The influence of milk in the diet on the toxicity of orally ingested lead in rats

Excessive dietary lead reduces growth performance and increases lead accumulation in pigs

Objective: The objective of this study was to investigate the influence of dietary lead (Pb) supplementation and feeding period on growth performance, organ weight, and Pb accumulation in pigs.Methods: In a 56-day feeding experiment, a total of 48 barrows with initial body weight 10.4±0.6 kg were allotted to 2 dietary treatments (0 and 200 mg/kg of supplemental Pb) in a completely randomized design with 6 replicates. Body weight and feed intake were recorded to calculate growth performance. At the end of each 14 day-period (on days 14, 28, 42, and 56), an animal was randomly selected from each pen and slaughtered to collect blood samples, hair samples, left 5th rib, heart, liver, kidneys, lungs, and longissimus dorsi muscle samples.Results: Average daily gain and average daily feed intake were reduced (p<0.05) by supplemental Pb during the day 42 to 56. Relative kidney weight to body weight was linearly increased with increasing feeding period in pigs fed the Pb-supplemented diet, but not in pigs fed the control diet (p<0.05). The Pb concentrations in hair, left 5th rib, kidneys, and lungs were linearly increased with longer feeding period in pigs fed the Pb-supplemented diet, but not in pigs fed the control diet (p<0.01).Conclusion: Dietary Pb supplementation caused growth retardation and Pb accumulation in most organs, particularly in hair, bone, and kidneys in a time-dependent manner.

Food influence on lead relative bioavailability in contaminated soils: Mechanisms and health implications

To determine the effects of dietary constituents on soil Pb oral bioavailability, Pb relative bioavailability (RBA) in 3 soils contaminated by zinc smelting (ZS), wire-rope production (WR), and metal mining (MM) was measured under fasted and fed states with 9 foods. Under fasted state, Pb-RBA was 84.4 ± 10.3, 82.6 ± 4.70, and 32.3 ± 1.10% for ZS, WR, and MM soils; however, it decreased by 1.3-3.5 fold to 23.9-58.8, 25.6-49.9, and 14.8-24.2% under fed states with foods excluding Pb-RBA with egg in WR soil (97.3 ± 4.46%), and with cabbage and egg in MM soil (40.0 ± 8.62 and 44.4 ± 0.96%). In the presence of foods, egg and pork with significantly higher protein and fat contents leaded to the highest soil Pb-RBA (44.4-97.3%), while Pb-RBA determined with mineral-rich mouse feed was 1.6-7.9 fold lower (9.41-13.5%), suggesting high fat and protein foods tended to increase soil Pb-RBA, while high mineral diets decreased soil Pb-RBA. The increased Pb-RBA of MM soil with cabbage compared to fasted state was due to high organic content in cabbage, which could increase soil Pb solubility by inhibiting Fe and Pb co-precipitation in the intestine. For accurate assessment of health risks of contaminated soils, dietary influence on soil Pb-RBA should be considered.

Transformation and bioaccessibility of lead induced by steamed bread feed in the gastrointestinal tract

Accidental ingestion of contaminated soil has been recognized as an important pathway of human exposure to lead (Pb), especially for children through hand-to-mouth activities. 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 on the transformation and subsequent bioaccessibility of Pb in two soils was determined by the physiologically based extraction test (PBET). Two compounds, Pb(NO₃)₂ and PbCO₃, were included in the evaluation for comparison. 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. Results from this study indicated that steamed bread had an influence on the Pb speciation transformation, correspondingly affecting Pb bioaccessibility in the gastrointestinal tract.

Experimental determination of the oral bioavailability and bioaccessibility of lead particles

In vivo estimations of Pb particle bioavailability are costly and variable, because of the nature of animal assays. The most feasible alternative for increasing the number of investigations carried out on Pb particle bioavailability is in vitro testing. This testing method requires calibration using in vivo data on an adapted animal model, so that the results will be valid for childhood exposure assessment. Also, the test results must be reproducible within and between laboratories. The Relative Bioaccessibility Leaching Procedure, which is calibrated with in vivo data on soils, presents the highest degree of validation and simplicity. This method could be applied to Pb particles, including those in paint and dust, and those in drinking water systems, which although relevant, have been poorly investigated up to now for childhood exposure assessment.

Recommending calcium to reduce lead toxicity in children: a critical review

Assertions that adequate or supplemental calcium intake can reduce lead absorption in children are based on liberal extrapolation from animal studies, experiments with human adults, and cross-sectional studies of children that have a variety of methodologic weaknesses. Without stronger supporting evidence, statements that diet can ameliorate the deleterious effects of environmental lead could provide a false sense of efficacy and divert efforts from lead abatement and from behavioral modifications that might have more impact.

Higher milk intake during pregnancy is associated with lower maternal and umbilical cord lead levels in postpartum women

Lead exposure and its deleterious effects continue to be a problem in many countries. The lack of effective and safe treatments for low-level intoxication has promoted environmental interventions to control different sources of lead. In this study we evaluated the effect of milk consumption in 1849 mother-and-child pairs participating in the lead surveillance program in Mexico City. The mean lead levels were 11.2 micrograms/dL for maternal blood lead (MBL) and 10.8 micrograms/dL in umbilical cord. The correlation between blood lead and umbilical cord lead was r = 0.74. Forty-eight percent of the MBL exceeded 10 micrograms/dL and 9.5% exceeded 20 micrograms/dL. Maternal blood lead was positively related to the use of lead-glazed ceramic were and to traffic exposure and was inversely related to the consumption of milk and orange juice. Women who reported the consumption of more than 7 glasses of milk per week had a blood lead level of 8.7 micrograms/dL; in comparison, those women who reported a consumption of less than 7 glasses per week had a blood lead level of 11.1 micrograms/dL. Similar findings were observed for lead measured in umbilical cord. The association between lead levels and milk intake remained unchanged after taking in consideration other predictors of blood lead. This study suggests that a simple intervention could reduce lead burden among women and their newborns.

The interaction of lead exposure and pregnancy

The toxic effects of low-level lead exposure have been the subject of a good deal of research and media attention in recent times. In most countries, the acceptable occupational exposure limit for lead is being progressively decreased as the adverse health effects of lead are being identified at levels approaching those found in non-occupational environments. Due to the sensitive nature of the fetus to hazardous substances, the exposure to lead of the unborn child via maternal sources is of critical concern. Preterm delivery, congenital abnormalities and decreases in growth stature have all been associated with prenatal lead exposure at "acceptable" levels. There is an accumulation of evidence which indicates that maternal exposures prior to conception can play an important role in determining blood lead levels during pregnancy. In light of these observations the practice of removing the pregnant woman from lead sources may be of questionable value with regards to providing sufficient protection for the fetus. This article reviews the relevant literature pertaining to the mobilization of lead from bone during pregnancy and the toxicity of low-level lead exposure to the fetus, and briefly discusses some factors which may affect this toxicity.

Lead exposure and diet: differential effects on social development in the rhesus monkey

Infant rhesus monkeys ingested 0 or 1.0 mg/kg lead acetate daily from birth to one year postpartum in dietary milk. Half the monkeys in each group were offered milk ad lib, and half were given restricted quantities. Chow was available ad lib to all monkeys. Groups of 4 monkeys interacted for 1.5 h/day, 5 days/week beginning at approximately 2 months of age. The social sessions were moved to a larger arena at about 9 months postpartum. Ongoing behavior was observed during social sessions twice weekly beginning at about 3 months of age for 28 weeks, and again beginning at about 16 months of age for 11 weeks. Play behaviors were particularly susceptible to lead; social play was more severely disrupted than nonsocial play. Lead suppressed play in both test environments during the first year postpartum while self-stimulation and fearful behaviors increased. Lead-associated alterations in behavior were still present several months following termination of lead intake. Restriction of milk resulted in increased chow consumption but had little impact on behavior. Effects of lead may have been more profound in monkeys maintained on the restricted milk diet than in monkeys given milk ad lib.

Environmental and occupational lead toxicity: some current considerations

The role of trace elements in human health is not well understood. Lead is generally regarded as a toxic trace element with no beneficial effects. However, the adverse effects of lead resulting from environmental and occupational exposure have been the subject of extensive research. There is still controversy over whether lead from petrol is the main source of lead for most people. There have been a number of reports of lead contamination of food, air and water, however there is some question about the accuracy of the reported data and hence the conclusions drawn.

Although certain aspects of lead toxicity are reasonably well understood there is still uncertainty about the maximum acceptable safe level and also about the wide variety of factors that affect the absorption and retention, and hence toxicity, of lead. Of particular interest is the Influence of dietary factors on lead toxicity.

The influence of milk diet, grain diet, and method of dosing on lead toxicity in young calves

Twenty 2- to 3-week-old calves were fed a milk diet or a mixture of grain and hay. After acclimatization, all calves were dosed po with lead acetate for 7 days, either in solution via a nursing bottle or in a gelatin capsule. At the end of the treatment period, 6 of 10 calves fed milk were either dead or showed multiple signs of Pb poisoning. All calves fed grain and hay appeared normal. Tissue Pb was significantly higher in calves on a milk diet (p less than 0.05) compared to tissue from calves on a grain and hay diet. No significant differences wee found when dosing methods wee compared. These data clearly show that diet but not dosing methods greatly influenced the absorption and tissue distribution of Pb in calves. delta-Aminolevulinic acid dehydratase (ALAD) activity in blood dropped to approximately 20% of pre-Pb exposure concentrations within 24 hr after the initial dose of Pb and remained at this concentration despite continued Pb administration. Blood Pb concentrations indicate that, in this model, the Pb enters the blood rapidly and retention is prolonged. The calf model warrants further studies on absorption and metabolism.

The influence of dietary citrate on the absorption and retention of orally ingested lead

The influence of dietary citrate on the toxicity of orally ingested lead was investigated in male weanling mice. Twenty-four animals were divided into three equal groups. Group 1 served as controls, groups 2 and 3 were given 20 micrograms lead (as lead acetate) per g/diet, group 3 also received 4% sodium citrate in the diet. After 5 weeks, blood and tissue lead levels were measured. All mice given lead-supplemented diets had higher concentrations of lead in blood, liver, kidney, brain and bone than the control group, but the increase was significantly greater in the group given 4% sodium citrate in the diet. This work demonstrated that dietary citrate at levels which can be present in food significantly increases lead toxicity.

The effect of lactose and iron on strontium absorption

In rats fed on a milk diet with or without the addition of lactose and/or iron the transileal strontium-85 transfer was higher by 14-38% and the intestinal strontium retention lower by 6-23% than in control rats fed on standard laboratory food.

Nutrition of lead

At the levels to which human beings are exposed in the workplace as well as in the general environment, lead has been shown to be a toxic element in most of its chemical forms, whether it is inhaled or ingested in water or food. The four main sources of contamination of food are soil, industrial pollution, agricultural technology and food processing. Reasonable quantities of the metal can be stored by humans in a relatively inert form in bone; lead has an affinity for bone and acts by replacing calcium. Gastrointestinal lead absorption and retention, the major pathway of lead intake, has been shown to vary widely depending on the chemical environment of the gastrointestinal lumen, age and iron stores (nutritional status of the subject). Studies in animals have shown that certain substances bind lead and increase its solubility, thus enhancing its absorption. These dietary components consist of sodium citrate, ascorbate, amino acids, vitamin D, protein and fat, and lactose. Data suggest a three-compartmental pool for lead metabolism: (1) blood; (2) soft tissue (hair, nails, sweat, salivary, gastric, pancreatic and biliary secretions); and (3) skeleton. Lead absorption occurs primarily in the duodenum where lead enters the epithelial mucosal cells. The total bodily amount of lead does not affect lead absorption; lead does not have a feedback mechanism which limits absorption. In the adult rat, lead absorption from the intestinal lumen appears to proceed by both active transport and passive diffusion. Bile is an important route of excretion in the gut.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of dietary fat on the toxicity of orally ingested lead in rats

The influence of dietary fat on the toxicity of orally ingested lead was investigated. Groups of ten male weanling Wistar rats were maintained on diets providing 11.5, 20, 40 or 60% of energy from fat for 8 wk. All diets were supplemented with a low level of lead--1.25 mg Pb (as lead acetate) per 1000 kJ energy in the diet. Groups receiving 11.5 and 20% of energy as fat had similar lead levels for each tissue studied. Raising the fat level to 40 or 60% of energy resulted in significant increases in tissue-lead concentrations with each increment in dietary fat. The groups receiving 60% of energy as fat had more than twice the level of lead in the femur, kidney, liver and brain than the control rats maintained on the diet containing 11.5% energy as fat, even though the amount of lead ingested was the same for all groups. delta-Aminolaevulinic acid dehydratase activity was not affected when dietary fat was increased from 11.5 to 20%. There was a significant reduction in activity when fat was increased to 40 or 60% of energy. Free erythrocyte protoporphyrin was not affected by the level of dietary fat. This work demonstrates that increasing the level of dietary fat significantly increases lead toxicity and indicates the need for further research on the interaction between dietary factors and lead toxicity.

The influence of dietary phosphate on the toxicity of orally ingested lead in rats

The influence of elevated dietary phosphate on the toxicity of orally ingested lead was investigated in male weanling Wistar rats. Two groups of 20 rats were fed diets containing either adequate (0.5%) or high (1.2%) levels of phosphorus (as phosphates). Half of the rats on each level of phosphorus were given 20 micrograms lead (as lead acetate)/g dry diet. After 8 wk, biochemical tests for lead toxicity were carried out and tissue-lead levels were measured. All of the rats given lead-supplemented diets had higher concentrations of lead in bone, brain, kidney and liver than those given diets without added lead but the increase was significantly greater in all tissues in the group given the 1.2% phosphorus diet. Lead supplementation increased the levels of free erythrocyte protoporphyrin and decreased the activity of delta-aminolaevulinic acid dehydratase. The lead-induced increase in the level of free erythrocyte protoporphyrin was no greater in the high-phosphate group than in the low-phosphate group but the decrease in delta-aminolaevulinic acid dehydratase activity was significantly larger in the high-phosphate group. This work demonstrates that excess dietary phosphate significantly increases lead toxicity and indicates the need for continued research on the interaction between dietary factors and lead toxicity.