Transformation And Bioaccessibility Of Lead In Soils Induced By Food/drink Feed In The Gastrointestinal Tract

Oral intake of lead?Pb?from the contaminated soils is one of the most important way to ingest Pb.And bioaccumulated into the human body.Then the Pb has harmful impact on human health.In vitro simulation?PBET?has been widely used to study the bioaccessibility of Pb.However,most of the studies have only simulated the bioaccessibility of Pb in the absence of food intake,and did not study the transformation of Pb during the whole simulation.Intake of food following the soil ingestion may affect the bioaccessibility of Pb in the gastrointestinal tract.In this study,the effect of steamed bread,cola and spinach on the transformation and subsequent bioaccessibility of Pb in two soils was determined by the physiologically based extraction test?PBET?.Two compounds,Pb?NO₃?₂and PbCO₃,were included in the evaluation for comparison.The main results were obtained as follows:?1?In the gastric phase,Pb bioaccessibility decreased as the steamed bread increased due to the sorption of Pb on the undissolved steamed bread,especially in PbCO₃,Pb bioaccessibility decreased from 95.03%to 85.40%.Whereas in the intestinal phase,Pb bioaccessibility increased from 1.85%to 5.66%and from 0.89%to 1.80%for Pb?NO₃?₂ and PbCO₃,respectively.The increase was attributed to the transformation of formed Pb carbonates into soluble organic-Pb complexes induced by the dissolved steamed bread at neutral pH as indicated by MINTEQ modeling.For the PbCO₃-contaminated soil,the change in Pb bioaccessibility in both gastric and intestinal phases behaved like that in the pure PbCO₃ compound,the steamed bread increased the bioaccessibility of Pb in the intestinal phase,but the decreased bioaccessibility of Pb was observed in the gastric phase after the steamed bread was added.However,in the soil contaminated with free Pb²⁺or sorbed Pb forms,the steamed bread increased the Pb bioaccessibility in both gastric and intestinal phases.This was probably due to the higher dissolved organic carbon induced transformation of sorbed Pb?Pb sorbed by Fe/Mn oxides?into soluble Pb-organic complex.?2?In the gastic phase,the Pb bioaccessibility drastically decreased and then slowly increased by the addition of spinach in both Pb componds solutions.It was indicated that the great amount of fiber in the spinach sorbed more Pb²⁺induced the bioaccessibility dropped dramatically.Then the more spinach addition,the more hydrolyzed carbohydrate and protein complexed to Pb.But in the intestinal phase,the change of Pb bioaccessibility showed an opposite results:slowly increase and then decrease.It was because in pH=7,the carbohydrate and protein was hydrolyzed to DOC.Then the DOC would complexed to Pb.In two soils,the Pb bioaccessibility decreased by the addition of spinach both in the gastic phase and intestinal phase.This was probably due to the higher fiber induced transformation of soluble Pb-organic complex and free Pb²⁺into sorbed Pb(Pb²⁺D?s??HAPb⁺?s?and HA₂Pb?s?).?3?The Pb bioaccessibility was decreasd by the addition of cola when in the gastric phase and the intestinal phase both in Pb compounds and two soils.In the gastric phase,in Pb?NO₃?₂ and PbCO₃ solutions,the decrease from 98.52%to 3.79%and 95.55%to 2.74%was attributed to the transformation of free Pb²⁺and soluble organic-Pb complexes to Pb₅?PO₄?₃Cl induced by the PO₄³⁺in the cola as indicated by MINTEQ modeling and XRD patterns.In the intestinal phase,the Pb bioaccessibility was increased when 43mL cola addition,but decreased when 48ml cola was added compared to the 43mL.It was because the cola has more DOC than that of none cola addition.And in the two soils,the Pb bioaccessibilty decreased from 58.95%to 5.95%and from 78.27%to 45.6%in the PbCO₃-contaminated soil and soil contaminated with free Pb²⁺or sorbed Pb forms in the gastric phase,it was probably due to the cola induced transformation of sorbed Pb?Pb sorbed by Fe/Mn oxides?into Pb₅?PO₄?₃Cl.In the intestinal phase,the change in Pb bioaccessibility behaved like that in the gastric phase,but it was because the formed PbCO₃ in the neutral condition transformed into Pb₅?PO₄?₃Cl.?4?The results showed that steamed bread,cola and spinach can affect the transformation and bioaccessibility of Pb,which is of great significance to guide us to eat properly after eating Pb.