Effect on blood,liver, and kidney variables of age and of dosing rats with lead acetate orally or via the drinking water

Levels of lead in the livers and kidneys of rats increased in proportion to the dose of lead acetate that the rats were given orally or in the drinking water. The activities of delta-aminolevulinic acid dehydratase (DALAD) in blood and liver decreased when the rats were dosed with lead, whereas glutathione levels in the blood increased. The decrease in the activity of blood DALAD was the most sensitive indicator of lead toxicity. Levels of lead in the livers and kidneys decreased after 3, 7, and 14 d of lead withdrawal. The activities of blood DALAD increased after 3 d of lead withdrawal. Groups of rats that initially weighted an average of 140 g were killed at weekly intervals for 6 wk. Blood hematocrits and liver glutathione levels increased, and blood DALAD and activated DALAD from blood decreased with increasing age of the rats. Activated DALAD activities from liver increased after the first week of the study.     

Effect of diet on the response in rats to lead acetate given orally or in the drinking water

Liver lead levels were higher for rats that were orally dosed with 100 mg lead acetate/kg body wt and fed a semipurified diet than those fed a pelleted diet. The activities of delta-aminolevulinic acid dehydratase in blood were decreased in the group given 10 μg lead acetate/mL in their drinking water and fed the semipurified diet, but not in the blood from the group treated with lead and fed the pelleted diet. The levels of glutathione in the liver decreased in response to lead acetate in the drinking water of rats fed the semipurified diet, but not in the livers from the group fed the pelleted diet and treated with lead. The levels of lead in the kidneys were higher in the group given lead acetate in their drinking water and fed the semipurified diet than in the lead treated group fed the pelleted diet. Rats dosed orally with lead or given lead in the drinking water and fed the semipurified diet were more sensitive to lead treatment than those fed the pelleted diet.     

Speciation and mobility of lead in shooting range soils

The mobility and bioavailability of lead (Pb) in seven military shooting range soils found in eastern and north eastern Botswana were studied using sequential extraction procedure. The different forms of Pb and their reactivity in the soil help explain their speciation, mobility and bioavailability in the environment. Mobility of Pb in the berm soils in all the seven shooting ranges was found to be over 90% implying high Pb lability. The bioavailability index of Pb was in the range 60–90%, an indication that most of the Pb can be available for plant uptake. Sequential extraction studies indicate that the partitioning of Pb was mostly confined to the carbonate compartment in all the shooting ranges. All the seven shooting ranges failed the Synthetic Precipitation Leaching Procedure (SPLP) with SPLP Pb concentrations exceeding United States Environmental Protection Agency (USEPA) 0.015 mg/kg critical level of hazardous waste, posing a pollution threat to surface and groundwater.     

Metabolic effects of low aflatoxin B1 levels on broiler chicks.

The effects of daily ingestion of aflatoxin B1 (AFB1) on growth, feed intake, plasma glucose, plasma cholesterol, plasma amino acids, plasma albumin, plasma ceruloplasmin, muscle amino acids, liver lipid, and bone strength were studied. For 3 weeks, beginning at an age of 2 days, broiler chicks were dosed daily per os with 50 or 100 micrograms of AFB1 per kg of body weight. Body weight and feed consumption were recorded daily, and metabolic responses were determined at 3 weeks. Treatment with AFB1 did not significantly alter body weight or feed intake. Relative liver weight showed a significant increase at the highest dose, with a significant concomitant increase in liver lipid and decrease in hepatic zinc. Relative spleen and heart weights were not affected by the toxin. Plasma glucose and cholesterol were significantly elevated at the highest dose. AFB1 significantly decreased plasma lysine and histidine and significantly increased muscle histidine, arginine, and valine. AFB1 decreased plasma albumin and markedly increased plasma ceruloplasmin. Dimensions of the long bones (femur and tibiotarsus) were not altered by the toxin. However, AFB1 caused a significant linear decline in the resistance of bone to breakage ("bone breaking strength"). The results indicate that low levels of AFB1 reduced bone strength in broiler chicks. The alterations in blood parameters indicated that AFB1 can disrupt metabolism even at low levels.     

Metabolic effects of low aflatoxin B1 levels on broiler chicks

The effects of daily ingestion of aflatoxin B1 (AFB1) on growth, feed intake, plasma glucose, plasma cholesterol, plasma amino acids, plasma albumin, plasma ceruloplasmin, muscle amino acids, liver lipid, and bone strength were studied. For 3 weeks, beginning at an age of 2 days, broiler chicks were dosed daily per os with 50 or 100 micrograms of AFB1 per kg of body weight. Body weight and feed consumption were recorded daily, and metabolic responses were determined at 3 weeks. Treatment with AFB1 did not significantly alter body weight or feed intake. Relative liver weight showed a significant increase at the highest dose, with a significant concomitant increase in liver lipid and decrease in hepatic zinc. Relative spleen and heart weights were not affected by the toxin. Plasma glucose and cholesterol were significantly elevated at the highest dose. AFB1 significantly decreased plasma lysine and histidine and significantly increased muscle histidine, arginine, and valine. AFB1 decreased plasma albumin and markedly increased plasma ceruloplasmin. Dimensions of the long bones (femur and tibiotarsus) were not altered by the toxin. However, AFB1 caused a significant linear decline in the resistance of bone to breakage ("bone breaking strength"). The results indicate that low levels of AFB1 reduced bone strength in broiler chicks. The alterations in blood parameters indicated that AFB1 can disrupt metabolism even at low levels.     

Reduction of Cadmium Availability to Tobacco (Nicotiana tabacum) Plants using Soil Amendments in Low Cadmium-contaminated Agricultural Soils: A Pot Experiment

Cadmium (Cd) concentration in field-grown tobacco leaves usually ranges from < 0.5 to 5 mg Cd kg^–1 dry matter (DM). Reducing bioavailability of soil Cd by adding amendments to the soil could be suitable to mitigate Cd uptake by tobacco plants. However, little is known on the effect of inorganic amendments on agricultural soils with low Cd concentrations. Therefore, we performed a pot experiment with tobacco plants that were grown during 56 days in two neutral to alkaline agricultural soils with low total Cd concentrations (soil 1 = 0.4, soil 2 = 0.7 mg kg^–1). Both soils were amended or not with 1 or 5% of sepiolite, zeolite, hydroxyapatite and apatite II™. Major and trace elements were measured in mid-stalk position leaves. Soil metals were measured in a DTPA soil extraction to assess the effect of the amendments on metal bioavailability. Some amendments significantly reduced Cd concentration in tobacco leaves, but the effect differed between the two soils tested. In soil 1, the use of zeolite at the 1% dose was the most efficient, reducing the average Cd concentration from 0.6 to 0.4 mg kg^–1. In soil 2, the 5% hydroxyapatite treatment led to the maximal reduction in Cd concentration (50%), with an average final Cd concentration in leaves of 0.7 mg kg^–1 (control: 1.5 mg kg^–1). There was a dose effect for some amendments in soil 2 (containing more Cd), suggesting a reduced efficiency of the amendment at the lowest addition rate. DTPA extractable Cd and Zn measured at the end of the pot experiment were correlated to the metal concentrations in tobacco leaves suggesting that (1) the reduction in leaf Cd concentration was due to a reduction in metal availability to tobacco and (2) DTPA may be a suitable extractant to estimate Cd availability to tobacco plants in these two soils. In addition, a batch experiment was performed with the same soils to test a larger number of amendments, including the four tested in the pot experiment. Results were compared to those of the pot experiment to assess whether a batch experiment may predict the efficiency of an amendment on a given soil. It gave results compatible with those from the pot experiment except for the sepiolite and highlighted the broad range of potential amendments available for heavy metal remediation in crop plants.     

Dermal Bioavailability of Toluene Aged in Soil

When organic chemicals age in soil, they can become more sequestered with time and less bioavailable. The impact of aging in soil was assessed on the dermal bioavailability of toluene. Comparisons were made between the dermal bioavailability of toluene aged in two soils (Atsion and Keyport) for 3 months, toluene in freshly spiked soil, and toluene without soil (pure chemical). In vitro flow-through diffusion cell methodology measured the amount of radioactive chemical that penetrated dermatomed male pig skin into receptor fluid, and that was detected in skin following soap and water decontamination. Volatilization reduced the amount of toluene that was available for skin penetration. Therefore, relative to the available dose, the total penetration of pure toluene (sum of the dose in the receptor fluid and skin) was 93%. The majority of pure toluene was found in skin (82%). The dermal bioavailability of non-aged and aged toluene was decreased to 4–6% and 3–4% of the available dose, respectively. The data suggest that there would be a lower potential risk to human health from dermal exposure to toluene in soil. However, lower soil loading and longer aging time are needed to quantitate the risk.     

环境重金属污染物的生物有效性

利用生态系统研究了白银有色金属冶炼矿区周围环境中重金属的分布及生物有效性。结果表明 ,工厂在冶炼过程中已造成 Pb、Cd、Cu、Zn对周围环境不同程度的污染 ,其含量与距工厂的距离呈负相关 ;重金属在各种生物体内均有不同程度的吸收和累积 ,其吸收累积量随重金属和生物种类的不同而有差异 ;土壤的污染 ,使农作物和牧草中 Pb、Cd含量超过动物的最大耐受量和中毒的临界值 ;动物研究发现 ,肾脏、骨骼和肝脏是机体内重金属蓄积的主要器官。因此 ,放牧动物可作为环境重金属污染状况的标识 ,对评价重金属环境污染对当地人群的危害也有重要意义     

Evaluating Risks to Terrestrial Wildlife from Environmental Fluoride

Information and approaches to evaluating health risks to terrestrial wildlife from fluoride contamination in the environment are few in the literature. We use environmental field data from a phosphate ore processing site, toxicity reference values (TRVs), and bioaccumulation factors relative to site conditions to develop risk-based concentrations (RBCs) for total fluoride in terrestrial biota and soil. RBCs were derived specifically for forage that are protective of terrestrial mammalian and avian ecological receptors through multiple exposure pathways, and which can be used to evaluate site remediation or as environmental monitoring action levels. Following review of the literature, we recommend fluoride TRVs for mammalian and avian wildlife, and bioavailability factors for estimating exposures related to aerial deposition of fluoride and fluoride gases. For large ungulates, information on fluoride bioavailability from feed and soil, and related effects thresholds, are summarized from studies on grazing livestock. The resultant RBCs for fluoride in forage range from 14 to 63 mg/kg dry weight, based on no-effect and low-effect concentrations, respectively. These concentrations bracket most state, provincial, and international regulatory standards of vegetation levels for protection of livestock and wildlife.     

The Influence of Liquid to Soil Ratios on Arsenic and Lead Bioaccessibility in Reference and Field Soil

In vitro bioaccessibility testing is gaining popularity as a tool to estimate the oral bioavailability of contaminants in soil for human health risk assessment (HHRA). Bioaccessibility tests are used to measure the bioaccessible fraction of a contaminant in soil, which can then be used to estimate the bioavailable fraction. Inherent uncertainties are associated with bioaccessibility tests. Various test parameters need to be carefully considered in their development, including the liquid to soil (L/S) ratio employed. We used L/S ratios (v:wt) ranging from 25 ml:1 g to 1,000 ml:1 g in a modified relative bioaccessibility extraction procedure to investigate the effects on bioaccessibility of lead and arsenic in field and reference soils. General trends of increased percent bioaccessibility of lead and arsenic with increasing L/S ratio were observed in the reference soil. A similar positive relationship was observed for lead in the field soil; soluble arsenic concentrations were below the detection limit and data were insufficient to observe a trend. Percent bioaccessibility was significantly affected at each extreme of the L/S ratios tested (p < .05). Biological relevance, technical feasibility, and mathematical relationships with in vivo results should be considered when selecting an appropriate L/S ratio for bioaccessibility testing.     

Assessing the in situ bioavailability of trace elements to snails using accumulation kinetics

The bioavailability of trace elements in soils is conditioned by both physico-chemical and biological parameters. In this study, the accumulation kinetics of cadmium (Cd), lead (Pb), arsenic (As) and antimony (Sb) were determined for 3 industrially impacted sites to assess the bioavailability of these contaminants to the garden snail (Cantareus aspersus). Mono and multivariate regressions allowed the identification of cation exchange capacity (CEC), silts and organic carbon content as the soil parameters modulating the in situ bioavailability of Cd and Pb. For all elements, the total concentrations in the soils were not good predictor (not significant correlation) of the bioavailability to snails. The Cd, As and Sb assimilation fluxes were correlated with the calcium chloride (CaCl₂) extract concentrations, but this correlation was not observed with Pb. The total soil concentration coupled with soil properties best explained the variation in Pb assimilation, whereas their influences on Cd bioavailability were lower, signifying that other parameters such as contamination sources may modulate Cd bioavailability. Here, the As and Sb in situ accumulation kinetics are described for the first time and highlighted a slight bioavailability to snails at the studied sites. The absence of a correlation between the As or Sb assimilation fluxes and total metals in the soil coupled with the absence of influence of soil properties on their bioavailability may result from the speciation of these metalloids, which are known to modulate their mobility in soils. This study highlights the need to consider both physico-chemical and biological aspects of metal and metalloid bioavailability to assess the risk of metal transfer from soil to organisms.     

Therapeutic potentials of combined use of DMSA with calcium and ascorbic acid in the treatment of mild to moderately lead intoxicated mice

The aim of this study was to explore the therapeutic efficacies of combined use of meso-2,3-dimercaptosuccinic acid (DMSA) with calcium and ascorbic acid in the treatment of mild to moderately lead-intoxicated mice. Female albino mice were exposed to lead by drinking water contaminated with 0.1% (moderate lead exposure) or 0.05% (mild lead exposure) lead acetate. After the cessation of lead exposure, mice were supplemented by gavage with saline solution, 50 mg/kg body weight (b.w) DMSA, 100 mg/kg b.w DMSA, calcium and ascorbic acid, or 50 mg/kg b.w DMSA and calcium as well as ascorbic acid, respectively. Atomic absorption spectrophotometric method was used to analyze lead levels in blood, bone, liver, kidney and brain. Activities of blood δ-aminolevulinic acid dehydratase (ALAD) were determined by colorimetric method. DMSA supplemented alone could reduce lead levels in both soft tissues and bone and reverse lead-inhibited activities of blood ALAD in mild to moderately lead-intoxicated mice. On the other hand, combined use of DMSA with calcium and ascorbic acid achieved better therapeutic efficacies in mobilizing lead in blood, liver and kidney, and reversing lead-inhibited activities of blood ALAD in moderately lead intoxicated mice than DMSA supplemented alone. Moreover, the better therapeutic efficacies were also found in mildly lead intoxicated mice in mobilizing lead in blood and bone achieved by combined use of DMSA with calcium and ascorbic acid. Combined use of DMSA with calcium and ascorbic acid seems to be the better choice in the treatment of mild to moderate lead-intoxication.     

Soil quality around a solid waste dumpsite in Port Harcourt, Nigeria

The levels of soil parameters and selected heavy metals around a solid waste dumpsite receiving untreated wastes from all sources and a control site within Port Harcourt, Nigeria have been examined. Top soil (0–15 cm) and sediment samples were collected and analysed for pH value, particle size, total nitrogen, potassium, available phosphorus, organic matter, effective cation exchange capacity, cadmium, nickel and lead using standard methods. The results showed that the waste dump contributed to the high levels of nutrients and heavy metals. The dry season mean concentrations were: organic matter (5.28 ± 1.34% or 132,422.4 kg ha^?1), K (1.60 ± 0.52 meq per 100 g), N (0.09 ± 0.06% or 2257.2 kg ha^?1), Av.P (15.11 ± 7.57 μg g^?1), Cd (1.34 ± 0.72 μg g^?1), Ni (4.10 ± 1.63 μg g^?1) and Pb (38.85 ± 22.18 μg g^?1) while the wet season mean concentrations were organic matter (5.46 ± 1.39% or 136,936.8 kg ha^?1), K (2.79 ± 0.81 meq per 100 g), N (0.10 ± 0.05% or 2508 kg ha^?1), Av.P (9.22 ± 2.69 μg g^?1), Cd (1.72 ± 1.22 μg g^?1), Ni (14.95 ± 14.94 μg g^?1) and Pb (53.50 ± 40.09 μg g^?1). There was efficient mineralization process in the area. The texture of soil on the main dumpsite was loamy sand, which suggests that the ground water in the area is susceptible to contamination by surface pollutants. The texture of soil at the control site is sandy loam while sediment has the textural class of sand. Decomposed organic materials and agricultural activities influenced the texture of soils. The soils from the main dump and sediment were slightly alkaline while the control soil was moderately acidic. In both seasons, a significant variation exists (P < 0.05) between the metal concentrations in soil at the main dump and those in the sediments with a positive correlation (r = 0.572149) in the wet season and (r = 0.956647) in the dry season. The presence of liming materials and activities of microorganisms on the waste dump increased the pH of the soils. The accumulation of nutrients results in the luxuriant growth of plants/crops on the waste dump.     

Impact of Aging Time on the Dermal Penetration of Phenol in Soil

Phenol is released to soil through accidental spills, manufacturing processes, and waste disposal. With time, chemicals can become more sequestered in soil (aging). Since skin is the body's primary route of entry for phenol, the impact of aging time on the dermal penetration of phenol was assessed in Atsion and Keyport soils. In vitro studies were conducted on dermatomed male pig skin using a flow-through diffusion cell methodology and radiolabeled phenol. After 3 and 6 months of aging in the Atsion soil, dermal penetration decreased from 84% of the initial dose for pure phenol (without soil) to 15% and 8%, respectively, while the dermal penetration of phenol aged in the Keyport soil was reduced to 22% and 17%, respectively. Atsion soil has a higher organic matter content (4.4%) than Keyport soil (1.6%) suggesting that the lower bioavailability of phenol aged in the Atsion soil may be due to the amount of organic matter in that soil. Although the data indicate that the potential health risk from dermal exposure to phenol would be lower after aging in soil than to pure chemical, further experiments are warranted at lower soil loads and with additional concentrations of phenol to quantify the risk.     

Phytoavailability and Leachability of Heavy Metals from Contaminated Soil Treated with Composted Livestock Manure

A study was carried out with maize as the test crop to investigate the bioavailability and leachability of heavy metals (HM) from HM-contaminated soils treated with composted manure. The application of composted manure increased the maize shoot growth by 32.3% and root growth by 30.5% compared with fresh manure. The concentration of HM in maize shoot varied in the order lead (Pb) > nickel (Ni) > zinc (Zn) > chromium (Cr) > copper (Cu) > cadmium (Cd). Whether for the shoot or root, the heavy metal concentrations decreased as the length of manure composting increased, but concentrations were higher in the root than the shoot. Composting decreased the bioavailability and leachability of HM and, hence, their export to the environment more effectively than direct use of fresh manure. Thus, the use of composted manure in place of fresh manure in polluted soils would be more beneficial for mitigating HM pollution.     

Efficacy of Allicin in Decreasing Lead (Pb) Accumulation in Selected Tissues of Lead-Exposed Common Carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>)

The objective of this study was to evaluate the effects of allicin, the main biologically active component of garlic clove extracts, on lead levels in different common carp tissues including liver, kidney, brain, bone, and blood following experimental lead poisoning. Fish were divided randomly into five groups depending on the combination of lead acetate and allicin treatments. Lead acetate exposure (7.0 mgL⁻¹, 10 days) caused a significant increase in mean Pb concentrations in all examined tissues in comparison to control unexposed fish (p < 0. 001). The results showed that allicin supplementation is effective in decreasing lead accumulation in all examined tissues of common carp. The promising ameliorative effects of allicin on tissue lead levels of common carp make it a good candidate for therapeutic intervention of lead poisoning. However, more studies are required to elucidate the pharmacokinetic effects of allicin and also molecular basis of the ameliorative properties of allicin in lead poisoning.     

Feasibility of Using Phytoextraction to Remediate a Compost-Based Soil Contaminated with Cadmium

Greenhouse and in-situ field experiments were used to determine the potential for phytoextraction to remediate soil contaminated with Cd from municipal solid waste (MSW) and sewage sludge (SS) compost application at a Peterborough (Canada) site. For the greenhouse experiment, one native (Chenopodium album) and three naturalized (Poa compressa, Brassica juncea, Helianthus annuus) plant species were planted in soil containing no detectable Cd (<1.0 μg·g^?1), and soil from the site containing low (5.0 ± 0.3 μg·g^?1 Cd), and high (16.5 ± 1.2 μg?g^?1 Cd) Cd concentrations. Plant uptake was low (root BAFs ≤0.5) for all species except P. compressa in the low Cd treatment (BAF 1.0). Only B. juncea accumulated Cd in its shoots, though uptake was low (BAF ≤0.3). For the field experiment, B. juncea was planted in-situ in areas of low and high Cd concentrations. Brassica juncea Cd uptake was low (root and shoot BAFs <0.2) in both treatments. Sequential extraction analysis indicated that Cd is retained primarily by low bioavailability soil fractions, and phytoextraction is therefore not feasible at this site. Though low Cd bioavailability has negative implications for Cd phytoextraction from MSW/SS compost-based soils, it may limit receptor exposure to Cd sufficiently to eliminate the potential for risk at this site.     

Effect of selenium fertilization on the accumulation of cadmium and lead in rice plants

Background and Aims

The accumulation of cadmium and lead in rice (Oryza sativa L.) grains is a potential threat to human health. In this study, the effect of selenium fertilization on the uptake and translocation of cadmium and lead in rice plants was investigated.

Methods

Rice plants were cultivated using cadmium and lead contaminated soils with selenium addition at three concentrations (0, 0.5 and 1 mg kg^?1). At maturity, plants were harvested, and element concentrations in rice tissues were analyzed by using ICP-MS.

Results

Selenium application significantly increased selenium accumulation in rice grain, and markedly decreased cadmium and lead concentrations in rice tissues. In brown rice grains, selenium application reduced cadmium concentrations by 44.4 %, but had no significant effect on lead accumulation. Selenium application significantly decreased metal mobility in soils, at 0.5 mg kg^?1 treatment, the translocation factor of cadmium and lead from soil to iron plaque decreased by 71 and 33 % respectively.

Conclusions

The mechanism of selenium mitigating of heavy metal accumulation in rice could be decreasing metal bioavailability in soil. Selenium fertilization could be an effective and feasible method to enrich selenium and reduce cadmium levels in brown rice.     

The Bioavailability of Lead in Mining Wastes: Physical/Chemical Considerations

Abstract

In this paper we review the physiological and geochemical factors affecting lead bioavailability, and particularly, the unique physical/chemical properties of lead derived from mining wastes based on both theory and empirical observations. The relationship between blood lead levels and soil lead concentrations derived from epidemiological studies indicates that lead in soil from mining sites appears to have less of an effect on blood lead levels in children than does lead at urban sites or sites with an active lead smelter. Differences in bioavailability of various lead species offers a plausible explanation for the relative differences in their impact on blood lead. In this paper, we evaluate from a physiological viewpoint aqueous solubility, absorption/desorption processes, and uptake mechanisms that may control lead bioavailability within the Gl tract. A number of these processes, including the role of passive diffusion, competition with calcium for a common transport mechanism, and the role of organic ligands, are discussed. Geochemical processes that relate to lead bioavailability in the Gl tract are also considered. Galena (PbS) and its alteration product, anglesite (PbSO⁴), are the primary forms of lead associated with mining wastes. Equilibrium thermodynamics and dissolution kinetics of PbSO⁴ are modeled because this solid is likely to control the concentration of dissolved lead from many mine wastes in the Gl tract. The geochemical models DIASTAB and MINTEAQ2 are used to calculate theoretical estimates of lead dissolution and a model is proposed to evaluate lead bioavailability by laboratory methods taking into account both kinetic and equilibrium considerations. This type of model requires calibration with animal toxicological studies of lead bioavailability and with epidemiological studies of different types of lead sites. Ultimately, such a geochemical model could be used to evaluate the potential for public health impacts from a particular type of lead in soil.     

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.