hypo-osmolar with $$\pu{272mOsm/L}$$. 6,7"

Regular $$\ce{NaCl}$$ solutions should have 7 as a pH, yet this solution is 5. A lactate ringer which has a similar composition to regular $$\ce{NaCl}$$ is 6.5.

I thought that the pH of 5 doesn't have anything to do with the $$\ce{NaCl}$$ but with the reaction of blood $$\ce{CO2}$$ with the water in the $$\ce{NaCl}$$ solution lowering the pH, but clearly that was wrong.

• Note that pH of water in equilibrium with air is expected to be about 5.6. NaCl itself does not cause pH lowering, but CO2 and possible impurities do. – Poutnik Jun 15 at 6:03
• Note that presence of lactate as salt of weak acid breaks the similarity from acid-base equilibrium point of view. – Poutnik Jun 16 at 14:45