Search

The effects of lead as a dietary pollutant remain a global public health concern that needs urgent resolution. Children are highly susceptible to the adverse outcomes of lead pollution, as even low levels of lead may cause irreversible damage to intellectual development. Since several sources of lead exposure are present in the environment, it is necessary to identify the attributable burden of lead-related diseases arising from different exposure sources. In the present study, we used epidemiological data from studies around the nation to estimate the burden of mild intellectual disability (MID) attributed to lead exposure sources by using disability-adjusted life years (DALYs). To this end, a dose-response approach was used and a model comprising three components was established: exposure, dose-response, and DALYs module. In Chinese children aged 0-6 years, blood lead levels (BLLs) of 5.34 ± 3.09 μg/dL resulted in a MID incidence rate of 12.84 cases per 1000 children, with an estimated burden of disease (BoD) of 42.23 DALYs per 1000 children. Owing to dietary lead exposure, 36.64 healthy life years per 1000 children were lost, which was notably higher than the outcomes associated with exposure from other sources. This was consistent with the result that dietary exposure was the main contributor to children's lead exposure, accounting for 86.76%. According to the regional distribution based on the existing literature, the areas in China with higher BLLs were Heilongjiang, Shanxi, and Jiangxi. Our findings provided the information for lead risk management decisions and policies making., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier Ltd.)

In this study, an in vitro in vivo correlation (IVIVC) between Pb in vitro bioaccessibility (IVBA) and relative bioavailability (RBA) was explored to determine whether the efficacy of Pb immobilization in phosphate amended soils could be predicted using an in vitro approach. Mining/smelting impacted soil from Broken Hill, Australia (582-3536 mg/kg of Pb in the <250 μm soil particle fraction) was amended with Phosphoric Acid (PA), Mono Ammonium Phosphate (MAP) or Triple Super Phosphate (TSP) at Pb:P molar ratios of 1:1-1:5. Pb speciation in pre- and post-treated soil was assessed using X-ray Absorption Spectroscopy (XAS), Pb IVBA was measured using the Solubility Bioaccessibility Research Consortium (SBRC) assay (gastric and intestinal phases), and Pb RBA was determined in mice using blood Pb concentration as the bioavailability endpoint. XAS analysis revealed a 3.75-6.00 fold increase in the weighted % of Pb phosphates in soil containing >1000 mg/kg Pb while treatment effect ratios of 0.89-0.99 (SBRC-G), 0.09-0.71 (SBRC-I) and 0.27-0.80 (RBA) were observed in PA amended soil (Pb:P = 1:5). Although significant (p < 0.05) correlation were obtained between Pb RBA and IVBA (%) determined using SBRC-G (r = 0.64) and SBRC-I (r = 0.67), the strengths of the relationships were weak (r 2  = 0.41-0.45). This research highlights the complexities associated with the prediction of Pb RBA in phosphate amended soil., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The robustness of in vitro bioaccessibility assays to predict oral relative bioavailability (RBA) of multiple metals in contaminated soils requires validation using additional soil samples. In this study, 11 contaminated soils from mining/smelting areas were analyzed for As-, Cd-, and Pb-RBA using a mouse bioassay and metal bioaccessibility via the UBM gastric phase assay. Metal-RBA varied considerably among soils, with As-RBA (2.5-23%, mean 12%) being generally lower than Cd-and Pb-RBA (3.4-88 and 3.3-59%, mean 42 and 28%), due to higher proportions of As in the residual fractions. Metal-RBA generally decreased with increasing metal concentrations probably due to reduced labile metal fractions. In addition, strong negative correlations were observed between total Fe with As-, Cd-, and Pb-RBA (R 2  = 0.46-0.77), suggesting the role of Fe in controlling metal-RBA in soils. Like RBA, metal bioaccessibility by the UBM assay also varied among samples. However, strong in vivo-in vitro correlations (IVIVCs) were observed between metal-RBA and bioaccessibility (R 2  = 0.52-0.81). Further, there were little differences when As-, Cd-, and Pb-IVIVCs established using soils from this study and soils pooled from literature were compared, suggesting the robustness of the UBM assay to predict metal-RBA in contaminated soils., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

To investigate the protective role of grape seed procyanidin extract (GSPE) against lead-induced heart injury and the possible molecular mechanism associated with this event, Wistar rats were orally given GSPE (200 mg/kg) daily with or without lead acetate (PbA) (0.5 g/L) in drinking water for 56 d. GSPE attenuated oxidative stress, heart dysfunction, and lead accumulation in lead-exposed rat hearts. Meanwhile, GSPE inhibited the protein kinase RNA-like endoplasmic reticulum (ER) kinase/eukaryotic initiation factor 2α signaling pathway, and promoted protein kinase B (AKT) and glycogen synthase kinase 3β phosphorylation altered by lead, and regulated lead-activated apoptosis and its related signaling pathway. This study suggests that dietary GSPE ameliorates lead-induced heart injury associated with ER stress inhibition and AKT activation. Dietary GSPE may be a protector against lead-induced heart injury and a novel therapy for lead exposure., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Both dietary and non-dietary pathways contribute to metal exposure in residents living near mining-impacted areas. In this study, bioavailability-based metal intake estimation coupled with stable Pb isotope ratio fingerprinting technique were used to discern dietary (i.e., rice consumption) and non-dietary (i.e., housedust ingestion) contribution to As, Cd, and Pb exposure in residents living near mining-impacted areas. Results showed that not only rice (n = 44; 0.10-0.56, 0.01-1.77, and 0.03-0.88 mg kg -1 ) but also housedust (n = 44; 2.15-2380, 2.55-329, and 87.0-56,184 mg kg -1 ) were contaminated with As, Cd, and Pb. Based on in vivo mouse bioassays, bioavailability of As, Cd, and Pb in rice (n = 11; 34 ± 15, 59 ± 13, and 31 ± 15%) were greater than housedust (n = 14; 17 ± 6.7, 46 ± 10, and 25 ± 6.8%). Estimated daily intake of As, Cd, and Pb after incorporating metal bioavailability showed that As intake via rice was 5-fold higher than housedust for adults, whereas As intake via housedust was 3-fold higher than rice for children. For both adults and children, rice was the main source for Cd exposure, while housedust was the predominant Pb contributor. To ascertain the dominant Pb source from housedust ingestion, stable Pb isotope ratios ( 207 Pb/ 206 Pb and 208 Pb/ 206 Pb) of hair samples of local residents (n = 27, 0.8481 ± 0.0049 and 2.0904 ± 0.0102) were compared to housedust (n = 27, 0.8485 ± 0.0047 and 2.0885 ± 0.0107) and rice (n = 27, 0.8369 ± 0.0057 and 2.0521 ± 0.0119), showing an overlap between hair and housedust, but not rice, confirming that incidental housedust ingestion was the main source of Pb exposure. This study coupled bioavailability and stable isotope techniques to accurately identify the source of metal exposure as well as their potential health risk., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Defining the precise clean-up goals for lead (Pb) contaminated sites requires site-specific information on relative bioavailability data (RBA). While in vivo measurement is reliable but resource insensitive, in vitro approaches promise to provide high-throughput RBA predictions. One challenge on using in vitro bioaccessibility (BAc) to predict in vivo RBA is how to minimize the heterogeneities associated with in vivo-in vitro correlations (IVIVCs) stemming from various biomarkers (kidney, blood, liver, urinary and femur), in vitro approaches and studies. In this study, 252 paired RBA-BAc data were retrieved from 9 publications, and then a Bayesian hierarchical model was implemented to address these random effects. A generic linear model (RBA (%)=(0.87±0.16)×BAc+(4.70±2.47)) of the IVIVCs was identified. While the differences of the IVIVCs among the in vitro approaches were significant, the differences among biomarkers were relatively small. The established IVIVCs were then applied to predict Pb RBA of which an overall Pb RBA estimation was 0.49±0.25. In particular the RBA in the residential land was the highest (0.58±0.19), followed by house dust (0.46±0.20) and mining/smelting soils (0.45±0.31). This is a new attempt to: firstly, use a meta-analysis to correlate Pb RBA and BAc; and secondly, estimate Pb RBA in relation to soil types., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This paper assesses the magnitude of Pb uptake in cortical and trabecular bones in healthy animals and animals with altered balance in bone turnover, and the impact of exposure to Pb on serum markers of bone formation and resorption. The results reported herein provide physiological evidence that Pb distributes differently in central compartments in Pb metabolism, such as cortical and trabecular bones, in healthy animals and animals with altered balance in bone turnover, and that exposure to Pb does have an impact on bone resorption resulting in OC-dependent osteopenia. These findings show that Pb may play a role in the etiology of osteoporosis and that its concentration in bones varies as a result of altered bone turnover characteristic of this disease, a long standing question in the field. In addition, data collected in this study are consistent with previous observations of increased half-life of Pb in bone at higher exposures. This evidence is relevant for the necessary revision of current physiologically based kinetic models for Pb in humans., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Internationally publicized impacts upon human health associated with potentially harmful element (PHE) exposure have been reported amongst internally displaced populations (IDPs) in Mitrovica, Kosovo, following the Kosovan War. Particular concern has surrounded the exposure to Pb indicated by the presence of highly elevated concentrations of Pb in blood and hair samples. This study utilizes a physiologically-based in-vitro extraction method to assess the bioaccessibility of PHEs in surface soils and metallurgical waste in Mitrovica and assesses the potential daily intake of soil-bound PHEs. Maximum As (210mgkg(-1)), Cd (38mgkg(-1)), Cu (410mgkg(-1)), Pb (18790mgkg(-1)) and Zn (8500mgkg(-1)) concentrations in surface soils (0-10cm) are elevated above guideline values. Samples with high PHE concentrations (e.g. As >1000mgkg(-1); Pb >1500mgkg(-1)) exhibit a wide range of bioaccessibilities (5.40 - 92.20% in the gastric (G) phase and 10.00 - 55.80% in the gastric-intestinal (G-I) phase). Samples associated with lower bioaccessibilities typically contain a number of XRD-identifiable primary and secondary mineral phases, particularly As- and Pb-bearing arsenian pyrite, beudantite, galena and cerrusite. Quantification of the potential human exposure risk associated with the ingestion of soil-associated PHEs indicates that on average, 0.01μg Cd kg(-1) BW d(-1), 0.16μg Cu kg(-1) BW d(--1), 0.12μg As kg(-1) BW d(-1), 7.81μg Pb kg(-1) BW d(-1), and 2.68μg Zn kg(-1) BW d(-1) could be bioaccessible following ingestion of PHE-rich soils in the Mitrovica region, with Pb, and to a lesser extent As, indicating the likely possibility of local populations exceeding the recommended tolerable daily intake. Lead present within surface soils of the area could indeed have contributed to the human Pb burden due to the high bioaccessibility of Pb present within these soils (13.40 - 92.20% in the gastric phase). Data for Pb levels in scalp hair (≤120μgg(-1)) and blood (≥650μgdL(-1); WHO, 2004) for children that have lived within IDP camps in Mitrovica indicate significant Pb uptake has indeed taken place. The highly bioaccessible nature of soil-associated PHEs in this study highlights the need for appropriate environmental management approaches that limit the exposure of local populations to these contaminated soils., (© 2013.)

Objective: We investigated the nature of nutritional deficiencies that arose in gastrectomy patients by comparing mineral absorption in patients with total and subtotal gastrectomies before and after operation., Methods: Levels of nutritional, micro, and toxic minerals were measured in a subject group of 20 patients with gastric cancer. Patients were grouped according to total versus subtotal gastrectomy. Hair tissue was collected 3 mo before and after operation from each patient. Tissue was analyzed by atomic absorption spectroscopy for levels of various minerals. Mineral ratios were computed to display changes in mineral levels, and results were statistically analyzed with SPSS 10.0 to obtain a measurement distribution. The t test was used to determine any significant difference between patients before and after operation., Results: In the preoperation test, sodium, potassium and iron levels were higher than normal, whereas boron and molybdenum levels were lower than normal. Although sodium levels decreased significantly after surgery, molybdenum, cadmium, and lead levels increased significantly. Potassium decreased slightly in the subtotal gastrectomy group, but increased significantly in the total gastrectomy group. However, there was no change between before and after surgery for most minerals., Conclusion: In the short term, gastrectomy does not seem to affect the levels of most minerals in the body. However, changes in sodium levels indicate that gastrectomy affects sodium absorbency in gastric cancer patients. Potassium levels increased significantly in patients who received total gastrectomies; this may also be an area that nutritional treatment should focus on.

The aim of the present study was to assess whether the use of pig slurry and associated copper accumulation in calves grazing pastures fertilized with pig slurry from the Deza region in NW Spain has a significant influence on toxic metal and essential metal levels, and to investigate whether copper accumulation is correlated with the levels of these other metals. Correlations between copper, toxic metals (cadmium, lead) and essential metals (molybdenum, iron, zinc, selenium, manganese and cobalt) concentrations were evaluated in liver and kidney of 195 calves from the region of Deza. Metal concentrations were determined by ICP-OES and correlations between pairs of elements by Pearson correlation analysis. There was a strongly significant positive association between copper and lead in the liver. Considering the trace metals, copper in the liver showed significant positive correlations with cobalt in both liver and kidney, and with molybdenum in the liver. In addition, significant correlations were observed between copper and most essential metals in kidney. These associations are similar to those found in different animal species experimentally dosed with copper and other metals, as well as in cattle exposed to normal copper concentrations.

Although lead is widely known as a potent neurotoxin, the effect of lead exposure on the expression of the polysialic acid linked neural cell adhesion molecule (PSA-NCAM) remains unclear. We exposed Wistar rat pups to 0.2% lead acetate from postnatal day (PND) 1 to PND 30. This exposure protocol resulted in pup blood lead levels, which increased to 29.3+/-5.0 mg/dl on PND 15, and subsequently rose to 34.2+/-5.8 mg/dl at weaning. Corresponding brain tissue lead levels were 456+/-23 ng/g on PND 15 and 781+/-87 ng/g on PND 30. Animals were sacrificed on PND 80, when the blood and brain lead concentrations did not differ from those of the control group. Lead exposure induced a significant increase in the total number of PSA-NCAM expressing cells, compared to the control group (p<0.01), and did not change the proportion of cells co-expressing PSA-NCAM with glial or neuronal markers (calbindin, TuJ1, GFAP). These results suggest that early post-natal lead exposure induces persistent changes in the number of PSA-NCAM expressing cells, which could be, at least, partly the basis of impairments in the learning and memory formation, which follows low-level lead exposure.

Lead is one of the most common metals in contaminated ecosystems. Although lead poisoning and mortality have long been known, little is known of the neurobehavioral effects produced by low levels of lead in wild animals. Herein we describe the neurobehavioral effects of lead on learning using herring gulls (Larus argentatus) as a model. Doses used in these studies conducted in the laboratory and in nature were sufficient to produce lead concentrations in feathers that were equivalent to those found in gulls living in the wild. The exposure consisted of a single intraperitoneal injection of 0 and 100mg/kg lead acetate on day 2; each experiment involved 20-30 chicks in a lead-exposed group, and 20-30 chicks in a control group. We examined walking, begging, feeding, behavioral thermoregulation, individual recognition, and treadmill learning. There were significant differences between control and lead-exposed gulls chicks on all testing days. Learning, as well as improvement of motor skills, was faster for control chicks than lead-injected chicks for the thermoregulatory test, individual recognition, and behavior on a treadmill. Lead-injected chicks improved faster than control chicks only for walking scores. In a test where chicks were shown food under a cup, and then tested with three overturned cups, lead-exposed chicks did not show much improvement, whereas control chicks quickly learned where the food was located. The greatest differences in improvement were on the behavioral thermoregulation test, where lead-exposed chicks showed no improvement with age. Overall, this series of experiments indicated that for tasks involving learning, the disparity in accuracy and ability remained regardless of the number of days since exposure-control chicks sometimes improved and learned quicker than did lead-exposed chicks.

A field survey of herbaceous growing on lead-zinc mining area in Yunnan, China were conducted to identify species accumulating exceptionally large concentrations of Pb, Zn and Cd in shoots. In total, 220 plant samples of 129 species of 50 families and 220 soil samples in which the plants were growing were collected. According to accumulation concentration in plant shoots and the concentration time levels compared to plants from non-polluted environments, 21 plant samples of 16 species were chosen as best-performing specimens, 11 plant samples of 10 species for Pb, 5 plant samples of 4 species for Zn and 5 plant samples of 5 species for Cd. Sonchus asper (L.) Hill in Qilinkeng had hyperaccumulation capacity to Pb and Zn. Corydalis pterygopetala Franch in Paomaping had hyperaccumulation capacity to Zn and Cd. All 5 Cd hyperaccumulators came from Lanping lead-zinc mining area. Out of 11 Pb hyperaccumulators, 7 came from Minbingying of Huice lead-zinc mining area. The average of the concentration time levels compared to plants from non-polluted environments were higher than 10 times in all plant samples, the concentration time levels changed from 203 times to 620 times for Pb, from 50 times to 70 times for Zn and from 145 times to 330 times for Cd. Out of 21 plant samples, translocation factor changed from 0.35 to 1.90, only translocation factor of 7 plant samples were higher than 1. Enrichment coefficients of all samples were lower than 1. These plant species were primarily heavy metal hyperaccumulator, and will be used in phytoremediation of the metallic pollutants in soils after further research in accumulation mechanism.

Since lead (Pb) accrued from environmental exposure accumulates in bone with a half life time between 6 and 10 years, a release of bone Pb into the circulation and/or urine (PbU) should be expected in diseases with increased bone metabolism such as hyperparathyroidism. We studied 60 patients with primary hyperparathyroidism (pHPT, 50 women, 10 men, aged 61.4 +/- 10.6 and 64.1 +/- 9.9 years, respectively) (a) before, (b) 1-6 months, and (c) 6-12 months after parathyroidectomy. Besides lead in blood (PbB) and lead in 24-h urine samples (PbU), parathyroid hormone (PTH), serum Ca2+, osteocalcin (OC), phosphate (PO4), and serum pyridinoline cross-linked telopeptide (cTP) were determined. Control data were determined in 20 healthy age-matched subjects. As expected, Ca2+ decreased after parathyroidectomy. Mean PbB in patients with pHPT was in the same range as in controls. A decrease of PbB after parathyroidectomy was found in the interval beyond 6 months. In contrast, mean PbU initially increased after surgery (3.05 +/- 1.94 vs. 4.25 +/- 2.65 microg/l, P = 0.004) and was not different beyond 6 months in comparison with preoperative values at (c). Investigating only patients with PTH < 150 ng/l, no significant PbB or PbU alterations were detected before and after parathyroidectomy. In patients with PTH > 150 ng/l, the decrease of PbB at (c) was more pronounced as was the increase of PbU at (b). In these patients, PbB and OC as well as PbB and cTP were correlated preoperatively. In conclusion, our data show that in environmentally lead-exposed (by food or by pollution) hyperparathyroid individuals, there is no hazardous PbB release from bone. The preoperative correlation between PbB and OC in pHPT patients with PTH > 150 ng/l provides evidence that in fact there is a Pb release from bone into the blood-pool by bone remodeling. The increase of PbU after parathyroidectomy is suspected to be caused by PTH-dependent Pb accumulation in the kidney, which seems to be restored with decreasing PTH. Moreover, our data confirm prior findings that bone remodeling seems to be normalized 6 months after parathyroidectomy.

As part of a project on phytoextraction of lead (Pb) in paddy soils around a lead/zinc (Pb/Zn) Mine in Lechang of Guangdong Province, South China, the concentration distribution of Pb in paddy soil-rice system was investigated, and its potential health risk to animal/human was evaluated. Total and diethylenetetraminepentaacetic acid (DTPA)-extractable Pb in soils averaged 1486 and 268 microg/g, respectively. According to sequential extraction procedure, soil Pb occurred primarily in the residual, carbonate and exchangeable fractions (30.2%, 26.7% and 19.1%, respectively). Lead extracted by the gastric juice simulation test (GJST) was 1068 microg/g and accounted for 75.4% of the total concentration. Mean Pb concentrations of 419 microg/g in rice root, 69.1 microg/g in whole straw, 51.0 microg/g in part straw (without two leaves near above the root), 44.9 microg/g in stalk, 21.9 microg/g in hull, 13.2 microg/g in grain with hull and 4.67microg/g in grain without hull (namely, unpolished rice) were found. Lead concentrations in both soil and rice plant were far above the corresponding tolerable levels. Lead daily intakes by local residents were 2.6 mg for adults and 1.2 mg for children, which were much higher than the allowable level. Thus, Pb in this area might pose a potential health risk to the local population.

In this study, we characterized lead (Pb2+) accumulation and storage by the aquatic fern Azolla filiculoides. Lead precipitates were detected in the vacuoles of mesophyll cells of Azolla plants cultured for 6 d in rich growth medium containing 20 mg l(-1) Pb2+. Energy dispersive spectroscopy (EDS) analysis of the relative element content of leaves collected from these plants revealed a 100% increase in the levels of P, S, Na and Ca and a 40% decrease in Mg and Cl compared to the untreated plants. Both Azolla whole plants and isolated apoplasts were incubated for 6 d in 20 mg l(-1) Pb2+. Lead content in the whole plant composed 0.37%, 2.3% and 1.8% of the dry weight after 2, 4 and 6 d of growth, respectively, while the isolated Azolla apoplast contained 0.125%, 1.22% and 1.4% Pb2+, respectively. Lead content in Azolla whole plant increase by 200%, 100% and 22% after 2, 4 and 6 d of growth, respectively, when compared to Azolla apoplast. Dark, electron dense deposits of lead were observed in light and transmission electron microscope in leaf cells treated with lead. All the observed lead deposits were localized in vacuoles while larger lead deposits were found in mature leaves than in young leaves. No lead deposits were found in cells of the cyanobiont Anabaena when the plants were exposed to similar conditions. Activity and content of V-H+-ATPase were studied in Azolla plants grown in the presence of 20, 40 and 80 mg l(-1) of lead for a period of 4 d. Activity of V-H+-ATPase was increased by 190%, 210% and 220%, respectively, but the content of V-H+-ATPase was reduced by all lead concentrations., (Copyright 2004 Elsevier SAS)

The addition of P-containing amendments was found to effectively reduce the bioaccessibility of Pb in soils to the human, using an in vitro test. For all treatments with P additions, the removal of soluble Pb in the small intestinal phase was observed. The effectiveness of various P treatments in the small intestinal phase generally followed this order at the equivalent P addition level: hydroxyapatite (HA)>phosphate rock (PR)>HA+single super-phosphate (SSP)>SSP. The relatively low effectiveness of P amendments at the gastric phase may be explained by the high solubility of pyromorphite at relatively low pH of 1.7, compared with that at the neutral small intestinal pH. Single super-phosphate showed the best performance in minimizing the bioaccessibility of Pb in the gastric phase, possibly due to its highest solubility at pH 1.7. Single super-phosphate showed the best performance in minimizing the bioaccessibility of Pb in gastric phase, possibly due its highest solubility at pH 1.7. However, in the small intestinal phase, SSP appears to be the least effective amendment, possibly due to its lowest Ca supply level to replace Pb form exchangeable sites, as reflected by its lowest molar Ca/P ratio of 1:2. The disagreement of the sequential extraction results with that of the in vitro test results indicated that the sequential extraction was not suitable for the assessment of the effect of P addition on minimizing the bioaccessibility of Pb to human due to the formation of pyromorphite during the extraction procedure. Results from this study also suggested that the time required for the in vitro test might be shortened for fast screening.

Previous studies have documented that phosphate compounds of lead (Pb) [e.g., pyromorphite Pb5(PO4)3-(X), where X=OH, F or Cl] are comparatively insoluble, and their formation in Pb-contaminated soil may be a means of reducing the bioavailability and chemical lability of Pb in soil. In this study, the effect of phosphate compound amendments on the bioavailability of Pb in a polluted alkaline soil was examined. A Pb-contaminated soil was treated with hydroxyapatite (HA), phosphate rock (PR), water-soluble P fertilizer (single superphosphate, SSP) and the combination of HA with SSP. The bioavailability of Pb was determined in plant uptake studies with vegetables (Brassica campetris L. var. communis, BC) and Brassica oleracea L. var. acephala, BO) and sequential extraction. The results indicated that the Pb concentrations in both shoots and roots of two vegetable plants decreased with increasing quantities of added P compound, and the HA treatment had the best effect at the level of 5000 mg of P kg(-1)as compared with other treatments in which the Pb concentrations in shoots of BO and BC decreased 51.9% and 65.5%, respectively, and the Pb concentrations in roots of BO and BC decreased 67.3% and 57.2%, respectively, as compared with the control treatment. The SSP treatment had little effect on the Pb concentrations in plant tissues. Sequential extraction results indicated that the addition of soil amendments transform soil Pb from nonresidual fractions to residual fraction substantially. The effect of treatments followed this order at the equivalent P addition: HA>PR>HA+SSP>SSP. The results suggested that HA amendments can lower the bioavailability and increase the geochemical stability of soil Pb, so it has the potential for in situ remediation in Pb-contaminated soils.

The antagonistic effects of supplementation of Zn and Se to the soil on vegetables were studied in this work. In the pot experiment, Se (Se4+) and Zn (Zn2+) were applied, respectively, to the soil, in which the Chinese cabbage (Brassica rapa) and the lettuce (Lactuca sativa L.) were planted. As a result, Se and Zn were enriched evidently in the two vegetables. The contents of Pb and Cd in the two vegetables were decreased markedly while contents of some healthy mineral elements, like Mn and Mg, were increased to some extent when Se and Zn were applied. The antagonism of Se and Zn against Pb and Cd in plants was suggested. The farmland experiment on the lettuce was conducted to explore further the effect of supplementation of Zn and Se under the actual field conditions. Result came out to be that the enrichment of Zn and Se restrained the accumulation of Pb and Cd in the lettuce remarkably, as well as enhanced the absorption of some other nutritional elements, like Fe, Mn, Cu, Ca and Mg. Therefore, application of Se and Zn was proved to be an effective and feasible method to improve trace elements nutrition in the vegetables.

Pollution distribution maps of copper (Cu), zinc (Zn) and lead (Pb) for Erzurum province were developed on the basis of chemical analysis of Scots pine (Pinus sylvestris L.) needles collected from randomly selected sampling points during 2 years. The maps show deposition zones for the studied elements and could help in identification of sources and directions of air pollution dispersion. This study indicated that vegetation in Erzurum was greatly endangered by sulphur dioxide (SO(2)), whereas Zn does not pose an immediate threat to vegetation in most of the country's territory. However, in the city center, main and secondary road agglomeration, very high pollution with Pb and Cu could limit growth. Higher levels of SO(2) measured in some areas of Erzurum might be harmful for human and animal health. Results of this study indicated that Scots pine needles were not contaminated by Zn.

Concentrations of cadmium (Cd), lead (Pb) and zinc (Zn) in total soft tissues (ST) and byssus (BYS) of the green-lipped mussel Perna viridis from 11 different geographical locations off the west coast of Peninsular Malaysia were determined. The metal concentrations distributed between the BYS and ST were compared. The results of this study indicated that higher levels of Cd (1.31 microg/g), Pb (38.49 microg/g) and Zn (206.52 microg/g) were accumulated in the BYS than in the total ST (Cd: 0.29 microg/g; Pb: 8.27 microg/g; Zn: 102.6 microg/g). Semi-static and short period controlled laboratory experiments were also conducted for the accumulation and depuration of Cd, Pb and Zn in the total ST and BYS of P. viridis. The ratios (BYS/ST) for Pb and Cd from the laboratory experiments showed that the total ST accumulated more metals than the BYS. Therefore, these laboratory results disagreed with those found for the field samples. However, the laboratory results for the Zn ratio (BYS/ST) agreed with those of the field samples. It was evident that when compared to the ST, the BYS was a more sensitive biomonitoring organ for Zn while it could be a complementary organ for Cd and Pb in the total ST. Since total ST of P. viridis had been reported to have regulative mechanism for Zn, its BYS can be used as a biomonitoring organ for the identification of coastal areas exposed to Zn pollution.

Chub experimentally infected with the acanthocephalan parasite Pomphorhynchus laevis were exposed to 0.01 mg l(-1) Pb(2+) over 5 weeks. Lead was rapidly accumulated in the intestinal worms reaching a steady-state concentration after 4 weeks. This concentration was significantly greater than in the host muscle, liver and intestine and more than 9,000 times higher than the exposure concentration. Lead accumulation in P. laevis increased at a higher exposure concentration but was not correlated with either parasite intensity or with pooled or individual worm weight. The highest lead concentrations were recorded in those specimen of P. laevis that were attached in the posterior intestine. Interestingly, parasitised chub accumulated less lead in their own tissues than uninfected conspecifics. A mechanism of lead uptake by P. laevis and the application of acanthocephalans as accumulation indicators of metal pollution is discussed.

Lead and cadmium levels of some species of brown-algae (Phaeophyta) from the mesolittoral (intertidal area) of the Island of Tenerife (central-eastern Atlantic) were determined by Atomic Absorption Spectrometry. The quality control was carried out using a standard "CRM 279 Ulva lactuca". The mean, minimum and maximum concentrations were 11.21, 2.090 and 81.795 microg/g/dw; and 1.13, 0.190 and 5.130 microg/g/dw for lead and cadmium, respectively. The fact that samples registering the highest cadmium concentrations were the same as those which showed the highest lead level corresponding to a sampling station nearby an urban water outlet could be relevant.

Non-specfic carboxylesterase and glutathione S-transferase activity was measured in the ground beetle, Pterosthicus oblongopunctatus (Coleoptera: Carabidae), from five sites along a gradient of heavy metal pollution. A previous study determined that beetles from the two most polluted sites (site codes OLK2 and OLK3) were more susceptible to additional stressors compared with beetles from the reference site (Stone et al., Environ. Pollut. 113, 239-244 2001), suggesting the possibility of physiological impairment. Metal body burdens in ground beetles from five sites along the gradient ranged from 79 to 201 microg/g Zn, 0.174 to 8.66 microg/g Pb and 1.14 to 10.8 microg/g Cd, whereas Cu seemed to be efficiently regulated regardless of metal levels in the soil. Beetle mid- and hindguts were homogenized and the soluble fraction containing glutathione S-transferase (GST) and carboxylesterase (CaE) was assayed using kinetic analyses. Significantly higher levels of GST were found only in female beetles from the most polluted sites (OLK2 and OLK3; P=0.049, P<0.001, respectively) compared with the reference site (OLK7). In addition, OLK3 females had significantly higher levels of CaE compared with the reference beetles (P=0.01). Male beetles did not differ in enzyme activity along the metal gradient. Overall, obvious trends in detoxification enzymes were not detected in ground beetles in association with metal body burdens.

Total concentrations and speciation of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) in surface sediment samples were correlated with the respective metal measured in the total soft tissue of the green-lipped mussel Perna viridis, collected from water off the west coast of Peninsular Malaysia. The aim of this study is to relate the possible differences in the accumulation patterns of the heavy metals in P. viridis to those in the surface sediment. The sequential extraction technique was employed to fractionate the sediment into 'freely leachable and exchangeable' (EFLE), 'acid-reducible,' 'oxidisable-organic' and 'resistant' fractions. The results showed that significant (P<.05) correlations were observed between Cd in P. viridis and Cd in the sediment (EFLE fraction and total Cd), Cu in P viridis and Cu in the sediment (EFLE and 'acid-reducible' fractions and total Cu) and Pb in P viridis and Pb in the sediment ('oxidisable-organic' fraction and total Pb). No significant correlation (P > .05) was found between Zn in P viridis and all the sediment geochemical fractions of Zn and total Zn in the sediment. This indicated that Zn was possibly regulated from the soft tissue of P. viridis. The present results supported the use of P viridis as a suitable biomonitoring agent for Cd, Cu and Pb.

The overall objective of this research was to monitor the uptake kinetics of lead in an amphibian model and correlate metal content with embryo development. Based upon the concentration of lead found in the water and sediment of a Louisiana swamp adjacent to a Superfund site, a controlled laboratory experiment exploring lead uptake from water and sediment by Xenopus laevis tadpoles was conducted. For 5 weeks, tadpoles were exposed to water and a simulated sediment, kaolin, spiked with 1, 5, or 10 times the concentration of lead found in field water and sediment samples. Additionally, organisms were exposed to the 5 x condition for 3 and 6 weeks. The experimental controls consisted of unexposed tadpoles and ones exposed to lead originating from water or sediment exclusively. At the end of the exposure periods, developmental data, i.e., body weight and developmental stage, were recorded, and the tadpoles were analyzed for whole body lead concentration. Lead extraction was accomplished by dry ashing, and its amount was quantified polarographically. Results showed that lead inhibited the normal development of these amphibians, in a manner that generally was more severe as exposure level increased. The hindrance of tadpole development also coincided with an increase in whole body lead concentration at higher exposures. Temporally, at the 5 x exposure concentration, the mean lead level increased with time, but this difference was not statistically significant (P<.05). Additionally, control animals exposed to lead (either in water or in sediment) showed no statistical difference with regard to weight and lead uptake, indicating that lead originating from both water and sediment is incorporated into the tadpole. The controlled laboratory experimental protocol used here is thus capable of investigating the uptake of a single metal (Pb in this case) and determining its effect on the development of tadpoles while differentiating the significance of multiple sources of exposure.

Using the perfusion method, we compared the accumulation and flux of inorganic mercury (Hg) and methylmercury (CH(3)Hg) across the gills and intestine of the blue crab, Callinectes sapidus. The accumulation and transfer processes were studied for each form by exposing the organs in the presence of specific ligands and other metals. While binding of Hg and CH(3)Hg to organic ligands reduced the rate of uptake in most instances, the differences in accumulation could not be explained only in terms of passive diffusive uptake. Thus, it appears that Hg and CH(3)Hg accumulation is dominated by ligand exchange or facilitated transport processes. Exposure of the gills and intestine in the presence of a suite of metals and metalloids showed that inorganic Hg and CH(3)Hg uptake was largely by different mechanisms to that of the other elements, as there was little interaction in terms of uptake rate. Overall, the results of this study suggest that inorganic Hg and CH(3)Hg uptake into the gills and intestine of this invertebrate is by a variety of pathways, both active and passive.

This experimental study assessed the role of the microhabitat in the uptake of metals by adult acanthocephalans. We examined the accumulation of lead by adult Pomphorhynchus laevis in the intestine of chub (Leuciscus cephalus) and compared it with that in goldfish, Carassius auratus auratus, in which the parasites penetrate the intestinal wall and enter the body cavity. Chub and goldfish experimentally infected with adult Pomphorhynchus laevis were exposed to 0.01 mg l(-1) Pb(2+) over 3 weeks. Lead was rapidly accumulated in the intestinal acanthocephalans reaching a mean concentration of 7.3 microg g(-1). This concentration was significantly greater than in the host muscle, liver and intestine and more than 730 times higher than the exposure concentration. Intraperitoneal P. laevis in goldfish exposed to lead did not accumulate the metal. Thus, it was conclusively shown that metal accumulation in acanthocephalans is associated with the intestinal location and does not occur in the body cavity.

Legumes are ideal for revegetation of metal-mined wastelands which lack nitrogen (N). A greenhouse study was conducted to investigate the feasibility of using Sesbania rostrata and S. cannabina for the reclamation of lead/zinc (Pb/Zn) mine tailings and to evaluate the effects of organic amendment using sewage sludge (0%, 25%, 50%, and 75%, v/v). The results showed that both species could continue to grow on the highly toxic tailings substrata for at least 80 days, although their growth suffered from adverse effects. That S. rostrata with stem and root nodules had better growth (biomass, growth rates, and biomass of nodules) than S. cannabina suggested that S. rostrata is a better choice as a pioneer species for revegetation of the mine tailings. Stem nodules had less obvious adverse effects imposed by tailings than root nodules. Application of sewage sludge increased contents of total carbon (C), N, phosphorus (P), and potassium (K), and reduced total Zn, Pb, Cd, and DTPA-extractable Pb and Cd in tailings substrata. These, in turn, reduced metal (Zn, Pb, and Cd) uptake and accumulation in plant tissues, and improved plant growth performance, including biomass, growth rates, stem nodulation. Fifty percent (v/v) of sludge application rate was the best loading rate for plant growth.

In the present study, an attempt has been made to investigate the effect of ethanol consumption on the distribution of lead in different regions of brain and body organs of male albino rats. Lead when administered intragastrically, for a period of eight weeks resulted in almost uniform accumulation of this metal in all the regions of brain, which increased by almost two fold when ethanol was given along with lead. Lead was also seen to compartmentalise in almost all the tissues of the body to varying extents, with the highest accumulation in the kidney. A progressive and appreciable accumulation of lead was seen in blood with a concomitant increase in ZPP levels in animals during the course of treatment, which increased further when ethanol was administered along with lead. The activity of delta-ALAD and AChE in blood was significantly decreased in lead as well as ethanol treated animals. However, in animals coexposed to lead and ethanol, the inhibition of delta-ALAD was not significantly different, when compared to only lead-treated animals. The results suggested that animals exposed to ethanol and lead simultaneously accumulate higher levels of lead in blood and brain of animals making them more vulnerable to the haematological and neurological toxic effects of lead.

Developmental exposure to lead (Pb) has long been associated with reductions in intellectual function in children and behavioral impairments in animal models of learning and memory. We have used long-term potentiation (LTP) in the dentate gyrus of the Pb-exposed rats to determine the potential of a reduced capacity for synaptic plasticity to contribute to Pb-induced cognitive dysfunction. Previous work demonstrated that developmental exposure resulting in moderate blood concentrations of Pb increase the threshold for induction of long-term potentiation (LTP) in the dentate gyrus in vivo. These findings were also suggestive of reductions in LTP magnitude (Gilbert et al., 1996). The present study was designed to further examine the effects of Pb on LTP magnitude and to determine if lower blood Pb levels commonly encountered in children are also effective in impairing synaptic plasticity in this rodent model. Pregnant dams were exposed to control tap water or 0.1, 0.2, 0.5 or 1.0% Pb-acetate in the drinking water beginning just prior to parturition (gestational day 16, GD16). Male offspring were weaned at 21 days of age (PN21) to the same solution given their dams and continued on this regimen until testing. As adults, animals were anesthetized with urethane and stimulating and recording electrodes placed in the perforant path and dentate gyrus, respectively. Post-train I/O functions taken 1 hour after delivery of a series of six high frequency (400Hz) trains revealed a reduced capacity for LTP of the PS amplitude and EPSP slope in Pb-exposed animals in all but the 1.0% group, indicative of a biphasic dose-effect relationship. The 1.0% Pb exposure was clearly less effective than the lower exposure levels in reducing LTP magnitude, and did not differ significantly from control values. The mechanisms underlying the reduced efficacy of higher exposure levels of Pb to impair LTP are not clear. Blood (26-117 microg/dl) and brain (220-1812 ng/g tissue) concentrations of Pb were elevated as a function of increasing exposure (0.1%-1.0%) and cannot readily account for the lack of an effect in the 1.0% group on LTP. We have observed a similar profile in hippocampal glutamate release employing a similar range of exposure levels, i.e., reduction of glutamate release that is absent at higher concentrations of Pb in the drinking water (Lasley et al., 1998). These and previously reported data suggest that the ability of Pb to diminish presynaptic transmitter release contributes to a reduced capacity for LTP at lower exposure levels. The reversal of the effect of Pb on glutamate release that accompanies higher exposure levels may serve to compensate for the mechanism underlying the LTP impairment and form the basis for the biphasic dose-response pattern seen with chronic developmental exposure.

Previous work has demonstrated an increase in the threshold for induction of long-term potentiation (LTP) in the dentate gyrus of animals chronically exposed to lead (Pb) from birth (Gilbert et al., 1996). The present study sought to extend these findings by evaluating the developmental periods critical for Pb-induced impairment of LTP. Rats were exposed to Pb through maternal milk and/or the drinking water over different developmental intervals: 1) beginning just prior to birth and continuing throughout life (PL); 2) beginning just prior to birth and terminating at weaning (PW); or 3) continuously from the early post-weaning period throughout life (WL). Pregnant dams received 0.2% Pb-acetate in the drinking water on gestational day (GD)16, with male offspring switched to the same solution (PL group) or tap water (PW group) at weaning on postnatal day (PND)21. Postweaning exposure began on PND30 and continued throughout life. As adults (PND130-210), field potentials evoked by perforant path stimulation were recorded in the dentate gyrus under urethane anesthesia, and an ascending series of stimulus trains was administered to induce LTP and to determine its threshold. The magnitude of population spike (PS) LTP was reduced relative to controls in animals exposed throughout life (PL) and in animals exposed after weaning (WL). No impairment in PS LTP was evident in animals removed from Pb at weaning and tested as adults (PW). Similarly, thresholds for induction of PS LTP were elevated relative to controls in the PL and WL groups, but were not affected by Pb exposure limited to the lactational period (PW). Reductions in the magnitude of LTP of the EPSP slope were evident in posttrain I/O functions in all Pb-exposed groups, including the PW group. An elevated LTP threshold was evident in the EPSP slope measure in the continuously exposed group (PL) only. Thus Pb exposure restricted to the lactational period appeared less disruptive to adult LTP in the dentate gyrus than continuous exposure beginning around birth or weaning. However, EPSP slope LTP was impaired in animals exposed to Pb for as little as 30 days in the early postnatal period. An attenuated ability to support neuroplastic change in synaptic function may contribute to cognitive deficits associated with Pb-induced toxicity.

Unlabelled: Lead is a known neurotoxicant, and concentrations of lead in the CNS after acute exposure to low doses have not been studied in detail. In this investigation, the temporal distribution of lead ([203Pb]), injected intravenously at no-carrier-added (NCA) (0.6-0.7 mumol/kg) and at carrier-added (7.0-62.3 mumol/kg) levels was determined in mice. Concentrations of [203Pb] were measured in major organs and in different regions of the brain. Ex-vivo autoradiographic visualization was used to confirm and extend the brain distribution findings., Results: The highest concentrations of NCA [203Pb] were observed initially in the kidneys (52% of the injected dose (ID)/g at 1 hr) and liver (10.5% ID/g at 30 min). Uptake into bone occurred gradually, reaching 25% ID/g at 24 hr. In accord with previous reports, excretion of the tracer was very slow. Approximately 80% of total ID remained in the body after 24 hr and 68% at 48 hr. Interestingly, in the mouse brain, the highest levels of [203Pb] were noted in the area of the hypothalamus. At all times between 30 min and 16 hr postinjection, and at all Pb dose levels injected, the accumulation of [203Pb] in the hypothalamic region exceeded that in all other brain regions examined. Autoradiography performed at the 16 hr time point confirmed the high uptake and strong retention of [203Pb] by the hypothalamus. These studies afford new insight into the distribution of acutely administered lead in the brain, and may have implications for the understanding of some of the neurotoxic effects of lead.

The effect of environmental temperature on lead accumulation in tissues of mice repeatedly treated with lead acetate (2 mg/kg per day and 5 mg/kg per day) for 3 or 6 weeks was studied. In blood, kidney and liver, the amount of lead accumulated after 3 weeks of treatment was markedly higher in animals exposed to 22 degrees C than those maintained at 35 degrees C. Conversely, when the treatment was extended to 6 weeks, lead concentrations in the liver and kidney were equal or higher respectively, in the mice exposed to 35 degrees C. In the brain, lead concentration was lower than that found in kidney and liver and it was independent of dose and ambient temperature of lead being higher at 35 degrees C than at 22 degrees C. These results demonstrate that environmental temperature influences the amount of lead accumulated in some rodent tissues, and that the duration of the treatment modifies the effect produced by temperature, suggesting that the changes elicited during the period of acclimation to the hot environment could be responsible for these findings.

1. The cytotoxic effects of various heavy metals were assayed by trypan blue exclusion in vitro in human peripheral immune cells separated to high purity. T and B lymphocytes and monocytes were equally sensitive to metals. The individual metals could be ranked in the following decreasing order of cytotoxic potency, Hg approximately Ag > Cd approximately Cu > Pb approximately Zn, based on exposure time and concentration needed to give a particular percentage of dead cells. 2. The cytotoxic effects became irreversible after about 13 hr of metal exposure. 3. Examination by scanning electron microscopy showed that the heavy metals caused serious destruction of the cell membranes. 4. Solubility and uptake of metals into the cells were studied and discussed in relation to the cytotoxic effects. It was concluded that metal binding to cell surfaces or precipitate formation could inhibit ordinary uptake, thereby affecting cytotoxicity. For Pb in monocytes this appeared to lead to uptake of non-toxic complexes, probably by phagocytosis.

It has been hypothesised that some motor neuron diseases may result from lead (Pb) being retrogradely transported in axons from muscle to spinal cord. To test this hypothesis, we injected mice in the right hindlimb with 0.1 ml of 0.25% or 2.5% Pb. In some animals the sciatic nerve was cut before injection. Pb levels were measured in the lumbar and thoracic spinal cord and the kidney with atomic absorption spectrophotometry (AAS). Four weeks after injection, Pb was found in the spinal cord on AAS, with higher levels in the lumbar than the thoracic cord only in the high-Pb group. Sciatic nerve cut did not inhibit the passage of Pb to the cord. The results suggest that most Pb injected into muscle reaches the spinal cord via the blood or damaged axons, rather than via intact axons. These data do not support the hypothesis of Pb-induced motor neuron disease via retrograde axonal transport from muscle.

This review examines the kinetics and possible mechanisms of lead transport into brain across the microvessel endothelium (the blood-brain barrier). Although severe lead poisoning both in neonatal rats and in young children may cause microvessel damage, there is little evidence that there is either damage or even disturbance of specific transport mechanisms at blood leads < 80 micrograms/dl. When 203Pb was continuously infused intravenously into adult rats, radiotracer uptake into different brain regions was linear with time up to 4 hours, reaching spaces in relation to plasma of 6.6 - 8.2 ml/100 g in cerebral tissues at one hour. The concentration of free Pb+ in serum is of the order of 10(-12)M, the majority of lead being bound to protein and to sulfhydryl compounds, such as L-cysteine. Transport into brain has been further studied during short vascular perfusion of one cerebral hemisphere of the rat with oxygenated and buffered physiological saline. This allows total control of the fluid perfusing the cerebral microvessels. In the absence of organic ligands for lead, 203Pb entered brain very fast, with a space of 9.7 ml/100 g in frontal cortex at one min. The presence of albumin, L-cysteine or EDTA abolished measurable uptake. Experiments designed to reveal a role for the anion exchanger or calcium channels gave negative results. However, the effects of potassium depolarization and of varying pH indicated that the lead species passively entering the endothelium might be PbOH+. Experiments with various metabolic inhibitors, including vanadate, suggested that Pb uptake in the endothelium is mitigated by active back transport of lead into blood by the Ca-ATPase pump.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuronal function depends on the activity of a variety of voltage-sensitive, ion-specific membrane channels, including channels permeable chiefly to sodium, potassium, and calcium. The plasma membranes of many neurons contain several types of each class of channel. In general, heavy metal ions exert little effect on voltage-sensitive sodium or potassium channels, but inhibit ion flow through voltage-sensitive calcium channels (VSCC). The literature abounds with descriptions of different types of calcium channels in vertebrate neurons. These descriptions suggest that there are many physiologically and pharmacologically distinct calcium channels, some of them possibly cell-type specific. Among the heavy metals, Pb2+ is one of the most potent inhibitors of VSCC in both vertebrate and invertebrate neurons. Some heavy metals, including Ni2+ and Cd2+, are fairly selective against certain types of calcium channels. Limited evidence suggests that Pb2+ inhibits all calcium channel types within a given cell, with only minor differences in potency. However, there appear to be substantial differences among cell types in the concentration dependence of calcium channel inhibition by Pb2+. Therefore, to appreciate the range of effects of Pb2+ on calcium channels throughout the nervous system, it will be important to examine a large number of cell types. Pb2+ is highly permeable through at least some types of VSCC. Entry of Pb2+ into the neuronal cytoplasm through VSCC, followed by disturbance of intracellular functions, may be a major mechanism of Pb2+ neurotoxicity.

An important determinant of body lead (Pb) burden and Pb toxicity in exposed humans is Pb metabolism, or more correctly, Pb toxicokinetics. It affects the former through the quantitative processes of uptake, distribution and retention/excretion and the latter via delivery of toxic doses to cellular/molecular sites of action. Pb toxicokinetics has useful application in understanding Pb's behavior in populations. Several of these applications have been studied and results are presented for the toxicokinetic basis of dose-neurotoxic effect relationships in selected longitudinal studies and the use of toxicokinetic modeling for estimation of body lead burden in early populations. Three well-known, ongoing longitudinal studies of developmental neurotoxicity--in Boston, Cincinnati, and Port Pirie, Australia--involve cohorts who differ markedly as to their pre- and postnatal lead exposure profiles. Toxicokinetic examination of these exposure differences helps to explain the temporal variability seen in blood Pb-toxic effect relationships and supports a causal role for lead. Toxicokinetic models of Pb uptake and in-vivo behavior are increasingly being considered for estimating Pb-B levels in lieu of direct measurement. A linear biokinetic model, using reliable input data for natural/prehistoric levels of Pb in sources, was applied to estimation of prehistoric/preindustrial children's blood lead. A range of 0.06 to 0.12 microgram/dl was estimated for two lead intakes. These estimates are still two orders of magnitude (85 to 165-fold) lower than the newly issued CDC toxicity guideline for children of 10 micrograms/dl. Lastly, the toxicokinetics of lead in bone, particularly its resorption with metabolic stimuli, is of concern, particularly for "baby boom" women who are either of childbearing age or approaching menopause and who had greatly elevated environmental lead exposures in the 1940s to 1970s.

The macrodistribution of lead within the skeletal system is not uniform, and is clearly dependent on bone type (compact or trabecular), age and (to a lesser extent) gender. During active growth, lead deposition favors trabecular bones sites but in adulthood lead accumulates more actively in compact bone. The extent and patterns of the higher variability in trabecular bone sites require better definition through further study. Lead tends to be deposited in bone at sites of most active calcification at the time it is absorbed. During the first 15 years of life the bone growth centers dominate the process of calcification. In adulthood osteon remodelling and trabecular plate mineral exchanges are the principal calcifying sites. Both patterns probably deteriorate in old age. Microdeposition patterns of lead could be expected to conform to these changes. However, it is difficult to integrate the reported information into a clearly defined chronological sequence, because many of the studies did not control for age and other variables with sufficient precision. Furthermore, kinetic studies suggest lead is deposited in multiple sites not only among soft tissues but also within bone in molecular forms possessing varying affinities. Current efforts to design instrumentation for in vivo diagnostic lead measurements as well as therapeutic methods to mobilize and remove lead in bone require more precise knowledge than is now available concerning lead macrodistribution, microdistribution and anatomic sites of kinetic compartments. Appropriately designed studies employing contemporary, sensitive techniques involving isotopes, microradiographs, autoradiographs, histology, tomography, and high energy x-ray fluorescence (synchrotron radiation-induced x-ray emission-SRIXE) are now capable of generating the needed data.

The principal repository of calcium is bone. Calcium enters bone largely via the trabeculae, with the rate of calcium clearance by bone approximating 50 percent. Calcium enters bone as an ion in solution, but undergoes a phase change to a solid as soon as in contact with the bone surfaces. Calcium removal from and redistribution in bone is mediated by the bone cells, principally osteoblasts and osteoclasts. Calcium enters the body via intestinal absorption, a transport process that is the vectorial result of a saturable and an non-saturable step. Calcium leaves the body in the urine and stool, with a circulating calcium ion having one chance in about four of being lost via excretion. Ions like lead can compete with calcium at the sites of calcium deposition and transport. Their rate in the body should therefore parallel that of calcium, but may be modified by differing binding affinities or interactions with specific sites and molecules.

The transport, retention, and excretion of transuranic elements from the body have been widely studied for many years. A summary of the results is given with an emphasis on the distribution of these elements in bone. Implications of these studies for understanding the relationships between lead in blood and lead in bone are presented. The expected distribution of lead at various bone sites is also considered.

The biological interactions between lead and calcium are complex and not well-understood, but can be demonstrated in virtually every tissue. High affinity lead-binding to intracellular calcium receptor and transport proteins as well as the involvement of lead in calcium-activated and calcium-regulating processes may provide a molecular basis for the broad spectrum cellular and systemic effects. The intestinal absorptive cells are responsible for transporting the entire body complement of calcium and most of the body lead burden. They represent, therefore, the first critical step in maintaining systemic and cellular calcium homeostasis, as well as the first line of defense against lead poisoning. Any interactions which occur at this level, either to enhance the body burden of lead or to diminish the transport of calcium, may have serious health-related repercussions. This article reviews research concerning those interactions involving calcium, lead and the vitamin D endocrine system which ultimately influence intestinal function, calcium homeostasis and body lead retention.