There is much interest into ways of minimizing the bioavailability of lead in so

Question

There is much interest into ways of minimizing the bioavailability of lead in soils (how much will be taken into blood following ingestion. The following is an excerpt of a figure in Environmental Science and Technology published by EPA scientists in 2016 (way back, last year when they still did research). In it, they examined how much of the soil Pb was bioavailable using extractions basedestimates (a variety of methods, acronyms of SBRC, IVG, PBET, UBM assays) and how they were similar (or not) to actual Pb uptake observed in a mouse model (DIN). They also did something quite unusual—they looked at the chemical form of the Pb after they did the extractions, and also studied the chemical form of residual Pb in the mouse gut and intestine to understand how the chemical form of Pb influenced the how much was bioavailable. Given the information above please do the following:

(a) Provide a reasonable chemical explanation for the partial (~25%) extraction of Pb from this soil

(b) What is the efficacy of treating the soils with phosphoric acid to affect Pb speciation? Explain.

(c) Explain the prevalence of the two major forms of Pb in the soil.

Explanation / Answer

(a) Pb exists in soil in three different forms as exchangeable, carbonate and Fe-Mn oxide .Pb sources entering the soil remain in relatively weakly bound forms, which are mobile and have potentially biological availability. Only the weakly bound ones can be removed therefore only partial extraction takes place.If the mobility factor increases then it becomes more difficult to extract.

(b) Under the influence of phosphoric acid lead extraction increases at a lower pH and decreases at a higher pH . Therefore the strength of phosphoric acid is important .

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