Selected Chemical and Physical Properties of Soils and Gut Physiological Processes that Influence Lead Bioavailability

Abstract

This paper considers selected field examples of physical and chemical properties of soil and some of the interactions with gut physiological processes that are related to lead bioavailability. The blood lead response to quantity of lead in mining and milling environments compared with urban and lead smelter conditions appears to be different. The emphasis of this paper is to understand the complexity of the urban environment.

Bioavailability appears to be related to physical and chemical qualities other than mere quantity of lead. Particle size is one physical quality that influences bioavailability. Compared to intact lead—based paint, small particle emissions from vehicles govern the general soil lead pattern in urban environments. Lead has accumulated in soils in proportion to city size, with the inner—city generally measuring the highest lead levels. The soil lead situation is further exacerbated by the chemical influence of other toxic substances such as zinc. In several cities, zinc levels of 1,500 ppm and higher, plus acid conditions (pH 5.4 and lower) have been observed. This condition is phytotoxic to plants and the deficiency of plant cover increases the likelihood for soil lead ingestion. After ingestion, nutritional status becomes an important factor with both iron and calcium deficiencies increasing lead bioavailability.

To complement the other discussions of the Gl tract and bioavailability in this volume, the following physiological responses of the gut that either increase or decrease soil lead bioavailability are described: (1) The role of the ‘normal’ microbial flora in altering baseline gut function, (2) effect of pH, (3) intestinal transit time, (4) role of mucus, and (5) barriers to lead transport. Physiologically there are nine physical and/or chemical barriers to soil lead absorption which tend to decrease bioavailability: any breakdown of or increased permeability in these barriers would have the opposite effect. The addition of a soil amendment, such as pathogen free processed sludge, would be expected to be a practical means for reducing soil lead bioavailability. The amendment should serve to bind lead and thus increase effective particle size. It would also have the benefit of improving plant growth as shown in the laboratory. Further study is needed to conduct toxicity testing and undertake field evaluation.     

Effect of Soil Dose on Bioavailability of Lead from Mining Waste Soil in Rats

Abstract

The purpose of this study was to determine the extent of absorption of lead (Pb) in mining waste soil from Butte, Montana. It is the first study to fully investigate the bioavailability of lead in soils containing mine waste using a soil dose response approach. Young 7–8 week-old male and female Sprague-Dawley rats (5 animals/sex/group) were given mining waste soil [810 ppm lead (Test Soil I) or 3,908 ppm lead (Test Soil III)] mixed in a purified diet (AIN—76?) at four different dose levels (0.2, 0.5, 2 and 5% dietary soil) for 30 consecutive days. The test soil dose levels at 2 and 5% were chosen to bracket a pica-for-soil child's soil exposure levels. A pica-for-soil child is a young child who eats large quantities of soil (10 g day^?1). Standard groups included untreated controls and dosed feed soluble lead acetate groups (1, 10, 25, 100 and 250 μg Pb g^?1 feed). The concentrations of lead acetate were chosen to bracket the test soil dose levels of lead. Liver, blood and femur, representing the three compartments in which lead is distributed in the body, were analyzed for total lead concentration using graphite furnace atomic absorption spectroscopy. Clinical signs, body weight, food consumption and liver weights for treated and standard groups were similar to control. Tissue lead concentrations from test soil animals were significantly lower than the tissue concentrations for the dosed feed lead acetate group. Group mean whole blood, bone and liver lead concentrations increased with increasing dose levels for most treatment groups. The increases in blood, bone and liver lead concentrations were not proportional with increasing dose levels and plateaued at the high dose levels. Relative percent bioavailability values, based on dosed feed soluble lead as the standard, were independent of the two different test soils, dose levels or sex, and only slightly dependent on the tissue (blood > bone, liver). Overall relative percent bioavailability values were 20% based on the blood data; 9% based on the bone data; and 8% based on the liver data (2 and 5% dose levels only). The results of this study will provide the scientific validity needed to determine the significance of lead exposure from Butte soils in assessing human health risks as part of the Superfund Remedial Investigation/Feasibility Study process.     

An In Vitro Procedure for Estimation of Lead Relative Bioavailability: With Validation

The relative bioaccessibility leaching procedure (RBALP) is a simple, reproducible, and rapid in vitro procedure for estimating the in vivo (juvenile swine) relative bioavailability (RBA) of lead in solid media. Control of pH, temperature, and agitation are the most critical parameters of this in vitro procedure. The performance of the method was evaluated by triplicate analyses of each of 19 different test substances by the author and three independent laboratories, and comparison of the results to relative bioavailability (RBA) values measured in vivo. The results indicate that the RBALP measurements are strongly correlated with the in vivo RBA values (r² = 0.924, p < 0.0001), with an average absolute error of 10% and an average predictive error of 20%. Comparison of results within and between laboratories indicates that the procedure is highly reproducible, with inter-and intra-laboratory coefficients of variation of 4% and 6%, respectively, and within-sample precision of approximately 7%. Based on the results reported here, the RBALP can be effective in providing reliable estimates of lead RBA as predicted by the immature swine model. The method may also be valuable in evaluating site-specific differences in bioaccessibility, assessing remedial technologies intended to reduce lead RBA, providing a screening mechanism for futurein vivo studies, and providing insight into the chemical and physical factors that control lead bioavailability.     

Silymarin Glyceryl Monooleate/Poloxamer 407 Liquid Crystalline Matrices: Physical Characterization and Enhanced Oral Bioavailability

Silymarin, a mixture of flavonolignans extracted from the seeds of milk thistle, is used clinically as a hepatoprotector to treat liver injuries and chronic hepatitis. However, its therapeutic effect is compromised by its poor oral bioavailability due to the poor solubility and low permeability across intestinal epithelia. The main purpose of this study was to prepare silymarin glyceryl monooleate/poloxamer 407 liquid crystalline matrices (GMO/P407 LCM) to improve the oral bioavailability of silymarin. GMO/P407 LCMs were prepared by a melting/congealing method. The isotropic phenomenon observed under polarized light microscope confirmed the liquid crystalline structure at the junction of LCM and water. Both differential scanning calorimetry and X-ray diffraction analysis confirmed disappearance of silymarin crystallinity after incorporation into the LCMs. In vitro release of silymarin from LCMs was limited, whereas LCMs were readily degraded by lipase and released silymarin quickly and completely. Pharmacokinetic study in beagle dogs showed significantly increased peak concentration for silymarin GMO/P407 LCM, and, most importantly, a 3.46-fold increase in oral bioavailability as compared with Legalon®, a commercial silymarin formulation.     

Effect of Soil Chemical and Physical Properties on Sorption and Desorption Behavior of Lead in Different Soils of India

Lead (Pb) is a non-biodegradable contaminant, present in the environment, especially near lead-based industrial sites, agricultural lands, and roadside soils. Bioavailability of Pb in the soil is controlled by the sorption and desorption behavior of Pb, which are further controlled by the soil chemical and physical properties. In this study, sorption and desorption amounts of Pb in soil were compared with soil physical (sand, silt, clay content) and chemical (pH; electrical conductivity, EC; percent organic carbon, (%OC); cation exchange capacity, CEC) properties. Twenty-six surface soils (0–5cm), expected to vary in physical and chemical properties, were collected from different parts of India and were treated with known concentration of Pb solution (40 μg/L). The amount of Pb sorbed and desorbed were measured and correlated with soil properties using simple linear regressions. Sorption was significantly (p ≤ 0.05) and positively correlated with pH, and %OC; desorption was significantly (p ≤ 0.05) negatively correlated with the same two factors. Stepwise multiple regressions were performed for better correlations. Predicted sorption and desorption amounts, based on multiple regression equations, showed reasonably good fit (R² = 0.79 and 0.83, respectively) with observed values. This regression model can be used for estimation of sorption and desorption amounts at contaminated sites.     

Spiked Sediment Toxicity Testing of Hydrophobic Organic Chemicals: Bioavailability,Technical Considerations,and Applications

Many evaluations estimating safe levels of hydrophobic organic chemicals in sediments do not account for confounding factors such as physical habitat quality or covariance among chemicals. Controlled experiments demonstrating cause and effect can be conducted with spiked sediment toxicity tests, but application of this methodology has been limited in part by concerns about chemical bioavailability and challenges in achieving target concentrations. Relevant literature was reviewed to assess the utility of standardizing sediment equilibration times; hydrophobicity, complex sediment characteristics, and temperature were identified as potentially equally important factors. Disequilibrium appears likely following limited equilibration time but should yield conservative toxicity test results relative to aged field sediments. Nominal and measured concentrations in over 20 published studies were compared to assess spiked chemical recovery (i.e., measured concentration/nominal concentration). Recovery varied substantially among studies and was not readily predictable based on spiking or extraction method, chemical properties, or measured sediment characteristics, although unmeasured differences between sediments appeared to be important. Factors affecting specific studies included chemical adsorption to glassware, biodegradation, and volatilization. Pre- and post-toxicity test analyses are recommended to confirm exposure concentrations. Studies with 2,3,7,8-tetrachloro-dibenzo-p-dioxin (2,3,7,8-TCDD) and hexachlorobenzene (HCB) exemplify the utility of verifying results of field studies using spiked sediment tests. Sediments spiked with these chemicals at concentrations greatly exceeding those in associated field studies caused no adverse effects in test organisms, demonstrating that other chemicals co-occurring in test sediment samples caused toxicity initially attributed to 2,3,7,8-TCDD and HCB in the field studies. Another key application of spiked sediment tests has been the investigation of TOC as the primary factor affecting bioavailability of hydrophobic organic chemicals. A review of LC50s for nine chemicals reported in 12 studies shows that comparable LC50s derived in different sediments generally agree within a factor of five when concentrations are normalized to a constant TOC. Additionally, use of spiked sediment toxicity testing to investigate toxicological interactions among chemicals provides a promising approach to improving the ability to predict sediment toxicity in the field.     

Using Earthworms to Assess Hg Distribution and Bioavailability in Gold Mining Soils

Between 1980 and 2000, the municipality of Cachoeira do Piriá, located in Pará State, Brazil, experienced an intense gold rush with approximately 5,000 artisanal miners discharging more than four tonnes of mercury into soils, air and aquatic systems. Mercury is dispersed across an area of approximately 2,100 ha and concentrations in soils and sediments frequently exceed 1,000 μg.kg^?1. The metallic mercury discharged by miners into the environment has the potential to be transformed into a highly toxic form of mercury, methylmercury. A 28-day bioassay with the earthworm Eisenia fetida was used to assess mercury bioavailability in mine tailings, soils, and sediments. Experiments indicated that the highest Hg concentration in earthworms was associated with low-Hg-organic-rich soils collected from densely vegetated areas despite higher mercury concentrations in organic-poor tailings. This indicates that reaction with organic acids is an important pathway for mercury incorporation into food chains. The quick, inexpensive, and simple bioassay also provided a means to evaluate remedial measures (i.e. by capping “hotspots” with local soils). Earthworm experiments indicate that covering “environmental hotspots” (sites with high Hg bioavailability) with local clay-rich sediments is very effective in terms of preventing uptake of mercury from tailings, while organic-rich sediments are relatively ineffective.     

Characteristics to Consider when Choosing an Animal Model for the Study of Lead Bioavailability

Abstract

Most animal studies conducted to determine the bioavailability of lead have, in the past, employed rodents or lagomorphs as experimental models. In this paper issues and data are presented which raise questions and uncertainties about employing rodents or lagomorphs for investigations into the bioavailability of lead. These issues include: (1) the possible role of coprophagy and feeding behavior in reducing estimates of lead bioavailability; (2) anatomical and physiological differences related to coprophagy which may influence estimates of lead bioavailability derived in rats or rabbits; (3) evidence for relatively high biliary excretion of lead by rats and rabbits; (4) the possibility of a strong developmental component to the active transport of lead. The importance of addressing these and other questions in studies designed to determine the bioavailability of lead is discussed.     

Chemical geometrodynamics: Physical fields can cause asymmetric synthesis

This paper presents theoretical arguments that suggest that chiral combinations of physical fields which can induce motion of elementary particles or molecular systems can in principle cause asymmetric synthesis. The theory is founded on the application of parity and time reversal operators to chiral dynamical systems. The motion of these systems induced by a chiral set of physical fields is shown not to be invariant on parity and time reflection. The relationship between tetrahedral dissymmetry and belical dissymmetry is analyzed in terms of the moments of inertin of a tetrahedrally dissymmetric rotor rotating around each of the four bond axes. The magnitude of anticipated enantiomeric excess which would result from conducting a prochiral chemical reaction in a chiral set of physical fields is estimated to be very small, parts per million or less, for virtually all sets of readily accessible physical fields. The results of experiments in which prochiral chemical reactions were conducted in a sealed tube which was spinning perpendicular or paralled to the earth's surface, are reviewed as are experiments in which prochiral chemical reactions were conducted in intense oriented magnetic fields. Enantiomeric recognition may have been one of the principal mechanisms for amplifying small differences in the rates of a given prochiral chemical reaction.     

Effects of Sterilization and Temperature on the Decrease Kinetic of Lead Bioavailability in Two Different Soil Groups

Sorption of metal ions by soil and clay minerals is a complex process involving different mechanisms, and controlled by different variables that can interact. The impacts of sterilization and incubation temperature on the decrease kinetic of Pb bioavailability in two different groups of soils were studied. Surface soils were sampled from Guilan and Hamadan provinces in the north and northwest of Iran with temperate and semiarid climates. The decrease kinetic of Pb bioavailability in the Pb(NO₃)₂ treated (400 μg Pb g^?1) soils has been studied in solid state incubation in sterile and unsterile conditions at 15, 27 and 37°C. The decrease of DTPA-extractable Pb in both groups of soils is often characterized by an initial rapid step followed by a slow step. The temperate soil with high affinity surface sites for Pb sorption compared to semiarid soils had a lower DTPA-extractable Pb in each time of extraction. Sterilization and soil incubation at lower temperature decreased the rate of Pb sorption/precipitation processes. Among the kinetic models the second order model and Elovich kinetic equation were the better choice to express the decrease kinetic of Pb bioavailability according to higher determined coefficient and the small standard error of the estimate. The determination coefficients of the mass transfer equation were increased and the standard errors of the estimates were decreased in sterile and unsterile conditions by increasing incubation temperature from 15 to 37°C.     

Annotated Chemical Patent Corpus: A Gold Standard for Text Mining

Exploring the chemical and biological space covered by patent applications is crucial in early-stage medicinal chemistry activities. Patent analysis can provide understanding of compound prior art, novelty checking, validation of biological assays, and identification of new starting points for chemical exploration. Extracting chemical and biological entities from patents through manual extraction by expert curators can take substantial amount of time and resources. Text mining methods can help to ease this process. To validate the performance of such methods, a manually annotated patent corpus is essential. In this study we have produced a large gold standard chemical patent corpus. We developed annotation guidelines and selected 200 full patents from the World Intellectual Property Organization, United States Patent and Trademark Office, and European Patent Office. The patents were pre-annotated automatically and made available to four independent annotator groups each consisting of two to ten annotators. The annotators marked chemicals in different subclasses, diseases, targets, and modes of action. Spelling mistakes and spurious line break due to optical character recognition errors were also annotated. A subset of 47 patents was annotated by at least three annotator groups, from which harmonized annotations and inter-annotator agreement scores were derived. One group annotated the full set. The patent corpus includes 400,125 annotations for the full set and 36,537 annotations for the harmonized set. All patents and annotated entities are publicly available at www.biosemantics.org.     

Lycopene in Tomatoes: Chemical and Physical Properties Affected by Food Processing

ABSTRACT:?

Lycopene is the pigment principally responsible for the characteristic deep-red color of ripe tomato fruits and tomato products. It has attracted attention due to its biological and physicochemical properties, especially related to its effects as a natural antioxidant. Although it has no provitamin A activity, lycopene does exhibit a physical quenching rate constant with singlet oxygen almost twice as high as that of β-carotene. This makes its presence in the diet of considerable interest. Increasing clinical evidence supports the role of lycopene as a micronutri-ent with important health benefits, because it appears to provide protection against a broad range of epithelial cancers. Tomatoes and related tomato products are the major source of lycopene compounds, and are also considered an important source of carotenoids in the human diet. Undesirable degradation of lycopene not only affects the sensory quality of the final products, but also the health benefit of tomato-based foods for the human body. Lycopene in fresh tomato fruits occurs essentially in the all-trans configuration. The main causes of tomato lycopene degradation during processing are isomerization and oxidation. Isomerization converts all-trans isomers to cis-isomers due to additional energy input and results in an unstable, energy-rich station. Determination of the degree of lycopene isomerization during processing would provide a measure of the potential health benefits of tomato-based foods. Thermal processing (bleaching, retorting, and freezing processes) generally cause some loss of lycopene in tomato-based foods. Heat induces isomerization of the all-trans to cis forms. The cis-isomers increase with temperature and processing time. In general, dehydrated and powdered tomatoes have poor lycopene stability unless carefully processed and promptly placed in a hermetically sealed and inert atmosphere for storage. A significant increase in the cis-isomers with a simultaneous decrease in the all-trans isomers can be observed in the dehydrated tomato samples using the different dehydration methods. Frozen foods and heat-sterilized foods exhibit excellent lycopene stability throughout their normal temperature storage shelf life.

Lycopene bioavailability (absorption) can be influenced by many factors. The bioavailability of cis-isomers in food is higher than that of all-trans isomers. Lycopene bioavailability in processed tomato products is higher than in unprocessed fresh tomatoes. The composition and structure of the food also have an impact on the bioavailability of lycopene and may affect the release of lycopene from the tomato tissue matrix. Food processing may improve lycopene bioavailability by breaking down cell walls, which weakens the bonding forces between lycopene and tissue matrix, thus making lycopene more accessible and enhancing the cis-isomerization. More information on lycopene bioavailability, however, is needed. The pharmacokinetic properties of lycopene remain particularly poorly understood. Further research on the bioavalability, pharmacology, biochemistry, and physiology must be done to reveal the mechanism of lycopene in human diet, and the in vivo metabolism of lycopene.

Consumer demand for healthy food products provides an opportunity to develop lycopene-rich food as new functional foods, as well as food-grade and pharmaceutical-grade lycopene as new nutraceutical products. An industrial scale, environmentally friendly lycopene extraction and purification procedure with minimal loss of bioactivities is highly desirable for the foods, feed, cosmetic, and pharmaceutical industries. High-quality lycopene products that meet food safety regulations will offer potential benefits to the food industry.     

Whey Protein/Arabic Gum Gels Formed by Chemical or Physical Gelation Process

Whey proteins (WP) gelation process with addition of Arabic gum (AG) was studied. Two different driving processes were employed to induce gelation: (1) heating of 12% whey protein isolate (WPI) solutions (w/w) or (2) acidification of previous thermal denatured WPI solutions (5% w/w) with glucono-δ-lactone (GDL). Protein concentrations were different because they were minimal to form gel in these two processes, but denaturation conditions were the same (90 °C/30 min). Water-holding capacity and mechanical properties of the gels were evaluated. The BST equation was used to evaluate the nonlinear part of the stress–strain data. Cold-set gels were weaker than heat-set gels at the pH range near the isoelectric point (pI) of the main whey proteins, but heated gels were more deformable (did not exhibit rupture point) and showed greater elasticity modulus. However, gels formed by heating far from the pI (pH 6.7 or 3.5) showed more fragile structure, indicating that, in these mixed gels, there are prevailing biopolymers interactions. Cold-set and heat-set gels at pH near or below the WP pI showed strain-weakening behavior, but heated gels at neutral pH showed strong strain-hardening behavior. Such results suggest that differences in stress–strain curve at the nonlinear part of the data could be correlated to structure particularities obtained from different gelation processes.     

Oral Bioavailability of Polychlorinated Dibenzo-p-Dioxins/Dibenzofurans in Industrial Soils

In this study, the oral bioavailabilities of numerous 2,3,7,8-PCDD/F congeners were evaluated in soil samples from an industrial site. The purpose of this study is several-fold: (1) to compare the soil bioavailability results of the different PCDD/F congeners; (2) to evaluate the consistency of the bioavailability results with those obtained in an in vitro bioaccessibility study with simulated GI tract fluids; and (3) to develop quantitative bioavailability measurements that are appropriate for use in a health risk assessment for this site. Soil samples containing PCDD/F toxic equivalent (TEQ) concentrations ranging from 0.53–45.2 ng/g were administered to female Sprague Dawley rats via oral gavage. Reference formulations of PCDD/Fs were administered intravenously or by oral gavage. The overall relative bioavailability of PCDD/Fs in the soil samples on a TEQ basis ranged from 17 to 51%, with a mean of 38%. The results of the in vitro bioaccessibility study were consistent with the bioavailability results (mean extracted TEQ of 22%). Because of the clear relationship between increasing chlorination and decreasing bioavailability and bioaccessibility observed in this study, we suggest that simply extrapolating results from one congener to another may be associated with a high degree of uncertainty.